Background/Purpose: Background: Dysbiosis of gut bacterial communities in rheumatoid arthritis (RA) is a noted phenomenon in both murine models and human patients; however, the mechanisms from dysbiosis that promote RA pathogenesis remain unclear. Our lab previously demonstrated that administration of antibiotics to deplete the microbiota late in the course of murine collagen-induced arthritis (CIA) significantly ameliorated disease and correlated with changes in total antibody glycosylation patterns, known to occur in RA patients and affect complement fixation and FC receptor engagement. We hypothesized that the microbiota mediated antibody glycosylation via production of bacteria-specific metabolites.

Methods: Methods: CIA was induced by immunization of male 6-8 week-old DBA/1 mice with bovine type II collagen emulsified in complete Freund’s adjuvant on days 0 and 21. To understand the mechanisms by which late micriobiota depletion would significantly decrease CIA, we analyzed concentrations of cecal metabolites by LC-MS during CIA and after antibiotic treatment (1 mg/ml each ampicillin, neomycin, metronidazole and 0.5 mg/ml vancomycin). 10 mM indole or vehicle was then added to the drinking water containing antibiotics. Arthritis was evaluated based on a score of 0 (no swelling) to 4 (ankylosis) for each paw and summed for the mouse. Assessment of cell populations was performed by flow cytometry. Splenic B cells were evaluated ex vivo after stimulation with LPS (5μg/mL) and/or anti-IgM (10μg/mL) and total RNA was collected and analyzed via qRT-PCR.

Results: Results: Metabolomic profiling demonstrated a significant increase in bacteria-produced indole, a byproduct of tryptophan metabolism, in mice with CIA compared to unimmunized controls and those with CIA treated with antibiotics. Interestingly, administration of indole after antibiotic treatment resulted in a partial restoration of a CIA phenotype. Indole administration also resulted in increased T follicular helper cell (Tfh) and B cell populations in the Peyer’s patches and mesenteric lymph nodes in mice, but not the spleen. Furthermore, ex vivo stimulation of murine splenic B cells with indole induced gene expression of the B4Galt and Fut8 genes, transferases critical in antibody glycosylation.

Conclusion: Conclusions: Our results suggest that gut dysbiosis due to RA results in bacterial production of indole, which promotes RA pathogenesis via activation of B cell populations and altered antibody glycosylation patterns. Precise understanding of which indole metabolites are involved and how they engage cellular receptors will help elucidate the role of intestinal dysbiosis in RA development.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/bacteria-derived-indole-drives-autoimmune-arthritis-by-altering-b-cell-glycosylation-of-autoantibodies-2/