Oxidative Stress as a Mechanistic Link Between Severe Respiratory Viral Infection and Pulmonary Fibrosis

Post-viral pulmonary fibrosis represents a clinically significant and mechanistically complex consequence of severe respiratory infection. The COVID-19 pandemic has highlighted that a subset of survivors, particularly those with severe pneumonia or acute respiratory distress syndrome, develop persistent fibrosis-like lung abnormalities, including reticulation and traction bronchiectasis, often accompanied by impaired gas transfer. Although the clinical course is heterogeneous and many lesions regress over time, longitudinal studies indicate that structural and functional impairment may persist for years in susceptible individuals. Oxidative stress has emerged as a plausible convergent mechanism linking acute epithelial injury, dysregulated inflammatory resolution, and chronic fibrotic remodeling. Reactive oxygen and nitrogen species amplify inflammatory signaling, promote epithelial cell death and senescence, influence macrophage polarization, and activate canonical profibrotic pathways, notably the TGF-β axis. Redox imbalance is embedded within reinforcing circuits involving NOX4-dependent ROS amplification, mitochondrial dysfunction, endoplasmic reticulum stress, inflammasome activation, and senescence-associated secretory programs. Persistent immune activation and organelle stress may sustain redox dysregulation beyond viral clearance, thereby bridging acute lung injury to maladaptive remodeling. This review integrates epidemiological, clinical, and mechanistic evidence to position oxidative stress as a central mediator of post-viral lung fibrosis and discusses therapeutic and translational implications.