Professor Sylhet Agricultural University Sylhet, Sylhet, Bangladesh
Disclosure(s):
Md Bashir Uddin, Dr.: No financial relationships to disclose
Introduction/Rationale: Secondary bacterial pneumonia following influenza A virus (IAV) infection significantly exacerbates lung inflammation and contributes to acute respiratory distress syndrome (ARDS), yet the underlying immunopathogenic mechanisms remain poorly understood.
Methods: Using a clinically relevant murine model of sublethal IAV infection followed by methicillin-resistant Staphylococcus aureus (MRSA) challenge under antibiotic therapy, this study investigated the dynamic role of type I interferon (IFN-I) signaling in disease progression.
Results: The findings demonstrate that IFN-I exerts dual and contrasting effects on the host inflammatory response: it enhances myeloid-derived TNF-α while indirectly suppressing T cell–derived IFN-γ. Reporter mouse models identified recruited monocytes and dendritic cells (DCs) as the primary IFN-I–targeted populations, whereas neutrophils, T cells, and resident alveolar macrophages exhibited limited direct responsiveness. Myeloid-specific deletion of IFNAR1 reduced TNF-α production, restrained inflammatory monocyte differentiation, and improved survival without disrupting IFN-γ and IL-10 balance. Temporal IFNAR1 blockade further revealed that early IFN-I signaling supports alveolar macrophage maintenance and primes monocytes/DCs for immune activation, whereas sustained signaling during bacterial superinfection drives persistent monocyte chemoattractant production, excessive monocyte activation, cytokine dysregulation, and delayed resolution of inflammation.
Conclusion: Collectively, these findings position IFN-I as a temporal immune rheostat—protective during acute viral infection but pathogenic when prolonged—and define a therapeutic window in which selective IFNAR inhibition can mitigate lung injury without impairing host defense. These insights highlight a promising immunomodulatory strategy to improve outcomes in severe viral–bacterial pneumonia and ARDS.
