IFNG and infection: Although some reports using mice of mixed 129/B6 background suggested that the production of IFNγ by NK cells may be a predominant antiviral mechanism in the liver at six days post-infection [21], [27], newer studies using mice of uniform C57BL/6 origin showed that IFNγ is required for the control of MCMV in the spleen and liver as early as three days post-infection [17].