CD4 and infection: In contrast, in WSX-1−/− mice the frequencies, and correspondingly the total numbers, of effector CD4+ T-bet+ T cells expressing KLRG-1 rapidly increased between day 9 and day 11 of infection, such that more than 50% of all splenic effector CD4+ T-bet+ cells expressed KLRG-1 on day 14 of infection (Figure 2A–C).