IRF7 deficiency increases disease severity independently of TLR7 recognition in Influenza A infection in mice
Influenza A virus (IAV) remains a major cause of respiratory morbidity and mortality, yet the role of Toll-like receptor 7 (TLR7), an RNA sensor, and its downstream signaling events, such as interferon regulatory factor 7 (IRF7), in IAV infection remain unclear. To address this question, we used single-cell RNA sequencing, genetic mouse models, and immunological analysis. Single -cell transcriptomic profiling of the infected lungs revealed robust upregulation of Tlr7 and genes associated with interferon pathways in dendritic cells and B cells, alongside widespread induction of Irf7 across immune and non-immune compartments. Tlr7-deficient mice exhibited normal viral control, lung pathology, and survival following IAV challenge. In contrast, Irf7 deficiency resulted in significantly increased disease severity, impaired early interferon responses, exacerbated bronchial epithelial hyperplasia, and defective early humoral priming. In assessing adaptive immunity, both Irf7-deficient andTlr7-deficient mice had reduced antihemagglutinin antibody production. Mechanistically, IRF7 protein expression and downstream signaling were largely preserved in TLR7-deficient mice, indicating that IRF7 activation during IAV infection occurs independently of TLR7. Collectively, these findings identify IRF7 as a non-redundant determinant of innate immunity and disease outcomes during IAV infection, while positioning TLR7 as a modulatory factor primarily influencing adaptive immune maturation. Our study refines current models of antiviral sensing by uncoupling receptor induction from functional necessity and highlights IRF7 as a critical downstream regulator dictating host defense against acute influenza A infection. ImportanceInfluenza A virus is a respiratory pathogen that remains a major threat to global health as a seasonal disease and a source of periodic pandemics. The outcomes of the infection can range from mild illness to severe pneumonia and death, particularly in vulnerable populations, yet the reasons why some individuals develop more severe disease are not fully understood. Early immune defenses in the lungs are critical for controlling the virus, but they can also contribute to harmful inflammation if not properly regulated. In particular, key sensors that detect viral genetic material and the signaling pathways that activate antiviral responses play an essential role in shaping these outcomes. The significance of our study lies in defining how these early immune mechanisms influence the course of influenza A infection, providing insight that may guide the development of improved therapies for influenza and related respiratory viruses.