IFNG and infection: To investigate the function of IFNs in shaping the host response to IAV infection, we first examined IFN gene expression and observed that while in WT mice type I IFNs Ifna and Ifnb were both rapidly up-regulated at day 3 post-infection (p.i.), the sole type II IFN, Ifng, was not significantly induced until day 7 p.i. (Fig 1B).