In contrast, the decline in cell-mediated immune responses to influenza is related to aging rather than previous exposures to the virus; after age 60, there is a progressive age-related decline in the levels of interferon-γ (IFNγ), IL-10, and the IFNγ:IL-10 ratio secreted by PBMC challenged ex vivo with A/H3N2, A/H1N1, or pH1N1 (Skowronski et al., 2011). This evidence concerns the gene IFNG and influenza.