Background/Purpose:  Regulator of G-protein Signaling (RGS) plays a key role in inhibiting chemokine signaling by desensitizing G-protein coupled receptor signals. RGS13 and RGS16 are two major regulators of B cell migration and regulate responses to CXCL12 and CXCL13 during development of germinal centers (GCs). We previously showed that IL-17 increased Rgs13 and Rgs16 in GC B cells, leading to high levels of activation-induced cytidine deaminase (AICDA), somatic hypermutation (SHM) and enabled development of pathogenic autoantibodies that cause immune complex nephritis and erosive arthritis. The objective of this work is to use BXD2-Rgs13^–/– and BXD2-Rgs16^–/– mice to determine if loss of RGS regulation suppressed the development of pathogenic autoantibodies.

Methods: BXD2-Rgs13^–/– and BXD2-Rgs16^–/– mice were produced by backcrossing BXD2 with B6-Rgs13^–/– and B6-Rgs16^–/– mice for > 7 generations.  Confocal imaging was used to determine the location of RGS13, RGS16, AID, and GC B cells in the spleen. Immunohistochemistry staining of spleen and kidney was used to determine the presence of plasmablasts and immune complex deposition. ELISA was used to determine serum levels of autoantibodies. The levels of GC B cell (Aicda, Pax5 and Bach2) and plasma cell (Irf4, Blimp1 and Xbp1) program transcripts in FACS purified GC B cells were determined by quantitative real-time PCR.  T-B conjugates were analyzed by sorting CD19⁺/CD4⁺doublets followed by EDTA dissociation and FACS identification of B-cell subsets.

Results:  In spleens of wild-type (WT) BXD2 mice, RGS13 was mainly expressed by GC B cells with light zone (LZ) B cells expressed slightly higher levels of Rgs13 compared to dark zone (DZ) B cells. RGS16 was expressed by LZ GC and marginal zone precursor (MZP) B cells in the LZ border. BXD2-Rgs13^–/–  mice exhibited higher IgM antibody titers at early age compared to WT mice; though smaller GCs, lower GC B-CD4 conjugates, and lower AID levels suggested a lesser extent of SHM and affinity maturation. RGS16 deficiency led to reduced aggregation of CD86^hi MZP B cells in GC LZ vicinity, reduced MZP-T conjugates, and significantly fewer GCs, suggesting its role in MZP stabilization in GC LZ.  Despite smaller GCs, there was increased IgM^bright plasmablasts, upregulation of Irf4, Blimp1 and Xbp1 and down regulation of Aicda, Pax5 and Bach2 in GC B cells of BXD2-Rgs13^–/– and BXD2-Rgs16^–/– mice. At older ages, BXD2-Rgs13^–/– and BXD2-Rgs16^–/–mice showed lower titers of IgG autoantibodies and IgG deposits in the glomeruli, suggesting reduced autoantibody pathogenicity.

Conclusion: Lack of either RGS13 or RGS16 signal is associated with reduction in GC program genes and premature exit of less pathogenic IgM plasmablasts. Our results suggest that, in autoimmune mice, prolonged B-T interactions in the GC light zone, mediated by upregulation RGS13 or RGS16, enhanced the selection and generation of high affinity pathogenic autoantibody producing B cells.  Redirection of B cell migration within different GC compartments via regulation of RGS13 and RGS16 and their associated signaling pathways may be a novel strategy to abrogate development of autoreactive B cells that produce pathogenic autoantibodies.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inhibition-of-pathogenic-autoantibodies-by-accelerating-the-exit-of-germinal-center-b-cells-via-manipulation-of-regulator-of-g-protein-signaling/