Regulatory mechanisms of B cells in immunoregulation. (A) B-cell-derived effector molecules, IL-10 and TGF-β that are produced in response to the stimulations via CD40, TLRs, or BCR, play important roles in suppressing inflammatory T cells. (B) Antibodies may participate in protective immunoregulation through several pathways by binding to FcγRIIB on DC and suppressing APC function, or neutralizing self-reactive Ags or labeling AC to diminish autoimmune responses. (C) Regulatory B cells suppress APC function by producing IL-10 or CXCL13, or down-regulating CD4+ T-cell responses via engagement with TCR expression on effector CD4+ T cells. Regulatory B cells can also activate iNKT cells through an increased CD1d expression and up-regulate iNKT-cell function and induce immune tolerance. (D) Regulatory B cells from MALT present antigenic peptides through MHC I or non-classic MHC I molecules, Qa-1 or MR1, to mediate the expansion of cytolytic CD8+ T cells in the intestine which monitor the activated CD4+ T cells and suppress mucosal inflammation.