IFNG and viral infectious disease: TH1 cells mainly produce IFN-γ, IL-2, and IL-12 and play a critical role in cell-mediated immune responses and therefore the clearance of viral infection (Lucin et al., 1992; Schijns et al., 1995); TH1 polarization is essential for the protective activity against influenza (Gu et al., 2011).