IGHG3 and rheumatoid arthritis: LPS plus IL-4 and CD154 plus IL-4 failed to induce Sμ–σδ recombination in Rad52−/− B cells but not in Rad52+/+ B cells, while either treatment efficiently induced Sμ–Sγ1 and Sμ–Sε recombinations in the same Rad52−/− B cells (Fig. 4a)—in Rad52−/− B cells, LPS, and LPS or CD154 plus TGF-β and RA induced CSR to IgG3 and IgA, respectively.