To further define the role of miR-146a in CSR, we stimulated miR-146a–/– and miR-146a+/+ B cells with LPS or CD154 plus IL-4 (to induce CSR to IgG1), LPS alone (CSR to IgG3), LPS or CD154 plus IL-4, IL-5, TGF-β, anti-δ mAb and RA (CSR to IgA). The gene discussed is TGFB1; the disease is rheumatoid arthritis.