IL21 and parasitic infectious disease: Previous work on the immune response to P. chabaudi shows that IFN-γ controls the height of the peak of parasitemia, whereas Tfh and IL-21 are required for antibodies to eliminate the parasite (Perez-Mazliah et al., 2015, 2017; Su and Stevenson, 2002; Gbedande et al., 2020; Meding and Langhorne, 1991).