The present study next suggests that CD40 engagement, in the absence of other (known) stimuli, is sufficient to effectively induce IgA switching in human B cells, in a NF-κB-dependent manner [46]. IL-10 is the pleiotropic regulator of the immune system toward infection. It plays a central role in B cell proliferation, survival, isotype switching and differentiation [47]. Our results Wnt assay indeed confirm the involvement of IL-10 in IgA production; however, as IL-10 induced STAT3 and CD40L NF-κB, we next attempted to elucidate their respective influences on IgA production. The STAT3 protein is a STAT family member with diverse biological functions, including cell growth,

cell survival, embryo development and cell motility [30,48,49]. STAT3 was shown to play a critical

role in mouse B cell development, particularly in the thymodependent terminal differentiation of B cells into IgG plasma cells [50]. STAT3 was also identified recently as a major player in hyper-IgE syndrome [51]. Diehl et al. used human B cells to show that the inducible activation of STAT3 triggers blimp1 gene expression and promotes plasma cell differentiation and Ig production [52]. STAT3 and/or IL-10 mutations have been shown to be involved Quizartinib supplier in inflammatory bowel disease, Crohn’s disease or ulcerative colitis, impairing the signalling pathways [53]. STAT3 plays a major role in the IL-23/Th17 pathway, maintaining intestinal immune homeostasis [54]. However, it is becoming increasingly clear that IL-10 signalling appears to play a central role in inflammatory bowel disease pathogenesis, with germline variants associated with ulcerative colitis and Crohn’s disease [55,56]. Here, we present evidence that the STAT3 pathway is also critical for either Ig (or more particularly IgA) production by human B cells or for export of IgA onto human B cells. Fan et al. showed that B cell stimulation by Ig triggering leads to STAT3 activation that depends on the combined effects of IL-6 and IL-10, whereas anti-Ig or pharmacological stimulation with phorbol

myristate acetate (PMA)/ionomycin leads to STAT3 activation that depends primarily on IL-10 [57]. IL-10 also mediates the differentiation of germinal centre B cells into memory and plasma cells Etomidate [58] and induces Janus kinase (JAK) proteins via the phosphorylation of STAT3 [59]. Here, we report that IL-10 by itself can lead to significant AID transcription and IgA production and that a combination of sCD40L and IL-10 induced comparable levels of IgA to those induced by IL-10 alone. Consequently, we propose that IgA synthesis by (in vitro) differentiated B cells is more dependent on the STAT3 pathway than on the NF-κB pathway. However, in the absence of IL-10 or when the STAT3 pathway is blocked, some IgA can still be produced by B cells, albeit in smaller quantities.