Background/Purpose: The human gut microbiome maintains normal immune homeostasis. Changes to the microbiota evolve with aging and have been implicated in the development of autoimmune disorders like rheumatoid arthritis (RA). Given the observed variability in microbiota composition among healthy individuals, immune responses to commensal microbiota may be more relevant to disease development. We compared adaptive immune responses to gut microbiota in RA patients and healthy controls and determined associations with RA autoantibodies.

Methods: IgG immune responses to intestinal microbiota were detected in sera of RA patients and controls using a protein microarray containing recombinant antigens cloned from murine microbiota that have been previously studied in humans (50 epitopes from >6 bacterial groups ). Each antigen was present in quadruplicate per slide. Bound human sera IgG was detected and quantitated using an Axon GenePix 4000B dual laser and its software. Levels are reported as median net fluorescent values with lower detectable cut-off being assigned 0. Anti-citrullinated peptide antibodies (ACPA) were measured by ELISA and rheumatoid factor (RF) by nephelometry. Associations of IgG microbiota responses with subject group and RA antibodies were tested by nonparametric tests. Patterns of microbiota responses were assessed using non-hierarchical clustering. Given multiple comparisons, p values<0.001 were considered significant.

Results: RA patients (n=121; 78% female, mean (SD) age 58 (14) years; 43 with symptoms less than 12 months (ERA)) were compared to healthy controls ( n=19, 63% female, mean(SD) age 39 (11)years). All anti-microbial IgG levels were detected in at least some subjects although there was individual variation in the expression patterns. No robust grouping of microbial responses was seen. Levels of 16 anti-microbial IgG titers were significantly elevated in RA compared to controls whereas levels of 2 anti-microbial IgGs titers were decreased (all p<0.001). The epitopes with the highest IgG titers in RA compared to controls were rIB2 (firmicutes/bacteroides) and Pmel. The epitopes with the most reduced IgG titers in RA compared to control were Ftsz (proteobacteria) and rib16 (firmicute). Of four known universal gut microbiotia antigens (rIB1, rIB2, rIB10 and rIB20), only anti-rIB2 IgG levels were increased in RA (p<0.001). There were no robust associations of individual IgG titers with ACPA or RF positivity. The levels of five anti-microbial antigen IgG titers (3-2, bir1, cbir15, cbir63, m18-1) were higher in RA of recent onset than long standing RA (all p<0.0001).

Conclusion: Adaptive immune responses to selective gut microbiota differ between RA and controls but do not associate with other RA autoantibodies. Although environmental influences such as diet and medication were not addressed here, these results suggest a broader immune response alteration to microbial organisms exists in persons with disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/human-seroreactivity-to-gut-microbiota-antigens-in-rheumatoid-arthritis-and-controls-lack-of-association-with-rheumatoid-arthritis-autoantibodies/