Dual IgA/IgG family plasmablast-derived mAbs from peripheral blood of individuals at risk for rheumatoid arthritis are polyreactive to autoantigens and intestinal bacteria

Abstract

Abstract A wide array of data supports rheumatoid arthritis (RA) as a disease with mucosal origins, including presence of IgA RA-associated autoantibodies in peripheral blood and biomarkers of inflammation at mucosal sites. Individuals at-risk for developing RA, (serum autoantibody+, without joint disease), can be characterized by an expansion in dual-family IgA/IgG circulating plasmablasts. We examined the characteristics of mAbs generated from these plasmablasts in at-risk (n=4) and early RA (<1 year from diagnosis, n=2) subjects. The variable regions of the plasmablasts were sequenced and clonal families mapped. 94 total heavy and light chain sequences were cloned into a mouse IgG2a constant region. All 94 expressed mAbs bound RA-related citrullinated/uncitrullinated synovial targets in an antigen array, demonstrating polyreactivity. As these mAbs were derived from IgA-containing clonal families, we queried if they have commensal bacterial targets by exposing them to a human fecal bacterial pool. 61.7% of mAbs had bacterial targets, suggesting additional polyreactivity. Bound bacteria were 16S rRNA sequenced. Interestingly, 56.31% ±12.85 of bound bacteria were of families Lachnospiraceae/Ruminococcaceae. A smaller subset of Vh genes were utilized among bacterially reactive plasmablast mAbs as compared to the wider population, though mutations from germline remained static between groups. Specifically, mAbs utilizing IgHV4-4, V3-64, V3-66, and V3-74 were bacterially reactive, and mAbs utilizing IgHV4-39, V4-59, V3-33, and V3-43 were not bacterially reactive. This demonstrates a link between mucosal and systemic immune systems in RA, suggesting an early mucosal trigger for disease-specific autoantibody development.