Since respiratory epithelial cells and alveolar macrophages are often the initial sources of cytokine and chemokine expression during the early stages of IAV infection, we speculate that the increased infection of alveolar cells in FGF9-OE lungs at 1 dpi provoked a surplus of cytokine and chemokine expression from both alveolar epithelial cells and alveolar macrophages. Here, FGF9 is linked to infection.