IL21 and infection: Blockade of the IL-21R using the IL-21R-Fc led to a reduction in TFH cells and GC B cell numbers toward the later phase of infection, suggesting the importance of the IL-21 expressed by γδ T-cell during the early phase of infection to promote the development of TFH cells as well as the GC B cells during the later course of infection (Inoue et al., 2018).