IL21 and infection: In addition to TFH cells, other immune cell types, including γδ T-cells and a TFH-like CD4+ T cell population expressing the surface molecule, NK1.1, and TFH cell markers simultaneously, have also been shown to express IL-21, as well as IFN-γ, during the early phase of infection with P. berghei and P. yoelii, respectively (Inoue et al., 2018; Wikenheiser et al., 2018).