CD4 and infection: The effector CD4+T-bet+ T cell population plateaued, or even contracted slightly, in WT mice from day 9 of infection, whereas the effector CD4+T-bet+ T cell population continued to expand in WSX-1−/− mice with both frequencies and numbers of effector CD4+T-bet+ T cells being significantly higher in WSX-1−/− mice than in WT mice on days 11 and 14 (Figure 1A–C).