IL6 and infection: Of these cytokines, IL-6 and IL-21 were of particular interest, as IL-6 has been associated with increased cell growth and survival in a number of in vitro studies (41–44) and affect GC B cells indirectly via differentiation of TFH cells in vivo (45) while IL-21 is known to drive both TFH and GC B cell populations in a virus-infection model (45).