IL-21 enhances the activity of the TLR-MyD88-STAT3 pathway but not the classical TLR-MyD88-NF-κB pathway in human B cells to boost antibody production.

Both IL-21 and TLR agonists are important regulators of B cell responses, and the combination of IL-21 and TLR stimulation results in increased Ab production. However, it is not clear yet how IL-21 interacts with TLR signaling in B cells. In this study, we show that IL-21 enhances TLR-induced IgG production, whereas it has no effect on TLR-induced IL-6 production by human B cell cultures. These observations are explained by the finding that IL-21 augments TLR-induced IgG production via the TLR-MyD88-STAT3 pathway but not the classical TLR-MyD88-NF-κB pathway. We further demonstrate that stimulation of human B cells with IL-21 and TLR7/8 or TLR9 agonists increases the phosphorylation of STAT3, whereas the activation of NF-κB is not affected. Interestingly, like IL-21, IL-10 in combination with TLR signaling also enhances phosphorylation of STAT3, resulting in an increase of IgG production. Hence, IL-21 and IL-10 increase the activity of the TLR-MyD88-STAT3 pathway in human B cells via enhancing the phosphorylation of STAT3 for Ab production.