A shift from Th1 cytokines (including IFN-γ) to Th2 cytokines (including IL-10) with aging has been associated with reduced cytotoxic T lymphocyte activity and diminished protection against influenza virus challenge [34], and age-related susceptibility to influenza can be reversed by the induction of a more potent IFN-γ response [35–37]. This evidence concerns the gene IL10 and influenza.