Dose-Dependent Alterations in Lung Immune Subpopulations in Influenza a Virus Infection

This study aimed to characterize the modulation in immune cell subpopulations in murine lungs following influenza A virus (IAV) infection, assessing the effects of infectious dose, viral adaptation, and NS1 expression. Immune cell subsets were profiled by surface receptor expression using multiparametric flow cytometry with a 10-antibody immunophenotyping panel. Neutrophils expressing Ly-6G were significantly increased in the lungs following lethal-dose infection with IAV, independently of NS1 expression; in contrast, lethal-dose infection with all viruses reduced CD163⁺ and F4/80⁺ neutrophil subpopulations. Lethal-dose infection increased pulmonary CD68⁺ macrophages while decreasing CD163⁺, CD193⁺, and F4/80⁺ macrophage subsets, as well as F4/80⁺ myeloid cells, by day 3 post-infection; these reductions were independent of NS1 expression and infectious dose. Following lethal-dose IAV infection, NK cells exhibited upregulation of IL-23R⁺ and IL-12Rβ2⁺ subsets, while the CD193⁺ NK subpopulation was decreased on day 3 post-infection. Profiling of NKT cells revealed an expansion of the IL-12Rβ2⁺ NKT subset on day 3 post-infection. Adaptive immune profiling of lung CD4⁺ T cells revealed a selective increase in Th1-like cells (IL-12Rβ2⁺ CD4⁺) after WSN infection, a marked reduction in Th2-like cells (CD193⁺ CD4⁺) following infection with IAV regardless of NS1 status or dose, and an expansion of CD4⁺NK1.1⁺ cells only after lethal-dose infection. Immune cell subset frequencies were comparable between infections with NS1-expressing and wild-type viruses; NS1 expression did not alter subset composition, whereas the infection dose modulated their abundance. These findings expand our understanding of the subpopulation of immune cells and their possible role in influenza virus pathogenesis.