As assessed by polyclonal activation ex vivo (Figure 1C and D), the frequency of splenic CD3ε+CD4+ IFNγ+ T cells increased from 2.4±0.4% in naïve mice to 44.4±3.0% (p<0.001) by day 28 of infection which, when taking into account splenomegaly, reflected a >500-fold increase in absolute number of cells committed to IFNγ production in the spleen. This evidence concerns the gene CD4 and infection.