Background/Purpose: Ongoing studies in rheumatoid arthritis (RA) implicate intestinal dysbiosis of bacteria as a contributing factor, though the mechanism(s) by which bacteria influence disease is not known. Our recent studies using the murine collagen-induced arthritis (CIA) model of inflammatory arthritis demonstrated a role of intestinal bacteria in influencing autoantibody pathogenicity through modulation of autoantibody glycosylation. As bacterial metabolites are potent immune modulators, we profiled intestinal metabolites generated during CIA to identify potential mediators of antibody glycosylation. We identified the bacteria-produced metabolite indole as significantly correlating with the development of disease. In this study, we aimed to further investigate the role of indole for antibody glycosylation during the development of CIA.

Methods: We utilized the murine collagen-induced arthritis (CIA) model in which mice are immunized with bovine type II collagen on days 0 and 21. To reduce the effect of microbe-produced metabolites during disease, we administered broad-spectrum antibiotics in the drinking water starting at day 21, which reduces intestinal bacteria >90% and CIA severity >95%. Indole was then added to this water at a concentration of 1 µM. Cecal contents with tissue were evaluated by LC-MS and 16s rRNA sequencing of bacteria. Cells in Peyer’s patches, mesenteric LNs, and spleens evaluated by flow cytometry and qPCR. Serum antibodies were measured by ELISA. For ex vivo stimulation of B cells with indole, splenic B cells were negatively sorted 10 days following CII-immunization and differentiated in culture with LPS ± indole. After 24 hours, RNA was isolated from cells and gene expression determined by qPCR.

Results: Profiling the metabolome during CIA identified the indole pathway as significantly altered and correlating with disease severity in CIA. Indole also correlated with the significant expansion of bacteria known to produce indole in the development of CIA. In mice protected from CIA by antibiotic administration (CIA+Abx) indole levels were significantly reduced (P<0.0001). Mice with CIA compared to CIA+Abx demonstrated significantly increased expression of β1,4-galactosyltransferase 1 (GalT) and β-galactoside α2, 6-sialyltransferase 1 (St6gal1), two enzymes important in mediating pathogenic antibody glycosylation. Administration of indole to mice with CIA+Abx resulted in significantly reversing the protective effects of antibiotics both on disease severity and expression of GalT and St6Gal1. Treatment of CII-primed B cells with indole ex vivo also resulted in a significant induction of expression of these enzymes.

Conclusion: Our data demonstrate that the bacteria-produced metabolite indole significantly drives the development of CIA. While the glycosylation status of antibodies from mice in our treatment groups needs to be confirmed, these results strongly suggest that the mechanism is via induction of B cell glycosylation enzymes that modulate autoantibody effector function towards a proinflammatory profile. Targeting this pathway has potential clinical implications in treating and/or preventing RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/bacteria-derived-indole-drives-autoimmune-arthritis-by-altering-b-cell-glycosylation-of-autoantibodies/