CD4 and parasitic infectious disease: Taken together, the findings of this study revealed that in non-lethal P.y17XNL infection, higher burden of parasitemia in children mice were associated with weakened Th1 cellular immune responses, down-regulated humoral immunity with decreased percentage and number of Th2 and Tfh cells as well as lower level of antibody secretion and enhanced PD-1 signaling on activated CD4+ T cells.