IL21 and parasitic infectious disease: WT mice showed significantly higher parasitemia that peaked around day 4 and was controlled by day 7 p.r.i. The proportion of IFN-γ+IL-21- T cells was higher in STAT3 TKO mice at day 7 p.r.i, and the numbers of IFN-γ+IL-21+ Teff were less (Figure 7B).