CD4 and infection: Splenic CD4+ T cell and CD8+ T cell activation was, however, largely unaltered, as determined by comparing the levels of granzyme B, KLRG-1, and Ki-67 expression in IFN-γR−/− mice to the levels in VAV-Cre+ IFN-γR2flox/flox mice and WT mice on day 7 of infection (Fig. 2C).