MC-derived IL-6 and CD40L-CD40 signaling induces IgA surface expression and secretion by activated B cells. Analysis of surface IgA by activated B cells in presence of cultured activated MCs. (A) MIFs of IgA surface expression on activated B cells cultured alone or with activated WT MCs and with IL-6^−/− MCs and in the presence of anti–IL-6R or anti-CD40L antibody are measured by flow cytometry. IgA surface expression on B cells alone with anti–IL-6R and of anti-CD40L isotype control antibody was also analyzed by flow cytometry (Ctrl). (B) Secreted IgA by activated B cells cultured alone, with activated WT MCs and with IL-6^−/− MCs and in the presence of anti–IL-6R or control antibody (Ctrl), and in the presence of anti-CD40L antibody or control antibody (Ctrl), was detected by ELISA. The results are the average ± SD of values from 3 separate experiments using at least 3 different cultures of MCs. *P < .05; **P < .001.