TLR-mediated STAT3 and ERK activation controls IL-10 secretion by human B cells.

IL-10-producing B cells have a regulatory effect in various mouse models for immune-mediated disorders via secretion of IL-10, a potent immunoregulatory cytokine. However, currently, the signaling pathways that regulate IL-10 production in B cells are not well understood. Here, we show that TLR signaling, but not BCR activation or CD40 ligation, induces potent production of IL-10 in human B cells. We demonstrate that the activation of STAT3 and ERK is required for TLR-induced IL-10 production by B cells, since inhibition of STAT3 or ERK activation abrogates TLR-induced IL-10 production. We also uncover a novel function of the TLR-MyD88-STAT3 pathway in B cells, namely controlling IL-10 production, in addition to the known role for this pathway in antibody production. Furthermore, IFN-α, a member of the type I IFN family, differentially modulates TLR7/8- and TLR9-activated STAT3 and ERK in B cells, which provides an explanation for our findings that IFN-α enhances TLR7/8-induced, but not TLR9-induced IL-10 production. These results yield insights into the mechanisms by which TLR signaling regulates IL-10 production in B cells and how type I IFN modulates TLR-mediated IL-10 production by B cells, therefore providing potential targets to modulate the function of IL-10-producing B cells.