Systems-level insights into age-dependent innate immune responses in influenza B infection.

Aging is known to alter innate immune function, increasing susceptibility to viral infections, yet its specific effects on influenza B virus (IBV) infection remain poorly characterized. To address this gap, we developed a preclinical mouse model using a clinically relevant IBV strain Inf B/Phuket/3073/2013 to compare innate immune responses between young adult and aged mice, with a particular focus on age-related transcriptional and proteomic alterations in lung during infection. Bulk RNA sequencing and proteomics analysis of lung tissue harvested post-infection revealed distinct age-dependent transcriptional profiles. Bulk RNA-seq analysis identified 1,350 differentially expressed genes (DEGs), of which 824 exhibited an aged-biased expression pattern and were significantly upregulated in the lungs of influenza B virus-infected aged mice. Functional enrichment of these DEGs indicated perturbations in innate immune signaling, apoptosis, and pathways related to cellular stress and DNA damage in aged mice. There are several differentially expressed proteins that have been identified in young adult and aged influenza B infection. Among these differentially expressed proteins, some commonly co-expressed proteins have a role in virus entry, signaling pathways, and interferon response. Real-time PCR analysis confirmed altered expression of key innate immune genes, including Toll-like receptors (TLRs), interferon regulatory factors (IRF7 and IRF9), key antiviral genes (IFIT -2, IFIT-3 and STAT-1) and type I and II interferons (IFN-α, IFN-β, IFN-γ). Notably, young adult mice exhibited a more coordinated and robust activation of antiviral pathways, whereas aged mice demonstrated delayed and aberrant immune responses, characterized by excessive inflammation and impaired interferon signaling. IMPORTANCE: This study provides a comprehensive system-level analysis of age-driven alterations in innate immunity during influenza B virus (IBV) infection. While prior evidence has established that aging impairs antiviral responses across various viral infections, our findings specifically demonstrate that IBV infection in aged mice leads to a disproportionate and dysregulated transcriptional activation of innate immune pathways, including excessive type I interferon signaling and altered inflammatory mediator profiles, and uncover the potential therapeutic targets to improve health outcomes in the elderly population on influenza infection.