Several additional studies provide potential insights into this discrepancy: First, while the loss of either IL-6 or IL-21 alone has only a marginal effect on TFH development and GC formation in response to acute viral infection, the simultaneous loss of both cytokines in Il6−/−Il21−/− mice (149) or the neutralization of IL-6 in Il21−/− mice (148), significantly blunts the antiviral Ab responses. Here, IL21 is linked to viral infectious disease.