Thus, IFN-γ production by CD4+ T cells is essentially unaltered in IL-27R deficient (WSX-1−/−) mice during the early stages of many infections and excessive IFN-γ production, in general, only occurs after day 10 [3], [7] suggesting that WSX-1 regulates established effector CD4+ T cells rather than naive or newly primed cells. Here, CD4 is linked to infection.