This is a mechanism module, not a disease. Do NOT create a Pleuropneumonia or Empyema Disease entry; MONDO:0001940 (pleuropneumonia) is an organism-agnostic organ syndrome, so per design decision 3e/R4 it is a module, not a disorder. Modules bind GO and CL terms only (plus UBERON locations); organism, chemistry and disease identity are described in prose. The key conformance target is "Intrapleural Procoagulant Shift with Suppressed Fibrinolysis". Out of scope: tuberculous pleurisy (granulomatous, mechanistically distinct), malignant effusion, and post-surgical/traumatic empyema (they share late stages but not the pneumonic trigger). Xogenesis anchor: the terminal output is an empyema (MPATH:609), an OGMS:0000079 portion of pathological body substance arising by OGMS:0000081 pathological derivation; process genus OGMS:0000061 pathological bodily process. SNOMED "Morphologically abnormal structure" (49755003) is an external census guide only and is not bound here. "Pleuropneumonia" is also a veterinary term (e.g. Actinobacillus pleuropneumoniae in pigs, equine pleuropneumonia); those animal syndromes are out of scope as conformance targets, though animal-model evidence can still support the human nodes with evidence_source: MODEL_ORGANISM.
Pneumonic Parenchymal Inflammation Adjacent to the Pleura
trigger
The trigger is an acute pneumonic inflammatory process in lung parenchyma that lies against the visceral pleura. Proinflammatory signalling at this front (IL-8, TNF-alpha) extends to the pleural surface. Conforming entries substitute the organism driving the pneumonia.
Downstream
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Visceral Pleural Mesothelial Activation and Barrier Injury
Show evidence (2 references)
"The inflammatory process of the pulmonary parenchyma extends to the visceral pleura causing changes to the mesothelial cells lining the pleura, allowing increased fluid movement."
States that parenchymal pneumonic inflammation extends to the visceral pleura, the module's initiating step.
"Ultrasound revealed pulmonary consolidation in all cases."
In a parapneumonic-effusion cohort every case had adjacent pulmonary consolidation, supporting the pneumonic parenchymal process as the substrate.
Visceral Pleural Mesothelial Activation and Barrier Injury
amplifier
Pleural mesothelial cells exposed to bacteria or bacterial products release angiogenic and inflammatory mediators (VEGF, IL-8) and lose monolayer barrier integrity. VEGF raises pleural vascular and mesothelial permeability, opening the route for protein-rich fluid into the pleural space.
Downstream
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Exudative Parapneumonic Effusion
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Intrapleural Procoagulant Shift with Suppressed Fibrinolysis
Show evidence (2 references)
"Exposure of pleural mesothelial cells to bacteria or lipopolysaccharide may increase release of angiogenic factors, including vascular endothelial growth factor (VEGF) and interleukin (IL)-8, induce vascular hyperpermeability and pleural fluid production, activate coagulation cascade, and..."
Directly states mesothelial exposure to bacteria raises permeability and fluid production and shifts the pleural coagulation/fibrinolysis balance.
"Our results suggest that bacterial pathogens induce VEGF release in mesothelial cells and alter mesothelial permeability, leading to protein exudation in empyema."
In a mesothelial monolayer model, bacterial infection raises VEGF and permeability, the mechanism of barrier injury at this node.
Exudative Parapneumonic Effusion
effector
Raised permeability lets protein-rich fluid and inflammatory cells pour into the pleural space (stage I). The fluid is clear, free-flowing and sterile, with normal pH and glucose. Many such effusions resolve with antibiotics alone; progression depends on the downstream fibrin and invasion steps.
Downstream
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Bacterial Pleural Invasion and Purulent Progression
Show evidence (2 references)
"In the early exudative stage there is a rapid outpouring of fluid and inflammatory cells into the pleural space due to increased capillary microvascular permeability."
Defines the exudative (stage I) effusion as a permeability-driven outpouring of fluid and cells.
"VEGF levels are raised in the majority of exudative effusions, implying a pathogenic role for this molecule in the development of pleural effusions."
Human pleural-fluid study linking raised VEGF to formation of exudative effusions, the mediator named at the upstream node.
Intrapleural Procoagulant Shift with Suppressed Fibrinolysis
central effector
The rate-limiting, disorder-agnostic step every conformer funnels through. Within the effusion, coagulation is activated while fibrinolysis is suppressed, chiefly by elevated plasminogen activator inhibitor-1 (PAI-1) against relatively reduced tissue plasminogen activator (tPA). The resulting PAI-1/tPA imbalance drives fibrin formation and is the target of intrapleural fibrinolytic therapy.
Downstream
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Fibrin Deposition and Loculation
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"An imbalance between PAI-1 and tissue type plasminogen activator (tPA) may elicit fibrin formation and subsequent pleural fluid loculation and fibrosis"
States that the PAI-1/tPA imbalance at this node drives the downstream fibrin, loculation and fibrosis.
"Loculation is promoted and then potentiated by inhibition of local fibrinolysis, in large part by elaboration of elevated levels of PAI-1."
Identifies suppressed local fibrinolysis via elevated PAI-1 as the driver of loculation, the central effector claim.
Fibrin Deposition and Loculation
effector
With fibrinolysis suppressed, fibrin clots and membranes are laid down across the pleural space, dividing the effusion into isolated loculi (stage II). Septation traps fluid that can no longer be drained by a single tube, which is why loculated collections are the ones that fail simple drainage.
Downstream
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Empyema (Pleural Pus Accumulation)
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Organizing Pleural Peel and Mesothelial-Mesenchymal Transition
Show evidence (2 references)
"This next stage is characterized by deposition of fibrin clots and fibrin membranes in the pleural space, leading to loculations and isolated collections of fluid."
Defines the fibrinopurulent stage as fibrin deposition producing loculated fluid collections.
"Pleural injury proceeds through a phase of acute inflammation followed by organization, a process that involves the deposition of intrapleural fibrin and its remodeling."
Places intrapleural fibrin deposition on the path from acute inflammation to organisation.
Bacterial Pleural Invasion and Purulent Progression
effector
Bacteria cross from the parenchyma into the pleural fluid, driving neutrophil influx and phagocytosis. Neutrophil metabolism and bacterial killing acidify the fluid and consume glucose (low pH, low glucose, high LDH), marking the complicated parapneumonic effusion. Pleural-fluid profiling shows severe effusions are enriched for neutrophil-driven inflammatory programmes.
Downstream
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Empyema (Pleural Pus Accumulation)
Show evidence (3 references)
"The combination of bacterial invasion and increased inflammatory response leads to increased lactic acid and carbon dioxide production, resulting in a fall in pleural fluid pH, increased glucose metabolism and a rise in LDH, consistent with “complicated” parapneumonic effusion."
Links bacterial invasion and neutrophilic inflammation to the pH/glucose/LDH changes defining a complicated effusion.
"Upregulated gene signatures associated with disease progression in severe PPE were enriched in neutrophil degranulation, glycolysis/gluconeogenesis, HIF-1 signaling, and inflammatory response pathways."
Pleural-fluid transcriptomics shows severe effusion progression is driven by neutrophil-degranulation and inflammatory programmes.
"Approximately 50% of community-acquired infections were streptococcal, and 20% included anaerobic bacteria."
Shows pleural infection is caused by a diverse set of organisms, supporting the module's organism-agnostic scope at the invasion step.
Empyema (Pleural Pus Accumulation)
consequence
The terminal fluid state: frank pus in the pleural space, defined by pus or bacteria in the pleural cavity. It is the fibrinopurulent process carried to its endpoint, and pleural-fluid profiling shows the empyema stage is enriched for the most intense neutrophil-driven, pro-inflammatory programmes, including neutrophil extracellular trap formation. This is the Xogenesis output of the module (see notes).
Downstream
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Organizing Pleural Peel and Mesothelial-Mesenchymal Transition
Show evidence (2 references)
"Empyema is defined by the presence of bacteria or pus in the pleural space."
Gives the defining criterion of empyema, the module's terminal structure.
"Patients with empyema exhibited significant enrichment of pathways in relation to IFN signaling, cytokine storm, pyroptosis, cachexia, and neutrophil extracellular trap formation, suggesting an amplified inflammatory and immunopathological response at the advanced stage of PPE"
Shows the empyema stage carries the most amplified neutrophil-driven inflammatory programmes, including NET formation, grounding the DNase arm of intrapleural therapy.
Organizing Pleural Peel and Mesothelial-Mesenchymal Transition
consequence
If the purulent, fibrin-laden fluid is not cleared, the pleura organises (stage III). Pleural mesothelial cells undergo mesothelial-mesenchymal transition into matrix-producing myofibroblasts, and fibroblasts invade and lay down collagen, forming a thick fibrous peel that can encase the lung ("trapped lung"). This node specialises the generic fibrotic_response mesenchymal-activation step to the pleural mesothelium.
Show evidence (3 references)
"This final stage is characterized by fibroblasts that proliferate and invade the pleural fluid from both the visceral and parietal pleura, forming a thick pleural peel."
Defines the organising stage as fibroblast proliferation forming a pleural peel.
"Through a process termed mesomesenchymal transition (MesoMT), mesothelial cells become matrix producing myofibroblasts."
Names mesothelial-mesenchymal transition into myofibroblasts as the cellular basis of pleural organisation.
"Pleural thickening was also notably reduced in 9ING41-treated mice"
In a mouse Streptococcus pneumoniae empyema model, blocking MesoMT (GSK-3beta inhibitor 9ING41) reduced pleural thickening, supporting MesoMT as the driver of the pleural peel.
Intrapleural Fibrinolytic and DNase Therapy (tPA plus DNase)
Platform:
Other
Combined intrapleural tissue plasminogen activator (tPA, alteplase) and human recombinant DNase (dornase alfa) is the drug-target design for this module, and the benefit requires both arms. tPA restores local fibrinolysis against the suppressed, PAI-1-dominated state at the central-effector node, dissolving fibrin septations; DNase degrades the extracellular DNA (neutrophil extracellular traps) that makes empyema pus viscous, acting on the downstream empyema node. In the MIST2 randomized trial the combination lowered radiographic pleural opacity and surgical referral, whereas tPA alone (the procoagulant-node arm) and DNase alone did not, which is why both nodes are targeted together rather than either alone.
Evidence: 1
Intrapleural Fibrinolytic Monotherapy
Platform:
Other
An intrapleural fibrinolytic agent given alone, without DNase. The MIST1 randomized trial of intrapleural streptokinase found no reduction in death or need for surgery, so fibrinolytic monotherapy is not effective and is the negative counterpoint to the two-arm tPA-DNase design above.
Evidence: 1