Deficiency in either perforin or IFN-γ production results in susceptibility to infection with MCMV, a viral infection that is largely controlled by NK cells (Table 1).91–93 MCMV belongs to the β-herpesvirus family of double-stranded DNA viruses that establish long term persistent infection in the host by manipulating the immune response and in particular MHC I expression and recognition by NK cells via NKG2D ligands. This evidence concerns the gene IFNG and infection.