Narrative Review of the Pathophysiology of Post-Infectious Bronchiolitis Obliterans.

Post-Infectious Bronchiolitis Obliterans (PIBO) is a rare chronic obstructive lung disease characterized by irreversible airflow limitation due to inflammation, fibrosis, and obliteration of the small airways following severe lower respiratory tract infection. Adenovirus is the most frequently associated pathogen, followed by other viruses and atypical bacteria. PIBO pathogenesis appears to result from a complex interaction between severe epithelial injury, dysregulated immune response, persistent neutrophilic inflammation, abnormal tissue repair, and genetic susceptibility. Epithelial damage triggers the release of inflammatory cytokines and epithelial-derived alarmins, promoting chronic inflammation and airway remodeling through fibrosis and airway obliteration driven by activation of the TGF-β/CTGF pathway, epithelial-mesenchymal transition, macrophage-fibroblast interactions, and extracellular matrix deposition. Genetic factors affecting mucociliary clearance, innate immunity, and fibrotic pathways may further predispose certain individuals to abnormal repair and fibrosis consequently. Histologically, PIBO progresses from inflammatory bronchiolitis to fibroproliferative remodeling and constrictive bronchiolitis with luminal obliteration. Understanding these mechanisms supports a stage-based therapeutic approach targeting inflammation in early disease and fibrotic remodeling in advanced stages.