Dances with cytokines, featuring TFH cells, IL-21, IL-4 and B cells

Follicular helper T cells (T-FH cells) sequentially acquire the potential to secrete interleukin 21 (IL-21) and IL-4. The shift from secretion of IL-21 to that of IL-4 modifies the nature of the 'help' signals delivered by T-FH cells to germinal center (GC) B cells.