Rad52 deficiency Increases immunoglobulin class switch DNA recombination (IRM8P.714)

Abstract

Class switch DNA recombination (CSR) plays a central role in the maturation of the antibody response. CSR entails the generation of double-strand DNA breaks (DSBs) mediated by activation-induced cytidine deaminase (AID). Resolution of these DSBs can occur through Ku70/Ku86 dependent classical non-homologous end-joining (C-NHEJ), or through an undefined alternative-end joining (A-EJ) that introduces microhomologies in the S-S junctions. Here we investigate the role of Rad52, an important DSB repair factor in CSR. We found that Rad52 deficiency elicits an increase in NP-specific IgG1 and IgG3 responses to T-dependent and T-independent antigens. The increased antibody response is not due to alterations in lymphoid differentiation, B cell proliferation or cell division but rather a direct effect on the CSR machinery. This phenomenon is B cell intrinsic, as CSR to IgG1, IgG2a, IgG3 and IgA virtually double in Rad52-/- B cells stimulated with LPS and respective cytokines. In CSR, both Rad52 and Ku70/Ku86 are specifically recruited to S region DNA in an AID-dependent manner. In the absence of Rad52, the recruitment of Ku70/Ku86 to the S regions was significantly increased. Finally, the frequency and length of microhomologies in the S-S junctions was significantly reduced in Rad52-/- B cells. Altogether, our findings suggest that Rad52 competes with Ku70/Ku86 in binding S region to repair DSBs in CSR possibly utilizing an alternative end-joining pathway.