Induction and Differentiation of IL-10-Producing Regulatory B Cells from Healthy Blood Donors and Rheumatoid Arthritis Patients.

The most important feature of B cells is the production of Abs upon activation; additionally, B cells produce pro- and anti-inflammatory cytokines in response to certain stimuli. IL-10–producing B cells represent a major subset of regulatory B cells (Bregs) that suppress autoimmune and inflammatory responses. B cells play a crucial role in the development and maintenance of the chronic inflammatory autoimmune disease rheumatoid arthritis (RA); however, controversial data are available on IL-10– producing Bregs in RA. Our aim was to identify the optimal conditions that induce IL-10 + Bregs and, furthermore, to shed light on the signaling pathways that are responsible for their expansion. The results show that dual stimulation by CpG and CD40L for 48 h is optimal for IL-10 induction, and this can be synergistically boosted by IL-21. We identified the CD19 + CD27 + memory B cell population as the major source of IL-10 + Bregs. We detected significantly fewer CD19 + CD27 + IL-10 + cells in RA patients compared with healthy controls, and these were functionally defective in suppressing IFN-γ production by CD4 + T cells in coculture. IL-21 drastically increased the number of IL-10 + Bregs within the CD19 + CD27 + and CD19 + CD27 − populations; furthermore, it induced the appearance of IL-10 + Blimp-1 + plasmablasts. Monitoring the phosphorylation of key signaling molecules revealed that activation of ERK, p38, and CREB is indispensable for the induction of IL-10 production, whereas phosphorylation of STAT3 further enhances IL-10 expression in human Bregs. We conclude that CREB and STAT3 are the key transcription factors responsible for the expansion and differentiation of human IL-10–producing Bregs.