Extension of the germinal center stage of B cell development promotes autoantibodies in BXD2 mice.

Objective Regulator of G protein signaling (RGS) proteins inhibit chemokine signaling by desensitizing G protein–coupled receptor signals. This study was undertaken to determine the mechanisms by which RGS13 promotes the generation of pathogenic autoantibodies in germinal centers (GCs), using BXD2-Rgs13−/− mice. Methods Confocal and light microscopy imaging techniques were used to determine the location of cells that express RGS13 and activation-induced cytidine deaminase (AID) in the mouse spleen, and the number of plasmablasts. The levels of GC and plasma cell program transcripts in GC B cells were determined by real-time quantitative polymerase chain reaction (qPCR). Differential interleukin-17 (IL-17)–mediated expression of RGS13 in GC versus non-GC B cells was analyzed using A20 and 70Z/3 B cells. Results In the spleens of BXD2 mice, RGS13 was mainly expressed by GC B cells and was stimulated by IL-17 but not IL-21. IL-17 up-regulated RGS13 in A20 GC cells but not 70Z/3 non-GC B cells. BXD2- Rgs13−/− mice exhibited smaller GCs and lower AID levels, suggesting lower somatic hypermutation and affinity maturation. However, GC B cells from BXD2- Rgs13−/− mice showed increased levels of IgMbright plasmablasts, up-regulation of the genes encoding plasma program, including interferon regulatory factor 4, B lymphocyte–induced maturation protein 1, and X-box binding protein 1 and the p-CREB target genes Fosb and Obf1, and down-regulation of the GC program genes Aid, Pax5, and Bach2 compared to BXD2 mice. BXD2-Rgs13−/− mice had lower titers of IgG autoantibodies and IgG deposits in the glomeruli, suggesting reduced autoantibody pathogenicity. Conclusion RGS13 deficiency is associated with a reduction in GC program genes and the exit of fewer pathogenic IgM plasmablasts in BXD2 mice. Our findings indicate that prolonged GC program, mediated by up-regulation of RGS13, enhances AID expression and enables the generation of pathogenic autoantibodies in autoreactive GCs.