Session Title: B cells in Human and Animal Arthritis
Session Type: Abstract Submissions (ACR)
Background/Purpose: Increased polyreactive B cells have been identified in patients with systemic lupus erythematous (SLE) and rheumatoid arthritis (RA). Such autoantibodies (autoAbs) were also identified in BXD2 mice that spontaneously develop IgG Immune complex glomerulonephritis and erosive arthritis. Most naturally occurring polyreactive autoantibodies are primarily IgM, germline and low affinity. Pathogenic autoAbs including anti-citrullinated protein antibodies, however, evolve through somatic hypermutation and class-switch recombination, suggesting that antigen (Ag)-selected affinity maturation is required. The purpose of this study is to identify and characterize the dominant autoAbs and their epitopes in BXD2 mice to determine if pathogenic autoAbs indeed react to immunodominant epitopes of self antigens.
Methods: A PEPperPRINT Autoimmunity Microarray which covers 2,733 linear B-cell autoepitopes from the Immune Epitope Database (IEDB) was used to identify BXD2 autoepitopes. Top peptides were selected based on the strength of reactivity and concordance with predictions made by DiscoTope, a structure-based computational program that predicts discontinuous B cell epitopes from protein three dimensional structures.
Results: The dominant epitopes recognized by BXD2 autoantibodies are those commonly found in human SLE and RA patients. The strongest response was observed with peptides of the 60 and 65 kDa heat shock proteins. Serum was also strongly reactive against a variety of arginine-rich peptides, including several that show shared consensus sequence derived from antigens U1 small nuclear ribonucleoprotein (U1snRNP), 70 kDa and small nuclear ribonucleoprotein Sm D1 (snRNP Sm D1), and 52 kDa Ro protein. The array further revealed reactivity with several citrulline-modified peptides, including fibrinogen beta chain (PA[Cit]KQCSKEDGGGWWY and WYNZCHAANPNGA[Cit]YY) as well as glucose regulated protein 78 (GRP78) (ALSSQHQAA[Cit]IEIESFYE). X-ray crystallography information is available for these two Ags. DiscoTope analysis shows that citrullination occurs in the highly immunogenic sites and are the immunoreactive epitopes of BXD2 autoantibodies.
Conclusion: The present results suggest that BXD2 mice exhibit a high tendency to develop autoAbs against nucleosome proteins and stress response proteins. Such results are consistent with our recent report showing defective marginal zone macrophages in clearance of apoptotic self antigens in BXD2 mice. Although cross-reactivtive epitopes are found, BXD2 autoAbs also react to autoAg at the major immunogenic sites that exhibit protein citrullination, suggesting that specific Ag engagement and selection are involved in the formation of autoAb producing B cells. Tetramers against the dominant epitopes are currently being generated to evaluate the immune checkpoint loss that leads to the generation of these B cells.
H. C. Hsu,
J. D. Mountz,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-throughput-epitope-mapping-of-autoantibodies-in-bxd2-mice-reveals-the-generation-of-autoantibodies-against-citrullinated-antigens-at-the-predicted-major-immunogenic-sites/