Regulation of Regulatory B Cells by Th2 Cytokines

Regulatory B cells (Breg) have emerged as important members of the immune regulatory network, particularly in the context of autoimmunity and tissue transplant. Previously we found that IL-5 supported the growth and functions of Breg cells, including production of IL-10 and FasL-mediated T cell killing. In contrast, IL-4 did not support regulatory B cells growth or function and instead antagonized the effects of IL-5. Signal transducer and activator of transcription-6 (STAT6) is the primary STAT activated by IL-4. We hypothesized IL-4 effects on B cells were mediated by STAT6, and that STAT6 −/− mice would have more abundant and effective regulatory B cells. Flow cytometric analysis of naive B cells from STAT6 −/− and BALB/c wild-type mice indicated differences in some Breg phenotypes. Culture with CD40L, IL-5, and/or IL-4 stimulation were used to assess the IL-10 production, FasL mediated killing, and activated phenotypes. As anticipated, STAT6 −/− B cells did not lose regulatory function when cultured with CD40L, IL-5, and IL-4. Interestingly, when BALB/c B cells were cultured with CD40L and IL-5 to expand regulatory B cells and then re-cultured in the presence of IL-4, regulatory functions were not affected. These results suggested the inhibitory effects of IL-4 on Breg cells is likely to be due to competition of other B cells in the culture rather than direct inhibition. To confirm these findings in vivo , STAT6 −/− and control mice were immunized with OVA emulsified in IFA and their B cells were compared phenotypically and functionally. Our data suggest that regulatory B cell growth, IL-10 production, and FasL mediated killing may be supported by IL-5 and CD40L stimulation, and are not directly affected by IL-4 as previously thought.