IgG4-Related Disease

Autoimmune MONDO:0017287 Pathograph 53 Show in embeddings browser Autoimmune Disease Fibroinflammatory Disease

An immune-mediated fibroinflammatory disease that produces tumefactive lesions in one or multiple organs, commonly involving the pancreas, bile ducts, salivary and lacrimal glands, kidneys, retroperitoneum and aorta. Characteristic pathology combines lymphoplasmacytic inflammation, often rich in IgG4-positive plasma cells, with storiform fibrosis and obliterative phlebitis; the full pattern varies by organ and disease stage. B-lineage, T-cell, myeloid and stromal mechanisms contribute, with unresolved initiating events and heterogeneous autoantibody effects. Recurrent inflammation and fibrosis can cause obstructive complications and irreversible organ dysfunction.

Ask OpenScientist

Ask a research question about IgG4-Related Disease. OpenScientist will conduct autonomous deep research using the Disorder Mechanisms Knowledge Base and PubMed literature (typically 10-30 minutes).

Submitting...

Do not include personal health information in your question. Questions and results are cached in your browser's local storage.

🏷

Classifications

Harrison's Part

◆

Subtypes

Pancreato-hepato-biliary pattern

Prominent pancreatic and biliary involvement. These are latent clinical patterns, not proven distinct immune mechanisms.

Show evidence (1 reference)

PMID:30612117 SUPPORT Human Clinical

"In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group 1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis; Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with..."

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

Retroperitoneal fibrosis and/or aortitis pattern

Prominent retroperitoneal and vascular involvement. These are latent clinical patterns, not proven distinct immune mechanisms.

Show evidence (1 reference)

PMID:30612117 SUPPORT Human Clinical

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

Head and neck-limited pattern

Disease concentrated in head and neck sites. These are latent clinical patterns, not proven distinct immune mechanisms.

Show evidence (1 reference)

PMID:30612117 SUPPORT Human Clinical

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

Mikulicz pattern with systemic involvement

Lacrimal and salivary involvement together with systemic disease. These are latent clinical patterns, not proven distinct immune mechanisms.

Show evidence (1 reference)

PMID:30612117 SUPPORT Human Clinical

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

◈

Mechanistic Hypotheses

Plasmablast-Autoantigen Fibrosis Driver Model

plasmablast_autoantigen_fibrosis_driver_model CANONICAL

Evidence balance 2 support

An adaptive immune framework in which antigen-experienced B cells, plasmablasts and T-cell populations participate in chronic fibroinflammation. Tfh cells enhance IgG4 production and plasmablast differentiation in coculture; B-lineage cells can directly stimulate fibroblast collagen production, and cytotoxic T cells show tissue injury and profibrotic mediator programs. Universal autoantigen identity, the precise B-cell-to-CTL interaction and the CTL-specific route to storiform architecture remain unresolved.

Pathograph links

Candidate Autoantigen Recognition and Antigen Presentation -> CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production INDIRECT UNKNOWN INTERMEDIATES Candidate antigen presentation may sustain the CTL response; the relevant antigen, presenting cell and functional interaction are unresolved.

Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation -> IgG4-Positive Plasmablast Expansion INDIRECT KNOWN INTERMEDIATES Tfh-derived help promotes B-cell differentiation into plasmablasts in patient-derived cultures.

IgG4-Positive Plasmablast Expansion -> CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production INDIRECT UNKNOWN INTERMEDIATES B-cell depletion-associated CTL reduction is compatible with B-lineage support through antigen presentation or other functions.

IgG4-Positive Plasmablast Expansion -> B-Lineage Profibrotic Signaling INDIRECT KNOWN INTERMEDIATES Expanded plasmablasts include cells with intrinsic profibrotic programs and collagen-promoting activity.

CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production -> Fibroblast Activation and Collagen Production INDIRECT UNKNOWN INTERMEDIATES CTL cytokine expression suggests a profibrotic signal, but direct IgG4-RD CTL-to-fibroblast perturbation remains unresolved.

CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production -> Cytotoxic T-Cell-Associated Mesenchymal Injury INDIRECT UNKNOWN INTERMEDIATES Lesional cytotoxic T-cell populations are associated with apoptosis of mesenchymal target cells; CTL-specific causation remains inferred.

Storiform Fibrosis -> Organ-Specific Fibroinflammatory Injury INDIRECT KNOWN INTERMEDIATES Persistent fibroblast and myofibroblast activation remodels affected organ tissue, with the clinical pattern shaped by organ-specific antigen, barrier, and injury contexts.

B-Lineage Profibrotic Signaling -> Fibroblast Activation and Collagen Production INDIRECT KNOWN INTERMEDIATES B-lineage soluble mediators stimulate fibroblast activation and collagen production, partly through PDGF-B.

Deep research

OpenScientist citations 33 citations 2026-06-04T08:55:22.739355

Show evidence (2 references)

PMID:24815737 SUPPORT Human Clinical

"Clonally expanded CD19(+)CD27(+)CD20(-)CD38(hi) plasmablasts are a hallmark of active IgG4-RD."

Human B-cell repertoire data support plasmablast expansion as a central disease-activity feature in the canonical adaptive immune model.

PMID:28166682 SUPPORT Other

"CD4+ CTLs in affected tissues secrete pro-fibrotic cytokines including IL-1β, TGF-β1, and IFN-γ as well as cytolytic molecules such as perforin and granzymes A and B."

Review-level synthesis supports CD4+ cytotoxic T cells as the immune-cell arm most directly linked to fibrogenic mediator production.

Innate-First Bystander Activation Model

innate_first_bystander_model ALTERNATIVE

Evidence balance 5 support

Innate receptor activation can promote B-cell responses and fibroinflammation in cell systems and mouse models. An innate-initiation/adaptive-amplification sequence is a plausible alternative in human IgG4-RD, but its temporal transition is unobserved. Established adaptive responses show clonal selection; that disfavors a purely nonspecific bystander explanation without excluding a concurrent or earlier nonspecific component.

The report is useful for innate component pathways but the distinctive composite hypothesis remains weakly supported/unresolved. Mouse initiation does not establish human initiation. Anti-CD19 efficacy shows therapeutic relevance of B-lineage functions, not universal necessity of antigen-specific adaptive immunity. NOD2/BAFF and basophil experiments concern cultured cells; the pDC pathway has separate primary evidence, although the report mislabels a review as an independent study. The two-phase transition remains an open alternative and is not encoded as a proven causal edge.

Pathograph links

Innate Receptor-Dependent BAFF Production -> Enhanced IgG4 Antibody Production INDIRECT KNOWN INTERMEDIATES BAFF-associated innate cell signals enhance B-cell IgG4 production in culture.

TLR7-Associated Macrophage IL-33 Production -> IL-33-Associated Macrophage Matrix Remodeling INDIRECT KNOWN INTERMEDIATES IL-33 is associated with macrophage ST2 signaling and MMP12 production in the lacrimal experimental system.

Conventional Dendritic Cell Chemokine Production -> CXCR3-Positive T-Cell Recruitment and CCL25 Production INDIRECT KNOWN INTERMEDIATES CXCL9/CXCL10 recruitment through CXCR3 is required for the full induced mouse phenotype.

CXCR3-Positive T-Cell Recruitment and CCL25 Production -> Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification INDIRECT KNOWN INTERMEDIATES T-cell CCL25 supports recruitment of CCR9-bearing pDCs in induced mouse pancreatitis.

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification -> CXCR3-Positive T-Cell Recruitment and CCL25 Production INDIRECT KNOWN INTERMEDIATES pDC-derived IFN-alpha enhances T-cell CCL25 secretion and sustains the observed mouse feedback loop.

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification -> Enhanced IgG4 Antibody Production INDIRECT KNOWN INTERMEDIATES NET-stimulated patient pDCs enhance control B-cell IgG4 production.

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification -> Fibroblast Activation and Collagen Production INDIRECT KNOWN INTERMEDIATES pDC-associated IFN-alpha and IL-33 signaling contributes to fibrotic sequelae in induced pancreatitis.

Gut Barrier and Microbiota-Dependent Innate Amplification -> Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification INDIRECT KNOWN INTERMEDIATES Gut perturbation increases pancreatic pDC accumulation under poly(I:C) induction.

Deep research

OpenScientist citations 25 citations 2026-07-06T02:12:13.712763

Show evidence (5 references)

PMID:31339007 SUPPORT Other

"TLR-7-expressing M2 macrophages may promote the activation of Th2 immune responses via IL-33 secretion in IgG4-RD."

This concluding sentence synthesizes human tissue, cultured macrophage and transgenic-mouse results. It supports an innate amplifier, not temporal priority in human disease.

PMID:39264798 SUPPORT Model Organism

"murine AIP was initiated by TLR3-bearing conventional DCs in the uninflamed pancreas whose activation by the TLR3 ligand poly(I:C) caused IFN-α, CXCL9, and CXCL10 secretion"

In the MRL/MpJ poly(I:C) autoimmune pancreatitis model, innate TLR3+ conventional dendritic cells act first in uninflamed tissue and only then recruit T cells and plasmacytoid DCs, providing the strongest temporal evidence for the innate-first component of the hypothesis.

PMID:41332187 SUPPORT Model Organism

"lysosomal accumulation of endogenous nucleosides is sufficient to drive autoimmune sialadenitis"

Slc29a3-deficient mice develop TLR7-associated autoimmune sialadenitis, a phenotype shared with other diseases. The experiment does not establish isolated innate-cell sufficiency without lymphocytes or reproduce systemic human IgG4-RD.

+ 2 more references

Discussions and Knowledge Gaps

What dominant autoantigen, antigen family, or antigen-presenting context initiates the coupled plasmablast and CD4-positive T-cell response in IgG4-RD?

KNOWLEDGE GAP OPEN gap_igg4rd_dominant_autoantigen_identity

Attached to

pathophysiology#Candidate Autoantigen Recognition and Antigen Presentation pathophysiology#IgG4-Positive Plasmablast Expansion pathophysiology#CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production

Candidate antigens explain subsets, and the precise B-lineage-to-CTL antigen-presentation step remains inferred. Direct B-cell-to-fibroblast signaling provides an additional route. A universal antigen is neither established nor required for every clinical pattern.

Proposed experiments

Paired BCR/TCR and autoantigen discovery across active IgG4-RD lesions

paired repertoire and antigen-discovery experiment

exp_igg4rd_paired_bcr_tcr_antigen_discovery

From paired blood and affected-organ biopsies, sequence plasmablast BCRs and expanded CD4+ CTL TCRs, express dominant antibodies and TCRs, and test candidate antigens by proteome arrays, immunoprecipitation-mass spectrometry, and antigen-presentation assays.

Model systems

Active human IgG4-RD blood and affected-organ biopsy pairs

Prospective patient samples spanning pancreatobiliary, salivary/lacrimal, renal, retroperitoneal, and vascular IgG4-RD manifestations.

OTHER

human NCBITaxon:9606

plasmablast CL:0000980 CD4-positive cytotoxic T lymphocyte CL:0000624

Readouts

Shared and organ-restricted antigen specificity

pathophysiology#Candidate Autoantigen Recognition and Antigen Presentation

Concordance between dominant plasmablast antibody specificity, expanded lesional TCR recognition, and organ expression of candidate antigens.

B cell receptor sequencing T cell receptor sequencing immunoprecipitation mass spectrometry

Direction: POSITIVE

Decision criterion

A dominant autoantigen model is supported if recurrent antigen specificities are shared across independent patients and mechanistically connect plasmablast BCRs to lesional CD4+ T-cell activation; a per-organ model is supported if specificity tracks organ tropism instead.

Would support

Show evidence (2 references)

PMID:31612628 SUPPORT Human Clinical

"While these findings suggest an underlying importance for B cell tolerance and the potential pathogenicity of autoantibodies in IgG4-RD, they also highlight the unmet need in identifying a dominant and specific antigen that may drive the pathogenesis of IgG4-RD."

The validation cohort explicitly frames dominant antigen identity as an unmet need despite several candidate autoantigens.

PMID:24815737 SUPPORT Human Clinical

"disease pathogenesis is linked to de novo recruitment of naive B cells into T cell-dependent responses by CD4(+) T cells, likely driving a self-reactive disease process."

The B-cell repertoire study motivates a specific antigen-discovery gap connecting plasmablasts to CD4+ T-cell-dependent responses.

Why do shared plasmablast, IgG4 class-switching, and CD4-positive cytotoxic-T-cell programs produce different organ manifestations such as pancreatitis, cholangitis, retroperitoneal fibrosis, kidney disease, and salivary/lacrimal gland enlargement?

KNOWLEDGE GAP OPEN gap_igg4rd_organ_tropism_and_fibroinflammation

Attached to

pathophysiology#Storiform Fibrosis pathophysiology#Organ-Specific Fibroinflammatory Injury

IgG4-RD has a conserved fibroinflammatory histology, but the current model cannot yet explain why particular organs are targeted in individual patients. Organ-restricted antigens, epithelial-barrier functions, chemokine niches, and local stromal repair programs remain plausible but incompletely connected mechanisms.

Proposed experiments

Multi-organ single-cell immune-stromal map of IgG4-RD lesions

multi-organ single-cell spatial profiling study

exp_igg4rd_multi_organ_single_cell_stromal_immune_map

Compare affected pancreas, bile duct, kidney, retroperitoneum, and salivary/lacrimal tissues using single-cell RNA sequencing, spatial transcriptomics, BCR/TCR sequencing, and autoantigen staining to separate shared fibroinflammatory circuitry from organ-specific injury programs.

Model systems

Human IgG4-RD affected-organ biopsy cohort

Cross-organ biopsy cohort with matched blood, histopathology, serum autoantibody, and treatment-response metadata.

OTHER

human NCBITaxon:9606

Readouts

Organ-specific antigen and stromal activation signatures

pathophysiology#Organ-Specific Fibroinflammatory Injury

Spatial colocalization of candidate autoantigens, plasmablasts/plasma cells, CD4+ CTLs, macrophages, fibroblasts, myofibroblasts, and extracellular matrix gene programs.

single-cell RNA sequencing spatial transcriptomics

Direction: POSITIVE

Decision criterion

Organ tropism is supported as antigen/barrier-driven if candidate autoantigen expression and barrier injury localize with immune clonotypes and stromal activation in the affected organ more strongly than in unaffected or disease-control tissue.

Would support

pathophysiology#Organ-Specific Fibroinflammatory Injury pathophysiology#Storiform Fibrosis

Show evidence (3 references)

PMID:38524667 SUPPORT In Vitro

"This makes it tempting to speculate that a decreased epithelial barrier function with attraction of immune cells and impaired bicarbonate secretion as a result of dysfunction of laminin 511 by autoantibody binding could potentially be a common systemic pathogenic mechanism in a subset of..."

Cholangitis data support a plausible epithelial-barrier mechanism, while the authors frame it as subset-level and still partly speculative.

PMID:34718050 SUPPORT In Vitro

"Binding of patient-derived annexin A11 autoantibodies inhibits annexin A11 function, possibly contributing to bile duct damage by weakening the biliary bicarbonate umbrella in patients with IRC."

Annexin A11 evidence supplies an organ-specific bile-duct injury model but does not explain non-biliary organ tropism.

PMID:39306708 SUPPORT Other

"Importantly, IgG4-RD can be classified into four clinical phenotypes based on the distribution of affected organs, with each phenotype showing different dominant immune cell subsets involved in its pathogenesis."

A review proposes that each organ-distribution phenotype carries its own dominant immune subset. This is the most explicit statement of the mechanism this gap asks about, but it is a synthesis rather than phenotype-matched immunophenotyping, so it motivates the gap instead of closing it.

Which cell and matrix interactions produce obliterative phlebitis, organ tropism and storiform architecture?

KNOWLEDGE GAP OPEN gap_igg4rd_vascular_and_stromal_specificity

Attached to

pathophysiology#Storiform Fibrosis pathophysiology#IL-33-Associated Macrophage Matrix Remodeling pathophysiology#Organ-Specific Fibroinflammatory Injury

B-cell cocultures establish collagen-promoting activity, but do not reproduce whorled architecture. MMP12 expression in macrophages does not establish a collagen-deposition edge. CTL-associated apoptosis does not by itself explain venous obliteration. The isolated-aortitis comparator is not confirmed IgG4-RD, and human organ distribution cannot be inferred from induced mouse pancreatic initiation. These remain gaps, with clinical and histological findings retained without invented arrows.

⚙

Pathophysiology

Candidate Autoantigen Recognition and Antigen Presentation

Mechanism confidence: Provisional

Oligoclonal self-reactive B-lineage responses and candidate autoantibodies support loss of tolerance in subsets. A universal initiating autoantigen is unknown. PHB1, annexin A11, laminin 511-E8 and galectin-3 binding results vary across cohorts; a negative four-antigen panel does not exclude other autoreactivity. B-lineage antigen presentation to cytotoxic T cells remains inferred rather than experimentally isolated.

Plasmablast-Autoantigen Fibrosis Driver Model

B cell CL:0000236

Antigen processing and presentation GO:0019882 B cell activation GO:0042113

Downstream

CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production Candidate antigen presentation may sustain the CTL response; the relevant antigen, presenting cell and functional interaction are unresolved.

Autoantibody-Mediated IL-1RA Neutralization A subset of autoreactive clones recognizes and functionally interferes with IL-1RA.

Cholangiocyte Protective Barrier Impairment Anti-annexin-containing serum can impair cholangiocyte protective machinery, while anti-laminin pathogenic effects remain incompletely isolated.

Show evidence (2 references)

PMID:24815737 SUPPORT Human Clinical

"Cloning and expression of immunoglobulin heavy and light chain genes from expanded plasmablasts at the peak of disease reveals that disease-associated IgG4 antibodies are self-reactive."

Plasmablast-derived antibody cloning supports autoreactivity in the active disease B-lineage response.

PMID:31612628 SUPPORT Human Clinical

"Of these 86 patients, 32 (37%) had IgG4 antibodies to ≥1 of the 4 autoantigens and 12 (14%) showed reactivity with ≥2 of the tested antigens."

Candidate autoantigens are documented, but the study also shows that none is a universal IgG4-RD antigen.

Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation

Follicular and extrafollicular helper T-cell populations provide B-cell help that promotes plasmablast differentiation and IgG4 production. Patient-derived circulating Tfh subsets and lesional salivary-gland Tfh cells have increased B-cell-helper activity in coculture. IL-4-positive BATF-positive and IL-10-positive LAG3-positive tissue populations are associated with polarized IgG4 responses; these phenotypes should not be treated as interchangeable with classical GATA3-positive Th2 cells.

Plasmablast-Autoantigen Fibrosis Driver Model

T follicular helper cell CL:0002038 B cell CL:0000236

Isotype switching GO:0045190 Plasma cell differentiation GO:0002317

Experimental models

Patient Tfh and B-cell coculture CO CULTURE

Downstream

IgG4-Positive Plasmablast Expansion Tfh-derived help promotes B-cell differentiation into plasmablasts in patient-derived cultures.

Enhanced IgG4 Antibody Production Lesional Tfh helper activity increases IgG4 production in B-cell coculture.

Show evidence (4 references)

PMID:29253269 SUPPORT Human Clinical

"The association found between Tfh cells and plasmablasts, linked with biological plausibility, suggests that Tfh cells contribute to the pathogenesis of IgG4-RD."

Human immunophenotyping supports the modeled Tfh-plasmablast axis upstream of IgG4 class switching and plasmablast expansion.

PMID:27411315 SUPPORT In Vitro

"In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells."

The patient-derived coculture directly tests B-cell help, while its subset definition and culture conditions limit in-vivo extrapolation.

PMID:28916523 SUPPORT In Vitro

"Tfh cells from IgG4-DS submandibular glands had higher expression of B cell lymphoma 6 and a greater capacity to help B cells produce IgG4 than did tonsillar Tfh cells."

Lesional Tfh cells support IgG4 production in the glandular disease context; tonsillar comparators are not matched unaffected salivary tissue.

+ 1 more reference

IgG4-Positive Plasmablast Expansion

Circulating plasmablasts, many of which are IgG4-positive and clonally expanded, are elevated in active disease and fall with B-cell depletion. They are modeled separately from mature tissue plasma cells because they report disease activity, relapse biology, and CD19-targeted therapeutic vulnerability.

Plasmablast-Autoantigen Fibrosis Driver Model

Plasmablast CL:0000980

B cell activation GO:0042113 Isotype switching GO:0045190

Downstream

CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production B-cell depletion-associated CTL reduction is compatible with B-lineage support through antigen presentation or other functions.

B-Lineage Profibrotic Signaling Expanded plasmablasts include cells with intrinsic profibrotic programs and collagen-promoting activity.

Show evidence (2 references)

PMID:24817416 SUPPORT Human Clinical

"Circulating plasmablasts are elevated in active IgG4-RD, even in patients with normal serum IgG4 concentrations."

Human flow-cytometry data support plasmablast expansion as a distinct active-disease B-lineage node.

PMID:24815737 SUPPORT Human Clinical

"These expanded plasmablasts are oligoclonal and exhibit extensive somatic hypermutation, and their numbers decrease after rituximab-mediated B-cell depletion therapy; this loss correlates with disease remission."

Repertoire sequencing and treatment-response data support a clonally expanded, disease-linked plasmablast compartment.

IgG4-Positive Plasma Cell Infiltration

IgG4-bearing plasma cells accumulate in affected tissues as a characteristic histological component. Plasmablasts and mature plasma cells differ in phenotype and treatment susceptibility. The exact contribution of each compartment to antibodies, matrix remodeling and tissue injury varies; IgG4 staining alone does not establish disease or antibody pathogenicity.

Plasma cell CL:0000786

Immune response GO:0006955 Inflammatory response GO:0006954

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"IgG4-related disease (IgG4-RD) has emerged over the last decade as a unique immune-mediated condition that links multiple fibro-inflammatory disorders previously regarded as separate entities"

Establishes IgG4-RD as a unified immune-mediated fibroinflammatory condition.

PMID:25988916 SUPPORT Human Clinical

"The gold-standard for the diagnosis of IgG4-RD, regardless of the organ(s) involved, is the identification of typical histopathology features (e.g., lymphoplasmacytic infiltrate, storiform fibrosis, obliterative phlebitis) in the context of a significant IgG4+ plasma cell infiltrate"

Confirms lymphoplasmacytic infiltrate with IgG4+ plasma cells as the histopathological hallmark.

CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production

Clonally expanded CD4-positive cytotoxic T lymphocytes infiltrate IgG4-RD lesions and produce inflammatory and profibrotic mediators, including IL-1beta, TGF-beta1, and IFN-gamma in salivary and lacrimal gland disease.

Plasmablast-Autoantigen Fibrosis Driver Model

CD4-positive cytotoxic T lymphocyte CL:0000624

Cytokine production GO:0001816 Inflammatory response GO:0006954

Downstream

Fibroblast Activation and Collagen Production CTL cytokine expression suggests a profibrotic signal, but direct IgG4-RD CTL-to-fibroblast perturbation remains unresolved.

Cytotoxic T-Cell-Associated Mesenchymal Injury Lesional cytotoxic T-cell populations are associated with apoptosis of mesenchymal target cells; CTL-specific causation remains inferred.

Show evidence (4 references)

PMID:26971690 SUPPORT Human Clinical

"IgG4-RD is prominently linked to clonally expanded IL-1β- and TGF-β1-secreting CD4(+) CTLs in both peripheral blood and inflammatory tissue lesions."

Human cohort data support clonally expanded IL-1beta- and TGF-beta1-secreting CD4+ CTLs as a distinct pathogenic effector node.

PMID:27358392 SUPPORT Human Clinical

"A large fraction of CD4+GZMA+ CTLs in SMGs from patients with IgG4-DS secreted IFN-γ."

This salivary-gland IgG4-RD study supports IFN-gamma secretion by lesional CD4+ cytotoxic T cells.

PMID:32485263 SUPPORT Human Clinical

"CD4+CTLs and CD8+CTLs may induce apoptotic cell death in tissues of patients with IgG4-RD with preferential targeting of nonendothelial, nonimmune cells of mesenchymal origin."

Human blood and tissue analyses link cytotoxic T-cell effector programs to mesenchymal-cell injury, a plausible bridge to fibrotic repair.

+ 1 more reference

Storiform Fibrosis

Fibrotic collagen remodeling can form a whorled or cartwheel storiform pattern. It is a characteristic microscopic architecture rather than a synonym for fibroblast activation. Fibrosis and inflammatory mass effects contribute to organ dysfunction; its prominence varies by organ and stage, and established scarring can be less reversible than active inflammation.

Plasmablast-Autoantigen Fibrosis Driver Model

Fibroblast CL:0000057 Myofibroblast CL:0000186

TGF-beta Receptor Signaling GO:0007179 ↑ INCREASED ECM Organization GO:0030198 ↑ INCREASED Collagen fibril organization GO:0030199 ↑ INCREASED

Downstream

Organ-Specific Fibroinflammatory Injury Persistent fibroblast and myofibroblast activation remodels affected organ tissue, with the clinical pattern shaped by organ-specific antigen, barrier, and injury contexts.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"The major histopathologic features include a dense lymphoplasmacytic infiltrate, fibrosis that has a storiform pattern in focal (or diffuse) areas, and obliterative phlebitis."

Storiform fibrosis identified as one of the three major histopathological features of IgG4-RD.

Organ-Specific Fibroinflammatory Injury

The same fibroinflammatory framework produces organ-specific syndromes such as autoimmune pancreatitis and IgG4-related cholangitis. Current evidence supports per-organ antigen and epithelial-barrier mechanisms in subsets, rather than a single universal tissue-tropism mechanism.

Animal models

Patient immunoglobulin passive transfer Mus musculus perturbs

Downstream

Pulmonary Involvement Thoracic fibroinflammatory involvement produces heterogeneous structural pulmonary abnormalities.

Pancreatobiliary Fibroinflammation and Ductal Obstruction Pancreatic and biliary localization produces inflammatory and obstructive digestive manifestations.

Renal Parenchymal Fibroinflammatory Injury Renal localization causes parenchymal inflammation and fibrosis.

Retroperitoneal Encasement and Urinary Obstruction Retroperitoneal localization can obstruct adjacent urinary structures.

Salivary and Lacrimal Gland Fibroinflammation Glandular localization produces lacrimal and salivary involvement.

Show evidence (3 references)

PMID:30089633 SUPPORT Other

"Autoimmune pancreatitis (AIP), a major manifestation of immunoglobulin G4-related disease (IgG4-RD), is an immune-mediated disorder, but the target autoantigens are still unknown."

Pancreatic disease illustrates organ-specific autoimmune injury while retaining uncertainty about the full target-antigen set.

PMID:38524667 SUPPORT In Vitro

"Laminin 511-E8 is an autoantigen in subsets of individuals with IRC."

Human serum and cholangiocyte experiments support a bile-duct-specific autoantigen/barrier-injury mechanism in a subset of IgG4-related cholangitis.

PMID:34718050 SUPPORT In Vitro

"Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary bicarbonate umbrella'."

This supports an organ-specific cholangiocyte-protection mechanism for bile-duct injury in IgG4-related cholangitis.

B-Lineage Profibrotic Signaling

Mechanism confidence: Provisional

Patient B cells and plasmablasts have soluble profibrotic activity involving PDGF-B and additional mediators. LOXL2 and collagen-related programs are expressed in plasmablasts and tissue plasma cells, but expression does not quantify matrix crosslinking or prove they are the dominant source of fibrosis. Healthy-control B cells also have weaker collagen-promoting activity.

Plasmablast-Autoantigen Fibrosis Driver Model

B cell CL:0000236 plasmablast CL:0000980

Downstream

Fibroblast Activation and Collagen Production B-lineage soluble mediators stimulate fibroblast activation and collagen production, partly through PDGF-B.

Show evidence (1 reference)

PMID:31319101 SUPPORT In Vitro

"These findings demonstrate that CD19+ B lymphocytes from patients with IgG4-RD and, to lesser extent, from healthy individuals are capable of driving myofibroblast differentiation and collagen production through the secretion of soluble factors rather than physical interactions."

Transwell cocultures establish a soluble B-cell-to-fibroblast mechanism, stronger with patient B cells, without proving its quantitative contribution in vivo.

Fibroblast Activation and Collagen Production

Activated fibroblasts produce collagen and express myofibroblast programs. Patient B-cell cocultures provide functional evidence for a PDGF-B-associated route; other immune mediators may converge. The experiments measure activation and collagen production, not the emergence of the disease-specific storiform architecture.

fibroblast CL:0000057 myofibroblast cell CL:0000186

collagen fibril organization GO:0030199

Experimental models

Patient B-cell and fibroblast coculture CO CULTURE

Downstream

Storiform Fibrosis Sustained collagen-producing stromal activity contributes to fibrotic tissue remodeling; the organization into storiform whorls is not reproduced by the coculture experiment.

Show evidence (1 reference)

PMID:31319101 SUPPORT In Vitro

"PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while nonimmune IgG of the same isotype did not inhibit the collagen production induced by the same B lymphocytes."

Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations with control B cells imply additional mediators.

Cytotoxic T-Cell-Associated Mesenchymal Injury

Mechanism confidence: Provisional

CD4-positive and CD8-positive cytotoxic T cells infiltrate lesions in association with HLA-DR-positive apoptotic cells, preferentially nonimmune and nonendothelial mesenchymal cells. GZMK-positive clones and extrafollicular B-cell proximity support coordinated inflammation. Human tissue data do not prove that CTLs cause obliterative phlebitis or that all T-cell populations are interchangeable.

Downstream

Organ-Specific Fibroinflammatory Injury Tissue apoptosis plausibly contributes to inflammatory injury; human CTL-specific causal mediation remains unresolved.

Show evidence (2 references)

PMID:32485263 SUPPORT Human Clinical

"Tissue studies revealed an abundance of cells undergoing apoptotic cell death disproportionately involving nonimmune, nonendothelial cells of mesenchymal origin."

Human imaging establishes the distribution of apoptotic cells.

PMID:38092138 SUPPORT Human Clinical

"GZMK+CD4+ cytotoxic T cells colocalized with MKI67+ B cells in the extrafollicular area from affected tissue sites."

Spatial proximity supports a candidate cellular interaction but does not establish antigen presentation.

Innate Receptor-Dependent BAFF Production

Mechanism confidence: Provisional

NOD2- or TLR-stimulated monocytes and TLR-stimulated basophils can support enhanced IgG4 production through BAFF-associated mechanisms in culture. Healthy-control cells also respond. These routes can coexist with Tfh help; neither their redundancy in vivo nor a universal innate initiating event is established.

Innate-First Bystander Activation Model

monocyte CL:0000576 basophil CL:0000767

Downstream

Enhanced IgG4 Antibody Production BAFF-associated innate cell signals enhance B-cell IgG4 production in culture.

Show evidence (2 references)

PMID:21971969 SUPPORT In Vitro

"Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells in a BAFF-dependent and T cell-independent manner."

The culture experiment separates BAFF-dependent IgG4 production from T-cell help; it does not establish de-novo class-switch recombination in vivo.

PMID:22744834 SUPPORT In Vitro

"Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13."

A distinct basophil culture route is supported; association with both mediators is not proof of BAFF-alone necessity.

Enhanced IgG4 Antibody Production

B-cell antibody production is enhanced through both T-cell-help and innate-cell-associated routes. Serum IgG4 does not faithfully report all lesions and can be normal. IgG4 enrichment is not itself proof that an antibody specificity is pathogenic; patient IgG4 can have inhibitory or pathogenic effects depending on context.

Show evidence (3 references)

PMID:21971969 SUPPORT In Vitro

"Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells in a BAFF-dependent and T cell-independent manner."

The culture experiment separates BAFF-dependent IgG4 production from T-cell help; it does not establish de-novo class-switch recombination in vivo.

PMID:22744834 SUPPORT In Vitro

"Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13."

A distinct basophil culture route is supported; association with both mediators is not proof of BAFF-alone necessity.

PMID:26297761 SUPPORT In Vitro

"patient pDCs cultured in the presence of NETs produced greatly increased levels of IFN-α and induced control B cells to produce IgG4 (but not IgG1) as compared with control pDCs."

This primary culture experiment supports an additional pDC-to-B-cell route; the innate report instead cited a review for this component.

TLR7-Associated Macrophage IL-33 Production

Mechanism confidence: Provisional

TLR7-expressing CD163-positive macrophages accumulate in affected salivary glands. TLR7 agonist stimulation increases IL-33 in cultured macrophages; huTLR7 mice show multi-organ inflammation and fibrosis with IgG1, rather than human IgG4. Human temporal initiation remains unresolved.

Innate-First Bystander Activation Model

macrophage CL:0000235

Animal models

Human TLR7 transgenic mouse Mus musculus perturbs

Downstream

IL-33-Associated Macrophage Matrix Remodeling IL-33 is associated with macrophage ST2 signaling and MMP12 production in the lacrimal experimental system.

Show evidence (1 reference)

PMID:31339007 SUPPORT In Vitro

"After in vitro stimulation with a TLR-7 agonist, CD163+ M2 macrophages produced higher levels of interleukin-33 (IL-33)"

Agonist stimulation links TLR7 activation to macrophage IL-33 in vitro; patient tissue colocalization alone does not establish temporal initiation.

IL-33-Associated Macrophage Matrix Remodeling

Mechanism confidence: Provisional

IL-33/ST2-associated macrophage activation and MMP12 expression provide a candidate matrix-remodeling route in lacrimal disease. The experimental and small human-tissue study does not establish that MMP12 causes storiform fibrosis or that IL-33 blockade is an effective human treatment.

macrophage CL:0000235

Show evidence (1 reference)

PMID:39299101 SUPPORT In Vitro

"an ELISA assay demonstrated that IL-33 upregulates MMP-12 in IgG4-ROD."

The experimental study supports IL-33-associated MMP12 induction; the nine-patient tissue component is observational.

Conventional Dendritic Cell Chemokine Production

Mechanism confidence: Provisional

In poly(I:C)-induced autoimmune pancreatitis, TLR3-bearing conventional dendritic cells produce type I interferons and CXCL9/CXCL10 early, promoting subsequent CXCR3-positive T-cell recruitment. This initiating sequence is experimentally defined in female MRL/MpJ mice; matching human serum chemokines provide association rather than proof of the same sequence.

Innate-First Bystander Activation Model

Downstream

CXCR3-Positive T-Cell Recruitment and CCL25 Production CXCL9/CXCL10 recruitment through CXCR3 is required for the full induced mouse phenotype.

Show evidence (1 reference)

PMID:39264798 SUPPORT In Vitro

"pancreatic cDCs, at this early phase of AIP induction, are indeed the main producers of type I IFNs upon sensing of poly(I:C) by TLR3"

Sorted-cell stimulation and depletion identify the early source in the induced mouse model.

CXCR3-Positive T-Cell Recruitment and CCL25 Production

Mechanism confidence: Provisional

CXCL9/CXCL10-associated recruitment places CXCR3-positive T cells in inflamed mouse pancreas. Under type I interferon stimulation these T cells produce CCL25, recruiting CCR9-positive pDCs. These cells are not established to be the same granzyme-positive CTLs found in human lesions.

Innate-First Bystander Activation Model

Downstream

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification T-cell CCL25 supports recruitment of CCR9-bearing pDCs in induced mouse pancreatitis.

Show evidence (1 reference)

PMID:39264798 SUPPORT Model Organism

"such blockade prevented the development of experimental AIP"

Anti-CXCR3 treatment during repeated poly(I:C) administration prevents pancreatic inflammation, supporting the chemokine recruitment step in this model.

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification

Mechanism confidence: Provisional

Recruited pDCs become a major source of IFN-alpha and IL-33 in induced mouse pancreatitis. Their IFN-alpha sustains T-cell CCL25 production, forming an experimentally supported feedback loop. TLR9 stimulation is required for maximal cytokine output in coculture; human NET-stimulated pDC experiments independently support enhanced IgG4 production.

Innate-First Bystander Activation Model

Animal models

Poly(I:C)-induced autoimmune pancreatitis Mus musculus perturbs

Downstream

CXCR3-Positive T-Cell Recruitment and CCL25 Production pDC-derived IFN-alpha enhances T-cell CCL25 secretion and sustains the observed mouse feedback loop.

Enhanced IgG4 Antibody Production NET-stimulated patient pDCs enhance control B-cell IgG4 production.

Fibroblast Activation and Collagen Production pDC-associated IFN-alpha and IL-33 signaling contributes to fibrotic sequelae in induced pancreatitis.

Show evidence (2 references)

PMID:39264798 SUPPORT Model Organism

"the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of experimental AIP"

The intervention reduces pancreatic pDC accumulation and inflammation in mice.

PMID:26297761 SUPPORT In Vitro

"patient pDCs cultured in the presence of NETs produced greatly increased levels of IFN-α and induced control B cells to produce IgG4 (but not IgG1) as compared with control pDCs."

This primary culture experiment supports an additional pDC-to-B-cell route; the innate report instead cited a review for this component.

Gut Barrier and Microbiota-Dependent Innate Amplification

Mechanism confidence: Provisional

Microbiota transfer and intestinal barrier disruption amplify poly(I:C)-induced pancreatitis through increased pancreatic pDC accumulation. Staphylococcus sciuri translocation and mono-colonization experiments support a model-specific modifier. Neither microbial sufficiency without the inducing regimen nor causal initiation of human systemic IgG4-RD is established.

Innate-First Bystander Activation Model

Downstream

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification Gut perturbation increases pancreatic pDC accumulation under poly(I:C) induction.

Show evidence (2 references)

PMID:31287532 SUPPORT Model Organism

"Fecal microbiota transplantation (FMT) from donor mice treated with 100 µg of poly (I:C) led to the development of severe AIP in the recipient mice upon injection with 10 µg of poly (I:C)."

Microbiota transfer amplifies pancreatitis under a continuing low-dose innate stimulus; it does not induce spontaneous human IgG4-RD.

PMID:36044992 SUPPORT Model Organism

"Mice co-treated with poly (I:C) and DSS, but not those treated with either agent alone, developed severe AIP, but not autoimmune sialadenitis"

Barrier disruption and poly(I:C) jointly exacerbate pancreatic disease; the effect is organ-specific in this experiment.

Autoantibody-Mediated IL-1RA Neutralization

Mechanism confidence: Provisional

Anti-IL-1RA antibodies in a subset can neutralize the endogenous IL-1 receptor antagonist and increase inflammatory and profibrotic mediator production. IgG4 predominates in many positive samples but other subclasses occur, and functional plasma experiments do not isolate IgG4-specific activity. The pathway is not universal or specific to IgG4-RD.

Experimental models

Anti-IL-1RA functional cell assays CELL LINE

Downstream

Fibroblast Activation and Collagen Production Unopposed IL-1 signaling increases profibrotic mediator production in cell assays; progression to human stromal fibrosis remains inferred.

Show evidence (1 reference)

PMID:33974929 SUPPORT In Vitro

"Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic mediator production in vitro."

Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.

Immune-Complex Complement Activation

Mechanism confidence: Provisional

IgG4-containing patient immune-complex fractions can activate and consume classical and lectin-pathway complement in vitro. Anti-C1q and hypocomplementemia are associated with renal involvement in clinical cohorts. The causal contribution of individual subclasses to human renal injury remains unresolved.

Show evidence (1 reference)

PMID:26357950 SUPPORT In Vitro

"We observed a marked reduction of CH50 and reduced complement activity in the classical complement pathway as well as the mannan-binding lectin complement pathway in NHS incubated with PEG-IC isolated from IgG4RD patients with hypocomplementemia."

Patient immune-complex fractions consume complement ex vivo; mixed complexes cannot assign causality to purified IgG4 alone.

Cholangiocyte Protective Barrier Impairment

Mechanism confidence: Provisional

Annexin A11 supports apical ANO1 trafficking and protective bicarbonate secretion; patient serum can inhibit this process. Laminin 511 independently supports epithelial barrier integrity and bile-acid resistance. Candidate autoantibodies occur in subsets, but laminin knockdown and patient autoantibody binding should not be equated.

cholangiocyte CL:1000488

Experimental models

Human cholangiocyte protective-barrier assays CELL LINE

Downstream

Pancreatobiliary Fibroinflammation and Ductal Obstruction Impaired protective secretion and barrier function may contribute to biliary injury in an autoantibody-positive subset.

Show evidence (2 references)

PMID:34718050 SUPPORT In Vitro

"Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression."

Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective secretory machinery; mixed serum is not an isolated isotype perturbation.

PMID:38524667 SUPPORT In Vitro

"Knockdown of laminin 511 constituents increased toxic bile acid permeation and GCDC-induced apoptosis."

Gene knockdown establishes laminin-dependent protection but does not by itself demonstrate that patient anti-laminin antibodies reproduce knockdown.

Pancreatobiliary Fibroinflammation and Ductal Obstruction

Lymphoplasmacytic inflammation and fibrosis affect pancreatic and biliary structures. Duct narrowing and inflammatory enlargement can cause obstructive jaundice; persistent pancreatic injury can leave exocrine or endocrine dysfunction. An IgG4-related pancreatic mass requires distinction from malignancy.

Downstream

Autoimmune Pancreatitis Organ-localized fibroinflammation produces this clinical manifestation or complication.

Sclerosing Cholangitis Organ-localized fibroinflammation produces this clinical manifestation or complication.

Jaundice Organ-localized fibroinflammation produces this clinical manifestation or complication.

Show evidence (1 reference)

PMID:32552502 SUPPORT Other

"Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis."

The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.

Renal Parenchymal Fibroinflammatory Injury

Tubulointerstitial inflammation with IgG4-rich plasma cells and fibrosis can impair intrinsic renal function. Membranous nephropathy occurs in a subset and may coexist. Hypocomplementemia is associated, but the reviewed evidence does not establish a single complement-mediated causal route for all renal injury.

Downstream

Renal Insufficiency Organ-localized fibroinflammation produces this clinical manifestation or complication.

Proteinuria Organ-localized fibroinflammation produces this clinical manifestation or complication.

Show evidence (1 reference)

PMID:30596168 SUPPORT Human Clinical

"tubulointerstitial nephritis with abundant IgG4+ plasma cells was the most common finding (n = 14; 93.3%), and 4 (26.7%) patients had membranous nephropathy."

Renal biopsy findings concern the selected 15-biopsy renal cohort, not the prevalence in all IgG4-RD.

Retroperitoneal Encasement and Urinary Obstruction

Periaortic and periureteric fibroinflammatory tissue can encase ureters and obstruct drainage, producing hydronephrosis and postrenal dysfunction. This route is distinct from intrinsic IgG4-related tubulointerstitial nephritis.

Downstream

Retroperitoneal Fibrosis Organ-localized fibroinflammation produces this clinical manifestation or complication.

Hydronephrosis Organ-localized fibroinflammation produces this clinical manifestation or complication.

Renal Insufficiency Organ-localized fibroinflammation produces this clinical manifestation or complication.

Show evidence (1 reference)

PMID:30596168 SUPPORT Human Clinical

"Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric obstruction in 6 patients (21.4%)"

Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal involvement.

Salivary and Lacrimal Gland Fibroinflammation

Immune-cell infiltration and tissue remodeling enlarge salivary and lacrimal glands. Persistent injury can compromise gland function; IgG4-rich inflammation alone does not distinguish this condition from all mimics.

Animal models

Slc29a3-deficient sialadenitis Mus musculus perturbs

Downstream

Enlarged Lacrimal Glands Organ-localized fibroinflammation produces this clinical manifestation or complication.

Salivary Gland Enlargement Organ-localized fibroinflammation produces this clinical manifestation or complication.

Show evidence (1 reference)

PMID:35425928 SUPPORT Other

"IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal tissues, aorta, kidneys, and lungs."

The primary trial provides a clinical background summary of characteristic involved organs.

✶

Histopathology

Dense Lymphoplasmacytic Infiltrate with IgG4-Positive Plasma Cells

Tissue biopsy shows a dense lymphoplasmacytic infiltrate with increased IgG4-positive plasma cells or an increased IgG4+/IgG+ plasma-cell ratio. The feature is not universal or sufficient by itself; prominence varies by organ and disease stage.

Show evidence (1 reference)

PMID:22596100 SUPPORT Other

"The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern of fibrosis, and obliterative phlebitis."

International pathology consensus identifies the triad and emphasizes clinicopathological correlation.

Storiform Fibrosis

Fibrosis in a storiform, whorled, or cartwheel pattern is one of the characteristic microscopic features of IgG4-RD. The feature is not universal or sufficient by itself; prominence varies by organ and disease stage.

Show evidence (1 reference)

PMID:22596100 SUPPORT Other

"The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern of fibrosis, and obliterative phlebitis."

International pathology consensus identifies the triad and emphasizes clinicopathological correlation.

Obliterative Phlebitis

Inflammatory and fibrotic obliteration of venous lumina is a characteristic but organ-variable finding. Arteritis and aortitis are separate vascular lesions; leukocytoclastic small-vessel vasculitis is not interchangeable with obliterative phlebitis.

Show evidence (1 reference)

PMID:22596100 SUPPORT Other

"The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern of fibrosis, and obliterative phlebitis."

International pathology consensus identifies the triad and emphasizes clinicopathological correlation.

Tissue eosinophilia

Eosinophils can accompany the tissue lymphoplasmacytic infiltrate. This supportive, nonspecific biopsy feature is distinct from peripheral blood eosinophilia and is insufficient for diagnosis.

Show evidence (1 reference)

PMID:39644037 SUPPORT Other

"Histological diagnosis is essential, and other key features include storiform fibrosis, lymphoplasmacytic infiltrate, tissue eosinophilia, and obliterative phlebitis."

The hematology review explicitly identifies the tissue finding.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

Blood 1

Peripheral Blood Eosinophilia OCCASIONAL Increased total eosinophil count HP:0001880

A systematic review and meta-analysis of 32 studies puts the pooled proportion with eosinophilia at 22%, alongside allergy in 44% and hyper-IgE in 73%. The co-occurrence is well replicated; whether the type 2 axis contributes causally to IgG4-RD or simply travels with it is unresolved, so no causal edge is drawn from this phenotype in the pathograph.

Show evidence (2 references)

PMID:41912044 SUPPORT Human Clinical

"The pooled proportion with eosinophilia was 0.22 (95% CI, 0.18, 0.26; p < 0.01; n = 4376), and with hyper-IgE was 0.73 (95% CI, 0.63, 0.83; p < 0.01; n = 2353)."

Pooled prevalence across 32 studies places blood eosinophilia in about a fifth of reported patients, which is the basis for the OCCASIONAL frequency band.

PMID:41912044 SUPPORT Human Clinical

"A notable proportion of IgG4-RD patients exhibit allergy, eosinophilia, and hyper-IgE. The frequent co-occurrence of these features highlights the need to investigate the underlying mechanisms, clarify the causal relationship between allergy and IgG4-RD"

The same authors record the causal relationship between these type 2 features and IgG4-RD as still open, and note that comparison against general-population rates is lacking. That is why the finding is kept as a phenotype without a causal edge.

Cardiovascular 2

Lymphadenopathy HP:0002716

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Among 34 patients with lymphadenopathy, 21 had undergone a lymph node biopsy."

The cohort establishes nodal disease and its ascertainment.

Aortitis HP:6001461

Show evidence (1 reference)

PMID:30612117 SUPPORT Human Clinical

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

Digestive 4

Autoimmune Pancreatitis HP:0001733

Type 1 autoimmune pancreatitis is a characteristic organ manifestation. Its frequency depends on referral setting; only 24/125 patients in the cited rheumatology cohort had pancreatic involvement. It is not uniformly the most common site.

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"The most commonly involved organs were the submandibular glands (35 cases, 28%), lymph nodes (34, 27%), orbits (28, 22%), pancreas (24, 19%), and retroperitoneum (23, 18%)."

The 125-person referral cohort defines pancreatic frequency in this setting.

PMID:32552502 SUPPORT Other

The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.

Sclerosing Cholangitis HP:0030991

IgG4-related sclerosing cholangitis can mimic primary sclerosing cholangitis or cholangiocarcinoma but responds to corticosteroids.

Show evidence (1 reference)

PMID:32552502 SUPPORT Other

The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.

Jaundice HP:0000952

Show evidence (1 reference)

PMID:32552502 SUPPORT Other

The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.

Retroperitoneal Fibrosis HP:0005200

Show evidence (1 reference)

PMID:30596168 SUPPORT Human Clinical

"Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric obstruction in 6 patients (21.4%)"

Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal involvement.

Genitourinary 3

Renal Insufficiency HP:0000083

IgG4-related tubulointerstitial nephritis or membranous nephropathy can lead to progressive renal dysfunction.

Show evidence (2 references)

PMID:30596168 SUPPORT Other

"Renal involvement may manifest as an intrinsic kidney disease (IgG4-RKD) or as a consequence of ureteric obstruction from retroperitoneal fibrosis (IgG4-RPF)."

The cohort distinguishes parenchymal and postrenal routes to kidney dysfunction.

PMID:30596168 SUPPORT Human Clinical

"Renal function deteriorated in 5 patients (20.8%), including 2 (8.3%) who reached end-stage renal disease (ESRD)."

Longitudinal renal outcomes in the selected renal/RPF cohort establish potential irreversible impairment.

Hydronephrosis HP:0000126

Show evidence (1 reference)

PMID:30596168 SUPPORT Human Clinical

"image of left-sided ureteric obstruction and hydronephrosis in IgG4-RPF."

Clinical imaging documents this complication.

Proteinuria HP:0000093

Show evidence (1 reference)

PMID:30596168 SUPPORT Human Clinical

"Mild-to-moderate hemoproteinuria occurred in just over half of the patients with IgG4-RKD"

Clinical cohort data support the phenotype in renal disease.

Head and Neck 2

Enlarged Lacrimal Glands HP:0007734

Show evidence (2 references)

PMID:35425928 SUPPORT Other

"IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal tissues, aorta, kidneys, and lungs."

The primary trial provides a clinical background summary of characteristic involved organs.

PMID:30612117 SUPPORT Human Clinical

Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort and are not mutually exclusive mechanistic classes.

Salivary Gland Enlargement Abnormal salivary gland morphology HP:0010286

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"The most commonly involved organs were the submandibular glands (35 cases, 28%)"

The cohort documents frequent submandibular involvement.

PMID:35425928 SUPPORT Other

"IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal tissues, aorta, kidneys, and lungs."

The primary trial provides a clinical background summary of characteristic involved organs.

Respiratory 1

Pulmonary Involvement Abnormal lung morphology HP:0002088

Show evidence (1 reference)

PMID:36437514 SUPPORT Other

"Chest CT findings are heterogeneous and primarily include peribronchovascular thickening, nodules, ground-glass opacities and lymphadenopathy."

The thoracic review describes structural imaging manifestations; the pattern is not specific to IgG4-RD.

🧬

Genetic Associations

HLA-DRB1

Gene: HLA-DRB1 hgnc:4948 gene page relationship_type: RISK_FACTOR

Show evidence (2 references)

PMID:38229354 SUPPORT Human Clinical

"We identified the HLA-DRB1 (p=1·1×10-11) and FCGR2B (p=2·0×10-8) regions as susceptibility loci for IgG4-related disease."

Japanese case-control GWAS supports association.

PMID:41298177 SUPPORT Human Clinical

"We identified 22 single nucleotide polymorphisms (SNPs) that surpassed genome-wide significance thresholds (P < 5E-08) and replicated consistently across both cohorts, defining 16 distinct genetic susceptibility loci."

Chinese Han GWAS supports a broader polygenic architecture, not fine-mapped causal genes for every locus.

FCGR2B

Gene: FCGR2B hgnc:3618 gene page relationship_type: RISK_FACTOR

Show evidence (3 references)

PMID:38229354 SUPPORT Human Clinical

"We identified the HLA-DRB1 (p=1·1×10-11) and FCGR2B (p=2·0×10-8) regions as susceptibility loci for IgG4-related disease."

Japanese case-control GWAS supports association.

PMID:41298177 SUPPORT Human Clinical

Chinese Han GWAS supports a broader polygenic architecture, not fine-mapped causal genes for every locus.

PMID:38229354 SUPPORT Human Clinical

"rs1340976 in FCGR2B showed an association with increased FCGR2B expression"

The expression direction corrects a consequential interpretation error.

💊

Medical Actions

Glucocorticoids

Action: glucocorticoid therapy Ontology label: Systemic Corticosteroid Therapy NCIT:C122080

Glucocorticoids are used to induce control of active disease, with treatment and taper tailored to involved organs and response. Relapse and cumulative toxicity can necessitate maintenance or steroid-sparing therapy. The 77% failure of sustained remission reported in one referral cohort is not a universal relapse rate.

Mechanism Target:

INHIBITS Organ-Specific Fibroinflammatory Injury — Suppresses active inflammation; fixed fibrosis and organ damage may persist.

Show evidence (1 reference)

PMID:32552502 SUPPORT Other

"Response to initial treatment should be assessed at week 2-4 with clinical, biochemical and morphological markers."

Response assessment captures inflammation and organ manifestations, rather than a specific cellular target.

Show evidence (2 references)

PMID:32552502 SUPPORT Other

"Maintenance treatment with glucocorticoids should be considered in multi-organ disease or history of relapse."

The digestive guideline supports individualized maintenance decisions.

PMID:25988916 SUPPORT Human Clinical

"This figure may be biased somewhat by the nature of our referral practice"

The primary cohort explicitly cautions against generalizing its 77% failure of sustained glucocorticoid-free remission.

Rituximab

Action: rituximab therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: rituximab NCIT:C1702

Anti-CD20 B-cell depletion used as a steroid-sparing approach. In an uncontrolled 30-patient trial, 97% had a disease response, 77% met the composite primary endpoint and 40% remained in complete remission at 12 months. These results support activity but do not constitute a randomized comparison or demonstrate elimination of mature plasma cells.

Mechanism Target:

INHIBITS IgG4-Positive Plasmablast Expansion — Depletion of CD20-positive B-cell precursors reduces the plasmablast-supporting lineage; long-lived plasma-cell persistence can contribute to incomplete serologic normalization.

Show evidence (1 reference)

PMID:24817416 SUPPORT Human Clinical

"The steep decline in plasmablast counts after anti-CD20 treatment likely stems from the depletion of CD20+ precursors."

The clinical study documents declining plasmablast counts after CD20 depletion and interprets this as loss of precursor support.

Show evidence (3 references)

PMID:25667206 SUPPORT Human Clinical

"The primary outcome was achieved by 23 participants (77%). Fourteen (47%) were in complete remission at 6 months, and 12 (40%) remained in complete remission at 12 months."

The denominators and endpoints concern an open-label 30-person trial.

PMID:38781535 SUPPORT Human Clinical

"Six months after rituximab, disease response was observed in all patients. Four patients (12%) achieved partial response, 11 patients (33%) achieved complete response, and 18 patients (54%) reached disease remission."

A retrospective 33-patient cohort corroborates the remission-inducing activity of rituximab induction outside the original open-label trial. It is uncontrolled, so it adds replication rather than comparative efficacy.

PMID:38781535 SUPPORT Human Clinical

"In this study we demonstrate that the degree of CD19+ B cell, naïve and memory B cell depletion after rituximab treatment predicts duration of response and patterns of IgG4-RD flare."

Depth of B-cell depletion, not depletion alone, tracks the duration of remission in this cohort. The observation does not identify which B-lineage function (antigen presentation, cytokine support, or antibody output) is the one that matters.

Inebilizumab

Action: Pharmacotherapy NCIT:C15986

Agent: inebilizumab NCIT:C88283

Platform: Monoclonal antibody

CD19-directed cytolytic antibody with an FDA indication for adult IgG4-RD. In MITIGATE, 135 participants received standardized glucocorticoid tapering; flare occurred in 10% versus 60% on placebo, with hazard ratio 0.13. Serious adverse events occurred in 18% versus 9%. Reduced flares demonstrate clinical efficacy but do not isolate antigen presentation, antibody production or direct profibrotic signaling as the necessary B-cell function.

Mechanism Target:

INHIBITS IgG4-Positive Plasmablast Expansion — Depletes CD19-positive B-lineage compartments. The trial establishes the value of targeting this lineage, not that every mature plasma cell is removed or that a specific B-to-CTL interaction is necessary.

Show evidence (1 reference)

PMID:39541094 SUPPORT Human Clinical

"Inebilizumab targets and depletes CD19+ B cells and may be effective for treating patients with IgG4-related disease."

The Phase 3 trial describes CD19-positive B-cell depletion as the mechanism motivating inebilizumab in IgG4-RD.

Show evidence (2 references)

PMID:39541094 SUPPORT Human Clinical

"Inebilizumab reduced the risk of flares of IgG4-related disease and increased the likelihood of flare-free complete remission at 1 year, confirming the role of CD19-targeted B-cell depletion as a potential treatment for IgG4-related disease."

MITIGATE provides randomized Phase 3 evidence that CD19-targeted B-cell depletion reduces IgG4-RD flares.

url:https://www.accessdata.fda.gov/drugsatfda/docs/label/2025/761142s003lbl.pdf SUPPORT Other

"UPLIZNA is indicated for the treatment of Immunoglobulin G4-related disease (IgG4-RD) in adult patients."

The FDA label revised April 2025 establishes the adult indication.

Obexelimab

Action: Pharmacotherapy NCIT:C15986

Agent: Obexelimab NCIT:C170236

Platform: Monoclonal antibody

Investigated as a nondepleting CD19/Fc-gamma-RIIb B-cell inhibitor. Phase III INDIGO showed fewer flares and less rescue glucocorticoid exposure over 52 weeks. The randomized result supports B-cell functional inhibition; it does not establish reversal of fixed fibrosis.

Show evidence (2 references)

PMID:42233621 SUPPORT Human Clinical

"Obexelimab is a bifunctional monoclonal antibody that inhibits B-cell activity through coengagement of CD19 and FcγRIIb without inducing B-cell depletion."

The drug tests nondepleting B-cell inhibition and should not be described as B-cell depletion.

PMID:42233621 SUPPORT Human Clinical

"flares were reported in 26 patients (26.8%) in the obexelimab group and in 53 patients (54.6%) in the placebo group."

INDIGO randomized 194 participants with standardized glucocorticoid tapering; the flare hazard ratio was 0.44.

Rilzabrutinib

Action: Pharmacotherapy NCIT:C15986

Agent: Rilzabrutinib NCIT:C174769

Platform: Small molecule

Investigational reversible BTK inhibitor in IgG4-RD. A 27-person open-label phase IIa trial, including rituximab-intolerant or refractory participants, reported 19/27 flare-free and off glucocorticoids/immunosuppressants at end of treatment. Diarrhea occurred in 11/27; two serious events, including one death, were judged unrelated to study drug. Larger controlled trials are needed.

Show evidence (1 reference)

PMID:42481271 SUPPORT Human Clinical

"At the end of treatment, 70.4% (19/27) of participants were flare-free and off GCs/immunosuppressants."

The 27-person open-label phase IIa trial supports feasibility and preliminary activity; it does not estimate comparative efficacy.

Abatacept

Action: Pharmacotherapy NCIT:C15986

Agent: Abatacept NCIT:C28898

Investigational costimulation blockade. In a 10-person open-label study, 5 maintained a response at 24 weeks and 3 achieved complete remission. Response correlated with reduced plasmablasts and activated Tfh2 cells; half discontinued for flare or lack of response. These exploratory data do not prove an obligatory Tfh pathway.

Mechanism Target:

INHIBITS Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation — Costimulation blockade is associated with reduced activated Tfh2 and plasmablast compartments among responders.

Show evidence (1 reference)

PMID:35425928 SUPPORT Human Clinical

"Reductions in serum IgE, circulating plasmablasts, and activated type 2 T follicular helper (TFH2) cells correlated with response to treatment."

Correlated immune changes support pharmacodynamic interpretation rather than causal mediation.

Show evidence (1 reference)

PMID:35425928 SUPPORT Human Clinical

"Three subjects (30%) achieved the primary endpoint."

Complete remission at week 24 occurred in 3/10 in this uncontrolled proof-of-concept trial; 5/10 maintained a treatment response.

Ureteral stenting

Action: Ureteral stenting Ontology label: Stenting NCIT:C71316

Relieves urinary obstruction when indicated, alongside management of active systemic disease.

Mechanism Target:

BYPASSES Retroperitoneal Encasement and Urinary Obstruction — Mechanically bypasses the obstructive component.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related to IgG4-RD (8 ureteral stents, 8 biliary stents)."

Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune disease.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related to IgG4-RD (8 ureteral stents, 8 biliary stents)."

Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune disease.

Biliary stenting

Action: Biliary stenting Ontology label: Stenting NCIT:C71316

Provides biliary drainage when clinically indicated; anti-inflammatory treatment addresses the disease process.

Mechanism Target:

BYPASSES Pancreatobiliary Fibroinflammation and Ductal Obstruction — Mechanically bypasses the obstructive component.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related to IgG4-RD (8 ureteral stents, 8 biliary stents)."

Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune disease.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related to IgG4-RD (8 ureteral stents, 8 biliary stents)."

Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune disease.

🌍

Environmental Factors

Occupational mineral dust, vapors, gases and fumes

A Dutch age- and sex-matched study compared 101 pancreatobiliary IgG4-RD cases with 303 digestive-disease controls. Blue-collar work for more than one year was associated with disease (OR 3.66, 95% CI 2.18–6.13). Job-exposure matrices implicated selected industrial exposures, with potential residual confounding and exposure misclassification. Findings do not establish an initiating antigen or apply uniformly to systemic IgG4-RD.

Show evidence (2 references)

PMID:34816110 SUPPORT Human Clinical

"We found that exposure to several compounds led to an increased OR for developing IgG4-RD"

The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.

PMID:34816110 SUPPORT Human Clinical

"including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos."

Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.

Mechanism Target:

PREDISPOSES Pancreatobiliary Fibroinflammation and Ductal Obstruction — Occupational exposure is associated with susceptibility to the pancreatobiliary phenotype. The initiating immune or epithelial intermediates were not measured.

Show evidence (2 references)

PMID:34816110 SUPPORT Human Clinical

"We found that exposure to several compounds led to an increased OR for developing IgG4-RD"

The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.

PMID:34816110 SUPPORT Human Clinical

"including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos."

Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.

Occupational asbestos exposure

Earlier asbestos studies included idiopathic retroperitoneal fibrosis without establishing IgG4-RD in every case; their estimates must not be relabeled as IgG4-specific RPF risks.

Show evidence (3 references)

PMID:34816110 SUPPORT Human Clinical

"We found that exposure to several compounds led to an increased OR for developing IgG4-RD"

The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.

PMID:34816110 SUPPORT Human Clinical

"including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos."

Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.

PMID:25089862 SUPPORT Human Clinical

"90 patients with idiopathic RPF and 270 control participants matched for age, sex, and region of residency."

Documents the broader RPF population behind the older asbestos association.

Mechanism Target:

Show evidence (2 references)

PMID:34816110 SUPPORT Human Clinical

"We found that exposure to several compounds led to an increased OR for developing IgG4-RD"

The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.

PMID:34816110 SUPPORT Human Clinical

"including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos."

Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.

Current cigarette smoking

In 234 IgG4-RD cases and 1170 matched controls, current smoking was associated with disease overall (OR 1.79, 95% CI 1.08–2.95), chiefly in the retroperitoneal-fibrosis subgroup. Excluding RPF removed the association. This is observational susceptibility evidence; effects of cessation on IgG4-RD activity were not tested.

Show evidence (2 references)

PMID:33751033 SUPPORT Human Clinical

"This association was strongest among female cases [13 (14%) vs 19 (4%);, OR 3.79 (95% CI 1.71, 8.39)] and those with retroperitoneal fibrosis [RPF; 13 (28%) vs 13 (6%);, OR 6.93 (95% CI 2.78, 17.26)]"

Matched case-control association supports a phenotype-specific susceptibility signal, not a demonstrated molecular smoking mechanism.

PMID:33751033 SUPPORT Human Clinical

"When RPF cases were excluded, there was no longer an association between current smoking and the odds of having IgG4-RD [12 (6%) vs 57 (6%); OR 0.95 (95% CI 0.49, 1.86)]."

The null estimate outside RPF limits generalization to all organ phenotypes.

Mechanism Target:

PREDISPOSES Retroperitoneal Encasement and Urinary Obstruction — Current smoking is associated with the retroperitoneal-fibrosis phenotype. The intervening fibroinflammatory mechanism is unknown and the study did not separately test obstruction severity.

Show evidence (2 references)

PMID:33751033 SUPPORT Human Clinical

Matched case-control association supports a phenotype-specific susceptibility signal, not a demonstrated molecular smoking mechanism.

PMID:33751033 SUPPORT Human Clinical

"When RPF cases were excluded, there was no longer an association between current smoking and the odds of having IgG4-RD [12 (6%) vs 57 (6%); OR 0.95 (95% CI 0.49, 1.86)]."

The null estimate outside RPF limits generalization to all organ phenotypes.

🔬

Biochemical Markers

Serum IgG4 (Elevated)

Context: A diagnostic adjunct with imperfect sensitivity and specificity. The cited rheumatology cohort found elevation in about half of active cases using 135 mg/dL; other organ-selected cohorts differ. A normal value does not exclude disease.

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"Only 51% of the patients with active disease had elevated serum IgG4 concentrations."

Large cohort study showing that nearly half of active IgG4-RD patients have normal serum IgG4, demonstrating imperfect sensitivity.

PMID:25988916 SUPPORT Human Clinical

"patients with active disease and elevated serum IgG4 concentrations were older, had a higher IgG4-RD RI score, a greater number of organs involved, lower complement levels, higher absolute eosinophil counts, and higher IgE levels"

Elevated serum IgG4 identifies a subset with more severe disease.

Total IgG (Elevated)

Context: Total IgG can be elevated but is not universal or specific. Twenty-eight percent of active patients in the cited cohort had an elevated value.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"Twenty-eight percent of patients with active disease at baseline had an elevated total IgG concentration"

This defines the denominator and limits generalization.

Complement C3 and C4 (Decreased)

Context: C3 and C4 may be low, particularly in intrinsic kidney disease. Complement consumption supports an immune-complex hypothesis without identifying the responsible immunoglobulin subclass.

Pathograph Readouts

Readout Of Immune-Complex Complement Activation Negative

Lower measured complement is compatible with consumption but is not a direct organ-injury assay.

Show evidence (1 reference)

PMID:26357950 SUPPORT In Vitro

Patient immune-complex fractions consume complement ex vivo; mixed complexes cannot assign causality to purified IgG4 alone.

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"patients with active disease and elevated serum IgG4 concentrations were older, had a higher IgG4-RD RI score, a greater number of organs involved, lower complement levels"

Lower complement levels associated with more severe IgG4-RD phenotype.

PMID:39798124 SUPPORT Human Clinical

"Anti-C1q antibody levels correlated negatively with levels of C3 and C4, and positively with levels of IgG1, IgG4, and serum free light chains."

Association supports the complement-related clinical subset; anti-C1q positivity did not predict relapse-free survival.

Circulating plasmablasts (Increased)

Context: Disease-activity biomarker that may be elevated even when serum IgG4 is normal; not a standalone diagnostic test.

Pathograph Readouts

Readout Of IgG4-Positive Plasmablast Expansion Positive

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"the levels of circulating plasmablasts – especially IgG4+ plasmablasts – correlate well with disease activity as assessed by the IgG4-RD RI."

The cohort supports activity association.

Soluble interleukin-2 receptor (Increased)

Context: Exploratory activity-associated marker. It also correlates with primary Sjogren disease activity, so neither disease specificity nor CTL-specific causality is established.

Show evidence (1 reference)

PMID:29465360 SUPPORT Human Clinical

"serum sIL-2R levels correlate with baseline IgG4-RD RI scores and the number of affected organs in IgG4-RD (ρ=0.74, p<0.0001 and ρ=0.75, p<0.0001, respectively)."

Clinical correlation supports an activity biomarker without proving that this signal is an upstream effector.

IFN-alpha, IL-33 and associated chemokines (Increased)

Context: Research biomarkers in selected autoimmune-pancreatitis/IgG4-RD cohorts. CXCL9/CXCL10/CCL25 were studied in 33 patients, with 14 paired steroid-treatment samples; human temporal causation was not tested.

Show evidence (1 reference)

PMID:39264798 SUPPORT Human Clinical

"serum concentrations of CXCL9, CXCL10, and CCL25 were markedly higher in patients with AIP/IgG4-RD as compared with those with CP and healthy controls"

The human component is serum comparison and treatment-associated change, not tissue or cellular perturbation.

🔬

Diagnosis

Integrated clinical, imaging, serologic and tissue assessment

Assess compatible organ manifestations and image the extent of disease. Biopsy interpretation integrates morphology with organ-appropriate IgG4 cell counts and ratios, while excluding malignancy and other inflammatory mimics. Serum IgG4 or immunostaining alone is insufficient.

Show evidence (2 references)

PMID:22596100 SUPPORT Other

"Tissue IgG4 counts and IgG4:IgG ratios are secondary in importance."

The pathology consensus prioritizes morphology and clinical context.

PMID:32552502 SUPPORT Other

"IgG4-related digestive disease can be diagnosed only with a comprehensive work-up that includes histology, organ morphology at imaging, serology, search for other organ involvement, and response to glucocorticoid treatment."

The guideline supports integrated evaluation.

ACR/EULAR research classification and revised comprehensive diagnostic criteria

The 2019 ACR/EULAR framework applies entry, exclusion and weighted inclusion domains for classification; classification thresholds do not replace clinical diagnosis. The 2020 revised comprehensive diagnostic framework integrates clinical/radiologic, serologic and pathologic domains.

Show evidence (2 references)

PMID:31793250 SUPPORT Human Clinical

"In the first validation cohort, a threshold of 20 points had a specificity of 99.2%"

The classifier was validated for research and should not be equated with a standalone diagnostic test.

PMID:33274670 SUPPORT Other

"which consists of 3 domains; 1) Clinical and radiological features, 2) Serological diagnosis and 3) Pathological diagnosis."

The revised diagnostic framework integrates independent dimensions.

📈

Progression

Relapsing fibroinflammation with possible irreversible damage

Organ distribution, treatment responsiveness and progression vary. Fibrotic damage can persist despite control of inflammation; referral cohorts and claims populations differ in sex distribution and outcomes.

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"IgG4-RD was associated with damage caused by the disease (as opposed to treatment) in a total of 73 patients (58%) at the time of the initial evaluation"

The referral cohort documents accumulated organ damage, not an incident risk estimate.

PMID:37137671 SUPPORT Human Clinical

"adjusted HR of 2.51 (95% CI 1.76 to 3.56)."

Matched claims analysis found excess all-cause mortality; observational data cannot isolate disease versus treatment or residual confounding.

Predominantly adult onset with cohort-dependent sex distribution

A 125-patient referral cohort included 76 men and 49 women. Among its 103 patients with active disease, mean age at onset was 50.5 years, with wide variation. Male predominance and onset estimates differ by organ phenotype and ascertainment and are not diagnostic requirements.

Show evidence (2 references)

PMID:25988916 SUPPORT Human Clinical

"the mean age at disease onset was 50.5 years (+/- 15.1)."

This estimate applies to the 103 patients with active disease in the referral cohort.

PMID:25988916 SUPPORT Human Clinical

"The gender disparity in this cohort, however, was less prominent than often reported in the literature (male:female 1.6:1)."

Sex distribution varies across selected cohorts.

Coexisting malignancy across the disease timeline

A Japanese hospital survey estimated malignancy in 10.9% of IgG4-RD cases and malignant lymphoma in approximately 2.0%. Cancers occurred before, near and after IgG4-RD diagnosis. These prevalence estimates are not an incident cancer probability caused by IgG4-RD; age, surveillance, treatment and selection can contribute.

Show evidence (2 references)

PMID:35229347 SUPPORT Human Clinical

"The overall prevalence of malignant disease in IgG4-RD cases was estimated to be 10 900 per 100 000 cases"

Hospital-survey prevalence does not establish a unidirectional causal relationship.

PMID:35229347 SUPPORT Human Clinical

"The prevalence of malignant lymphoma in IgG4-RD cases was the highest and was estimated to be 1985 per 100 000 cases."

The lymphoma estimate is expressed per IgG4-RD cases, not the general population.

📊

Prevalence

United States, commercially insured adults; age- and sex-standardized claims-based estimate on 2019-01-01

Point Prevalence 5.3 per 100,000

Show evidence (1 reference)

PMID:37137671 SUPPORT Human Clinical

"The point prevalence ... was 5.3/100 000 persons."

Validated claims algorithm estimate; ascertainment and insured-population selection limit generalization.

United States, commercially insured adults; age- and sex-standardized 2019 estimate

Annual Incidence 1.39 per 100,000

Show evidence (1 reference)

PMID:37137671 SUPPORT Human Clinical

"The incidence of IgG4-RD increased during the study period from 0.78 to 1.39 per 100 000 person-years in 2015 and 2019, respectively."

Calendar-year incidence is distinguished from point prevalence.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from IgG4-Related Disease:

Malignancy involving affected organs

Overlapping Features Pancreatic, biliary, glandular and lymphoid malignancies can mimic mass-forming inflammation.

Distinguishing Features

Use imaging and appropriate tissue assessment to establish morphology and clonality; avoid attributing a mass to IgG4-RD on serum IgG4 alone.

Show evidence (1 reference)

PMID:25988916 SUPPORT Human Clinical

"The surgical procedures were usually performed for the purpose of diagnosis or for erroneous diagnoses of cancer."

The cohort demonstrates the importance of this differential.

Sjogren disease

Overlapping Features Lacrimal/salivary disease and tubulointerstitial nephritis can overlap.

Distinguishing Features

Clinical distribution, tissue morphology and anti-SSA/Ro or anti-SSB/La antibodies help distinguish the diseases; antibody negativity alone is not conclusive.

Show evidence (1 reference)

PMID:30596168 SUPPORT Other

"anti-SSA/Ro and anti-SSB/La antigens are normally detectable in primary Sjögren’s syndrome−TIN."

The kidney cohort discusses differentiation from Sjogren-associated nephritis.

📊

Related Datasets

Transcriptomic analysis of double-negative B cell subsets in IgG4-related disease geo:GSE220582

IgD-CD27- “double negative” (DN) B cells are known to be expanded in the blood in many disease contexts and the IgD-CD27-CXCR5-CD11c+ DN2 B cell subset has been most widely studied in autoimmune diseases. In addition to DN2 B cells, a distinct IgD-CD27-CXCR5-CD11c- DN3 B cell subset accumulates in the blood both in IgG4-related disease, an autoimmune disease in which inflammation and fibrosis can be reversed by B cell depletion, and in severe COVID-19. DN3 B cells, but not DN2 B cells, prominently accumulate in the blood and end-organs of IgG4-related disease.

human BULK RNA SEQ n=15

PMID:37300833

Identified by GEO DataSets index search for IgG4-Related Disease (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.

Gene expression of CD4+CD8+ Tfh cells in lesions of IgG4-related disease and CD4+CD8+ Tfh in tonsil. geo:GSE202617

To further know features of CD4+CD8+ Double positive (DP)-Tfh cells in respective lymphoid tissues, we subsequently investigated transcriptomes of DP-Tfh cells in submandibular gland lesions of IgG4-RD in comparison to those of DP-Tfh cells in tonsils. Results showed that DP-Tfh cells of IgG4-RD lesions were more apt to present CTL-related genes such as Eomes and granzymes than DP-Tfh cells in tonsils. It was also noted that the level of CD70 in DP-Tfh cells of IgG4-RD lesions was higher than that of tonsillar DP-Tfh cells. Genes related to Tfh cell function were seemed to be presented in DP-Tfh cells of tonsils compared to DP-Tfh cells of IgG4-RD lesions.

human MICROARRAY n=8

PMID:36091071

🔬

Clinical Trials

NCT04540497 PHASE_III ACTIVE_NOT_RECRUITING

MITIGATE, 135 participants; published randomized phase III flare results, with long-term follow-up ongoing.

Show evidence (1 reference)

clinicaltrials:NCT04540497 SUPPORT Other

"This study aims to evaluate the efficacy and safety of inebilizumab for the prevention of flare of Immunoglobulin G4-related disease (IgG4-RD)."

The registry establishes study design and purpose, not efficacy results.

NCT05662241 PHASE_III ACTIVE_NOT_RECRUITING

INDIGO, 194 participants; published randomized phase III nondepleting B-cell inhibition results, with long-term follow-up ongoing.

Show evidence (1 reference)

clinicaltrials:NCT05662241 SUPPORT Other

"This study aims to examine the efficacy and safety of obexelimab for the prevention of flare of IgG4-related disease (IgG4-RD)"

The registry establishes study design and purpose, not efficacy results.

NCT04660565 PHASE_IV UNKNOWN

Randomized open-label belimumab maintenance study, registered in 2020 with planned enrollment 60. Registry status is UNKNOWN; the listed phase IV does not establish an IgG4-RD regulatory indication or efficacy.

Show evidence (1 reference)

clinicaltrials:NCT04660565 SUPPORT Other

"This randomized, control clinical trial aimed to evaluate the tolerability and the efficacy of Belimumab for maintenance treatment for IgG4-RD."

The registry establishes study design and purpose, not efficacy results.

NCT03669861 PHASE_II COMPLETED

Completed 10-person phase II abatacept proof-of-concept study, with published heterogeneous response.

Show evidence (1 reference)

clinicaltrials:NCT03669861 SUPPORT Other

"This is a Phase 2, single center, proof of concept clinical trial in subjects with active IgG4-Related Disease (IgG4-RD). Approximately 10 subjects with active IgG4-RD will be enrolled into this study. Subjects will receive weekly subcutaneous doses of abatacept (125mg) for 24 doses (24 weeks)."

The registry establishes study design and purpose, not efficacy results.

NCT04520451 PHASE_II COMPLETED

Completed 27-person phase IIa rilzabrutinib study; published results are uncontrolled.

Show evidence (1 reference)

clinicaltrials:NCT04520451 SUPPORT Other

"This is a Phase 2a, multi-center, open-label, two-arm study of approximately 25 patients with active IgG4-related disease (IgG4-RD). The two arms include (1) Experimental: rilzabrutinib with glucocorticoids and (2) Active Comparator: glucocorticoids only."

The registry establishes study design and purpose, not efficacy results.

NCT07148791 PHASE_II RECRUITING

Recruiting phase II anti-BCMA/CD19 CAR-T study, planned enrollment nine. Registry design is prospective evidence of investigation, not evidence of benefit.

Show evidence (1 reference)

clinicaltrials:NCT07148791 SUPPORT Other

"The goal of this clinical trial is to test the safety and potential benefit of a new immune cell therapy called anti-BCMA-CD19 CAR-T cells"

The registry establishes study design and purpose, not efficacy results.

🧫

Experimental Models

Patient B-cell and fibroblast coculture CO_CULTURE

Patient B cells or sorted plasmablasts cocultured with primary pancreatic or skin fibroblasts; transwells and PDGF-B blocking test soluble collagen-promoting activity.

Cell source

Circulating patient B cells and sorted plasmablasts with primary human pancreatic or skin fibroblasts

Publication

PMID:31319101

Pathograph links

Fibroblast Activation and Collagen Production perturbs fidelity: moderate

Limitations: Small patient samples and cultured-cell activation do not reproduce storiform tissue architecture or establish dominance in vivo.

Readouts

Fibroblast collagen production after PDGF-B blockade

Direction: DECREASED

Interpretation: Blocking PDGF-B reduces the collagen-promoting effect of patient B cells compared with an isotype control; residual activity supports additional mediators.

Show evidence (1 reference)

PMID:31319101 SUPPORT In Vitro

Blocking PDGF-B reduces the collagen-promoting effect of patient B cells compared with an isotype control; residual activity supports additional mediators.

Show evidence (1 reference)

PMID:31319101 SUPPORT In Vitro

Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations with control B cells imply additional mediators.

Show evidence (1 reference)

PMID:31319101 SUPPORT In Vitro

Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations with control B cells imply additional mediators.

Patient Tfh and B-cell coculture CO_CULTURE

Circulating patient Tfh subsets tested for plasmablast-differentiation and IgG4-production helper activity.

Cell source

Circulating human Tfh subsets and naive B cells

Publication

PMID:27411315

Pathograph links

Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation perturbs fidelity: moderate

Limitations: Stimulated cultures and circulating subset definitions do not establish that every tissue Tfh population has the same function.

Readouts

Naive B-cell differentiation into plasmablasts

Direction: INCREASED

Interpretation: Tfh2 cocultures produce more plasmablast differentiation than the tested Tfh1 and Tfh17 cocultures, measuring helper function rather than tissue fibrosis.

Show evidence (1 reference)

PMID:27411315 SUPPORT In Vitro

"In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells."

Tfh2 cocultures produce more plasmablast differentiation than the tested Tfh1 and Tfh17 cocultures, measuring helper function rather than tissue fibrosis.

Show evidence (1 reference)

PMID:27411315 SUPPORT In Vitro

"In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells."

Patient-derived helper-cell coculture tests a functional B-cell differentiation output.

Show evidence (1 reference)

PMID:27411315 SUPPORT In Vitro

"In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells."

Patient-derived helper-cell coculture tests a functional B-cell differentiation output.

Anti-IL-1RA functional cell assays CELL_LINE

Recombinant plasmablast antibody and patient plasma tested with IL-1 signaling reporter and epithelial/fibroblast mediator assays.

Cell source

HEK-Blue IL-1beta reporter cells, A549 lung epithelial cells and MRC-5 lung fibroblasts with patient-derived antibody or plasma

Publication

PMID:33974929

Pathograph links

Autoantibody-Mediated IL-1RA Neutralization perturbs fidelity: moderate

Limitations: Subset autoantibody activity and mixed plasma do not isolate IgG4-only causality or show human tissue fibrosis.

Readouts

SEAP release from IL-1 receptor reporter cells

Direction: INCREASED

Interpretation: The patient-derived G4-21 antibody increases IL-1 receptor reporter output by interfering with added IL-1RA under IL-1beta stimulation.

Show evidence (1 reference)

PMID:33974929 SUPPORT In Vitro

"Incubating IL-1RA/IL-1β-stimulated reporter cells with the patient-derived mAb G4–21 resulted in a significant increase in SEAP production as compared to control antibodies"

The patient-derived G4-21 antibody increases IL-1 receptor reporter output by interfering with added IL-1RA under IL-1beta stimulation.

Show evidence (1 reference)

PMID:33974929 SUPPORT In Vitro

Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.

Show evidence (1 reference)

PMID:33974929 SUPPORT In Vitro

Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.

Human cholangiocyte protective-barrier assays CELL_LINE

H69 cholangiocytes with ANXA11 knockdown and antibody-containing patient serum test ANO1 trafficking and bicarbonate-associated protection.

Cell source

Human H69 cholangiocyte cell line with ANXA11 knockdown or patient serum

Publication

PMID:34718050

Pathograph links

Cholangiocyte Protective Barrier Impairment perturbs fidelity: moderate

Limitations: Mixed serum exposure and knockdown are distinct perturbations; results do not prove sufficiency for human biliary fibrosis.

Readouts

ANO1 surface expression after patient-serum exposure

Direction: DECREASED

Interpretation: Patient-serum exposure reduces cholangiocyte ANO1 surface expression; reduced transporter localization is a readout of impaired protective secretory machinery.

Show evidence (1 reference)

PMID:34718050 SUPPORT In Vitro

"Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression."

Patient-serum exposure reduces cholangiocyte ANO1 surface expression; reduced transporter localization is a readout of impaired protective secretory machinery.

Show evidence (1 reference)

PMID:34718050 SUPPORT In Vitro

"Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression."

Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective secretory machinery; mixed serum is not an isolated isotype perturbation.

Show evidence (1 reference)

PMID:34718050 SUPPORT In Vitro

"Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression."

Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective secretory machinery; mixed serum is not an isolated isotype perturbation.

🐁

Animal Models

Poly(I:C)-induced autoimmune pancreatitis

Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.

Species

Mus musculus

Genotype

Female MRL/MpJ mice receiving repeated poly(I:C)

Publication

PMID:39264798

Pathograph links

Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification perturbs fidelity: moderate

Limitations: Induced female-mouse pancreatitis is not spontaneous systemic human disease; serum associations in 33 patients do not validate temporal initiation.

Readouts

Pancreatic pDC abundance after CCL25 blockade

Direction: DECREASED

Interpretation: Anti-CCL25 treatment reduces pancreatic pDC recruitment compared with control antibody, testing the recruitment arm of the induced cytokine loop.

Show evidence (1 reference)

PMID:39264798 SUPPORT Model Organism

"treatment with anti-CCL25 Ab significantly reduced the percentages of pDCs, CD11b+myeloid cells, and CD11c+DCs as compared with the administration of control Ab"

Anti-CCL25 treatment reduces pancreatic pDC recruitment compared with control antibody, testing the recruitment arm of the induced cytokine loop.

Show evidence (1 reference)

PMID:39264798 SUPPORT Model Organism

"the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of experimental AIP"

Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.

Show evidence (1 reference)

PMID:39264798 SUPPORT Model Organism

"the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of experimental AIP"

Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.

Human TLR7 transgenic mouse

TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.

Species

Mus musculus

Genotype

huTLR7-transgenic C57BL/6

Publication

PMID:31339007

Pathograph links

TLR7-Associated Macrophage IL-33 Production perturbs fidelity: moderate

Limitations: Mouse IgG1 is not human IgG4 and transgenic TLR7 activation does not establish a common human initiating lesion.

Readouts

Submandibular, pancreatic and lung focus and fibrosis scores

Direction: INCREASED

Interpretation: Histological inflammation and fibrosis scores are higher in huTLR7-transgenic than wild-type animals; these scores do not identify human IgG4 antibody function.

Show evidence (1 reference)

PMID:31339007 SUPPORT Model Organism

"In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice"

Histological inflammation and fibrosis scores are higher in huTLR7-transgenic than wild-type animals; these scores do not identify human IgG4 antibody function.

Show evidence (1 reference)

PMID:31339007 SUPPORT Model Organism

"In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice"

TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.

Show evidence (1 reference)

PMID:31339007 SUPPORT Model Organism

"In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice"

TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.

Slc29a3-deficient sialadenitis

Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.

Species

Mus musculus

Genotype

Slc29a3-/-

Publication

PMID:41332187

Pathograph links

Salivary and Lacrimal Gland Fibroinflammation perturbs fidelity: moderate

Limitations: Sialadenitis overlaps Sjogren disease; lymphocyte infiltration is present, so innate-only sufficiency and systemic IgG4-RD fidelity are not established.

Readouts

Damage to Aqp5-positive salivary acinar and intercalated duct cells

Direction: INCREASED

Interpretation: Loss of salivary epithelial integrity is the measured tissue injury; it supports sialadenitis overlap without validating a model of every IgG4-RD organ.

Show evidence (1 reference)

PMID:41332187 SUPPORT Model Organism

"SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs"

Loss of salivary epithelial integrity is the measured tissue injury; it supports sialadenitis overlap without validating a model of every IgG4-RD organ.

Show evidence (1 reference)

PMID:41332187 SUPPORT Model Organism

"SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs"

Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.

Show evidence (1 reference)

PMID:41332187 SUPPORT Model Organism

"SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs"

Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.

Patient immunoglobulin passive transfer

Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.

Species

Mus musculus

Genotype

Neonatal male BALB/c recipient mice

Publication

PMID:26964842

Pathograph links

Organ-Specific Fibroinflammatory Injury perturbs fidelity: moderate

Limitations: Neonatal xenotransfer models context-dependent antibody effects, not spontaneous adult disease or universal protection by IgG4.

Readouts

Pancreatic injury after IgG4 coadministration with patient IgG1

Direction: DECREASED

Interpretation: Coadministration reduces IgG1-driven injury relative to IgG1 alone; this does not negate injury caused by separately administered patient IgG4.

Show evidence (1 reference)

PMID:26964842 SUPPORT Model Organism

"The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4."

Coadministration reduces IgG1-driven injury relative to IgG1 alone; this does not negate injury caused by separately administered patient IgG4.

Show evidence (1 reference)

PMID:26964842 SUPPORT Model Organism

"The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4."

Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.

Show evidence (1 reference)

PMID:26964842 SUPPORT Model Organism

"The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4."

Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.

{ }

Source YAML

click to show

name: IgG4-Related Disease
creation_date: '2026-03-06T00:00:00Z'
category: Autoimmune
disease_term:
  preferred_term: IgG4-related disease
  term:
    id: MONDO:0017287
    label: immunoglobulin G4-related sclerosing disease
parents:
- Autoimmune Disease
- Fibroinflammatory Disease
description: >-
  An immune-mediated fibroinflammatory disease that produces tumefactive lesions in one or multiple organs,
  commonly involving the pancreas, bile ducts, salivary and lacrimal glands, kidneys, retroperitoneum
  and aorta. Characteristic pathology combines lymphoplasmacytic inflammation, often rich in IgG4-positive
  plasma cells, with storiform fibrosis and obliterative phlebitis; the full pattern varies by organ and
  disease stage. B-lineage, T-cell, myeloid and stromal mechanisms contribute, with unresolved initiating
  events and heterogeneous autoantibody effects. Recurrent inflammation and fibrosis can cause obstructive
  complications and irreversible organ dysfunction.
has_subtypes:
- name: Pancreato-hepato-biliary pattern
  description: >-
    Prominent pancreatic and biliary involvement. These are latent clinical patterns, not proven distinct
    immune mechanisms.
  evidence:
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
- name: Retroperitoneal fibrosis and/or aortitis pattern
  description: >-
    Prominent retroperitoneal and vascular involvement. These are latent clinical patterns, not proven
    distinct immune mechanisms.
  evidence:
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
- name: Head and neck-limited pattern
  description: >-
    Disease concentrated in head and neck sites. These are latent clinical patterns, not proven distinct
    immune mechanisms.
  evidence:
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
- name: Mikulicz pattern with systemic involvement
  description: >-
    Lacrimal and salivary involvement together with systemic disease. These are latent clinical patterns,
    not proven distinct immune mechanisms.
  evidence:
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
mechanistic_hypotheses:
- hypothesis_group_id: plasmablast_autoantigen_fibrosis_driver_model
  hypothesis_label: Plasmablast-Autoantigen Fibrosis Driver Model
  status: CANONICAL
  description: >-
    An adaptive immune framework in which antigen-experienced B cells, plasmablasts and T-cell populations
    participate in chronic fibroinflammation. Tfh cells enhance IgG4 production and plasmablast differentiation
    in coculture; B-lineage cells can directly stimulate fibroblast collagen production, and cytotoxic
    T cells show tissue injury and profibrotic mediator programs. Universal autoantigen identity, the
    precise B-cell-to-CTL interaction and the CTL-specific route to storiform architecture remain unresolved.
  evidence:
  - reference: PMID:24815737
    reference_title: De novo oligoclonal expansions of circulating plasmablasts in active and relapsing IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Clonally expanded CD19(+)CD27(+)CD20(-)CD38(hi) plasmablasts are a hallmark of active IgG4-RD.
    explanation: >-
      Human B-cell repertoire data support plasmablast expansion as a central disease-activity feature
      in the canonical adaptive immune model.
  - reference: PMID:28166682
    reference_title: Clonally expanded cytotoxic CD4(+) T cells and the pathogenesis of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      CD4+ CTLs in affected tissues secrete pro-fibrotic cytokines including IL-1β, TGF-β1, and IFN-γ
      as well as cytolytic molecules such as perforin and granzymes A and B.
    explanation: >-
      Review-level synthesis supports CD4+ cytotoxic T cells as the immune-cell arm most directly linked
      to fibrogenic mediator production.
- hypothesis_group_id: innate_first_bystander_model
  hypothesis_label: Innate-First Bystander Activation Model
  status: ALTERNATIVE
  description: >-
    Innate receptor activation can promote B-cell responses and fibroinflammation in cell systems and
    mouse models. An innate-initiation/adaptive-amplification sequence is a plausible alternative in human
    IgG4-RD, but its temporal transition is unobserved. Established adaptive responses show clonal selection;
    that disfavors a purely nonspecific bystander explanation without excluding a concurrent or earlier
    nonspecific component.
  evidence:
  - reference: PMID:31339007
    reference_title: Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      TLR-7-expressing M2 macrophages may promote the activation of Th2 immune responses via IL-33 secretion
      in IgG4-RD.
    explanation: >-
      This concluding sentence synthesizes human tissue, cultured macrophage and transgenic-mouse results.
      It supports an innate amplifier, not temporal priority in human disease.
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      murine AIP was initiated by TLR3-bearing conventional DCs in the uninflamed pancreas whose activation
      by the TLR3 ligand poly(I:C) caused IFN-α, CXCL9, and CXCL10 secretion
    explanation: >-
      In the MRL/MpJ poly(I:C) autoimmune pancreatitis model, innate TLR3+ conventional dendritic cells
      act first in uninflamed tissue and only then recruit T cells and plasmacytoid DCs, providing the
      strongest temporal evidence for the innate-first component of the hypothesis.
  - reference: PMID:41332187
    reference_title: TLR7 responses to nucleosides drive sialadenitis in Slc29a3-deficient mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: lysosomal accumulation of endogenous nucleosides is sufficient to drive autoimmune sialadenitis
    explanation: >-
      Slc29a3-deficient mice develop TLR7-associated autoimmune sialadenitis, a phenotype shared with
      other diseases. The experiment does not establish isolated innate-cell sufficiency without lymphocytes
      or reproduce systemic human IgG4-RD.
  - reference: PMID:21971969
    reference_title: Involvement of activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors in enhanced IgG4 responses in autoimmune pancreatitis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells
      in a BAFF-dependent and T cell-independent manner
    explanation: >-
      NOD2 activation induces BAFF-dependent, T-cell-independent IgG4 production in cultured healthy-control
      cells; this does not by itself establish in-vivo class-switch kinetics or human disease initiation.
  - reference: PMID:39541094
    reference_title: Inebilizumab for Treatment of IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Inebilizumab reduced the risk of flares of IgG4-related disease and increased the likelihood of
      flare-free complete remission at 1 year, confirming the role of CD19-targeted B-cell depletion as
      a potential treatment for IgG4-related disease
    explanation: >-
      The randomized trial establishes substantial flare reduction through CD19-targeted intervention.
      It limits an exclusively irrelevant-B-cell account but does not identify the relevant B-lineage
      function or prove universal biological necessity.
  notes: >-
    The report is useful for innate component pathways but the distinctive composite hypothesis remains
    weakly supported/unresolved. Mouse initiation does not establish human initiation. Anti-CD19 efficacy
    shows therapeutic relevance of B-lineage functions, not universal necessity of antigen-specific adaptive
    immunity. NOD2/BAFF and basophil experiments concern cultured cells; the pDC pathway has separate
    primary evidence, although the report mislabels a review as an independent study. The two-phase transition
    remains an open alternative and is not encoded as a proven causal edge.
pathophysiology:
- name: Candidate Autoantigen Recognition and Antigen Presentation
  mechanism_confidence: PROVISIONAL
  description: >-
    Oligoclonal self-reactive B-lineage responses and candidate autoantibodies support loss of tolerance
    in subsets. A universal initiating autoantigen is unknown. PHB1, annexin A11, laminin 511-E8 and galectin-3
    binding results vary across cohorts; a negative four-antigen panel does not exclude other autoreactivity.
    B-lineage antigen presentation to cytotoxic T cells remains inferred rather than experimentally isolated.
  role: trigger
  cell_types:
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  biological_processes:
  - preferred_term: Antigen processing and presentation
    term:
      id: GO:0019882
      label: antigen processing and presentation
  - preferred_term: B cell activation
    term:
      id: GO:0042113
      label: B cell activation
  downstream:
  - target: CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production
    description: >-
      Candidate antigen presentation may sustain the CTL response; the relevant antigen, presenting cell
      and functional interaction are unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27667138
      reference_title: '"How I manage" IgG4-Related Disease.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        This cell is presumed to be sustained by continuous antigen presentation by cells of the B cell
        lineage, particularly plasmablasts.
      explanation: >-
        The review explicitly labels B-lineage antigen presentation to the pathogenic CTL population presumed.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  - target: Autoantibody-Mediated IL-1RA Neutralization
    description: A subset of autoreactive clones recognizes and functionally interferes with IL-1RA.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33974929
      reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared
        with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic
        mediator production in vitro.
      explanation: >-
        Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in
        a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.
  - target: Cholangiocyte Protective Barrier Impairment
    description: >-
      Anti-annexin-containing serum can impair cholangiocyte protective machinery, while anti-laminin
      pathogenic effects remain incompletely isolated.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34718050
      reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface
        expression.
      explanation: >-
        Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective
        secretory machinery; mixed serum is not an isolated isotype perturbation.
    - reference: PMID:38524667
      reference_title: Laminin 511-E8, an autoantigen in IgG4-related cholangitis, contributes to cholangiocyte protection.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Knockdown of laminin 511 constituents increased toxic bile acid permeation and GCDC-induced apoptosis.
      explanation: >-
        Gene knockdown establishes laminin-dependent protection but does not by itself demonstrate that
        patient anti-laminin antibodies reproduce knockdown.
  evidence:
  - reference: PMID:24815737
    reference_title: De novo oligoclonal expansions of circulating plasmablasts in active and relapsing IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cloning and expression of immunoglobulin heavy and light chain genes from expanded plasmablasts
      at the peak of disease reveals that disease-associated IgG4 antibodies are self-reactive.
    explanation: >-
      Plasmablast-derived antibody cloning supports autoreactivity in the active disease B-lineage response.
  - reference: PMID:31612628
    reference_title: Disease Severity Linked to Increase in Autoantibody Diversity in IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of these 86 patients, 32 (37%) had IgG4 antibodies to ≥1 of the 4 autoantigens and 12 (14%) showed
      reactivity with ≥2 of the tested antigens.
    explanation: >-
      Candidate autoantigens are documented, but the study also shows that none is a universal IgG4-RD
      antigen.
- name: Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation
  description: >-
    Follicular and extrafollicular helper T-cell populations provide B-cell help that promotes plasmablast
    differentiation and IgG4 production. Patient-derived circulating Tfh subsets and lesional salivary-gland
    Tfh cells have increased B-cell-helper activity in coculture. IL-4-positive BATF-positive and IL-10-positive
    LAG3-positive tissue populations are associated with polarized IgG4 responses; these phenotypes should
    not be treated as interchangeable with classical GATA3-positive Th2 cells.
  cell_types:
  - preferred_term: T follicular helper cell
    term:
      id: CL:0002038
      label: T follicular helper cell
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  biological_processes:
  - preferred_term: Isotype switching
    term:
      id: GO:0045190
      label: isotype switching
  - preferred_term: Plasma cell differentiation
    term:
      id: GO:0002317
      label: plasma cell differentiation
  downstream:
  - target: IgG4-Positive Plasmablast Expansion
    description: Tfh-derived help promotes B-cell differentiation into plasmablasts in patient-derived cultures.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27411315
      reference_title: Enhanced IgG4 production by follicular helper 2 T cells and the involvement of follicular helper 1 T cells in the pathogenesis of IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts
        compared to Tfh1 or Tfh17 cells.
      explanation: >-
        The patient-derived coculture directly tests B-cell help, while its subset definition and culture
        conditions limit in-vivo extrapolation.
    - reference: PMID:28916523
      reference_title: 'Cutting Edge: A Critical Role of Lesional T Follicular Helper Cells in the Pathogenesis of IgG4-Related Disease.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Tfh cells from IgG4-DS submandibular glands had higher expression of B cell lymphoma 6 and a greater
        capacity to help B cells produce IgG4 than did tonsillar Tfh cells.
      explanation: >-
        Lesional Tfh cells support IgG4 production in the glandular disease context; tonsillar comparators
        are not matched unaffected salivary tissue.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  - target: Enhanced IgG4 Antibody Production
    description: Lesional Tfh helper activity increases IgG4 production in B-cell coculture.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:28916523
      reference_title: 'Cutting Edge: A Critical Role of Lesional T Follicular Helper Cells in the Pathogenesis of IgG4-Related Disease.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: a greater capacity to help B cells produce IgG4 than did tonsillar Tfh cells.
      explanation: Functional coculture supports this helper route.
  evidence:
  - reference: PMID:29253269
    reference_title: Correlation of T follicular helper cells and plasmablasts with the development of organ involvement in patients with IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The association found between Tfh cells and plasmablasts, linked with biological plausibility, suggests
      that Tfh cells contribute to the pathogenesis of IgG4-RD.
    explanation: >-
      Human immunophenotyping supports the modeled Tfh-plasmablast axis upstream of IgG4 class switching
      and plasmablast expansion.
  - reference: PMID:27411315
    reference_title: Enhanced IgG4 production by follicular helper 2 T cells and the involvement of follicular helper 1 T cells in the pathogenesis of IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts
      compared to Tfh1 or Tfh17 cells.
    explanation: >-
      The patient-derived coculture directly tests B-cell help, while its subset definition and culture
      conditions limit in-vivo extrapolation.
  - reference: PMID:28916523
    reference_title: 'Cutting Edge: A Critical Role of Lesional T Follicular Helper Cells in the Pathogenesis of IgG4-Related Disease.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Tfh cells from IgG4-DS submandibular glands had higher expression of B cell lymphoma 6 and a greater
      capacity to help B cells produce IgG4 than did tonsillar Tfh cells.
    explanation: >-
      Lesional Tfh cells support IgG4 production in the glandular disease context; tonsillar comparators
      are not matched unaffected salivary tissue.
  - reference: PMID:35568079
    reference_title: 'Distinct disease-specific Tfh cell populations in 2 different fibrotic diseases: IgG(4)-related disease and Kimura disease.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We encountered abundant infiltrating IL-10-expressing LAG3+ Tfh cells in patients with IgG4-RD.
    explanation: >-
      Human single-cell and tissue imaging identifies an IL-10-positive population without proving its
      independent necessity.
- name: IgG4-Positive Plasmablast Expansion
  description: >-
    Circulating plasmablasts, many of which are IgG4-positive and clonally expanded, are elevated in active
    disease and fall with B-cell depletion. They are modeled separately from mature tissue plasma cells
    because they report disease activity, relapse biology, and CD19-targeted therapeutic vulnerability.
  cell_types:
  - preferred_term: Plasmablast
    term:
      id: CL:0000980
      label: plasmablast
  biological_processes:
  - preferred_term: B cell activation
    term:
      id: GO:0042113
      label: B cell activation
  - preferred_term: Isotype switching
    term:
      id: GO:0045190
      label: isotype switching
  downstream:
  - target: CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production
    description: >-
      B-cell depletion-associated CTL reduction is compatible with B-lineage support through antigen presentation
      or other functions.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27667138
      reference_title: '"How I manage" IgG4-Related Disease.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        This cell is presumed to be sustained by continuous antigen presentation by cells of the B cell
        lineage, particularly plasmablasts.
      explanation: >-
        The review explicitly labels B-lineage antigen presentation to the pathogenic CTL population presumed.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  - target: B-Lineage Profibrotic Signaling
    description: >-
      Expanded plasmablasts include cells with intrinsic profibrotic programs and collagen-promoting activity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        fibroblasts cultured with circulating plasmablasts produced significantly more collagen compared
        to control fibroblasts.
      explanation: >-
        Sorted patient plasmablasts stimulate collagen in coculture; the experiment does not isolate antibody
        isotype as the cause.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  evidence:
  - reference: PMID:24817416
    reference_title: Plasmablasts as a biomarker for IgG4-related disease, independent of serum IgG4 concentrations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Circulating plasmablasts are elevated in active IgG4-RD, even in patients with normal serum IgG4
      concentrations.
    explanation: >-
      Human flow-cytometry data support plasmablast expansion as a distinct active-disease B-lineage node.
  - reference: PMID:24815737
    reference_title: De novo oligoclonal expansions of circulating plasmablasts in active and relapsing IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These expanded plasmablasts are oligoclonal and exhibit extensive somatic hypermutation, and their
      numbers decrease after rituximab-mediated B-cell depletion therapy; this loss correlates with disease
      remission.
    explanation: >-
      Repertoire sequencing and treatment-response data support a clonally expanded, disease-linked plasmablast
      compartment.
- name: IgG4-Positive Plasma Cell Infiltration
  description: >-
    IgG4-bearing plasma cells accumulate in affected tissues as a characteristic histological component.
    Plasmablasts and mature plasma cells differ in phenotype and treatment susceptibility. The exact contribution
    of each compartment to antibodies, matrix remodeling and tissue injury varies; IgG4 staining alone
    does not establish disease or antibody pathogenicity.
  cell_types:
  - preferred_term: Plasma cell
    term:
      id: CL:0000786
      label: plasma cell
  biological_processes:
  - preferred_term: Immune response
    term:
      id: GO:0006955
      label: immune response
  - preferred_term: Inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IgG4-related disease (IgG4-RD) has emerged over the last decade as a unique immune-mediated condition
      that links multiple fibro-inflammatory disorders previously regarded as separate entities
    explanation: Establishes IgG4-RD as a unified immune-mediated fibroinflammatory condition.
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The gold-standard for the diagnosis of IgG4-RD, regardless of the organ(s) involved, is the identification
      of typical histopathology features (e.g., lymphoplasmacytic infiltrate, storiform fibrosis, obliterative
      phlebitis) in the context of a significant IgG4+ plasma cell infiltrate
    explanation: >-
      Confirms lymphoplasmacytic infiltrate with IgG4+ plasma cells as the histopathological hallmark.
- name: CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production
  description: >-
    Clonally expanded CD4-positive cytotoxic T lymphocytes infiltrate IgG4-RD lesions and produce inflammatory
    and profibrotic mediators, including IL-1beta, TGF-beta1, and IFN-gamma in salivary and lacrimal gland
    disease.
  cell_types:
  - preferred_term: CD4-positive cytotoxic T lymphocyte
    term:
      id: CL:0000624
      label: CD4-positive, alpha-beta T cell
  biological_processes:
  - preferred_term: Cytokine production
    term:
      id: GO:0001816
      label: cytokine production
  - preferred_term: Inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Fibroblast Activation and Collagen Production
    description: >-
      CTL cytokine expression suggests a profibrotic signal, but direct IgG4-RD CTL-to-fibroblast perturbation
      remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:26971690
      reference_title: Clonal expansion of CD4(+) cytotoxic T lymphocytes in patients with IgG4-related disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The dominant T cells infiltrating a range of inflamed IgG4-RD tissue sites were clonally expanded CD4(+) CTLs that expressed SLAMF7, granzyme A, IL-1β, and TGF-β1.
      explanation: Lesional CTL cytokine expression supplies a positive but indirect profibrotic rationale; it does not isolate a CTL-to-fibroblast response.
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: NO_EVIDENCE
      evidence_source: OTHER
      snippet: conclusive evidence that they drive fibrosis have not yet been obtained
      explanation: >-
        The primary B-cell study explicitly distinguishes CTL cytokine associations from demonstrated
        CTL-driven fibrosis.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  - target: Cytotoxic T-Cell-Associated Mesenchymal Injury
    description: >-
      Lesional cytotoxic T-cell populations are associated with apoptosis of mesenchymal target cells;
      CTL-specific causation remains inferred.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32485263
      reference_title: CD4(+) and CD8(+) cytotoxic T lymphocytes may induce mesenchymal cell apoptosis in IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        CD4+CTLs and CD8+CTLs may induce apoptotic cell death in tissues of patients with IgG4-RD with
        preferential targeting of nonendothelial, nonimmune cells of mesenchymal origin.
      explanation: >-
        The human tissue study links cytotoxic effectors and apoptosis without a target-cell killing perturbation.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
  evidence:
  - reference: PMID:26971690
    reference_title: Clonal expansion of CD4(+) cytotoxic T lymphocytes in patients with IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IgG4-RD is prominently linked to clonally expanded IL-1β- and TGF-β1-secreting CD4(+) CTLs in both
      peripheral blood and inflammatory tissue lesions.
    explanation: >-
      Human cohort data support clonally expanded IL-1beta- and TGF-beta1-secreting CD4+ CTLs as a distinct
      pathogenic effector node.
  - reference: PMID:27358392
    reference_title: Lesional CD4+ IFN-γ+ cytotoxic T lymphocytes in IgG4-related dacryoadenitis and sialoadenitis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: A large fraction of CD4+GZMA+ CTLs in SMGs from patients with IgG4-DS secreted IFN-γ.
    explanation: >-
      This salivary-gland IgG4-RD study supports IFN-gamma secretion by lesional CD4+ cytotoxic T cells.
  - reference: PMID:32485263
    reference_title: CD4(+) and CD8(+) cytotoxic T lymphocytes may induce mesenchymal cell apoptosis in IgG(4)-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      CD4+CTLs and CD8+CTLs may induce apoptotic cell death in tissues of patients with IgG4-RD with preferential
      targeting of nonendothelial, nonimmune cells of mesenchymal origin.
    explanation: >-
      Human blood and tissue analyses link cytotoxic T-cell effector programs to mesenchymal-cell injury,
      a plausible bridge to fibrotic repair.
  - reference: PMID:41766862
    reference_title: 'Beyond the Th2 paradigm: CD4+ cytotoxic T lymphocytes as key drivers of tissue damage and fibrosis in IgG4-related disease.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Emerging data highlight the extensive, oligoclonally expanded infiltration of CD4+ cytotoxic T lymphocytes
      (CTLs) deep within lesions. These cells possess dual cytotoxic and profibrotic properties.
    explanation: >-
      A recent review treats lesional CD4-positive CTLs as the core effector population for tissue damage
      and fibrosis. It reaches that attribution from their cytotoxic and cytokine profile rather than from
      a fibroblast-activation experiment, which is why the downstream fibroblast edge from this node is kept
      indirect.
- name: Storiform Fibrosis
  conforms_to: fibrotic_response#Excessive ECM Deposition
  description: >-
    Fibrotic collagen remodeling can form a whorled or cartwheel storiform pattern. It is a characteristic
    microscopic architecture rather than a synonym for fibroblast activation. Fibrosis and inflammatory
    mass effects contribute to organ dysfunction; its prominence varies by organ and stage, and established
    scarring can be less reversible than active inflammation.
  cell_types:
  - preferred_term: Fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: Myofibroblast
    term:
      id: CL:0000186
      label: myofibroblast cell
  biological_processes:
  - preferred_term: TGF-beta Receptor Signaling
    term:
      id: GO:0007179
      label: transforming growth factor beta receptor signaling pathway
    modifier: INCREASED
  - preferred_term: ECM Organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: INCREASED
  - preferred_term: Collagen fibril organization
    term:
      id: GO:0030199
      label: collagen fibril organization
    modifier: INCREASED
  downstream:
  - target: Organ-Specific Fibroinflammatory Injury
    description: >-
      Persistent fibroblast and myofibroblast activation remodels affected organ tissue, with the clinical
      pattern shaped by organ-specific antigen, barrier, and injury contexts.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        When dysregulated, fibrosis can become irreversible and lead to tissue distortion and organ damage
      explanation: >-
        Fibrotic remodeling can cause irreversible tissue distortion; precise organ tropism remains unresolved.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The major histopathologic features include a dense lymphoplasmacytic infiltrate, fibrosis that has
      a storiform pattern in focal (or diffuse) areas, and obliterative phlebitis.
    explanation: Storiform fibrosis identified as one of the three major histopathological features of IgG4-RD.
- name: Organ-Specific Fibroinflammatory Injury
  description: >-
    The same fibroinflammatory framework produces organ-specific syndromes such as autoimmune pancreatitis
    and IgG4-related cholangitis. Current evidence supports per-organ antigen and epithelial-barrier mechanisms
    in subsets, rather than a single universal tissue-tropism mechanism.
  role: consequence
  evidence:
  - reference: PMID:30089633
    reference_title: Laminin 511 is a target antigen in autoimmune pancreatitis.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Autoimmune pancreatitis (AIP), a major manifestation of immunoglobulin G4-related disease (IgG4-RD),
      is an immune-mediated disorder, but the target autoantigens are still unknown.
    explanation: >-
      Pancreatic disease illustrates organ-specific autoimmune injury while retaining uncertainty about
      the full target-antigen set.
  - reference: PMID:38524667
    reference_title: Laminin 511-E8, an autoantigen in IgG4-related cholangitis, contributes to cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Laminin 511-E8 is an autoantigen in subsets of individuals with IRC.
    explanation: >-
      Human serum and cholangiocyte experiments support a bile-duct-specific autoantigen/barrier-injury
      mechanism in a subset of IgG4-related cholangitis.
  - reference: PMID:34718050
    reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary
      bicarbonate umbrella'.
    explanation: >-
      This supports an organ-specific cholangiocyte-protection mechanism for bile-duct injury in IgG4-related
      cholangitis.
  downstream:
  - target: Pulmonary Involvement
    description: Thoracic fibroinflammatory involvement produces heterogeneous structural pulmonary abnormalities.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:36437514
      reference_title: Thoracic manifestations of IgG4-related disease.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: Chest CT findings are heterogeneous and primarily include peribronchovascular thickening, nodules, ground-glass opacities and lymphadenopathy.
      explanation: The thoracic review describes structural imaging manifestations; the pattern is not specific to IgG4-RD.
  - target: Pancreatobiliary Fibroinflammation and Ductal Obstruction
    description: >-
      Pancreatic and biliary localization produces inflammatory and obstructive digestive manifestations.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32552502
      reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain,
        posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related
        cholangitis.
      explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
  - target: Renal Parenchymal Fibroinflammatory Injury
    description: Renal localization causes parenchymal inflammation and fibrosis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        tubulointerstitial nephritis with abundant IgG4+ plasma cells was the most common finding (n =
        14; 93.3%), and 4 (26.7%) patients had membranous nephropathy.
      explanation: >-
        Renal biopsy findings concern the selected 15-biopsy renal cohort, not the prevalence in all IgG4-RD.
  - target: Retroperitoneal Encasement and Urinary Obstruction
    description: Retroperitoneal localization can obstruct adjacent urinary structures.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
        obstruction in 6 patients (21.4%)
      explanation: >-
        Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal
        involvement.
  - target: Salivary and Lacrimal Gland Fibroinflammation
    description: Glandular localization produces lacrimal and salivary involvement.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:35425928
      reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts,
        retroperitoneal tissues, aorta, kidneys, and lungs.
      explanation: The primary trial provides a clinical background summary of characteristic involved organs.
- name: B-Lineage Profibrotic Signaling
  mechanism_confidence: PROVISIONAL
  description: >-
    Patient B cells and plasmablasts have soluble profibrotic activity involving PDGF-B and additional
    mediators. LOXL2 and collagen-related programs are expressed in plasmablasts and tissue plasma cells,
    but expression does not quantify matrix crosslinking or prove they are the dominant source of fibrosis.
    Healthy-control B cells also have weaker collagen-promoting activity.
  evidence:
  - reference: PMID:31319101
    reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      These findings demonstrate that CD19+ B lymphocytes from patients with IgG4-RD and, to lesser extent,
      from healthy individuals are capable of driving myofibroblast differentiation and collagen production
      through the secretion of soluble factors rather than physical interactions.
    explanation: >-
      Transwell cocultures establish a soluble B-cell-to-fibroblast mechanism, stronger with patient B
      cells, without proving its quantitative contribution in vivo.
  cell_types:
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  - preferred_term: plasmablast
    term:
      id: CL:0000980
      label: plasmablast
  downstream:
  - target: Fibroblast Activation and Collagen Production
    description: >-
      B-lineage soluble mediators stimulate fibroblast activation and collagen production, partly through
      PDGF-B.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while
        nonimmune IgG of the same isotype did not inhibit the collagen production induced by the same
        B lymphocytes.
      explanation: >-
        Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations
        with control B cells imply additional mediators.
    hypothesis_groups:
    - plasmablast_autoantigen_fibrosis_driver_model
- name: Fibroblast Activation and Collagen Production
  conforms_to: "fibrotic_response#Mesenchymal Cell Activation"
  description: >-
    Activated fibroblasts produce collagen and express myofibroblast programs. Patient B-cell cocultures
    provide functional evidence for a PDGF-B-associated route; other immune mediators may converge. The
    experiments measure activation and collagen production, not the emergence of the disease-specific
    storiform architecture.
  evidence:
  - reference: PMID:31319101
    reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while nonimmune
      IgG of the same isotype did not inhibit the collagen production induced by the same B lymphocytes.
    explanation: >-
      Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations
      with control B cells imply additional mediators.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  - preferred_term: myofibroblast cell
    term:
      id: CL:0000186
      label: myofibroblast cell
  biological_processes:
  - preferred_term: collagen fibril organization
    term:
      id: GO:0030199
      label: collagen fibril organization
  downstream:
  - target: Storiform Fibrosis
    description: >-
      Sustained collagen-producing stromal activity contributes to fibrotic tissue remodeling; the organization
      into storiform whorls is not reproduced by the coculture experiment.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        In general, tissue fibrosis arises from the deposition of collagenous proteins synthesized by
        activated fibroblasts
      explanation: >-
        The paper gives the established fibrosis framework; its experiments support collagen production
        but not storiform geometry.
- name: Cytotoxic T-Cell-Associated Mesenchymal Injury
  mechanism_confidence: PROVISIONAL
  description: >-
    CD4-positive and CD8-positive cytotoxic T cells infiltrate lesions in association with HLA-DR-positive
    apoptotic cells, preferentially nonimmune and nonendothelial mesenchymal cells. GZMK-positive clones
    and extrafollicular B-cell proximity support coordinated inflammation. Human tissue data do not prove
    that CTLs cause obliterative phlebitis or that all T-cell populations are interchangeable.
  evidence:
  - reference: PMID:32485263
    reference_title: CD4(+) and CD8(+) cytotoxic T lymphocytes may induce mesenchymal cell apoptosis in IgG(4)-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tissue studies revealed an abundance of cells undergoing apoptotic cell death disproportionately
      involving nonimmune, nonendothelial cells of mesenchymal origin.
    explanation: Human imaging establishes the distribution of apoptotic cells.
  - reference: PMID:38092138
    reference_title: Granzyme K- and amphiregulin-expressing cytotoxic T cells and activated extrafollicular B cells are potential drivers of IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GZMK+CD4+ cytotoxic T cells colocalized with MKI67+ B cells in the extrafollicular area from affected
      tissue sites.
    explanation: >-
      Spatial proximity supports a candidate cellular interaction but does not establish antigen presentation.
  downstream:
  - target: Organ-Specific Fibroinflammatory Injury
    description: >-
      Tissue apoptosis plausibly contributes to inflammatory injury; human CTL-specific causal mediation
      remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32485263
      reference_title: CD4(+) and CD8(+) cytotoxic T lymphocytes may induce mesenchymal cell apoptosis in IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        CD4+CTLs and CD8+CTLs may induce apoptotic cell death in tissues of patients with IgG4-RD with
        preferential targeting of nonendothelial, nonimmune cells of mesenchymal origin.
      explanation: Human tissue data support the association and proposed injury route.
- name: Innate Receptor-Dependent BAFF Production
  mechanism_confidence: PROVISIONAL
  description: >-
    NOD2- or TLR-stimulated monocytes and TLR-stimulated basophils can support enhanced IgG4 production
    through BAFF-associated mechanisms in culture. Healthy-control cells also respond. These routes can
    coexist with Tfh help; neither their redundancy in vivo nor a universal innate initiating event is
    established.
  evidence:
  - reference: PMID:21971969
    reference_title: Involvement of activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors in enhanced IgG4 responses in autoimmune pancreatitis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells
      in a BAFF-dependent and T cell-independent manner.
    explanation: >-
      The culture experiment separates BAFF-dependent IgG4 production from T-cell help; it does not establish
      de-novo class-switch recombination in vivo.
  - reference: PMID:22744834
    reference_title: Toll-like receptor activation in basophils contributes to the development of IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which
      effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13.
    explanation: >-
      A distinct basophil culture route is supported; association with both mediators is not proof of
      BAFF-alone necessity.
  cell_types:
  - preferred_term: monocyte
    term:
      id: CL:0000576
      label: monocyte
  - preferred_term: basophil
    term:
      id: CL:0000767
      label: basophil
  downstream:
  - target: Enhanced IgG4 Antibody Production
    description: BAFF-associated innate cell signals enhance B-cell IgG4 production in culture.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:21971969
      reference_title: Involvement of activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors in enhanced IgG4 responses in autoimmune pancreatitis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells
        in a BAFF-dependent and T cell-independent manner.
      explanation: >-
        The culture experiment separates BAFF-dependent IgG4 production from T-cell help; it does not
        establish de-novo class-switch recombination in vivo.
    - reference: PMID:22744834
      reference_title: Toll-like receptor activation in basophils contributes to the development of IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which
        effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13.
      explanation: >-
        A distinct basophil culture route is supported; association with both mediators is not proof of
        BAFF-alone necessity.
    hypothesis_groups:
    - innate_first_bystander_model
- name: Enhanced IgG4 Antibody Production
  description: >-
    B-cell antibody production is enhanced through both T-cell-help and innate-cell-associated routes.
    Serum IgG4 does not faithfully report all lesions and can be normal. IgG4 enrichment is not itself
    proof that an antibody specificity is pathogenic; patient IgG4 can have inhibitory or pathogenic effects
    depending on context.
  evidence:
  - reference: PMID:21971969
    reference_title: Involvement of activation of toll-like receptors and nucleotide-binding oligomerization domain-like receptors in enhanced IgG4 responses in autoimmune pancreatitis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Activation of NOD-2 in monocytes from healthy control subjects induced IgG4 production by B cells
      in a BAFF-dependent and T cell-independent manner.
    explanation: >-
      The culture experiment separates BAFF-dependent IgG4 production from T-cell help; it does not establish
      de-novo class-switch recombination in vivo.
  - reference: PMID:22744834
    reference_title: Toll-like receptor activation in basophils contributes to the development of IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Activation of TLRs in basophils from healthy controls induced IgG4 production by B cells, which
      effect was associated with enhanced production of B cell activating factor (BAFF) and IL-13.
    explanation: >-
      A distinct basophil culture route is supported; association with both mediators is not proof of
      BAFF-alone necessity.
  - reference: PMID:26297761
    reference_title: Plasmacytoid Dendritic Cell Activation and IFN-α Production Are Prominent Features of Murine Autoimmune Pancreatitis and Human IgG4-Related Autoimmune Pancreatitis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      patient pDCs cultured in the presence of NETs produced greatly increased levels of IFN-α and induced
      control B cells to produce IgG4 (but not IgG1) as compared with control pDCs.
    explanation: >-
      This primary culture experiment supports an additional pDC-to-B-cell route; the innate report instead
      cited a review for this component.
- name: TLR7-Associated Macrophage IL-33 Production
  mechanism_confidence: PROVISIONAL
  description: >-
    TLR7-expressing CD163-positive macrophages accumulate in affected salivary glands. TLR7 agonist stimulation
    increases IL-33 in cultured macrophages; huTLR7 mice show multi-organ inflammation and fibrosis with
    IgG1, rather than human IgG4. Human temporal initiation remains unresolved.
  evidence:
  - reference: PMID:31339007
    reference_title: Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      After in vitro stimulation with a TLR-7 agonist, CD163+ M2 macrophages produced higher levels of
      interleukin-33 (IL-33)
    explanation: >-
      Agonist stimulation links TLR7 activation to macrophage IL-33 in vitro; patient tissue colocalization
      alone does not establish temporal initiation.
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
  downstream:
  - target: IL-33-Associated Macrophage Matrix Remodeling
    description: >-
      IL-33 is associated with macrophage ST2 signaling and MMP12 production in the lacrimal experimental
      system.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39299101
      reference_title: IL-33/ST2 enhances MMP-12 expression by macrophages to mediate inflammatory and immune response in IgG4-Related Ophthalmic Disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: an ELISA assay demonstrated that IL-33 upregulates MMP-12 in IgG4-ROD.
      explanation: >-
        The experimental study supports IL-33-associated MMP12 induction; the nine-patient tissue component
        is observational.
    hypothesis_groups:
    - innate_first_bystander_model
- name: IL-33-Associated Macrophage Matrix Remodeling
  mechanism_confidence: PROVISIONAL
  description: >-
    IL-33/ST2-associated macrophage activation and MMP12 expression provide a candidate matrix-remodeling
    route in lacrimal disease. The experimental and small human-tissue study does not establish that MMP12
    causes storiform fibrosis or that IL-33 blockade is an effective human treatment.
  evidence:
  - reference: PMID:39299101
    reference_title: IL-33/ST2 enhances MMP-12 expression by macrophages to mediate inflammatory and immune response in IgG4-Related Ophthalmic Disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: an ELISA assay demonstrated that IL-33 upregulates MMP-12 in IgG4-ROD.
    explanation: >-
      The experimental study supports IL-33-associated MMP12 induction; the nine-patient tissue component
      is observational.
  cell_types:
  - preferred_term: macrophage
    term:
      id: CL:0000235
      label: macrophage
- name: Conventional Dendritic Cell Chemokine Production
  mechanism_confidence: PROVISIONAL
  description: >-
    In poly(I:C)-induced autoimmune pancreatitis, TLR3-bearing conventional dendritic cells produce type
    I interferons and CXCL9/CXCL10 early, promoting subsequent CXCR3-positive T-cell recruitment. This
    initiating sequence is experimentally defined in female MRL/MpJ mice; matching human serum chemokines
    provide association rather than proof of the same sequence.
  evidence:
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      pancreatic cDCs, at this early phase of AIP induction, are indeed the main producers of type I IFNs
      upon sensing of poly(I:C) by TLR3
    explanation: Sorted-cell stimulation and depletion identify the early source in the induced mouse model.
  downstream:
  - target: CXCR3-Positive T-Cell Recruitment and CCL25 Production
    description: CXCL9/CXCL10 recruitment through CXCR3 is required for the full induced mouse phenotype.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: such blockade prevented the development of experimental AIP
      explanation: >-
        Anti-CXCR3 treatment during repeated poly(I:C) administration prevents pancreatic inflammation,
        supporting the chemokine recruitment step in this model.
    hypothesis_groups:
    - innate_first_bystander_model
- name: CXCR3-Positive T-Cell Recruitment and CCL25 Production
  mechanism_confidence: PROVISIONAL
  description: >-
    CXCL9/CXCL10-associated recruitment places CXCR3-positive T cells in inflamed mouse pancreas. Under
    type I interferon stimulation these T cells produce CCL25, recruiting CCR9-positive pDCs. These cells
    are not established to be the same granzyme-positive CTLs found in human lesions.
  evidence:
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: such blockade prevented the development of experimental AIP
    explanation: >-
      Anti-CXCR3 treatment during repeated poly(I:C) administration prevents pancreatic inflammation,
      supporting the chemokine recruitment step in this model.
  downstream:
  - target: Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification
    description: T-cell CCL25 supports recruitment of CCR9-bearing pDCs in induced mouse pancreatitis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development
        of experimental AIP
      explanation: The intervention reduces pancreatic pDC accumulation and inflammation in mice.
    hypothesis_groups:
    - innate_first_bystander_model
- name: Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification
  mechanism_confidence: PROVISIONAL
  description: >-
    Recruited pDCs become a major source of IFN-alpha and IL-33 in induced mouse pancreatitis. Their IFN-alpha
    sustains T-cell CCL25 production, forming an experimentally supported feedback loop. TLR9 stimulation
    is required for maximal cytokine output in coculture; human NET-stimulated pDC experiments independently
    support enhanced IgG4 production.
  evidence:
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of
      experimental AIP
    explanation: The intervention reduces pancreatic pDC accumulation and inflammation in mice.
  - reference: PMID:26297761
    reference_title: Plasmacytoid Dendritic Cell Activation and IFN-α Production Are Prominent Features of Murine Autoimmune Pancreatitis and Human IgG4-Related Autoimmune Pancreatitis.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      patient pDCs cultured in the presence of NETs produced greatly increased levels of IFN-α and induced
      control B cells to produce IgG4 (but not IgG1) as compared with control pDCs.
    explanation: >-
      This primary culture experiment supports an additional pDC-to-B-cell route; the innate report instead
      cited a review for this component.
  downstream:
  - target: CXCR3-Positive T-Cell Recruitment and CCL25 Production
    description: >-
      pDC-derived IFN-alpha enhances T-cell CCL25 secretion and sustains the observed mouse feedback loop.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        such secretion was greatly augmented by the presence of pDCs, particularly when the latter cells
        were stimulated by TLR9 ligand (CpG)
      explanation: Sorted mouse T-cell/pDC cocultures show enhanced T-cell CCL25 production with pDC support.
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        pDC augmentation was substantially blocked by anti-IFNAR Ab, indicating that this effect was dependent
        on IFN-α production by pDCs
      explanation: IFNAR blockade supports the pDC-to-T-cell return arm of the experimental feedback loop.
    hypothesis_groups:
    - innate_first_bystander_model
  - target: Enhanced IgG4 Antibody Production
    description: NET-stimulated patient pDCs enhance control B-cell IgG4 production.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:26297761
      reference_title: Plasmacytoid Dendritic Cell Activation and IFN-α Production Are Prominent Features of Murine Autoimmune Pancreatitis and Human IgG4-Related Autoimmune Pancreatitis.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        patient pDCs cultured in the presence of NETs produced greatly increased levels of IFN-α and induced
        control B cells to produce IgG4 (but not IgG1) as compared with control pDCs.
      explanation: >-
        This primary culture experiment supports an additional pDC-to-B-cell route; the innate report
        instead cited a review for this component.
    hypothesis_groups:
    - innate_first_bystander_model
  - target: Fibroblast Activation and Collagen Production
    description: >-
      pDC-associated IFN-alpha and IL-33 signaling contributes to fibrotic sequelae in induced pancreatitis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        depletion of these cells or blockade of IFN-α– or IL-33–mediated signaling pathways almost completely
        protected the mice from the development of pancreatitis and its fibrotic sequelae
      explanation: >-
        The primary paper summarizes its preceding mouse perturbation studies; human cytokine dependence
        is not established.
    hypothesis_groups:
    - innate_first_bystander_model
- name: Gut Barrier and Microbiota-Dependent Innate Amplification
  mechanism_confidence: PROVISIONAL
  description: >-
    Microbiota transfer and intestinal barrier disruption amplify poly(I:C)-induced pancreatitis through
    increased pancreatic pDC accumulation. Staphylococcus sciuri translocation and mono-colonization experiments
    support a model-specific modifier. Neither microbial sufficiency without the inducing regimen nor
    causal initiation of human systemic IgG4-RD is established.
  evidence:
  - reference: PMID:31287532
    reference_title: Intestinal dysbiosis mediates experimental autoimmune pancreatitis via activation of plasmacytoid dendritic cells.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Fecal microbiota transplantation (FMT) from donor mice treated with 100 µg of poly (I:C) led to
      the development of severe AIP in the recipient mice upon injection with 10 µg of poly (I:C).
    explanation: >-
      Microbiota transfer amplifies pancreatitis under a continuing low-dose innate stimulus; it does
      not induce spontaneous human IgG4-RD.
  - reference: PMID:36044992
    reference_title: Disruption of the intestinal barrier exacerbates experimental autoimmune pancreatitis by promoting the translocation of Staphylococcus sciuri into the pancreas.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Mice co-treated with poly (I:C) and DSS, but not those treated with either agent alone, developed
      severe AIP, but not autoimmune sialadenitis
    explanation: >-
      Barrier disruption and poly(I:C) jointly exacerbate pancreatic disease; the effect is organ-specific
      in this experiment.
  downstream:
  - target: Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification
    description: Gut perturbation increases pancreatic pDC accumulation under poly(I:C) induction.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:31287532
      reference_title: Intestinal dysbiosis mediates experimental autoimmune pancreatitis via activation of plasmacytoid dendritic cells.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Fecal microbiota transplantation (FMT) from donor mice treated with 100 µg of poly (I:C) led to
        the development of severe AIP in the recipient mice upon injection with 10 µg of poly (I:C).
      explanation: >-
        Microbiota transfer amplifies pancreatitis under a continuing low-dose innate stimulus; it does
        not induce spontaneous human IgG4-RD.
    - reference: PMID:36044992
      reference_title: Disruption of the intestinal barrier exacerbates experimental autoimmune pancreatitis by promoting the translocation of Staphylococcus sciuri into the pancreas.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Mice co-treated with poly (I:C) and DSS, but not those treated with either agent alone, developed
        severe AIP, but not autoimmune sialadenitis
      explanation: >-
        Barrier disruption and poly(I:C) jointly exacerbate pancreatic disease; the effect is organ-specific
        in this experiment.
    hypothesis_groups:
    - innate_first_bystander_model
- name: Autoantibody-Mediated IL-1RA Neutralization
  mechanism_confidence: PROVISIONAL
  description: >-
    Anti-IL-1RA antibodies in a subset can neutralize the endogenous IL-1 receptor antagonist and increase
    inflammatory and profibrotic mediator production. IgG4 predominates in many positive samples but other
    subclasses occur, and functional plasma experiments do not isolate IgG4-specific activity. The pathway
    is not universal or specific to IgG4-RD.
  evidence:
  - reference: PMID:33974929
    reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared
      with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic
      mediator production in vitro.
    explanation: >-
      Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a
      subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.
  downstream:
  - target: Fibroblast Activation and Collagen Production
    description: >-
      Unopposed IL-1 signaling increases profibrotic mediator production in cell assays; progression to
      human stromal fibrosis remains inferred.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:33974929
      reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared
        with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic
        mediator production in vitro.
      explanation: >-
        Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in
        a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.
- name: Immune-Complex Complement Activation
  mechanism_confidence: PROVISIONAL
  description: >-
    IgG4-containing patient immune-complex fractions can activate and consume classical and lectin-pathway
    complement in vitro. Anti-C1q and hypocomplementemia are associated with renal involvement in clinical
    cohorts. The causal contribution of individual subclasses to human renal injury remains unresolved.
  evidence:
  - reference: PMID:26357950
    reference_title: Possible participation of IgG4 in the activation of complement in IgG4-related disease with hypocomplementemia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We observed a marked reduction of CH50 and reduced complement activity in the classical complement
      pathway as well as the mannan-binding lectin complement pathway in NHS incubated with PEG-IC isolated
      from IgG4RD patients with hypocomplementemia.
    explanation: >-
      Patient immune-complex fractions consume complement ex vivo; mixed complexes cannot assign causality
      to purified IgG4 alone.
- name: Cholangiocyte Protective Barrier Impairment
  mechanism_confidence: PROVISIONAL
  description: >-
    Annexin A11 supports apical ANO1 trafficking and protective bicarbonate secretion; patient serum can
    inhibit this process. Laminin 511 independently supports epithelial barrier integrity and bile-acid
    resistance. Candidate autoantibodies occur in subsets, but laminin knockdown and patient autoantibody
    binding should not be equated.
  evidence:
  - reference: PMID:34718050
    reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface
      expression.
    explanation: >-
      Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective
      secretory machinery; mixed serum is not an isolated isotype perturbation.
  - reference: PMID:38524667
    reference_title: Laminin 511-E8, an autoantigen in IgG4-related cholangitis, contributes to cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Knockdown of laminin 511 constituents increased toxic bile acid permeation and GCDC-induced apoptosis.
    explanation: >-
      Gene knockdown establishes laminin-dependent protection but does not by itself demonstrate that
      patient anti-laminin antibodies reproduce knockdown.
  cell_types:
  - preferred_term: cholangiocyte
    term:
      id: CL:1000488
      label: cholangiocyte
  downstream:
  - target: Pancreatobiliary Fibroinflammation and Ductal Obstruction
    description: >-
      Impaired protective secretion and barrier function may contribute to biliary injury in an autoantibody-positive
      subset.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34718050
      reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary
        bicarbonate umbrella'.
      explanation: >-
        The experiment supports a candidate contribution to biliary injury, not sufficiency for ductal
        fibrosis.
- name: Pancreatobiliary Fibroinflammation and Ductal Obstruction
  description: >-
    Lymphoplasmacytic inflammation and fibrosis affect pancreatic and biliary structures. Duct narrowing
    and inflammatory enlargement can cause obstructive jaundice; persistent pancreatic injury can leave
    exocrine or endocrine dysfunction. An IgG4-related pancreatic mass requires distinction from malignancy.
  evidence:
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior
      pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis.
    explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
  downstream:
  - target: Autoimmune Pancreatitis
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32552502
      reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain,
        posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related
        cholangitis.
      explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
  - target: Sclerosing Cholangitis
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32552502
      reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain,
        posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related
        cholangitis.
      explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
  - target: Jaundice
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32552502
      reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain,
        posterior pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related
        cholangitis.
      explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
- name: Renal Parenchymal Fibroinflammatory Injury
  description: >-
    Tubulointerstitial inflammation with IgG4-rich plasma cells and fibrosis can impair intrinsic renal
    function. Membranous nephropathy occurs in a subset and may coexist. Hypocomplementemia is associated,
    but the reviewed evidence does not establish a single complement-mediated causal route for all renal
    injury.
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      tubulointerstitial nephritis with abundant IgG4+ plasma cells was the most common finding (n = 14;
      93.3%), and 4 (26.7%) patients had membranous nephropathy.
    explanation: >-
      Renal biopsy findings concern the selected 15-biopsy renal cohort, not the prevalence in all IgG4-RD.
  downstream:
  - target: Renal Insufficiency
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        tubulointerstitial nephritis with abundant IgG4+ plasma cells was the most common finding (n =
        14; 93.3%), and 4 (26.7%) patients had membranous nephropathy.
      explanation: >-
        Renal biopsy findings concern the selected 15-biopsy renal cohort, not the prevalence in all IgG4-RD.
  - target: Proteinuria
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        tubulointerstitial nephritis with abundant IgG4+ plasma cells was the most common finding (n =
        14; 93.3%), and 4 (26.7%) patients had membranous nephropathy.
      explanation: >-
        Renal biopsy findings concern the selected 15-biopsy renal cohort, not the prevalence in all IgG4-RD.
- name: Retroperitoneal Encasement and Urinary Obstruction
  description: >-
    Periaortic and periureteric fibroinflammatory tissue can encase ureters and obstruct drainage, producing
    hydronephrosis and postrenal dysfunction. This route is distinct from intrinsic IgG4-related tubulointerstitial
    nephritis.
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
      obstruction in 6 patients (21.4%)
    explanation: >-
      Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal involvement.
  downstream:
  - target: Retroperitoneal Fibrosis
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
        obstruction in 6 patients (21.4%)
      explanation: >-
        Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal
        involvement.
  - target: Hydronephrosis
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
        obstruction in 6 patients (21.4%)
      explanation: >-
        Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal
        involvement.
  - target: Renal Insufficiency
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:30596168
      reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
        obstruction in 6 patients (21.4%)
      explanation: >-
        Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal
        involvement.
- name: Salivary and Lacrimal Gland Fibroinflammation
  description: >-
    Immune-cell infiltration and tissue remodeling enlarge salivary and lacrimal glands. Persistent injury
    can compromise gland function; IgG4-rich inflammation alone does not distinguish this condition from
    all mimics.
  evidence:
  - reference: PMID:35425928
    reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal
      tissues, aorta, kidneys, and lungs.
    explanation: The primary trial provides a clinical background summary of characteristic involved organs.
  downstream:
  - target: Enlarged Lacrimal Glands
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:35425928
      reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts,
        retroperitoneal tissues, aorta, kidneys, and lungs.
      explanation: The primary trial provides a clinical background summary of characteristic involved organs.
  - target: Salivary Gland Enlargement
    description: Organ-localized fibroinflammation produces this clinical manifestation or complication.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:35425928
      reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts,
        retroperitoneal tissues, aorta, kidneys, and lungs.
      explanation: The primary trial provides a clinical background summary of characteristic involved organs.
histopathology:
- name: Dense Lymphoplasmacytic Infiltrate with IgG4-Positive Plasma Cells
  finding_term:
    preferred_term: Dense IgG4-positive lymphoplasmacytic infiltrate
    term:
      id: NCIT:C35984
      label: Lymphoplasmacytic Infiltrate
  diagnostic: true
  description: >-
    Tissue biopsy shows a dense lymphoplasmacytic infiltrate with increased IgG4-positive plasma cells
    or an increased IgG4+/IgG+ plasma-cell ratio. The feature is not universal or sufficient by itself;
    prominence varies by organ and disease stage.
  evidence:
  - reference: PMID:22596100
    reference_title: Consensus statement on the pathology of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern
      of fibrosis, and obliterative phlebitis.
    explanation: >-
      International pathology consensus identifies the triad and emphasizes clinicopathological correlation.
- name: Storiform Fibrosis
  finding_term:
    preferred_term: Storiform fibrosis
    term:
      id: NCIT:C3044
      label: Fibrosis
  diagnostic: true
  description: >-
    Fibrosis in a storiform, whorled, or cartwheel pattern is one of the characteristic microscopic features
    of IgG4-RD. The feature is not universal or sufficient by itself; prominence varies by organ and disease
    stage.
  evidence:
  - reference: PMID:22596100
    reference_title: Consensus statement on the pathology of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern
      of fibrosis, and obliterative phlebitis.
    explanation: >-
      International pathology consensus identifies the triad and emphasizes clinicopathological correlation.
- name: Obliterative Phlebitis
  diagnostic: true
  description: >-
    Inflammatory and fibrotic obliteration of venous lumina is a characteristic but organ-variable finding.
    Arteritis and aortitis are separate vascular lesions; leukocytoclastic small-vessel vasculitis is
    not interchangeable with obliterative phlebitis.
  evidence:
  - reference: PMID:22596100
    reference_title: Consensus statement on the pathology of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern
      of fibrosis, and obliterative phlebitis.
    explanation: >-
      International pathology consensus identifies the triad and emphasizes clinicopathological correlation.
- name: Tissue eosinophilia
  diagnostic: false
  description: Eosinophils can accompany the tissue lymphoplasmacytic infiltrate. This supportive, nonspecific biopsy feature is distinct from peripheral blood eosinophilia and is insufficient for diagnosis.
  evidence:
  - reference: PMID:39644037
    reference_title: IgG4-related disease for the hematologist.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Histological diagnosis is essential, and other key features include storiform fibrosis, lymphoplasmacytic infiltrate, tissue eosinophilia, and obliterative phlebitis.
    explanation: The hematology review explicitly identifies the tissue finding.
phenotypes:
- category: Gastrointestinal
  name: Autoimmune Pancreatitis
  diagnostic: true
  notes: >-
    Type 1 autoimmune pancreatitis is a characteristic organ manifestation. Its frequency depends on referral
    setting; only 24/125 patients in the cited rheumatology cohort had pancreatic involvement. It is not
    uniformly the most common site.
  phenotype_term:
    preferred_term: Pancreatitis
    term:
      id: HP:0001733
      label: Pancreatitis
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most commonly involved organs were the submandibular glands (35 cases, 28%), lymph nodes (34,
      27%), orbits (28, 22%), pancreas (24, 19%), and retroperitoneum (23, 18%).
    explanation: The 125-person referral cohort defines pancreatic frequency in this setting.
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior
      pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis.
    explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
- category: Ophthalmologic
  name: Enlarged Lacrimal Glands
  phenotype_term:
    preferred_term: Enlarged lacrimal glands
    term:
      id: HP:0007734
      label: Enlarged lacrimal glands
  evidence:
  - reference: PMID:35425928
    reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal
      tissues, aorta, kidneys, and lungs.
    explanation: The primary trial provides a clinical background summary of characteristic involved organs.
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
- category: Hepatobiliary
  name: Sclerosing Cholangitis
  notes: >-
    IgG4-related sclerosing cholangitis can mimic primary sclerosing cholangitis or cholangiocarcinoma
    but responds to corticosteroids.
  phenotype_term:
    preferred_term: Sclerosing cholangitis
    term:
      id: HP:0030991
      label: Sclerosing cholangitis
  evidence:
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior
      pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis.
    explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
- category: Hepatobiliary
  name: Jaundice
  phenotype_term:
    preferred_term: Jaundice
    term:
      id: HP:0000952
      label: Jaundice
  evidence:
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Indications for treatment are symptomatic patients with obstructive jaundice, abdominal pain, posterior
      pancreatic pain, and involvement of extra-pancreatic digestive organs, including IgG4-related cholangitis.
    explanation: The digestive guideline recognizes pancreatic/biliary manifestations and obstruction.
- category: Abdominal
  name: Retroperitoneal Fibrosis
  phenotype_term:
    preferred_term: Retroperitoneal fibrosis
    term:
      id: HP:0005200
      label: Retroperitoneal fibrosis
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Para-aortic or peri-ureteric RPF was evident in 14 patients (50%). This was associated with ureteric
      obstruction in 6 patients (21.4%)
    explanation: >-
      Imaging documents the obstructive mechanism within 28 patients with kidney or retroperitoneal involvement.
- category: Renal
  name: Renal Insufficiency
  notes: >-
    IgG4-related tubulointerstitial nephritis or membranous nephropathy can lead to progressive renal
    dysfunction.
  phenotype_term:
    preferred_term: Renal insufficiency
    term:
      id: HP:0000083
      label: Renal insufficiency
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Renal involvement may manifest as an intrinsic kidney disease (IgG4-RKD) or as a consequence of
      ureteric obstruction from retroperitoneal fibrosis (IgG4-RPF).
    explanation: The cohort distinguishes parenchymal and postrenal routes to kidney dysfunction.
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Renal function deteriorated in 5 patients (20.8%), including 2 (8.3%) who reached end-stage renal
      disease (ESRD).
    explanation: >-
      Longitudinal renal outcomes in the selected renal/RPF cohort establish potential irreversible impairment.
- name: Hydronephrosis
  category: Renal
  description: Urinary obstruction from retroperitoneal fibrosis can dilate the collecting system.
  phenotype_term:
    preferred_term: Hydronephrosis
    term:
      id: HP:0000126
      label: Hydronephrosis
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: image of left-sided ureteric obstruction and hydronephrosis in IgG4-RPF.
    explanation: Clinical imaging documents this complication.
- name: Salivary Gland Enlargement
  category: Head and Neck
  description: >-
    Salivary gland enlargement, especially submandibular involvement, is characteristic; enlargement and
    secretory dysfunction are distinct findings. The ontology anchor is broader than enlargement because
    a gland-general enlargement term was not identified.
  phenotype_term:
    preferred_term: Salivary gland enlargement
    term:
      id: HP:0010286
      label: Abnormal salivary gland morphology
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The most commonly involved organs were the submandibular glands (35 cases, 28%)
    explanation: The cohort documents frequent submandibular involvement.
  - reference: PMID:35425928
    reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      IgG4-RD most commonly involves the major salivary glands, lacrimal glands, orbits, bile ducts, retroperitoneal
      tissues, aorta, kidneys, and lungs.
    explanation: The primary trial provides a clinical background summary of characteristic involved organs.
- name: Lymphadenopathy
  category: Hematologic
  description: >-
    Regional or generalized lymph-node involvement occurs; lymph-node IgG4 staining alone requires caution
    because histology can overlap other conditions.
  phenotype_term:
    preferred_term: Lymphadenopathy
    term:
      id: HP:0002716
      label: Lymphadenopathy
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Among 34 patients with lymphadenopathy, 21 had undergone a lymph node biopsy.
    explanation: The cohort establishes nodal disease and its ascertainment.
- name: Proteinuria
  category: Renal
  description: >-
    Intrinsic renal disease can produce urinary protein, with marked nephrosis in some membranous-nephropathy
    cases.
  phenotype_term:
    preferred_term: Proteinuria
    term:
      id: HP:0000093
      label: Proteinuria
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mild-to-moderate hemoproteinuria occurred in just over half of the patients with IgG4-RKD
    explanation: Clinical cohort data support the phenotype in renal disease.
- name: Aortitis
  category: Cardiovascular
  description: >-
    Aortic inflammation can occur with or without retroperitoneal fibrosis. It is an arterial manifestation
    and must not be relabeled obliterative phlebitis.
  phenotype_term:
    preferred_term: Aortitis
    term:
      id: HP:6001461
      label: Aortitis
  evidence:
  - reference: PMID:30612117
    reference_title: 'Clinical phenotypes of IgG4-related disease: an analysis of two international cross-sectional cohorts.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the derivation cohort (n=493), we identified four groups with distinct manifestations: Group
      1 (31%), Pancreato-Hepato-Biliary disease; Group 2 (24%), Retroperitoneal Fibrosis and/or Aortitis;
      Group 3 (24%), Head and Neck-Limited disease and Group 4 (22%), classic Mikulicz syndrome with systemic
      involvement.
    explanation: >-
      Latent clinical organ-pattern groups were replicated; percentages describe the derivation cohort
      and are not mutually exclusive mechanistic classes.
- name: Pulmonary Involvement
  category: Respiratory
  description: Peribronchovascular thickening, nodules and ground-glass opacities may occur, with or without cough, dyspnea or chest pain. Thoracic disease can additionally involve pleura, mediastinum and lymph nodes; imaging and tissue findings require exclusion of infection, vasculitis and malignancy.
  phenotype_term:
    preferred_term: Abnormal lung morphology
    term:
      id: HP:0002088
      label: Abnormal lung morphology
  evidence:
  - reference: PMID:36437514
    reference_title: Thoracic manifestations of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Chest CT findings are heterogeneous and primarily include peribronchovascular thickening, nodules, ground-glass opacities and lymphadenopathy.
    explanation: The thoracic review describes structural imaging manifestations; the pattern is not specific to IgG4-RD.
- name: Peripheral Blood Eosinophilia
  category: Hematologic
  frequency: OCCASIONAL
  description: >-
    Raised blood eosinophil counts occur as part of an atopy-associated cluster alongside allergic comorbidity
    and elevated serum IgE. This is a blood finding and is distinct from the tissue eosinophilia recorded
    as a supportive histopathologic feature.
  notes: >-
    A systematic review and meta-analysis of 32 studies puts the pooled proportion with eosinophilia at 22%,
    alongside allergy in 44% and hyper-IgE in 73%. The co-occurrence is well replicated; whether the type
    2 axis contributes causally to IgG4-RD or simply travels with it is unresolved, so no causal edge is drawn
    from this phenotype in the pathograph.
  phenotype_term:
    preferred_term: Peripheral blood eosinophilia
    term:
      id: HP:0001880
      label: Increased total eosinophil count
  evidence:
  - reference: PMID:41912044
    reference_title: 'The risk of allergy in patients with IgG4-related disease: A systematic review and meta-analysis.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The pooled proportion with eosinophilia was 0.22 (95% CI, 0.18, 0.26; p < 0.01; n = 4376), and with
      hyper-IgE was 0.73 (95% CI, 0.63, 0.83; p < 0.01; n = 2353).
    explanation: >-
      Pooled prevalence across 32 studies places blood eosinophilia in about a fifth of reported patients,
      which is the basis for the OCCASIONAL frequency band.
  - reference: PMID:41912044
    reference_title: 'The risk of allergy in patients with IgG4-related disease: A systematic review and meta-analysis.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A notable proportion of IgG4-RD patients exhibit allergy, eosinophilia, and hyper-IgE. The frequent
      co-occurrence of these features highlights the need to investigate the underlying mechanisms, clarify
      the causal relationship between allergy and IgG4-RD
    explanation: >-
      The same authors record the causal relationship between these type 2 features and IgG4-RD as still
      open, and note that comparison against general-population rates is lacking. That is why the finding
      is kept as a phenotype without a causal edge.
biochemical:
- name: Serum IgG4
  presence: Elevated
  context: >-
    A diagnostic adjunct with imperfect sensitivity and specificity. The cited rheumatology cohort found
    elevation in about half of active cases using 135 mg/dL; other organ-selected cohorts differ. A normal
    value does not exclude disease.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Only 51% of the patients with active disease had elevated serum IgG4 concentrations.
    explanation: >-
      Large cohort study showing that nearly half of active IgG4-RD patients have normal serum IgG4, demonstrating
      imperfect sensitivity.
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      patients with active disease and elevated serum IgG4 concentrations were older, had a higher IgG4-RD
      RI score, a greater number of organs involved, lower complement levels, higher absolute eosinophil
      counts, and higher IgE levels
    explanation: Elevated serum IgG4 identifies a subset with more severe disease.
- name: Total IgG
  presence: Elevated
  context: >-
    Total IgG can be elevated but is not universal or specific. Twenty-eight percent of active patients
    in the cited cohort had an elevated value.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Twenty-eight percent of patients with active disease at baseline had an elevated total IgG concentration
    explanation: This defines the denominator and limits generalization.
- name: Complement C3 and C4
  presence: Decreased
  context: >-
    C3 and C4 may be low, particularly in intrinsic kidney disease. Complement consumption supports an
    immune-complex hypothesis without identifying the responsible immunoglobulin subclass.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      patients with active disease and elevated serum IgG4 concentrations were older, had a higher IgG4-RD
      RI score, a greater number of organs involved, lower complement levels
    explanation: Lower complement levels associated with more severe IgG4-RD phenotype.
  - reference: PMID:39798124
    reference_title: Anti-C1q antibodies in IgG4-related disease are common and associated with renal involvement and cutaneous small-vessel vasculitis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Anti-C1q antibody levels correlated negatively with levels of C3 and C4, and positively with levels
      of IgG1, IgG4, and serum free light chains.
    explanation: >-
      Association supports the complement-related clinical subset; anti-C1q positivity did not predict
      relapse-free survival.
  readouts:
  - target: Immune-Complex Complement Activation
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: >-
      Lower measured complement is compatible with consumption but is not a direct organ-injury assay.
    evidence:
    - reference: PMID:26357950
      reference_title: Possible participation of IgG4 in the activation of complement in IgG4-related disease with hypocomplementemia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We observed a marked reduction of CH50 and reduced complement activity in the classical complement
        pathway as well as the mannan-binding lectin complement pathway in NHS incubated with PEG-IC isolated
        from IgG4RD patients with hypocomplementemia.
      explanation: >-
        Patient immune-complex fractions consume complement ex vivo; mixed complexes cannot assign causality
        to purified IgG4 alone.
- name: Circulating plasmablasts
  presence: Increased
  context: >-
    Disease-activity biomarker that may be elevated even when serum IgG4 is normal; not a standalone diagnostic
    test.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the levels of circulating plasmablasts – especially IgG4+ plasmablasts – correlate well with disease
      activity as assessed by the IgG4-RD RI.
    explanation: The cohort supports activity association.
  readouts:
  - target: IgG4-Positive Plasmablast Expansion
    relationship: READOUT_OF
    direction: POSITIVE
- name: Soluble interleukin-2 receptor
  presence: Increased
  context: >-
    Exploratory activity-associated marker. It also correlates with primary Sjogren disease activity,
    so neither disease specificity nor CTL-specific causality is established.
  evidence:
  - reference: PMID:29465360
    reference_title: Serum soluble interleukin-2 receptor is a useful biomarker for disease activity but not for differential diagnosis in IgG4-related disease and primary Sjögren's syndrome adults from a defined population.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      serum sIL-2R levels correlate with baseline IgG4-RD RI scores and the number of affected organs
      in IgG4-RD (ρ=0.74, p<0.0001 and ρ=0.75, p<0.0001, respectively).
    explanation: >-
      Clinical correlation supports an activity biomarker without proving that this signal is an upstream
      effector.
- name: IFN-alpha, IL-33 and associated chemokines
  presence: Increased
  context: >-
    Research biomarkers in selected autoimmune-pancreatitis/IgG4-RD cohorts. CXCL9/CXCL10/CCL25 were studied
    in 33 patients, with 14 paired steroid-treatment samples; human temporal causation was not tested.
  evidence:
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      serum concentrations of CXCL9, CXCL10, and CCL25 were markedly higher in patients with AIP/IgG4-RD
      as compared with those with CP and healthy controls
    explanation: >-
      The human component is serum comparison and treatment-associated change, not tissue or cellular
      perturbation.
treatments:
- name: Glucocorticoids
  description: >-
    Glucocorticoids are used to induce control of active disease, with treatment and taper tailored to
    involved organs and response. Relapse and cumulative toxicity can necessitate maintenance or steroid-sparing
    therapy. The 77% failure of sustained remission reported in one referral cohort is not a universal
    relapse rate.
  evidence:
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Maintenance treatment with glucocorticoids should be considered in multi-organ disease or history
      of relapse.
    explanation: The digestive guideline supports individualized maintenance decisions.
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This figure may be biased somewhat by the nature of our referral practice
    explanation: >-
      The primary cohort explicitly cautions against generalizing its 77% failure of sustained glucocorticoid-free
      remission.
  treatment_term:
    preferred_term: glucocorticoid therapy
    term:
      id: NCIT:C122080
      label: Systemic Corticosteroid Therapy
  target_mechanisms:
  - target: Organ-Specific Fibroinflammatory Injury
    treatment_effect: INHIBITS
    description: Suppresses active inflammation; fixed fibrosis and organ damage may persist.
    evidence:
    - reference: PMID:32552502
      reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Response to initial treatment should be assessed at week 2-4 with clinical, biochemical and morphological
        markers.
      explanation: >-
        Response assessment captures inflammation and organ manifestations, rather than a specific cellular
        target.
- name: Rituximab
  description: >-
    Anti-CD20 B-cell depletion used as a steroid-sparing approach. In an uncontrolled 30-patient trial,
    97% had a disease response, 77% met the composite primary endpoint and 40% remained in complete remission
    at 12 months. These results support activity but do not constitute a randomized comparison or demonstrate
    elimination of mature plasma cells.
  treatment_term:
    preferred_term: rituximab therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: rituximab
      term:
        id: NCIT:C1702
        label: Rituximab
  evidence:
  - reference: PMID:25667206
    reference_title: 'Rituximab for IgG4-related disease: a prospective, open-label trial.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The primary outcome was achieved by 23 participants (77%). Fourteen (47%) were in complete remission
      at 6 months, and 12 (40%) remained in complete remission at 12 months.
    explanation: The denominators and endpoints concern an open-label 30-person trial.
  - reference: PMID:38781535
    reference_title: B cell depletion after treatment with rituximab predicts relapse of IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Six months after rituximab, disease response was observed in all patients. Four patients (12%) achieved
      partial response, 11 patients (33%) achieved complete response, and 18 patients (54%) reached disease
      remission.
    explanation: >-
      A retrospective 33-patient cohort corroborates the remission-inducing activity of rituximab induction
      outside the original open-label trial. It is uncontrolled, so it adds replication rather than comparative
      efficacy.
  - reference: PMID:38781535
    reference_title: B cell depletion after treatment with rituximab predicts relapse of IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this study we demonstrate that the degree of CD19+ B cell, naïve and memory B cell depletion after
      rituximab treatment predicts duration of response and patterns of IgG4-RD flare.
    explanation: >-
      Depth of B-cell depletion, not depletion alone, tracks the duration of remission in this cohort. The
      observation does not identify which B-lineage function (antigen presentation, cytokine support, or
      antibody output) is the one that matters.
  target_mechanisms:
  - target: IgG4-Positive Plasmablast Expansion
    treatment_effect: INHIBITS
    description: >-
      Depletion of CD20-positive B-cell precursors reduces the plasmablast-supporting lineage; long-lived
      plasma-cell persistence can contribute to incomplete serologic normalization.
    evidence:
    - reference: PMID:24817416
      reference_title: Plasmablasts as a biomarker for IgG4-related disease, independent of serum IgG4 concentrations.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The steep decline in plasmablast counts after anti-CD20 treatment likely stems from the depletion
        of CD20+ precursors.
      explanation: >-
        The clinical study documents declining plasmablast counts after CD20 depletion and interprets
        this as loss of precursor support.
- name: Inebilizumab
  description: >-
    CD19-directed cytolytic antibody with an FDA indication for adult IgG4-RD. In MITIGATE, 135 participants
    received standardized glucocorticoid tapering; flare occurred in 10% versus 60% on placebo, with hazard
    ratio 0.13. Serious adverse events occurred in 18% versus 9%. Reduced flares demonstrate clinical
    efficacy but do not isolate antigen presentation, antibody production or direct profibrotic signaling
    as the necessary B-cell function.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  target_mechanisms:
  - target: IgG4-Positive Plasmablast Expansion
    treatment_effect: INHIBITS
    description: >-
      Depletes CD19-positive B-lineage compartments. The trial establishes the value of targeting this
      lineage, not that every mature plasma cell is removed or that a specific B-to-CTL interaction is
      necessary.
    evidence:
    - reference: PMID:39541094
      reference_title: Inebilizumab for Treatment of IgG4-Related Disease.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Inebilizumab targets and depletes CD19+ B cells and may be effective for treating patients with
        IgG4-related disease.
      explanation: >-
        The Phase 3 trial describes CD19-positive B-cell depletion as the mechanism motivating inebilizumab
        in IgG4-RD.
  evidence:
  - reference: PMID:39541094
    reference_title: Inebilizumab for Treatment of IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Inebilizumab reduced the risk of flares of IgG4-related disease and increased the likelihood of
      flare-free complete remission at 1 year, confirming the role of CD19-targeted B-cell depletion as
      a potential treatment for IgG4-related disease.
    explanation: >-
      MITIGATE provides randomized Phase 3 evidence that CD19-targeted B-cell depletion reduces IgG4-RD
      flares.
  - reference: url:https://www.accessdata.fda.gov/drugsatfda/docs/label/2025/761142s003lbl.pdf
    reference_title: https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/761142s003lbl.pdf
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      UPLIZNA is indicated for the treatment of Immunoglobulin G4-related disease (IgG4-RD) in adult patients.
    explanation: The FDA label revised April 2025 establishes the adult indication.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: inebilizumab
      term:
        id: NCIT:C88283
        label: Inebilizumab
- name: Obexelimab
  description: >-
    Investigated as a nondepleting CD19/Fc-gamma-RIIb B-cell inhibitor. Phase III INDIGO showed fewer
    flares and less rescue glucocorticoid exposure over 52 weeks. The randomized result supports B-cell
    functional inhibition; it does not establish reversal of fixed fibrosis.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Obexelimab
      term:
        id: NCIT:C170236
        label: Obexelimab
  evidence:
  - reference: PMID:42233621
    reference_title: Obexelimab for the Treatment of IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Obexelimab is a bifunctional monoclonal antibody that inhibits B-cell activity through coengagement
      of CD19 and FcγRIIb without inducing B-cell depletion.
    explanation: The drug tests nondepleting B-cell inhibition and should not be described as B-cell depletion.
  - reference: PMID:42233621
    reference_title: Obexelimab for the Treatment of IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      flares were reported in 26 patients (26.8%) in the obexelimab group and in 53 patients (54.6%) in
      the placebo group.
    explanation: >-
      INDIGO randomized 194 participants with standardized glucocorticoid tapering; the flare hazard ratio
      was 0.44.
- name: Rilzabrutinib
  description: >-
    Investigational reversible BTK inhibitor in IgG4-RD. A 27-person open-label phase IIa trial, including
    rituximab-intolerant or refractory participants, reported 19/27 flare-free and off glucocorticoids/immunosuppressants
    at end of treatment. Diarrhea occurred in 11/27; two serious events, including one death, were judged
    unrelated to study drug. Larger controlled trials are needed.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Rilzabrutinib
      term:
        id: NCIT:C174769
        label: Rilzabrutinib
  evidence:
  - reference: PMID:42481271
    reference_title: A phase 2 trial of rilzabrutinib in IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the end of treatment, 70.4% (19/27) of participants were flare-free and off GCs/immunosuppressants.
    explanation: >-
      The 27-person open-label phase IIa trial supports feasibility and preliminary activity; it does
      not estimate comparative efficacy.
- name: Abatacept
  description: >-
    Investigational costimulation blockade. In a 10-person open-label study, 5 maintained a response at
    24 weeks and 3 achieved complete remission. Response correlated with reduced plasmablasts and activated
    Tfh2 cells; half discontinued for flare or lack of response. These exploratory data do not prove an
    obligatory Tfh pathway.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Abatacept
      term:
        id: NCIT:C28898
        label: Abatacept
  evidence:
  - reference: PMID:35425928
    reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Three subjects (30%) achieved the primary endpoint.
    explanation: >-
      Complete remission at week 24 occurred in 3/10 in this uncontrolled proof-of-concept trial; 5/10
      maintained a treatment response.
  target_mechanisms:
  - target: Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation
    treatment_effect: INHIBITS
    description: >-
      Costimulation blockade is associated with reduced activated Tfh2 and plasmablast compartments among
      responders.
    evidence:
    - reference: PMID:35425928
      reference_title: 'Abatacept in IgG4-related disease: a prospective, open-label, single-arm, single-centre, proof-of-concept study.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Reductions in serum IgE, circulating plasmablasts, and activated type 2 T follicular helper (TFH2)
        cells correlated with response to treatment.
      explanation: Correlated immune changes support pharmacodynamic interpretation rather than causal mediation.
- name: Ureteral stenting
  description: Relieves urinary obstruction when indicated, alongside management of active systemic disease.
  treatment_term:
    preferred_term: Ureteral stenting
    term:
      id: NCIT:C71316
      label: Stenting
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related
      to IgG4-RD (8 ureteral stents, 8 biliary stents).
    explanation: >-
      Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune
      disease.
  target_mechanisms:
  - target: Retroperitoneal Encasement and Urinary Obstruction
    treatment_effect: BYPASSES
    description: Mechanically bypasses the obstructive component.
    evidence:
    - reference: PMID:25988916
      reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sixteen patients (13%) had received either ureteral or biliary tract stents for complications
        related to IgG4-RD (8 ureteral stents, 8 biliary stents).
      explanation: >-
        Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune
        disease.
- name: Biliary stenting
  description: >-
    Provides biliary drainage when clinically indicated; anti-inflammatory treatment addresses the disease
    process.
  treatment_term:
    preferred_term: Biliary stenting
    term:
      id: NCIT:C71316
      label: Stenting
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sixteen patients (13%) had received either ureteral or biliary tract stents for complications related
      to IgG4-RD (8 ureteral stents, 8 biliary stents).
    explanation: >-
      Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune
      disease.
  target_mechanisms:
  - target: Pancreatobiliary Fibroinflammation and Ductal Obstruction
    treatment_effect: BYPASSES
    description: Mechanically bypasses the obstructive component.
    evidence:
    - reference: PMID:25988916
      reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sixteen patients (13%) had received either ureteral or biliary tract stents for complications
        related to IgG4-RD (8 ureteral stents, 8 biliary stents).
      explanation: >-
        Clinical experience supports mechanical relief of obstruction; stents do not treat systemic immune
        disease.
discussions:
- discussion_id: gap_igg4rd_dominant_autoantigen_identity
  prompt: >-
    What dominant autoantigen, antigen family, or antigen-presenting context initiates the coupled plasmablast
    and CD4-positive T-cell response in IgG4-RD?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Candidate Autoantigen Recognition and Antigen Presentation
  - pathophysiology#IgG4-Positive Plasmablast Expansion
  - pathophysiology#CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production
  rationale: >-
    Candidate antigens explain subsets, and the precise B-lineage-to-CTL antigen-presentation step remains
    inferred. Direct B-cell-to-fibroblast signaling provides an additional route. A universal antigen
    is neither established nor required for every clinical pattern.
  proposed_experiments:
  - experiment_id: exp_igg4rd_paired_bcr_tcr_antigen_discovery
    name: Paired BCR/TCR and autoantigen discovery across active IgG4-RD lesions
    description: >-
      From paired blood and affected-organ biopsies, sequence plasmablast BCRs and expanded CD4+ CTL TCRs,
      express dominant antibodies and TCRs, and test candidate antigens by proteome arrays, immunoprecipitation-mass
      spectrometry, and antigen-presentation assays.
    experiment_type:
      preferred_term: paired repertoire and antigen-discovery experiment
    model_systems:
    - name: Active human IgG4-RD blood and affected-organ biopsy pairs
      description: >-
        Prospective patient samples spanning pancreatobiliary, salivary/lacrimal, renal, retroperitoneal,
        and vascular IgG4-RD manifestations.
      experimental_model_type: OTHER
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: plasmablast
        term:
          id: CL:0000980
          label: plasmablast
      - preferred_term: CD4-positive cytotoxic T lymphocyte
        term:
          id: CL:0000624
          label: CD4-positive, alpha-beta T cell
    readouts:
    - name: Shared and organ-restricted antigen specificity
      target: pathophysiology#Candidate Autoantigen Recognition and Antigen Presentation
      description: >-
        Concordance between dominant plasmablast antibody specificity, expanded lesional TCR recognition,
        and organ expression of candidate antigens.
      assays:
      - preferred_term: B cell receptor sequencing
      - preferred_term: T cell receptor sequencing
      - preferred_term: immunoprecipitation mass spectrometry
      direction: POSITIVE
    decision_criterion: >-
      A dominant autoantigen model is supported if recurrent antigen specificities are shared across independent
      patients and mechanistically connect plasmablast BCRs to lesional CD4+ T-cell activation; a per-organ
      model is supported if specificity tracks organ tropism instead.
    would_support:
    - pathophysiology#Candidate Autoantigen Recognition and Antigen Presentation
    - pathophysiology#IgG4-Positive Plasmablast Expansion
    - pathophysiology#CD4-Positive Cytotoxic T-Lymphocyte Fibrogenic Cytokine Production
  evidence:
  - reference: PMID:31612628
    reference_title: Disease Severity Linked to Increase in Autoantibody Diversity in IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While these findings suggest an underlying importance for B cell tolerance and the potential pathogenicity
      of autoantibodies in IgG4-RD, they also highlight the unmet need in identifying a dominant and specific
      antigen that may drive the pathogenesis of IgG4-RD.
    explanation: >-
      The validation cohort explicitly frames dominant antigen identity as an unmet need despite several
      candidate autoantigens.
  - reference: PMID:24815737
    reference_title: De novo oligoclonal expansions of circulating plasmablasts in active and relapsing IgG4-related disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      disease pathogenesis is linked to de novo recruitment of naive B cells into T cell-dependent responses
      by CD4(+) T cells, likely driving a self-reactive disease process.
    explanation: >-
      The B-cell repertoire study motivates a specific antigen-discovery gap connecting plasmablasts to
      CD4+ T-cell-dependent responses.
- discussion_id: gap_igg4rd_organ_tropism_and_fibroinflammation
  prompt: >-
    Why do shared plasmablast, IgG4 class-switching, and CD4-positive cytotoxic-T-cell programs produce
    different organ manifestations such as pancreatitis, cholangitis, retroperitoneal fibrosis, kidney
    disease, and salivary/lacrimal gland enlargement?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Storiform Fibrosis
  - pathophysiology#Organ-Specific Fibroinflammatory Injury
  rationale: >-
    IgG4-RD has a conserved fibroinflammatory histology, but the current model cannot yet explain why
    particular organs are targeted in individual patients. Organ-restricted antigens, epithelial-barrier
    functions, chemokine niches, and local stromal repair programs remain plausible but incompletely connected
    mechanisms.
  proposed_experiments:
  - experiment_id: exp_igg4rd_multi_organ_single_cell_stromal_immune_map
    name: Multi-organ single-cell immune-stromal map of IgG4-RD lesions
    description: >-
      Compare affected pancreas, bile duct, kidney, retroperitoneum, and salivary/lacrimal tissues using
      single-cell RNA sequencing, spatial transcriptomics, BCR/TCR sequencing, and autoantigen staining
      to separate shared fibroinflammatory circuitry from organ-specific injury programs.
    experiment_type:
      preferred_term: multi-organ single-cell spatial profiling study
    model_systems:
    - name: Human IgG4-RD affected-organ biopsy cohort
      description: >-
        Cross-organ biopsy cohort with matched blood, histopathology, serum autoantibody, and treatment-response
        metadata.
      experimental_model_type: OTHER
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
    readouts:
    - name: Organ-specific antigen and stromal activation signatures
      target: pathophysiology#Organ-Specific Fibroinflammatory Injury
      description: >-
        Spatial colocalization of candidate autoantigens, plasmablasts/plasma cells, CD4+ CTLs, macrophages,
        fibroblasts, myofibroblasts, and extracellular matrix gene programs.
      assays:
      - preferred_term: single-cell RNA sequencing
      - preferred_term: spatial transcriptomics
      direction: POSITIVE
    decision_criterion: >-
      Organ tropism is supported as antigen/barrier-driven if candidate autoantigen expression and barrier
      injury localize with immune clonotypes and stromal activation in the affected organ more strongly
      than in unaffected or disease-control tissue.
    would_support:
    - pathophysiology#Organ-Specific Fibroinflammatory Injury
    - pathophysiology#Storiform Fibrosis
  evidence:
  - reference: PMID:38524667
    reference_title: Laminin 511-E8, an autoantigen in IgG4-related cholangitis, contributes to cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      This makes it tempting to speculate that a decreased epithelial barrier function with attraction
      of immune cells and impaired bicarbonate secretion as a result of dysfunction of laminin 511 by
      autoantibody binding could potentially be a common systemic pathogenic mechanism in a subset of
      patients with IgG4-RD.
    explanation: >-
      Cholangitis data support a plausible epithelial-barrier mechanism, while the authors frame it as
      subset-level and still partly speculative.
  - reference: PMID:34718050
    reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Binding of patient-derived annexin A11 autoantibodies inhibits annexin A11 function, possibly contributing
      to bile duct damage by weakening the biliary bicarbonate umbrella in patients with IRC.
    explanation: >-
      Annexin A11 evidence supplies an organ-specific bile-duct injury model but does not explain non-biliary
      organ tropism.
  - reference: PMID:39306708
    reference_title: The immunological pathogenesis of IgG4-related disease categorized by clinical characteristics.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Importantly, IgG4-RD can be classified into four clinical phenotypes based on the distribution of
      affected organs, with each phenotype showing different dominant immune cell subsets involved in its
      pathogenesis.
    explanation: >-
      A review proposes that each organ-distribution phenotype carries its own dominant immune subset. This
      is the most explicit statement of the mechanism this gap asks about, but it is a synthesis rather than
      phenotype-matched immunophenotyping, so it motivates the gap instead of closing it.
- discussion_id: gap_igg4rd_vascular_and_stromal_specificity
  prompt: >-
    Which cell and matrix interactions produce obliterative phlebitis, organ tropism and storiform architecture?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Storiform Fibrosis
  - pathophysiology#IL-33-Associated Macrophage Matrix Remodeling
  - pathophysiology#Organ-Specific Fibroinflammatory Injury
  rationale: >-
    B-cell cocultures establish collagen-promoting activity, but do not reproduce whorled architecture.
    MMP12 expression in macrophages does not establish a collagen-deposition edge. CTL-associated apoptosis
    does not by itself explain venous obliteration. The isolated-aortitis comparator is not confirmed
    IgG4-RD, and human organ distribution cannot be inferred from induced mouse pancreatic initiation.
    These remain gaps, with clinical and histological findings retained without invented arrows.
datasets:
- accession: geo:GSE220582
  title: Transcriptomic analysis of double-negative B cell subsets in IgG4-related disease
  description: >-
    IgD-CD27- “double negative” (DN) B cells are known to be expanded in the blood in many disease contexts
    and the IgD-CD27-CXCR5-CD11c+ DN2 B cell subset has been most widely studied in autoimmune diseases.
    In addition to DN2 B cells, a distinct IgD-CD27-CXCR5-CD11c- DN3 B cell subset accumulates in the
    blood both in IgG4-related disease, an autoimmune disease in which inflammation and fibrosis can be
    reversed by B cell depletion, and in severe COVID-19. DN3 B cells, but not DN2 B cells, prominently
    accumulate in the blood and end-organs of IgG4-related disease.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 15
  publication: PMID:37300833
  notes: >-
    Identified by GEO DataSets index search for IgG4-Related Disease (scripts/discover_datasets.py); accession
    and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are
    GEO's own values.
- accession: geo:GSE202617
  title: Gene expression of CD4+CD8+ Tfh cells in lesions of IgG4-related disease and CD4+CD8+ Tfh in tonsil.
  description: >-
    To further know features of CD4+CD8+ Double positive (DP)-Tfh cells in respective lymphoid tissues,
    we subsequently investigated transcriptomes of DP-Tfh cells in submandibular gland lesions of IgG4-RD
    in comparison to those of DP-Tfh cells in tonsils. Results showed that DP-Tfh cells of IgG4-RD lesions
    were more apt to present CTL-related genes such as Eomes and granzymes than DP-Tfh cells in tonsils.
    It was also noted that the level of CD70 in DP-Tfh cells of IgG4-RD lesions was higher than that of
    tonsillar DP-Tfh cells. Genes related to Tfh cell function were seemed to be presented in DP-Tfh cells
    of tonsils compared to DP-Tfh cells of IgG4-RD lesions.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MICROARRAY
  sample_count: 8
  publication: PMID:36091071
  notes: >-
    Identified by GEO DataSets index search for IgG4-Related Disease (scripts/discover_datasets.py); accession
    and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are
    GEO's own values.
references:
- reference: PMID:22596100
  title: Consensus statement on the pathology of IgG4-related disease.
- reference: PMID:32552502
  title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
- reference: PMID:31793250
  title: The 2019 American College of Rheumatology/European League Against Rheumatism Classification Criteria for IgG4-Related Disease.
- reference: PMID:33274670
  title: The 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD.
notes: >-
  The pathograph distinguishes human associations, patient-derived cell experiments and mouse perturbations.
  No initiating antigen or innate-first sequence is established for all human IgG4-RD. Clinical organ-pattern
  clusters are not validated exclusive immunological subtypes. IgG4-positive cells and serum IgG4 are
  informative but are neither specific nor universally elevated. The two OpenScientist reports and prior
  assessments were independently reviewed; experimental provenance and consequential corrections are recorded
  in the paired assessment sidecars.
classifications:
  harrisons_chapter:
  - classification_value: IMMUNE_RHEUMATOLOGIC
    evidence:
    - reference: PMID:25988916
      reference_title: "IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        IgG4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory
        condition that can affect nearly any organ.
      explanation: >-
        IgG4-RD is defined as an immune-mediated fibroinflammatory condition
        without a single dominant organ system, so its clinical home is
        Harrison's Immune-Mediated, Inflammatory, and Rheumatologic Part rather
        than any one organ-system Part.
genetic:
- name: HLA-DRB1
  gene_term:
    preferred_term: HLA-DRB1
    term:
      id: hgnc:4948
      label: HLA-DRB1
  relationship_type: RISK_FACTOR
  notes: >-
    Replicated susceptibility association; this is not a monogenic diagnostic genotype. HLA peptide-binding
    and Fc-receptor biology can involve adaptive and innate cells, so the associations do not establish
    an innate-first temporal sequence.
  evidence:
  - reference: PMID:38229354
    reference_title: 'IgG4-related disease in the Japanese population: a genome-wide association study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified the HLA-DRB1 (p=1·1×10-11) and FCGR2B (p=2·0×10-8) regions as susceptibility loci
      for IgG4-related disease.
    explanation: Japanese case-control GWAS supports association.
  - reference: PMID:41298177
    reference_title: Genome-wide association studies reveal new insights into the genetic basis of IgG4-related disease in the Chinese Han population.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified 22 single nucleotide polymorphisms (SNPs) that surpassed genome-wide significance
      thresholds (P < 5E-08) and replicated consistently across both cohorts, defining 16 distinct genetic
      susceptibility loci.
    explanation: >-
      Chinese Han GWAS supports a broader polygenic architecture, not fine-mapped causal genes for every
      locus.
- name: FCGR2B
  gene_term:
    preferred_term: FCGR2B
    term:
      id: hgnc:3618
      label: FCGR2B
  relationship_type: RISK_FACTOR
  notes: >-
    FCGR2B-region susceptibility is replicated in Japanese and Chinese studies. The rs1340976 risk-associated
    signal was linked to increased, not decreased, FCGR2B expression. Fc-gamma-RIIb acts in B-lineage
    as well as innate immune contexts; the GWAS alone does not establish pathway direction or cellular
    causality.
  evidence:
  - reference: PMID:38229354
    reference_title: 'IgG4-related disease in the Japanese population: a genome-wide association study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified the HLA-DRB1 (p=1·1×10-11) and FCGR2B (p=2·0×10-8) regions as susceptibility loci
      for IgG4-related disease.
    explanation: Japanese case-control GWAS supports association.
  - reference: PMID:41298177
    reference_title: Genome-wide association studies reveal new insights into the genetic basis of IgG4-related disease in the Chinese Han population.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified 22 single nucleotide polymorphisms (SNPs) that surpassed genome-wide significance
      thresholds (P < 5E-08) and replicated consistently across both cohorts, defining 16 distinct genetic
      susceptibility loci.
    explanation: >-
      Chinese Han GWAS supports a broader polygenic architecture, not fine-mapped causal genes for every
      locus.
  - reference: PMID:38229354
    reference_title: 'IgG4-related disease in the Japanese population: a genome-wide association study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: rs1340976 in FCGR2B showed an association with increased FCGR2B expression
    explanation: The expression direction corrects a consequential interpretation error.
prevalence:
- population: United States, commercially insured adults; age- and sex-standardized claims-based estimate on 2019-01-01
  measure_type: POINT_PREVALENCE
  rate_per_100000: 5.3
  evidence:
  - reference: PMID:37137671
    reference_title: 'Incidence, prevalence and mortality of IgG4-related disease in the USA: a claims-based analysis of commercially insured adults.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The point prevalence ... was 5.3/100 000 persons.
    explanation: >-
      Validated claims algorithm estimate; ascertainment and insured-population selection limit generalization.
- population: United States, commercially insured adults; age- and sex-standardized 2019 estimate
  measure_type: ANNUAL_INCIDENCE
  rate_per_100000: 1.39
  evidence:
  - reference: PMID:37137671
    reference_title: 'Incidence, prevalence and mortality of IgG4-related disease in the USA: a claims-based analysis of commercially insured adults.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The incidence of IgG4-RD increased during the study period from 0.78 to 1.39 per 100 000 person-years
      in 2015 and 2019, respectively.
    explanation: Calendar-year incidence is distinguished from point prevalence.
progression:
- phase: Relapsing fibroinflammation with possible irreversible damage
  notes: >-
    Organ distribution, treatment responsiveness and progression vary. Fibrotic damage can persist despite
    control of inflammation; referral cohorts and claims populations differ in sex distribution and outcomes.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IgG4-RD was associated with damage caused by the disease (as opposed to treatment) in a total of
      73 patients (58%) at the time of the initial evaluation
    explanation: The referral cohort documents accumulated organ damage, not an incident risk estimate.
  - reference: PMID:37137671
    reference_title: 'Incidence, prevalence and mortality of IgG4-related disease in the USA: a claims-based analysis of commercially insured adults.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: adjusted HR of 2.51 (95% CI 1.76 to 3.56).
    explanation: >-
      Matched claims analysis found excess all-cause mortality; observational data cannot isolate disease
      versus treatment or residual confounding.
- phase: Predominantly adult onset with cohort-dependent sex distribution
  notes: A 125-patient referral cohort included 76 men and 49 women. Among its 103 patients with active disease, mean age at onset was 50.5 years, with wide variation. Male predominance and onset estimates differ by organ phenotype and ascertainment and are not diagnostic requirements.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the mean age at disease onset was 50.5 years (+/- 15.1).
    explanation: This estimate applies to the 103 patients with active disease in the referral cohort.
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The gender disparity in this cohort, however, was less prominent than often reported in the literature (male:female 1.6:1).
    explanation: Sex distribution varies across selected cohorts.
- phase: Coexisting malignancy across the disease timeline
  notes: A Japanese hospital survey estimated malignancy in 10.9% of IgG4-RD cases and malignant lymphoma in approximately 2.0%. Cancers occurred before, near and after IgG4-RD diagnosis. These prevalence estimates are not an incident cancer probability caused by IgG4-RD; age, surveillance, treatment and selection can contribute.
  evidence:
  - reference: PMID:35229347
    reference_title: Nationwide epidemiological survey of immunoglobulin G4-related disease with malignancy in Japan.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The overall prevalence of malignant disease in IgG4-RD cases was estimated to be 10 900 per 100 000 cases
    explanation: Hospital-survey prevalence does not establish a unidirectional causal relationship.
  - reference: PMID:35229347
    reference_title: Nationwide epidemiological survey of immunoglobulin G4-related disease with malignancy in Japan.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The prevalence of malignant lymphoma in IgG4-RD cases was the highest and was estimated to be 1985 per 100 000 cases.
    explanation: The lymphoma estimate is expressed per IgG4-RD cases, not the general population.
diagnosis:
- name: Integrated clinical, imaging, serologic and tissue assessment
  description: >-
    Assess compatible organ manifestations and image the extent of disease. Biopsy interpretation integrates
    morphology with organ-appropriate IgG4 cell counts and ratios, while excluding malignancy and other
    inflammatory mimics. Serum IgG4 or immunostaining alone is insufficient.
  evidence:
  - reference: PMID:22596100
    reference_title: Consensus statement on the pathology of IgG4-related disease.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: Tissue IgG4 counts and IgG4:IgG ratios are secondary in importance.
    explanation: The pathology consensus prioritizes morphology and clinical context.
  - reference: PMID:32552502
    reference_title: European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      IgG4-related digestive disease can be diagnosed only with a comprehensive work-up that includes
      histology, organ morphology at imaging, serology, search for other organ involvement, and response
      to glucocorticoid treatment.
    explanation: The guideline supports integrated evaluation.
- name: ACR/EULAR research classification and revised comprehensive diagnostic criteria
  description: >-
    The 2019 ACR/EULAR framework applies entry, exclusion and weighted inclusion domains for classification;
    classification thresholds do not replace clinical diagnosis. The 2020 revised comprehensive diagnostic
    framework integrates clinical/radiologic, serologic and pathologic domains.
  evidence:
  - reference: PMID:31793250
    reference_title: The 2019 American College of Rheumatology/European League Against Rheumatism Classification Criteria for IgG4-Related Disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In the first validation cohort, a threshold of 20 points had a specificity of 99.2%
    explanation: >-
      The classifier was validated for research and should not be equated with a standalone diagnostic
      test.
  - reference: PMID:33274670
    reference_title: The 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      which consists of 3 domains; 1) Clinical and radiological features, 2) Serological diagnosis and
      3) Pathological diagnosis.
    explanation: The revised diagnostic framework integrates independent dimensions.
differential_diagnoses:
- name: Malignancy involving affected organs
  description: Pancreatic, biliary, glandular and lymphoid malignancies can mimic mass-forming inflammation.
  distinguishing_features:
  - Use imaging and appropriate tissue assessment to establish morphology and clonality; avoid attributing a mass to IgG4-RD on serum IgG4 alone.
  evidence:
  - reference: PMID:25988916
    reference_title: 'IgG4-Related Disease: Clinical and Laboratory Features in One Hundred Twenty-Five Patients.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The surgical procedures were usually performed for the purpose of diagnosis or for erroneous diagnoses
      of cancer.
    explanation: The cohort demonstrates the importance of this differential.
- name: Sjogren disease
  description: Lacrimal/salivary disease and tubulointerstitial nephritis can overlap.
  distinguishing_features:
  - Clinical distribution, tissue morphology and anti-SSA/Ro or anti-SSB/La antibodies help distinguish the diseases; antibody negativity alone is not conclusive.
  evidence:
  - reference: PMID:30596168
    reference_title: Clinical Manifestations and Long-term Outcomes of IgG4-Related Kidney and Retroperitoneal Involvement in a United Kingdom IgG4-Related Disease Cohort.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: anti-SSA/Ro and anti-SSB/La antigens are normally detectable in primary Sjögren’s syndrome−TIN.
    explanation: The kidney cohort discusses differentiation from Sjogren-associated nephritis.
clinical_trials:
- name: NCT04540497
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    MITIGATE, 135 participants; published randomized phase III flare results, with long-term follow-up
    ongoing.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT04540497
    reference_title: A Phase 3, Randomized, Double-blind, Multicenter, Placebo Controlled Study of Inebilizumab Efficacy and Safety in IgG4-Related Disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This study aims to evaluate the efficacy and safety of inebilizumab for the prevention of flare
      of Immunoglobulin G4-related disease (IgG4-RD).
    explanation: The registry establishes study design and purpose, not efficacy results.
- name: NCT05662241
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    INDIGO, 194 participants; published randomized phase III nondepleting B-cell inhibition results, with
    long-term follow-up ongoing.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT05662241
    reference_title: A Phase 3, Multicenter, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy and Safety of Obexelimab in Patients With IgG4-Related Disease (INDIGO)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This study aims to examine the efficacy and safety of obexelimab for the prevention of flare of
      IgG4-related disease (IgG4-RD)
    explanation: The registry establishes study design and purpose, not efficacy results.
- name: NCT04660565
  phase: PHASE_IV
  status: UNKNOWN
  description: >-
    Randomized open-label belimumab maintenance study, registered in 2020 with planned enrollment 60.
    Registry status is UNKNOWN; the listed phase IV does not establish an IgG4-RD regulatory indication
    or efficacy.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT04660565
    reference_title: Belimumab Treatment for IgG4-related Disease, a Prospective, Open-label Clinical Trial
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This randomized, control clinical trial aimed to evaluate the tolerability and the efficacy of Belimumab
      for maintenance treatment for IgG4-RD.
    explanation: The registry establishes study design and purpose, not efficacy results.
- name: NCT03669861
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Completed 10-person phase II abatacept proof-of-concept study, with published heterogeneous response.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT03669861
    reference_title: A Prospective, Open-label, Single Center Abatacept in IgG4-Related Disease 10-patient Proof-of-concept Study
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This is a Phase 2, single center, proof of concept clinical trial in subjects with active IgG4-Related
      Disease (IgG4-RD). Approximately 10 subjects with active IgG4-RD will be enrolled into this study.
      Subjects will receive weekly subcutaneous doses of abatacept (125mg) for 24 doses (24 weeks).
    explanation: The registry establishes study design and purpose, not efficacy results.
- name: NCT04520451
  phase: PHASE_II
  status: COMPLETED
  description: Completed 27-person phase IIa rilzabrutinib study; published results are uncontrolled.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT04520451
    reference_title: An Open Label, Two-Arm Study to Evaluate the Effect of Rilzabrutinib (PRN1008/SAR444671) on Safety and Disease Activity in ParticipantsWith IgG4-Related Disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      This is a Phase 2a, multi-center, open-label, two-arm study of approximately 25 patients with active
      IgG4-related disease (IgG4-RD). The two arms include (1) Experimental: rilzabrutinib with glucocorticoids
      and (2) Active Comparator: glucocorticoids only.
    explanation: The registry establishes study design and purpose, not efficacy results.
- name: NCT07148791
  phase: PHASE_II
  status: RECRUITING
  description: >-
    Recruiting phase II anti-BCMA/CD19 CAR-T study, planned enrollment nine. Registry design is prospective
    evidence of investigation, not evidence of benefit.
  notes: >-
    ClinicalTrials.gov protocol and status independently checked 2026-09-04. Overall completion can extend
    beyond the published primary endpoint.
  evidence:
  - reference: clinicaltrials:NCT07148791
    reference_title: Exploratory Clinical Study of Anti-BCMA-CD19 CAR-T Cell Therapy for Relapsed/Refractory IgG4-Related Disease
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The goal of this clinical trial is to test the safety and potential benefit of a new immune cell
      therapy called anti-BCMA-CD19 CAR-T cells
    explanation: The registry establishes study design and purpose, not efficacy results.
animal_models:
- name: Poly(I:C)-induced autoimmune pancreatitis
  species: Mus musculus
  genotype: Female MRL/MpJ mice receiving repeated poly(I:C)
  description: Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.
  publication: PMID:39264798
  evidence:
  - reference: PMID:39264798
    reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of experimental AIP
    explanation: Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.
  modeled_mechanisms:
  - target: Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Induced female-mouse pancreatitis is not spontaneous systemic human disease; serum associations in 33 patients do not validate temporal initiation.
    evidence:
    - reference: PMID:39264798
      reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: the blockade of the CCR9-CCL25 interaction by anti-CCL25 Ab markedly inhibited the development of experimental AIP
      explanation: Experimental cDC/T-cell/pDC recruitment and cytokine feedback with pancreatic inflammation and fibrosis.
    readouts:
    - name: Pancreatic pDC abundance after CCL25 blockade
      target: Plasmacytoid Dendritic Cell Recruitment and Cytokine Amplification
      direction: DECREASED
      interpretation: Anti-CCL25 treatment reduces pancreatic pDC recruitment compared with control antibody, testing the recruitment arm of the induced cytokine loop.
      evidence:
      - reference: PMID:39264798
        reference_title: A positive cytokine/chemokine feedback loop establishes plasmacytoid DC-driven autoimmune pancreatitis in IgG4-related disease.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: treatment with anti-CCL25 Ab significantly reduced the percentages of pDCs, CD11b+myeloid cells, and CD11c+DCs as compared with the administration of control Ab
        explanation: Anti-CCL25 treatment reduces pancreatic pDC recruitment compared with control antibody, testing the recruitment arm of the induced cytokine loop.
- name: Human TLR7 transgenic mouse
  species: Mus musculus
  genotype: huTLR7-transgenic C57BL/6
  description: TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.
  publication: PMID:31339007
  evidence:
  - reference: PMID:31339007
    reference_title: Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice
    explanation: TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.
  modeled_mechanisms:
  - target: TLR7-Associated Macrophage IL-33 Production
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Mouse IgG1 is not human IgG4 and transgenic TLR7 activation does not establish a common human initiating lesion.
    evidence:
    - reference: PMID:31339007
      reference_title: Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice
      explanation: TLR7 gain increases glandular and systemic inflammation/fibrosis, with IgG1 and IL-33 responses.
    readouts:
    - name: Submandibular, pancreatic and lung focus and fibrosis scores
      target: TLR7-Associated Macrophage IL-33 Production
      direction: INCREASED
      interpretation: Histological inflammation and fibrosis scores are higher in huTLR7-transgenic than wild-type animals; these scores do not identify human IgG4 antibody function.
      evidence:
      - reference: PMID:31339007
        reference_title: Activated M2 Macrophages Contribute to the Pathogenesis of IgG4-Related Disease via Toll-like Receptor 7/Interleukin-33 Signaling.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: In huTLR-7-transgenic mice, the focus and fibrosis scores in SMGs, pancreas, and lungs were significantly higher than those in wild-type mice
        explanation: Histological inflammation and fibrosis scores are higher in huTLR7-transgenic than wild-type animals; these scores do not identify human IgG4 antibody function.
- name: Slc29a3-deficient sialadenitis
  species: Mus musculus
  genotype: Slc29a3-/-
  description: Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.
  publication: PMID:41332187
  evidence:
  - reference: PMID:41332187
    reference_title: TLR7 responses to nucleosides drive sialadenitis in Slc29a3-deficient mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs
    explanation: Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.
  modeled_mechanisms:
  - target: Salivary and Lacrimal Gland Fibroinflammation
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Sialadenitis overlaps Sjogren disease; lymphocyte infiltration is present, so innate-only sufficiency and systemic IgG4-RD fidelity are not established.
    evidence:
    - reference: PMID:41332187
      reference_title: TLR7 responses to nucleosides drive sialadenitis in Slc29a3-deficient mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs
      explanation: Endogenous nucleoside accumulation is associated with TLR7 activation, glandular chemokines and impaired saliva production.
    readouts:
    - name: Damage to Aqp5-positive salivary acinar and intercalated duct cells
      target: Salivary and Lacrimal Gland Fibroinflammation
      direction: INCREASED
      interpretation: Loss of salivary epithelial integrity is the measured tissue injury; it supports sialadenitis overlap without validating a model of every IgG4-RD organ.
      evidence:
      - reference: PMID:41332187
        reference_title: TLR7 responses to nucleosides drive sialadenitis in Slc29a3-deficient mice.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs
        explanation: Loss of salivary epithelial integrity is the measured tissue injury; it supports sialadenitis overlap without validating a model of every IgG4-RD organ.
- name: Patient immunoglobulin passive transfer
  species: Mus musculus
  genotype: Neonatal male BALB/c recipient mice
  description: Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.
  publication: PMID:26964842
  evidence:
  - reference: PMID:26964842
    reference_title: Pathogenicity of IgG in patients with IgG4-related disease.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4.
    explanation: Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.
  modeled_mechanisms:
  - target: Organ-Specific Fibroinflammatory Injury
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Neonatal xenotransfer models context-dependent antibody effects, not spontaneous adult disease or universal protection by IgG4.
    evidence:
    - reference: PMID:26964842
      reference_title: Pathogenicity of IgG in patients with IgG4-related disease.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4.
      explanation: Patient IgG1 and IgG4 can each cause pancreatic injury, while coadministered IgG4 reduces IgG1-driven injury.
    readouts:
    - name: Pancreatic injury after IgG4 coadministration with patient IgG1
      target: Organ-Specific Fibroinflammatory Injury
      direction: DECREASED
      interpretation: Coadministration reduces IgG1-driven injury relative to IgG1 alone; this does not negate injury caused by separately administered patient IgG4.
      evidence:
      - reference: PMID:26964842
        reference_title: Pathogenicity of IgG in patients with IgG4-related disease.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: The potent pathogenic activity of patient IgG1 was significantly inhibited by simultaneous injection of patient IgG4.
        explanation: Coadministration reduces IgG1-driven injury relative to IgG1 alone; this does not negate injury caused by separately administered patient IgG4.
experimental_models:
- name: Patient B-cell and fibroblast coculture
  experimental_model_type: CO_CULTURE
  publication: PMID:31319101
  description: Patient B cells or sorted plasmablasts cocultured with primary pancreatic or skin fibroblasts; transwells and PDGF-B blocking test soluble collagen-promoting activity.
  cell_source: Circulating patient B cells and sorted plasmablasts with primary human pancreatic or skin fibroblasts
  evidence:
  - reference: PMID:31319101
    reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while nonimmune IgG of the same isotype did not inhibit the collagen production induced by the same B lymphocytes.
    explanation: Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations with control B cells imply additional mediators.
  modeled_mechanisms:
  - target: Fibroblast Activation and Collagen Production
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Small patient samples and cultured-cell activation do not reproduce storiform tissue architecture or establish dominance in vivo.
    evidence:
    - reference: PMID:31319101
      reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while nonimmune IgG of the same isotype did not inhibit the collagen production induced by the same B lymphocytes.
      explanation: Blocking PDGF-B attenuates collagen production in skin-fibroblast cocultures. Similar PDGF-B concentrations with control B cells imply additional mediators.
    readouts:
    - name: Fibroblast collagen production after PDGF-B blockade
      target: Fibroblast Activation and Collagen Production
      direction: DECREASED
      interpretation: Blocking PDGF-B reduces the collagen-promoting effect of patient B cells compared with an isotype control; residual activity supports additional mediators.
      evidence:
      - reference: PMID:31319101
        reference_title: B lymphocytes directly contribute to tissue fibrosis in patients with IgG(4)-related disease.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: PDGF-B blockade attenuated the fibrotic effect induced by B cells from IgG4-RD patients while nonimmune IgG of the same isotype did not inhibit the collagen production induced by the same B lymphocytes.
        explanation: Blocking PDGF-B reduces the collagen-promoting effect of patient B cells compared with an isotype control; residual activity supports additional mediators.
- name: Patient Tfh and B-cell coculture
  experimental_model_type: CO_CULTURE
  publication: PMID:27411315
  description: Circulating patient Tfh subsets tested for plasmablast-differentiation and IgG4-production helper activity.
  cell_source: Circulating human Tfh subsets and naive B cells
  evidence:
  - reference: PMID:27411315
    reference_title: Enhanced IgG4 production by follicular helper 2 T cells and the involvement of follicular helper 1 T cells in the pathogenesis of IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells.
    explanation: Patient-derived helper-cell coculture tests a functional B-cell differentiation output.
  modeled_mechanisms:
  - target: Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Stimulated cultures and circulating subset definitions do not establish that every tissue Tfh population has the same function.
    evidence:
    - reference: PMID:27411315
      reference_title: Enhanced IgG4 production by follicular helper 2 T cells and the involvement of follicular helper 1 T cells in the pathogenesis of IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells.
      explanation: Patient-derived helper-cell coculture tests a functional B-cell differentiation output.
    readouts:
    - name: Naive B-cell differentiation into plasmablasts
      target: Tfh-Mediated IgG4 Class Switching and Plasma Cell Differentiation
      direction: INCREASED
      interpretation: Tfh2 cocultures produce more plasmablast differentiation than the tested Tfh1 and Tfh17 cocultures, measuring helper function rather than tissue fibrosis.
      evidence:
      - reference: PMID:27411315
        reference_title: Enhanced IgG4 production by follicular helper 2 T cells and the involvement of follicular helper 1 T cells in the pathogenesis of IgG4-related disease.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: In vitro, Tfh2 cells more efficiently induced the differentiation of naïve B cells into plasmablasts compared to Tfh1 or Tfh17 cells.
        explanation: Tfh2 cocultures produce more plasmablast differentiation than the tested Tfh1 and Tfh17 cocultures, measuring helper function rather than tissue fibrosis.
- name: Anti-IL-1RA functional cell assays
  experimental_model_type: CELL_LINE
  publication: PMID:33974929
  description: Recombinant plasmablast antibody and patient plasma tested with IL-1 signaling reporter and epithelial/fibroblast mediator assays.
  cell_source: HEK-Blue IL-1beta reporter cells, A549 lung epithelial cells and MRC-5 lung fibroblasts with patient-derived antibody or plasma
  evidence:
  - reference: PMID:33974929
    reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic mediator production in vitro.
    explanation: Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.
  modeled_mechanisms:
  - target: Autoantibody-Mediated IL-1RA Neutralization
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Subset autoantibody activity and mixed plasma do not isolate IgG4-only causality or show human tissue fibrosis.
    evidence:
    - reference: PMID:33974929
      reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Plasma from patients with IgG4-RD exhibited elevated levels of reactivity against IL-1RA compared with plasma from the controls and neutralized IL-1RA activity, resulting in inflammatory and fibrotic mediator production in vitro.
      explanation: Patient-derived antibody and plasma experiments demonstrate functional IL-1RA interference in a subset. They do not isolate an IgG4-only mechanism or prove tissue fibrosis in vivo.
    readouts:
    - name: SEAP release from IL-1 receptor reporter cells
      target: Autoantibody-Mediated IL-1RA Neutralization
      direction: INCREASED
      interpretation: The patient-derived G4-21 antibody increases IL-1 receptor reporter output by interfering with added IL-1RA under IL-1beta stimulation.
      evidence:
      - reference: PMID:33974929
        reference_title: Neutralizing anti-IL-1 receptor antagonist autoantibodies induce inflammatory and fibrotic mediators in IgG4-related disease.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: Incubating IL-1RA/IL-1β-stimulated reporter cells with the patient-derived mAb G4–21 resulted in a significant increase in SEAP production as compared to control antibodies
        explanation: The patient-derived G4-21 antibody increases IL-1 receptor reporter output by interfering with added IL-1RA under IL-1beta stimulation.
- name: Human cholangiocyte protective-barrier assays
  experimental_model_type: CELL_LINE
  publication: PMID:34718050
  description: H69 cholangiocytes with ANXA11 knockdown and antibody-containing patient serum test ANO1 trafficking and bicarbonate-associated protection.
  cell_source: Human H69 cholangiocyte cell line with ANXA11 knockdown or patient serum
  evidence:
  - reference: PMID:34718050
    reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression.
    explanation: Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective secretory machinery; mixed serum is not an isolated isotype perturbation.
  modeled_mechanisms:
  - target: Cholangiocyte Protective Barrier Impairment
    relationship: PERTURBS
    fidelity: MODERATE
    limitations: Mixed serum exposure and knockdown are distinct perturbations; results do not prove sufficiency for human biliary fibrosis.
    evidence:
    - reference: PMID:34718050
      reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression.
      explanation: Human cholangiocyte cultures exposed to antibody-containing patient serum show disturbed protective secretory machinery; mixed serum is not an isolated isotype perturbation.
    readouts:
    - name: ANO1 surface expression after patient-serum exposure
      target: Cholangiocyte Protective Barrier Impairment
      direction: DECREASED
      interpretation: Patient-serum exposure reduces cholangiocyte ANO1 surface expression; reduced transporter localization is a readout of impaired protective secretory machinery.
      evidence:
      - reference: PMID:34718050
        reference_title: Role of the IgG4-related cholangitis autoantigen annexin A11 in cholangiocyte protection.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression.
        explanation: Patient-serum exposure reduces cholangiocyte ANO1 surface expression; reduced transporter localization is a readout of impaired protective secretory machinery.
environmental:
- name: Occupational mineral dust, vapors, gases and fumes
  description: A Dutch age- and sex-matched study compared 101 pancreatobiliary IgG4-RD cases with 303 digestive-disease controls. Blue-collar work for more than one year was associated with disease (OR 3.66, 95% CI 2.18–6.13). Job-exposure matrices implicated selected industrial exposures, with potential residual confounding and exposure misclassification. Findings do not establish an initiating antigen or apply uniformly to systemic IgG4-RD.
  exposure_term:
    preferred_term: Occupational exposure to industrial mixtures
  evidence:
  - reference: PMID:34816110
    reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We found that exposure to several compounds led to an increased OR for developing IgG4-RD
    explanation: The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.
  - reference: PMID:34816110
    reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos.
    explanation: Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.
  influences_mechanisms:
  - target: Pancreatobiliary Fibroinflammation and Ductal Obstruction
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Occupational exposure is associated with susceptibility to the pancreatobiliary phenotype. The initiating immune or epithelial intermediates were not measured.
    evidence:
    - reference: PMID:34816110
      reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We found that exposure to several compounds led to an increased OR for developing IgG4-RD
      explanation: The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.
    - reference: PMID:34816110
      reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos.
      explanation: Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.
- name: Occupational asbestos exposure
  description: A Dutch age- and sex-matched study compared 101 pancreatobiliary IgG4-RD cases with 303 digestive-disease controls. Blue-collar work for more than one year was associated with disease (OR 3.66, 95% CI 2.18–6.13). Job-exposure matrices implicated selected industrial exposures, with potential residual confounding and exposure misclassification. Findings do not establish an initiating antigen or apply uniformly to systemic IgG4-RD.
  exposure_term:
    preferred_term: exposure to asbestos
    term:
      id: ECTO:9000033
      label: exposure to asbestos
  evidence:
  - reference: PMID:34816110
    reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We found that exposure to several compounds led to an increased OR for developing IgG4-RD
    explanation: The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.
  - reference: PMID:34816110
    reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos.
    explanation: Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.
  - reference: PMID:25089862
    reference_title: 'Asbestos and smoking as risk factors for idiopathic retroperitoneal fibrosis: a case-control study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 90 patients with idiopathic RPF and 270 control participants matched for age, sex, and region of residency.
    explanation: Documents the broader RPF population behind the older asbestos association.
  influences_mechanisms:
  - target: Pancreatobiliary Fibroinflammation and Ductal Obstruction
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Occupational exposure is associated with susceptibility to the pancreatobiliary phenotype. The initiating immune or epithelial intermediates were not measured.
    evidence:
    - reference: PMID:34816110
      reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We found that exposure to several compounds led to an increased OR for developing IgG4-RD
      explanation: The post hoc exposure analysis concerns pancreatobiliary IgG4-RD; individual exposure mechanisms and causation remain unproven.
    - reference: PMID:34816110
      reference_title: Blue-collar work is a risk factor for developing IgG4-related disease of the biliary tract and pancreas.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: including ALOHA compounds (mineral dusts and VDGF), and the DOM compound asbestos.
      explanation: Identifies the associated exposure categories; the broader job-history association is not proof that every solvent, oil or metal causes IgG4-RD.
  notes: Earlier asbestos studies included idiopathic retroperitoneal fibrosis without establishing IgG4-RD in every case; their estimates must not be relabeled as IgG4-specific RPF risks.
- name: Current cigarette smoking
  description: In 234 IgG4-RD cases and 1170 matched controls, current smoking was associated with disease overall (OR 1.79, 95% CI 1.08–2.95), chiefly in the retroperitoneal-fibrosis subgroup. Excluding RPF removed the association. This is observational susceptibility evidence; effects of cessation on IgG4-RD activity were not tested.
  exposure_term:
    preferred_term: exposure to tobacco smoking
    term:
      id: ECTO:6000029
      label: exposure to tobacco smoking
  evidence:
  - reference: PMID:33751033
    reference_title: 'The association of smoking with immunoglobulin G4-related disease: a case-control study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This association was strongest among female cases [13 (14%) vs 19 (4%);, OR 3.79 (95% CI 1.71, 8.39)] and those with retroperitoneal fibrosis [RPF; 13 (28%) vs 13 (6%);, OR 6.93 (95% CI 2.78, 17.26)]
    explanation: Matched case-control association supports a phenotype-specific susceptibility signal, not a demonstrated molecular smoking mechanism.
  - reference: PMID:33751033
    reference_title: 'The association of smoking with immunoglobulin G4-related disease: a case-control study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: When RPF cases were excluded, there was no longer an association between current smoking and the odds of having IgG4-RD [12 (6%) vs 57 (6%); OR 0.95 (95% CI 0.49, 1.86)].
    explanation: The null estimate outside RPF limits generalization to all organ phenotypes.
  influences_mechanisms:
  - target: Retroperitoneal Encasement and Urinary Obstruction
    environmental_effect: PREDISPOSES
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Current smoking is associated with the retroperitoneal-fibrosis phenotype. The intervening fibroinflammatory mechanism is unknown and the study did not separately test obstruction severity.
    evidence:
    - reference: PMID:33751033
      reference_title: 'The association of smoking with immunoglobulin G4-related disease: a case-control study.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: This association was strongest among female cases [13 (14%) vs 19 (4%);, OR 3.79 (95% CI 1.71, 8.39)] and those with retroperitoneal fibrosis [RPF; 13 (28%) vs 13 (6%);, OR 6.93 (95% CI 2.78, 17.26)]
      explanation: Matched case-control association supports a phenotype-specific susceptibility signal, not a demonstrated molecular smoking mechanism.
    - reference: PMID:33751033
      reference_title: 'The association of smoking with immunoglobulin G4-related disease: a case-control study.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: When RPF cases were excluded, there was no longer an association between current smoking and the odds of having IgG4-RD [12 (6%) vs 57 (6%); OR 0.95 (95% CI 0.49, 1.86)].
      explanation: The null estimate outside RPF limits generalization to all organ phenotypes.

📚

References & Deep Research

References

PMID:22596100

Consensus statement on the pathology of IgG4-related disease.

No top-level findings curated for this source.

PMID:32552502

European Guideline on IgG4-related digestive disease - UEG and SGF evidence-based recommendations.

No top-level findings curated for this source.

PMID:31793250

The 2019 American College of Rheumatology/European League Against Rheumatism Classification Criteria for IgG4-Related Disease.

No top-level findings curated for this source.

PMID:33274670

The 2020 revised comprehensive diagnostic (RCD) criteria for IgG4-RD.

No top-level findings curated for this source.

Deep Research

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Falcon ▸

1. Disease Information

Edison Scientific Literature 34 citations 2026-05-09T09:36:38.889176

1. Disease Information

1.1 Concise overview (current understanding)

IgG4-related disease is a systemic, immune-mediated fibroinflammatory disorder that can produce tumefactive (mass-like) lesions in one or multiple organs and is unified by characteristic histopathology and clinicopathologic correlation (wallace2024currentandfuture pages 2-4, chen2024igg4relateddiseasefor pages 1-2). A core reason IgG4-RD is diagnostically challenging is that no single serologic test is both sensitive and specific, so biopsy and integrative assessment are central (wallace2024currentandfuture pages 2-4, bartoszek2024igg4relateddiseasecomprehensive pages 4-7).

Key diagnostic concept: tissue lesions typically show (i) dense lymphoplasmacytic infiltrate enriched for IgG4+ plasma cells, (ii) storiform fibrosis, and (iii) obliterative phlebitis, often with eosinophilia (chen2024igg4relateddiseasefor pages 1-2, wallace2024currentandfuture pages 2-4).

Direct abstract quote (identifier resource): Pieringer et al. state: “Immunoglobulin G4- related disease (IgG4-RD) is a rare systemic fibro-inflammatory disorder (ORPHA284264).” (pieringer2014igg4relateddisease pages 1-2)

1.2 Synonyms / alternative names

Commonly used alternative phrasings include “IgG4-related disease,” “IgG4-RD,” and organ-specific manifestations (e.g., type 1 autoimmune pancreatitis; IgG4-related sclerosing cholangitis; retroperitoneal fibrosis as a phenotype) (chen2024igg4relateddiseasefor pages 1-2, pieringer2014igg4relateddisease pages 2-4, wallace2024currentandfuture pages 2-4).

1.3 Evidence source type

The information below is derived primarily from aggregated disease-level resources (peer-reviewed reviews and guidelines) and from human cohort studies/registries and clinical trial registry records (wallace2024currentandfuture pages 2-4, wallace2020the2019american pages 1-1, wallace2024currentandfuture pages 1-2, NCT07148791 chunk 2).

2. Etiology

2.1 Disease causal factors (mechanistic)

The aetiology remains incompletely resolved, but convergent evidence indicates a B cell–T cell–driven immune disorder with downstream fibroinflammation (wallace2024currentandfuture pages 2-4, hao2023thespectrumof pages 2-4).

2.2 Risk factors

Genetic risk factors (susceptibility)

HLA associations have been reported in IgG4-RD and related phenotypes. Examples in the retrieved corpus include:
HLA-DRB1*03 association reported for retroperitoneal fibrosis (RPF) subtype (bartoszek2024igg4relateddiseasecomprehensive pages 4-7).
HLA-DR4 proposed susceptibility in autoimmune pancreatitis (AIP; an IgG4-RD manifestation) (wallace2019immunoglobuling4relateddisease. pages 1-2).
HLA-DRB1*16 and HLA-DQB1*05 described as “strongly associated” with autoimmune pancreatitis in one cohort (motta2024igg4autoantibodiesand pages 15-15).

Environmental / occupational risk factors

A Dutch study associated occupational exposure to solvents, oils, and industrial/metal dusts with IgG4-related cholangitis/pancreatitis (bartoszek2024igg4relateddiseasecomprehensive pages 4-7).
Smoking and asbestos exposure have been linked to retroperitoneal fibrosis risk (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, wallace2019immunoglobuling4relateddisease. pages 1-2).

Infectious triggers

No unifying infectious trigger is established in the retrieved evidence; reviews emphasize the absence of a consistent infectious cause (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, wallace2019immunoglobuling4relateddisease. pages 1-2).

2.3 Protective factors

No specific protective genetic or environmental factors were identified in the retrieved corpus.

2.4 Gene–environment interactions

Not clearly established in the retrieved corpus; current data support multifactorial susceptibility with organ-specific exposures and HLA background (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, wallace2019immunoglobuling4relateddisease. pages 1-2).

3. Phenotypes (clinical manifestations)

3.1 Common organ involvement and clinical phenotypes

Contemporary clinical practice recognizes reproducible organ-pattern phenotypes, including: - Pancreato-hepatobiliary (type 1 autoimmune pancreatitis; sclerosing cholangitis) (wallace2024currentandfuture pages 2-4, chen2024igg4relateddiseasefor pages 1-2) - Retroperitoneum/aorta (retroperitoneal fibrosis; aortitis/large-vessel disease) (wallace2024currentandfuture pages 2-4, chen2024igg4relateddiseasefor pages 1-2) - Head-and-neck limited (salivary/lacrimal gland enlargement; orbital adnexal disease) (wallace2024currentandfuture pages 2-4) - Mikulicz/systemic (symmetric lacrimal/salivary enlargement plus systemic involvement; typically very high serum IgG4) (wallace2024currentandfuture pages 2-4)

Multi-organ involvement is common (reported as 60–90% in one review) (bartoszek2024igg4relateddiseasecomprehensive pages 4-7).

3.2 Frequencies and statistics from recent cohorts/surveys

In a large international cohort analysis, mean organ involvement was 2.9 organs (SD 1.8), serum IgG4 was elevated in 78.7%, and classic storiform fibrosis was reported in 39.6% (illustrating that classic histology is not always captured in routine reporting) (wallace2019clinicalphenotypesof pages 2-3).
In a Japanese nationwide survey focused on IgG4-RD with malignancy, organ frequencies included: autoimmune pancreatitis 44.7%, sialadenitis 20.8%, eye disease 14.0%, kidney disease 5.16%, retroperitoneal fibrosis 5.12% (sumimoto2022nationwideepidemiologicalsurvey pages 1-1).

3.3 Thoracic (lung/mediastinal) phenotype

Thoracic disease is clinically important and often incidental: - Up to 30% of systemic IgG4-RD patients may have thoracic involvement; thoracic disease is the sole manifestation in ~10% (muller2023thoracicmanifestationsof pages 1-2). - Reported estimates across cohorts are ~15–35% thoracic involvement (muller2023thoracicmanifestationsof pages 2-3).

3.4 Suggested HPO terms (examples; not exhaustive)

(These are ontology suggestions for knowledge-base encoding; mapping not directly cited in the retrieved literature.) - Tumefactive lesion / mass effect: HP:0002664 (Neoplasm) (used as proxy for mass-like lesion), HP:0033694 (Organomegaly) depending on organ. - Salivary/lacrimal enlargement: HP:0000217 (Xerostomia), HP:0001097 (Dry eyes), HP:0000175 (Parotid enlargement). - Obstructive jaundice (pancreatobiliary): HP:0000952 (Jaundice). - Retroperitoneal fibrosis-related obstruction: HP:0000795 (Ureteral obstruction). - Eosinophilia: HP:0001880 (Eosinophilia). - Hypergammaglobulinemia: HP:0012204 (Hypergammaglobulinemia).

4. Genetic / Molecular Information

4.1 Causal genes

IgG4-RD is not established as a monogenic disorder in the retrieved evidence. Genetic findings are primarily susceptibility associations (HLA and selected non-HLA loci) rather than causal variants (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, motta2024igg4autoantibodiesand pages 15-15).

4.2 Pathogenic variants

No recurrent pathogenic germline variants defining IgG4-RD were identified in the retrieved corpus.

4.3 Autoantigens / autoantibodies (molecular targets)

Multiple candidate autoantigens have been reported in IgG4-RD. Examples include galectin-3 (reported in 28% of a cohort) and laminin-511 (detected in 50% of subjects with IgG4-related pancreatitis), supporting antigen-driven immunity in at least some patients (wallace2019immunoglobuling4relateddisease. pages 1-2).

5. Environmental Information

Environmental associations appear phenotype-specific: - Occupational exposure to solvents/oils/industrial & metal dusts has been associated with IgG4-related cholangitis/pancreatitis (bartoszek2024igg4relateddiseasecomprehensive pages 4-7). - Smoking and asbestos exposure have been linked to retroperitoneal fibrosis risk (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, wallace2019immunoglobuling4relateddisease. pages 1-2).

No consistent infectious agent trigger is supported in the retrieved evidence (bartoszek2024igg4relateddiseasecomprehensive pages 4-7, wallace2019immunoglobuling4relateddisease. pages 1-2).

6. Mechanism / Pathophysiology (current model)

6.1 Core cellular players (with CL term suggestions)

Evidence converges on immune dysregulation involving: - B-lineage cells, especially plasmablasts (suggest CL:0000946 plasma cell; plasmablasts are a transitional phenotype). - T follicular helper (Tfh) cells (suggest CL:0000907 T follicular helper cell). - CD4+ cytotoxic T lymphocytes (CD4+ CTLs) (suggest CL:0000899 CD4-positive, alpha-beta T cell; “cytotoxic CD4” is a functional state).

6.2 B-cell/plasmablast axis and fibrosis linkage

Circulating plasmablasts are an important mechanistic and biomarker node: plasmablast levels correlate with serum IgG4, inflammatory markers, number of involved organs, and disease activity, and they fall with effective therapy and rise with relapse (hao2023thespectrumof pages 2-4, hao2023thespectrumof pages 4-6). A mechanistic link to fibrosis is proposed through plasmablast profibrotic programs (e.g., LOXL2 expression and PDGF-B secretion) (hao2023thespectrumof pages 2-4).

6.3 Tfh-driven class switching and plasmablast generation

Tfh cells provide B-cell help and promote IgG4 class-switching via IL-4/IL-21 and co-stimulatory interactions. Circulating PD-1+ Tfh measures correlate with serum IgG/IgG4 metrics and the number of organs involved (xu2024pathogenicrolesof pages 2-4). A 2024 review explicitly notes that “the expansion of circulating Tfh2 cells and plasmablasts may also serve as novel biomarkers for disease diagnosis and activity monitoring” (xu2024pathogenicrolesof pages 1-2).

6.4 CD4+ CTLs and profibrotic mediators

CD4+ CTLs infiltrate lesions and can produce profibrotic mediators such as TGF-β, providing a plausible bridge between immune activation and storiform fibrosis (hao2023thespectrumof pages 2-4).

6.5 Suggested GO biological process terms (examples)

(These are ontology suggestions; not directly asserted as GO annotations in the retrieved papers.) - GO:0006954 inflammatory response - GO:0042113 B cell activation - GO:0002460 adaptive immune response based on somatic recombination of immune receptors built from immunoglobulin superfamily domains - GO:0001525 angiogenesis / vascular remodeling (for obliterative phlebitis context) - GO:0042060 wound healing and GO:0006959 humoral immune response - GO:0045429 positive regulation of nitric oxide biosynthetic process (macrophage-related; hypothesis-level)

6.6 Suggested causal chain (integrated)

A plausible chain supported by current evidence is: antigen-driven or dysregulated immune activation → expansion of Tfh (especially Tfh2-like) and plasmablasts → IgG4 class switching and oligoclonal plasmablast expansion → recruitment/activation of profibrotic T-cell and myeloid programs (including CD4+ CTLs) → storiform fibrosis and organ dysfunction (hao2023thespectrumof pages 2-4, xu2024pathogenicrolesof pages 2-4, wallace2024currentandfuture pages 2-4).

7. Anatomical Structures Affected

7.1 Organs and systems (examples)

IgG4-RD can affect virtually any organ; commonly involved sites include pancreas and hepatobiliary system, salivary/lacrimal glands and orbit, retroperitoneum/aorta, kidney, lung/mediastinum, and lymph nodes (chen2024igg4relateddiseasefor pages 1-2, pieringer2014igg4relateddisease pages 2-4, wallace2024currentandfuture pages 2-4).

7.2 UBERON suggestions (examples)

Pancreas: UBERON:0001264
Lacrimal gland: UBERON:0001813
Major salivary gland: UBERON:0001044
Lung: UBERON:0002048
Kidney: UBERON:0002113
Retroperitoneum: UBERON:0003698

8. Temporal Development

8.1 Onset

IgG4-RD typically affects middle-aged to older adults (median around late 50s–60 in major cohorts) (chen2024igg4relateddiseasefor pages 1-2, muller2023thoracicmanifestationsof pages 2-3).

8.2 Course and progression

The disease often follows a relapsing–remitting course; if under-treated, it can cause irreversible fibrotic organ damage (wallace2024currentandfuture pages 2-4, chen2024igg4relateddiseasefor pages 1-2). Proliferative manifestations tend to respond better than chronic fibrotic disease, which may be less reversible (chen2024igg4relateddiseasefor pages 1-2).

9. Inheritance and Population

9.1 Epidemiology (recent estimates prioritized)

A 2024 practice review summarized a US claims-based analysis reporting: - Incidence: 0.78–1.39 per 100,000 person-years (2015–2019) - Point prevalence: 5.3 per 100,000 persons (as of 1 Jan 2019) (wallace2024currentandfuture pages 1-2)

A thoracic-manifestations review summarizes additional estimates, e.g., Japan incidence approximated at ~1 per 100,000 and prevalence ~0.8 per 100,000 (muller2023thoracicmanifestationsof pages 2-3), while also emphasizing heterogeneity.

9.2 Demographics

Male predominance is frequently reported overall, but varies by phenotype; head-and-neck–limited disease shows less male predominance (wallace2024currentandfuture pages 2-4, wallace2019clinicalphenotypesof pages 2-3).
In an international cohort, Asians had higher median serum IgG4 (median 666 vs 240.5 mg/dL in non-Asians), and males were older at onset/diagnosis than females (wallace2019clinicalphenotypesof pages 2-3).

10. Diagnostics

10.1 Histopathology and core features

Hallmark tissue features include dense lymphoplasmacytic infiltrate rich in IgG4+ plasma cells, storiform fibrosis, obliterative phlebitis, and eosinophilia. A common supportive threshold is an IgG4/IgG ratio >40% in tissue (chen2024igg4relateddiseasefor pages 1-2).

10.2 Classification criteria (2019 ACR/EULAR)

The 2019 ACR/EULAR criteria provide a validated, points-based framework requiring: entry organ involvement, exclusion criteria application, and weighted inclusion domains across clinical/serologic/radiologic/pathologic data, with classification at ≥20 points (wallace2020the2019american pages 1-1). Performance: - Derived/validated in 1,879 subjects (1,086 cases; 793 mimickers) (wallace2020the2019american pages 1-1) - Validation cohort 1: specificity 99.2%, sensitivity 85.5% at threshold 20 (wallace2020the2019american pages 1-1) - Validation cohort 2: specificity 97.8%, sensitivity 82.0% at threshold 20 (wallace2020the2019american pages 1-1)

10.3 Biomarkers

Serum IgG4 is often elevated and correlates with extent of organ involvement and relapse risk, but is not specific (wallace2024currentandfuture pages 2-4).
Circulating plasmablasts and Tfh-derived measures (e.g., PD-1+ cTfh metrics) are proposed activity biomarkers (hao2023thespectrumof pages 2-4, xu2024pathogenicrolesof pages 2-4).

10.4 Imaging and diagnostic pitfalls

Thoracic IgG4-RD has heterogeneous CT patterns and can mimic malignancy or vasculitis; cautious diagnosis includes searching for extra-thoracic disease and integrating serum IgG4/plasmablast measures plus pathology (muller2023thoracicmanifestationsof pages 1-2).

11. Outcome / Prognosis

11.1 Organ damage and reversibility

Clinical outcomes vary by phenotype: proliferative manifestations generally respond well to immunosuppression, whereas established fibrotic disease may be less reversible (chen2024igg4relateddiseasefor pages 1-2).

11.2 Malignancy association (statistics)

A Japanese nationwide survey reported an estimated overall prevalence of malignancy among IgG4-RD cases of ~10.9% (10,900 per 100,000 cases), and malignant lymphoma ~2.0% (1,985 per 100,000). IgG4-related kidney disease had the highest associated malignancy frequency (17.1%) (sumimoto2022nationwideepidemiologicalsurvey pages 1-1). These data are context-specific (survey methodology) and should be interpreted accordingly.

12. Treatment

12.1 Standard of care: glucocorticoids (real-world implementation)

European evidence-based guidance for IgG4-related digestive disease recommends: - Induction: oral glucocorticoids 0.6–0.8 mg/kg/day for 1 month (typical 30–40 mg/day prednisone equivalent) (lohr2020europeanguidelineon pages 17-19, lohr2020europeanguidelineon pages 1-2) - Response assessment: at week 2–4 using clinical/biochemical/morphological markers (lohr2020europeanguidelineon pages 17-19, lohr2020europeanguidelineon pages 1-2) - Taper: e.g., 5 mg every 2 weeks, over 3–6 months (lohr2020europeanguidelineon pages 17-19) - Relapse: common; guideline notes relapse rates 26–70% and high re-induction success with glucocorticoids (>95%) (lohr2020europeanguidelineon pages 19-20)

12.2 B-cell depletion and steroid-sparing therapy

B-cell depletion (rituximab) is widely used in relapsing/refractory disease and is supported by the central role of B cells/plasmablasts (hao2023thespectrumof pages 2-4, wallace2024currentandfuture pages 2-4).
A phase 1–2 registry trial entry exists for rituximab (NCT01584388) and cites a prospective open-label study publication (PMID: 25667206) (NCT01584388 chunk 2).

12.3 Emerging and investigational immunomodulators (clinical trials)

Belimumab (BAFF inhibition) RCT: NCT04660565 is described as an RCT of belimumab + glucocorticoids vs glucocorticoids alone, primary outcome relapse rate, 12-month follow-up (wallace2024currentandfuture pages 7-8). Registry: https://clinicaltrials.gov/study/NCT04660565 (post date and version dates vary by record).
Abatacept (CTLA4-Ig; co-stimulation blockade): NCT03669861 (Massachusetts General Hospital) (NCT03669861 chunk 2). Registry: https://clinicaltrials.gov/study/NCT03669861.
Anti-CD19/BCMA-CD19 CAR-T exploratory trial for relapsed/refractory IgG4-RD: NCT07148791, with key efficacy endpoint change in IgG4-RD Responder Index at baseline, week 12, week 26, and intensive safety monitoring for CRS/ICANS (NCT07148791 chunk 2). Registry: https://clinicaltrials.gov/study/NCT07148791.

Note: A placebo-controlled inebilizumab study is referenced in a 2024 table, but the excerpt available here is truncated and does not provide full registry detail (wallace2024currentandfuture pages 7-8).

12.4 MAXO term suggestions (examples)

Glucocorticoid therapy: MAXO:0000155 (glucocorticoid therapy)
B-cell depletion therapy (rituximab): MAXO:0001181 (B cell depletion therapy) (term may vary)
Abatacept therapy: MAXO: immunomodulatory therapy
Belimumab therapy: MAXO: monoclonal antibody therapy
CAR-T cell therapy: MAXO:0001503 (CAR T cell therapy)

13. Prevention

Primary prevention

No established primary prevention strategies are supported by the retrieved evidence.

Secondary/tertiary prevention (practical)

Early recognition and clinicopathologic confirmation (biopsy) are emphasized to avoid diagnostic delay and prevent irreversible fibrosis (wallace2024currentandfuture pages 2-4, bartoszek2024igg4relateddiseasecomprehensive pages 4-7).
Relapse prevention/monitoring: maintenance glucocorticoids may be considered in multi-organ disease or prior relapse; response monitoring at week 2–4; add immunosuppressives when relapse occurs early during taper or when disease is not controlled (lohr2020europeanguidelineon pages 1-2, lohr2020europeanguidelineon pages 19-20).

14. Other Species / Natural Disease

No evidence for naturally occurring IgG4-RD in non-human species was retrieved in this run.

15. Model Organisms

No standardized animal model systems were retrieved in the accessible corpus. A mouse immunization experiment linked to laminin-511 is mentioned as supporting an antigen-driven mechanism but details were not available in the retrieved text segments (wallace2019immunoglobuling4relateddisease. pages 1-2).

Key curated summary table

Category	Item	Summary	Publication	URL	Citation
Identifier	Orphanet ID	IgG4-related disease is identified as a rare systemic fibro-inflammatory disorder with Orphanet identifier ORPHA284264.	Pieringer et al., 2014	https://doi.org/10.1186/s13023-014-0110-z	(pieringer2014igg4relateddisease pages 1-2)
Defining histopathology	Lymphoplasmacytic infiltrate rich in IgG4+ plasma cells	Hallmark lesion includes a dense lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cells; tissue diagnosis is essential.	Chen, 2024	https://doi.org/10.1182/hematology.2024000584	(chen2024igg4relateddiseasefor pages 1-2)
Defining histopathology	Storiform fibrosis	Storiform fibrosis is a core histopathologic feature and part of the classic triad used in diagnosis/classification.	Chen, 2024	https://doi.org/10.1182/hematology.2024000584	(chen2024igg4relateddiseasefor pages 1-2)
Defining histopathology	Obliterative phlebitis	Obliterative phlebitis is a characteristic histologic feature supporting IgG4-RD diagnosis.	Chen, 2024	https://doi.org/10.1182/hematology.2024000584	(chen2024igg4relateddiseasefor pages 1-2)
Supportive finding	Tissue eosinophilia	Tissue eosinophilia is a common supportive feature accompanying the histopathologic triad.	Chen, 2024	https://doi.org/10.1182/hematology.2024000584	(chen2024igg4relateddiseasefor pages 1-2)
Supportive finding	Serum IgG4 elevation	Many patients have elevated serum IgG4; this correlates with extent of organ involvement and relapse risk, but is not specific enough to diagnose disease alone.	Wallace et al., 2024	https://doi.org/10.1093/rap/rkae020	(wallace2024currentandfuture pages 2-4)
Supportive finding	Tissue IgG4/IgG ratio	A commonly used supportive tissue threshold is an IgG4:IgG plasma-cell ratio >40%.	Chen, 2024	https://doi.org/10.1182/hematology.2024000584	(chen2024igg4relateddiseasefor pages 1-2)
Classification criteria	2019 ACR/EULAR entry and threshold	Classification uses a 3-step process (typical organ involvement, exclusion criteria, weighted inclusion criteria) with a threshold of ≥20 points.	Wallace et al., 2020	https://doi.org/10.1136/annrheumdis-2019-216561	(wallace2020the2019american pages 1-1)
Classification performance	Cohort size used in development/validation	Criteria were developed/validated using 1,879 subjects total (1,086 cases and 793 mimickers).	Wallace et al., 2020	https://doi.org/10.1136/annrheumdis-2019-216561	(wallace2020the2019american pages 1-1)
Classification performance	Validation cohort 1	At ≥20 points, specificity was 99.2% (95% CI 97.2–99.8) and sensitivity was 85.5% (95% CI 81.9–88.5).	Wallace et al., 2020	https://doi.org/10.1136/annrheumdis-2019-216561	(wallace2020the2019american pages 1-1)
Classification performance	Validation cohort 2	At ≥20 points, specificity was 97.8% (95% CI 93.7–99.2) and sensitivity was 82.0% (95% CI 77.0–86.1).	Wallace et al., 2020	https://doi.org/10.1136/annrheumdis-2019-216561	(wallace2020the2019american pages 1-1)

Table: This table summarizes the core disease identifier, defining pathology, supportive findings, and validated 2019 ACR/EULAR classification performance for IgG4-related disease. It is useful as a compact reference for knowledge-base curation and diagnostic context.

Notes on evidence gaps and limitations

Ontology identifiers (MONDO, MeSH, ICD) were not retrievable from the current tool-accessible literature corpus; the report therefore does not assert them.
Several important 2023–2025 primary studies (e.g., single-cell transcriptomics; some therapeutics RCT publications) were listed as unobtainable in tool retrieval; mechanistic and treatment sections thus emphasize accessible, high-quality reviews/cohorts and clinical trial registry records.
HPO/GO/UBERON/MAXO terms are provided as suggestions for encoding and were not directly mapped in the cited papers.

References

(pieringer2014igg4relateddisease pages 1-2): Herwig Pieringer, Ilse Parzer, Adelheid Wöhrer, Petra Reis, Bastian Oppl, and Jochen Zwerina. Igg4- related disease: an orphan disease with many faces. Orphanet Journal of Rare Diseases, 9:110-110, Jul 2014. URL: https://doi.org/10.1186/s13023-014-0110-z, doi:10.1186/s13023-014-0110-z. This article has 142 citations and is from a peer-reviewed journal.
(wallace2024currentandfuture pages 2-4): Zachary S Wallace, Guy Katz, Yasmin G Hernandez-Barco, and Matthew C Baker. Current and future advances in practice: igg4-related disease. Rheumatology Advances in Practice, Apr 2024. URL: https://doi.org/10.1093/rap/rkae020, doi:10.1093/rap/rkae020. This article has 71 citations and is from a peer-reviewed journal.
(chen2024igg4relateddiseasefor pages 1-2): Luke Y. C. Chen. Igg4-related disease for the hematologist. Hematology, 2024:594-603, Dec 2024. URL: https://doi.org/10.1182/hematology.2024000584, doi:10.1182/hematology.2024000584. This article has 15 citations and is from a peer-reviewed journal.
(bartoszek2024igg4relateddiseasecomprehensive pages 4-7): Lidia Bartoszek, Dominika Orłowska, Joanna Olszak, Karolina Zalewa, Wojciech Kapłan, Jakub Starownik, and Bartłomiej Gastoł. Igg4-related disease: comprehensive overview of pathogenesis, clinical manifestations, and diagnostic challenges. Quality in Sport, 22:54293, Sep 2024. URL: https://doi.org/10.12775/qs.2024.22.54293, doi:10.12775/qs.2024.22.54293. This article has 0 citations.
(pieringer2014igg4relateddisease pages 2-4): Herwig Pieringer, Ilse Parzer, Adelheid Wöhrer, Petra Reis, Bastian Oppl, and Jochen Zwerina. Igg4- related disease: an orphan disease with many faces. Orphanet Journal of Rare Diseases, 9:110-110, Jul 2014. URL: https://doi.org/10.1186/s13023-014-0110-z, doi:10.1186/s13023-014-0110-z. This article has 142 citations and is from a peer-reviewed journal.
(wallace2020the2019american pages 1-1): Zachary S Wallace, Ray P Naden, Suresh Chari, Hyon K Choi, Emanuel Della-Torre, Jean-Francois Dicaire, Phillip A Hart, Dai Inoue, Mitsuhiro Kawano, Arezou Khosroshahi, Marco Lanzillotta, Kazuichi Okazaki, Cory A Perugino, Amita Sharma, Takako Saeki, Nicolas Schleinitz, Naoki Takahashi, Hisanori Umehara, Yoh Zen, and John H Stone. The 2019 american college of rheumatology/european league against rheumatism classification criteria for igg4-related disease. Annals of the Rheumatic Diseases, 79:77-87, Jan 2020. URL: https://doi.org/10.1136/annrheumdis-2019-216561, doi:10.1136/annrheumdis-2019-216561. This article has 1362 citations and is from a highest quality peer-reviewed journal.
(wallace2024currentandfuture pages 1-2): Zachary S Wallace, Guy Katz, Yasmin G Hernandez-Barco, and Matthew C Baker. Current and future advances in practice: igg4-related disease. Rheumatology Advances in Practice, Apr 2024. URL: https://doi.org/10.1093/rap/rkae020, doi:10.1093/rap/rkae020. This article has 71 citations and is from a peer-reviewed journal.
(NCT07148791 chunk 2): Jian Zhu. Exploratory Study of Anti-BCMA-CD19 CAR-T Cell Therapy in Relapsed or Refractory IgG4-Related Disease. Chinese PLA General Hospital. 2025. ClinicalTrials.gov Identifier: NCT07148791
(hao2023thespectrumof pages 2-4): Qiyuan Hao, Meng Sun, and Yanying Liu. The spectrum of b cells in the pathogenesis, diagnosis and therapeutic applications of immunoglobulin g4‐related disease. Clinical & Translational Immunology, Jan 2023. URL: https://doi.org/10.1002/cti2.1477, doi:10.1002/cti2.1477. This article has 7 citations and is from a peer-reviewed journal.
(wallace2019immunoglobuling4relateddisease. pages 1-2): Zachary S. Wallace, Cory Perugino, Mark Matza, Vikram Deshpande, Amita Sharma, and John H. Stone. Immunoglobulin g4-related disease. Clinics in chest medicine, 40 3:583-597, Sep 2019. URL: https://doi.org/10.1016/j.ccm.2019.05.005, doi:10.1016/j.ccm.2019.05.005. This article has 70 citations and is from a peer-reviewed journal.
(motta2024igg4autoantibodiesand pages 15-15): Rodrigo V. Motta and Emma L. Culver. Igg4 autoantibodies and autoantigens in the context of igg4-autoimmune disease and igg4-related disease. Frontiers in Immunology, Feb 2024. URL: https://doi.org/10.3389/fimmu.2024.1272084, doi:10.3389/fimmu.2024.1272084. This article has 30 citations and is from a peer-reviewed journal.
(wallace2019clinicalphenotypesof pages 2-3): Zachary S Wallace, Yuqing Zhang, Cory A Perugino, Ray Naden, Hyon K Choi, and John H Stone. Clinical phenotypes of igg4-related disease: an analysis of two international cross-sectional cohorts. Annals of the Rheumatic Diseases, 78:406-412, Mar 2019. URL: https://doi.org/10.1136/annrheumdis-2018-214603, doi:10.1136/annrheumdis-2018-214603. This article has 422 citations and is from a highest quality peer-reviewed journal.
(sumimoto2022nationwideepidemiologicalsurvey pages 1-1): Kimi Sumimoto, Kazushige Uchida, Tsukasa Ikeura, Kenji Hirano, Motohisa Yamamoto, Hiroki Takahashi, Takayoshi Nishino, Ichiro Mizushima, Mitsuhiro Kawano, Terumi Kamisawa, Takako Saeki, Hiroyuki Maguchi, Tomoyuki Ushijima, Masahiro Shiokawa, Hiroshi Seno, Hiroshi Goto, Seiji Nakamura, and Kazuichi Okazaki. Nationwide epidemiological survey of immunoglobulin g4‐related disease with malignancy in japan. Journal of Gastroenterology and Hepatology, 37:1022-1033, Mar 2022. URL: https://doi.org/10.1111/jgh.15809, doi:10.1111/jgh.15809. This article has 26 citations and is from a peer-reviewed journal.
(muller2023thoracicmanifestationsof pages 1-2): Romain Muller, Mikael Ebbo, Paul Habert, Laurent Daniel, Antoine Briantais, Pascal Chanez, Jean Yves Gaubert, and Nicolas Schleinitz. Thoracic manifestations of igg4‐related disease. Respirology (Carlton, Vic.), 28:120-131, Nov 2023. URL: https://doi.org/10.1111/resp.14422, doi:10.1111/resp.14422. This article has 58 citations.
(muller2023thoracicmanifestationsof pages 2-3): Romain Muller, Mikael Ebbo, Paul Habert, Laurent Daniel, Antoine Briantais, Pascal Chanez, Jean Yves Gaubert, and Nicolas Schleinitz. Thoracic manifestations of igg4‐related disease. Respirology (Carlton, Vic.), 28:120-131, Nov 2023. URL: https://doi.org/10.1111/resp.14422, doi:10.1111/resp.14422. This article has 58 citations.
(hao2023thespectrumof pages 4-6): Qiyuan Hao, Meng Sun, and Yanying Liu. The spectrum of b cells in the pathogenesis, diagnosis and therapeutic applications of immunoglobulin g4‐related disease. Clinical & Translational Immunology, Jan 2023. URL: https://doi.org/10.1002/cti2.1477, doi:10.1002/cti2.1477. This article has 7 citations and is from a peer-reviewed journal.
(xu2024pathogenicrolesof pages 2-4): Jingyi Xu, Jiayu Zhai, and Jinxia Zhao. Pathogenic roles of follicular helper t cells in igg4-related disease and implications for potential therapy. Frontiers in Immunology, Jun 2024. URL: https://doi.org/10.3389/fimmu.2024.1413860, doi:10.3389/fimmu.2024.1413860. This article has 18 citations and is from a peer-reviewed journal.
(xu2024pathogenicrolesof pages 1-2): Jingyi Xu, Jiayu Zhai, and Jinxia Zhao. Pathogenic roles of follicular helper t cells in igg4-related disease and implications for potential therapy. Frontiers in Immunology, Jun 2024. URL: https://doi.org/10.3389/fimmu.2024.1413860, doi:10.3389/fimmu.2024.1413860. This article has 18 citations and is from a peer-reviewed journal.
(lohr2020europeanguidelineon pages 17-19): J‐Matthias Löhr, Ulrich Beuers, Miroslav Vujasinovic, Domenico Alvaro, Jens Brøndum Frøkjær, Frank Buttgereit, Gabriele Capurso, Emma L Culver, Enrique de‐Madaria, Emanuel Della‐Torre, Sönke Detlefsen, Enrique Dominguez‐Muñoz, Piotr Czubkowski, Nils Ewald, Luca Frulloni, Natalya Gubergrits, Deniz Guney Duman, Thilo Hackert, Julio Iglesias‐Garcia, Nikolaos Kartalis, Andrea Laghi, Frank Lammert, Fredrik Lindgren, Alexey Okhlobystin, Grzegorz Oracz, Andrea Parniczky, Raffaella Maria Pozzi Mucelli, Vinciane Rebours, Jonas Rosendahl, Nicolas Schleinitz, Alexander Schneider, Eric FH van Bommel, Caroline Sophie Verbeke, Marie Pierre Vullierme, and Heiko Witt. European guideline on igg4‐related digestive disease – ueg and sgf evidence‐based recommendations. United European Gastroenterology Journal, 8:637-666, Jul 2020. URL: https://doi.org/10.1177/2050640620934911, doi:10.1177/2050640620934911. This article has 272 citations and is from a peer-reviewed journal.
(lohr2020europeanguidelineon pages 1-2): J‐Matthias Löhr, Ulrich Beuers, Miroslav Vujasinovic, Domenico Alvaro, Jens Brøndum Frøkjær, Frank Buttgereit, Gabriele Capurso, Emma L Culver, Enrique de‐Madaria, Emanuel Della‐Torre, Sönke Detlefsen, Enrique Dominguez‐Muñoz, Piotr Czubkowski, Nils Ewald, Luca Frulloni, Natalya Gubergrits, Deniz Guney Duman, Thilo Hackert, Julio Iglesias‐Garcia, Nikolaos Kartalis, Andrea Laghi, Frank Lammert, Fredrik Lindgren, Alexey Okhlobystin, Grzegorz Oracz, Andrea Parniczky, Raffaella Maria Pozzi Mucelli, Vinciane Rebours, Jonas Rosendahl, Nicolas Schleinitz, Alexander Schneider, Eric FH van Bommel, Caroline Sophie Verbeke, Marie Pierre Vullierme, and Heiko Witt. European guideline on igg4‐related digestive disease – ueg and sgf evidence‐based recommendations. United European Gastroenterology Journal, 8:637-666, Jul 2020. URL: https://doi.org/10.1177/2050640620934911, doi:10.1177/2050640620934911. This article has 272 citations and is from a peer-reviewed journal.
(lohr2020europeanguidelineon pages 19-20): J‐Matthias Löhr, Ulrich Beuers, Miroslav Vujasinovic, Domenico Alvaro, Jens Brøndum Frøkjær, Frank Buttgereit, Gabriele Capurso, Emma L Culver, Enrique de‐Madaria, Emanuel Della‐Torre, Sönke Detlefsen, Enrique Dominguez‐Muñoz, Piotr Czubkowski, Nils Ewald, Luca Frulloni, Natalya Gubergrits, Deniz Guney Duman, Thilo Hackert, Julio Iglesias‐Garcia, Nikolaos Kartalis, Andrea Laghi, Frank Lammert, Fredrik Lindgren, Alexey Okhlobystin, Grzegorz Oracz, Andrea Parniczky, Raffaella Maria Pozzi Mucelli, Vinciane Rebours, Jonas Rosendahl, Nicolas Schleinitz, Alexander Schneider, Eric FH van Bommel, Caroline Sophie Verbeke, Marie Pierre Vullierme, and Heiko Witt. European guideline on igg4‐related digestive disease – ueg and sgf evidence‐based recommendations. United European Gastroenterology Journal, 8:637-666, Jul 2020. URL: https://doi.org/10.1177/2050640620934911, doi:10.1177/2050640620934911. This article has 272 citations and is from a peer-reviewed journal.
(NCT01584388 chunk 2): John H. Stone, MD. Rituximab in IgG4-RD: A Phase 1-2 Trial. Massachusetts General Hospital. 2012. ClinicalTrials.gov Identifier: NCT01584388
(wallace2024currentandfuture pages 7-8): Zachary S Wallace, Guy Katz, Yasmin G Hernandez-Barco, and Matthew C Baker. Current and future advances in practice: igg4-related disease. Rheumatology Advances in Practice, Apr 2024. URL: https://doi.org/10.1093/rap/rkae020, doi:10.1093/rap/rkae020. This article has 71 citations and is from a peer-reviewed journal.
(NCT03669861 chunk 2): Stone, John H, M.D., M.P.H. Safety and Efficacy of Abatacept in IgG4-Related Disease. Massachusetts General Hospital. 2018. ClinicalTrials.gov Identifier: NCT03669861

Ask OpenScientist

OpenScientist Report

Classifications

Subtypes

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Environmental Factors

Biochemical Markers

Diagnosis

Progression

Prevalence

Differential Diagnoses

Related Datasets

Clinical Trials

Experimental Models

Animal Models

Source YAML

References & Deep Research

References

Deep Research

1. Disease Information

1.1 Concise overview (current understanding)

1.2 Synonyms / alternative names

1.3 Evidence source type

2. Etiology

2.1 Disease causal factors (mechanistic)

2.2 Risk factors

Genetic risk factors (susceptibility)

Environmental / occupational risk factors

Infectious triggers

2.3 Protective factors

2.4 Gene–environment interactions

3. Phenotypes (clinical manifestations)

3.1 Common organ involvement and clinical phenotypes

3.2 Frequencies and statistics from recent cohorts/surveys

3.3 Thoracic (lung/mediastinal) phenotype

3.4 Suggested HPO terms (examples; not exhaustive)

4. Genetic / Molecular Information

4.1 Causal genes

4.2 Pathogenic variants

4.3 Autoantigens / autoantibodies (molecular targets)

5. Environmental Information

6. Mechanism / Pathophysiology (current model)

6.1 Core cellular players (with CL term suggestions)

6.2 B-cell/plasmablast axis and fibrosis linkage

6.3 Tfh-driven class switching and plasmablast generation

6.4 CD4+ CTLs and profibrotic mediators

6.5 Suggested GO biological process terms (examples)

6.6 Suggested causal chain (integrated)

7. Anatomical Structures Affected

7.1 Organs and systems (examples)

7.2 UBERON suggestions (examples)

8. Temporal Development

8.1 Onset

8.2 Course and progression

9. Inheritance and Population

9.1 Epidemiology (recent estimates prioritized)

9.2 Demographics

10. Diagnostics

10.1 Histopathology and core features

10.2 Classification criteria (2019 ACR/EULAR)

10.3 Biomarkers

10.4 Imaging and diagnostic pitfalls

11. Outcome / Prognosis

11.1 Organ damage and reversibility

11.2 Malignancy association (statistics)

12. Treatment

12.1 Standard of care: glucocorticoids (real-world implementation)

12.2 B-cell depletion and steroid-sparing therapy

12.3 Emerging and investigational immunomodulators (clinical trials)

12.4 MAXO term suggestions (examples)

13. Prevention

Primary prevention

Secondary/tertiary prevention (practical)