Pneumocystis pneumonia (PCP/PJP) is an opportunistic fungal pneumonia caused by Pneumocystis jirovecii, occurring almost exclusively in hosts with impaired cell-mediated immunity. Risk factors include HIV infection (classically with CD4 counts <200 cells/µL), solid-organ transplantation, malignancy, and inflammatory or rheumatologic conditions and their immunosuppressive therapies. The organism attaches to the alveolar epithelium and produces a diffuse alveolar pneumonia with hypoxemia. First-line therapy and prophylaxis is trimethoprim-sulfamethoxazole, which targets the folate-synthesis pathway; adjunctive corticosteroids reduce mortality in hypoxemic HIV-associated disease.
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name: Pneumocystis Pneumonia
creation_date: "2026-06-28T00:00:00Z"
description: >
Pneumocystis pneumonia (PCP/PJP) is an opportunistic fungal pneumonia caused by
Pneumocystis jirovecii, occurring almost exclusively in hosts with impaired
cell-mediated immunity. Risk factors include HIV infection (classically with CD4
counts <200 cells/µL), solid-organ transplantation, malignancy, and inflammatory
or rheumatologic conditions and their immunosuppressive therapies. The organism
attaches to the alveolar epithelium and produces a diffuse alveolar pneumonia
with hypoxemia. First-line therapy and prophylaxis is
trimethoprim-sulfamethoxazole, which targets the folate-synthesis pathway; adjunctive
corticosteroids reduce mortality in hypoxemic HIV-associated disease.
category: Infectious Disease
parents:
- Fungal Respiratory Infection
synonyms:
- PCP
- PJP
- Pneumocystis jirovecii pneumonia
disease_term:
preferred_term: Pneumocystis pneumonia
term:
id: MONDO:0005923
label: Pneumocystis infectious disease
pathophysiology:
- name: Opportunistic Infection in Cell-Mediated Immunodeficiency
role: trigger
description: >
Pneumocystis jirovecii is an opportunistic fungal pathogen that causes severe
pneumonia in immunocompromised hosts. Disease requires impaired cell-mediated
immunity — HIV (classically CD4 <200 cells/µL), organ transplantation,
malignancy, and inflammatory/rheumatologic conditions and their
immunosuppressive therapies — which permits uncontrolled alveolar replication.
biological_processes:
- preferred_term: symbiont entry into host cell
term:
id: GO:0046718
label: symbiont entry into host cell
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Pneumocystis jirovecii (PJ) is an opportunistic fungal pathogen that can
cause severe pneumonia in immunocompromised hosts.
explanation: >-
Establishes P. jirovecii as an opportunistic fungal pathogen causing severe
pneumonia in immunocompromised hosts. Evidence source is OTHER as this is a
review article.
- reference: PMID:27242349
reference_title: Pneumocystis jirovecii Pneumonia in the Non-HIV-Infected Population.
supports: SUPPORT
evidence_source: OTHER
snippet: >-
CD4+ lymphocyte count <200 cells/µL is the primary risk factor for PJP
presentation in these patients.
explanation: >-
Identifies CD4 <200 cells/µL as the primary risk factor, anchoring the
cell-mediated-immunodeficiency trigger. Evidence source is OTHER as this is a
review article.
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Risk factors for Pneumocystis jirovecii pneumonia (PJP) include HIV, organ
transplant, malignancy, certain inflammatory or rheumatologic conditions,
and associated therapies and conditions that result in cell-mediated immune
deficiency.
explanation: >-
Enumerates the immunocompromising risk-factor spectrum (HIV, organ
transplant, malignancy, inflammatory/rheumatologic conditions and their
therapies) that produces the cell-mediated-immune deficiency required for
PJP, grounding the trigger node's risk-factor list. Evidence source is OTHER
as this is a review article.
downstream:
- target: Alveolar Pneumonia and Respiratory Compromise
description: >-
Uncontrolled alveolar replication produces a diffuse pneumonia with impaired
gas exchange.
- name: Alveolar Pneumonia and Respiratory Compromise
role: consequence
description: >
P. jirovecii attaches to the alveolar epithelium (type I pneumocytes) and
produces a diffuse alveolar pneumonia with impaired gas exchange and hypoxemia;
clinical signs are nonspecific and definitive diagnosis requires direct
detection of the organism in lower respiratory secretions or tissue.
cell_types:
- preferred_term: pulmonary alveolar type 1 cell
term:
id: CL:0002062
label: pulmonary alveolar type 1 cell
biological_processes:
- preferred_term: inflammatory response
term:
id: GO:0006954
label: inflammatory response
modifier: INCREASED
locations:
- preferred_term: lung
term:
id: UBERON:0002048
label: lung
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Clinical signs of PJP are nonspecific and definitive diagnosis requires
direct detection of the organism in lower respiratory secretions or tissue.
explanation: >-
Supports the nonspecific pneumonia presentation and the requirement for direct
organism detection. Evidence source is OTHER as this is a review article.
downstream: []
- name: Folate Synthesis (Antifolate Target)
role: therapeutic_vulnerability
description: >
P. jirovecii depends on de novo folate synthesis. Trimethoprim-sulfamethoxazole
inhibits this pathway (sulfamethoxazole inhibits dihydropteroate synthase;
trimethoprim inhibits dihydrofolate reductase), and is the first-line treatment
and prophylaxis. (This antifolate target is analogous to the bacterial folate
pathway but is not modeled here as conforming to the bacterial folate module,
since Pneumocystis is a fungus.)
biological_processes:
- preferred_term: folic acid biosynthetic process
term:
id: GO:0046656
label: folic acid biosynthetic process
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
First-line therapy for prophylaxis and treatment remains
trimethoprim-sulfamethoxazole
explanation: >-
Identifies trimethoprim-sulfamethoxazole (a folate-synthesis inhibitor) as
first-line therapy and prophylaxis. Evidence source is OTHER as this is a
review article.
downstream: []
phenotypes:
- category: Respiratory
name: Pneumonia
description: >
Diffuse alveolar pneumonia is the defining manifestation.
phenotype_term:
preferred_term: Pneumonia
term:
id: HP:0002090
label: Pneumonia
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
Pneumocystis jirovecii (PJ) is an opportunistic fungal pathogen that can
cause severe pneumonia in immunocompromised hosts.
explanation: >-
Severe pneumonia is the defining manifestation of PJP. Evidence source is
OTHER as this is a review article.
- category: Respiratory
name: Dyspnea
description: >
Progressive dyspnea with hypoxemia is characteristic of PCP.
phenotype_term:
preferred_term: Dyspnea
term:
id: HP:0002094
label: Dyspnea
- category: Constitutional
name: Fever
description: >
Fever commonly accompanies Pneumocystis pneumonia.
phenotype_term:
preferred_term: Fever
term:
id: HP:0001945
label: Fever
treatments:
- name: Trimethoprim-Sulfamethoxazole
description: >
Co-trimoxazole (trimethoprim plus sulfamethoxazole) inhibits the folate-synthesis
pathway (DHFR and dihydropteroate synthase, respectively); it is the first-line
treatment and prophylaxis for Pneumocystis pneumonia. Alternatives for
intolerance or treatment failure include dapsone, atovaquone, pentamidine, and
clindamycin-primaquine.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: trimethoprim
term:
id: CHEBI:45924
label: trimethoprim
- preferred_term: sulfamethoxazole
term:
id: CHEBI:9332
label: sulfamethoxazole
target_mechanisms:
- target: Folate Synthesis (Antifolate Target)
treatment_effect: INHIBITS
description: >-
Trimethoprim-sulfamethoxazole inhibits dihydrofolate reductase and
dihydropteroate synthase, blocking folate synthesis the organism requires.
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
First-line therapy for prophylaxis and treatment remains
trimethoprim-sulfamethoxazole
explanation: >-
TMP-SMX is first-line therapy and prophylaxis for PJP. Evidence source is
OTHER as this is a review article.
- name: Adjunctive Corticosteroids
description: >
In HIV-associated PCP with hypoxemia, adjunctive corticosteroids (typically
prednisone) reduce mortality.
therapeutic_modality: SMALL_MOLECULE
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
therapeutic_agent:
- preferred_term: prednisone
term:
id: CHEBI:8382
label: prednisone
evidence:
- reference: PMID:33870843
reference_title: "Pneumocystis jirovecii: a review with a focus on prevention and treatment."
supports: SUPPORT
evidence_source: OTHER
snippet: >-
In people living with HIV (PLWH), adjunctive corticosteroid use in treatment
has shown a mortality benefit.
explanation: >-
Supports adjunctive corticosteroids reducing mortality in HIV-associated PCP.
Evidence source is OTHER as this is a review article.
notes: >-
Created as part of the Respiratory Infections project (opportunistic fungal
pneumonia). Deliberately NOT conformed to the bacterial_folate_synthesis_inhibition
module: although TMP-SMX targets the same folate enzymes, that module's selectivity
rationale is prokaryote-specific and Pneumocystis is a fungus. disease_term uses
MONDO:0005923 (Pneumocystis infectious disease) with a more specific preferred_term
because MONDO lacks a dedicated "Pneumocystis pneumonia" term. The infectious_agent
(NCBITaxon) block was omitted at creation and P. jirovecii is described in text.
datasets:
- accession: geo:GSE320199
title: Transcriptomic analyses of mortality in HIV-associated Pneumocystis pneumonia
description: Pneumocystis jirovecii pneumonia (PCP) remains a leading cause of respiratory failure and mortality in individuals with advanced HIV. While severe disease is classically attributed to hyperinflammation, the specific biological determinants driving fatal outcomes in patients remain poorly understood. To address this, we employed an integrated systems biology approach, performing transcriptomics, proteomics, and metabolomics on bronchoalveolar lavage fluid from a prospective cohort of 42 patients with HIV-associated PCP. We demonstrate that mortality is not primarily driven by uncontrolled fungal burden or isolated hyperinflammation, but by profound immunometabolic failure.
organism:
preferred_term: human
term:
id: NCBITaxon:9606
label: Homo sapiens
data_type: BULK_RNA_SEQ
sample_count: 24
notes: Identified by GEO DataSets index search for Pneumocystis Pneumonia (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:GSE79079
title: β-glucans are Masked but Contribute to Pulmonary Inflammation During Pneumocystis Pneumonia
description: β-glucans, which can activate innate immune responses, are a major component in the cell wall of the cyst form of Pneumocystis. In the current study we examined whether β-1,3 glucans are masked by surface proteins in Pneumocystis, and what role β-glucans play in Pneumocystis-associated inflammation. For 3 species, including P. jirovecii, which causes Pneumocystis pneumonia (PCP) in humans, P. carinii, and P. murina, β-1,3 glucans were masked in most organisms, as demonstrated by increased exposure following trypsin treatment.
organism:
preferred_term: mouse
term:
id: NCBITaxon:10090
label: Mus musculus
data_type: MICROARRAY
sample_count: 11
publication: PMID:27324243
notes: Identified by GEO DataSets index search for Pneumocystis Pneumonia (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:GSE157627
title: The dynamic immune cell landscape in the lungs of Pneumocystis infected mice
description: Pneumocystis pneumonia is an opportunistic pneumonia that has been increasing in non-HIV patients in recent years. To obtain a better understanding of the cellular and molecular mechanisms involved in disease pathogenesis, we profile the transcriptomes of mouse lungs with Pneumocystis pneumonia and from uninfected control subjects using single-cell RNA sequencing, yielding multiple populations of myeloid cells, T cells and B cells. We uncover a PCP-associated TREM2+ subpopulation of interstitial macrophages, which expands in PCP, differentiates from Ly6C+ monocytes. We also define the subsets of effector CD4+ T cells that expand after the infection of Pneumocystis.
organism:
preferred_term: mouse
term:
id: NCBITaxon:10090
label: Mus musculus
data_type: SINGLE_CELL_RNA_SEQ
sample_count: 6
publication: PMID:33959105
notes: Identified by GEO DataSets index search for Pneumocystis Pneumonia (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.