CD4 and infection: Eight days postinfection, an increase in T-bet– and IFN-γ–expressing CD4 T cells was detected in CD2-specific Egr2/3−/− mice (Fig. 2E), suggesting that the high levels of T-bet–expressing T cells in CD2-specific Egr2/3−/− mice result from hyperactivation of T cells at late stages of infection.