Background/Purpose: Circulating autoantibodies, including anti-CCP and RF, develop years before physical manifestations of rheumatoid arthritis (RA), with several lines of evidence suggesting that these autoantibodies may be driven in part by microbial-mucosal interactions. We hypothesized that discrete bacterial strains in the gut may drive autoantibody generation, inducing a systemic breach of tolerance in the autoantibody positive preclinical RA period that leads to the future development of joint inflammation.

Methods: Human fecal samples were obtained from 16 healthy controls (HC), 12 at-risk individuals (AR) (serum anti-CCP+ in the absence of current or prior arthritis), and 13 individuals with early RA (< 1 year duration). Antibody-seq was performed by flow sorting bacteria endogenously coated with human IgA, followed by 16S rRNA sequencing. Plasmablasts (PB) were isolated from 4 additional AR individuals, defined by serum CCP+ (83%) and/or RF+ (83%), and from 2 individuals with early RA (CCP+). Subdomains of the antigen binding region from PB-produced antibodies were selected by sequence analysis for their origin in a dual IgA/IgG isotype family, cloned onto a mouse IgG2a framework and expressed as monoclonal antibodies (mAbs). 94 mAbs were chosen for further study based on recombinant antibody reactivity with synovial antigens. Lachno(spiraceae)/Rumino(coccaceae) strains were isolated from the feces of an AR subject. After culture in anaerobic media, 7 strains of interest were identified by 16S sequencing.

Results: The closely related families Lachno/Rumino were expanded in AR and RA compared to HC. This expansion was accompanied by increased IgA coating of Lachno/Rumino in AR when compared to family abundance.  62% of 94 PB-derived mAbs that bound synovial antigens also targeted intestinal bacteria, specifically Lachno/Rumino. Together these suggest altered mucosal responses to these families and cross-reactivity between Lachno/Rumino bacterial and host self-antigens in RA joints. To analyze phenotypic effects of these families, primary human bacterial strain isolates within Lachno/Rumino were verified as targeted by representative PB-derived mAbs. Germ-free DBA/1j mice were mono-colonized with Lachno/Rumino strain isolates, Prevotella copri, or culture media. Within 14 days arthritis, characterized by joint swelling and bone loss, was observed in mono-colonized mice receiving one Lachno/Rumino strain.

Conclusion: In a cohort of AR and RA individuals, we identified altered mucosal and systemic immunity to Lachno/Rumino. Germ-free mice mono-colonized with a strain derived from an AR individual developed arthritis. Although the full mechanism has not been fully elucidated, the observed cross-recognition of Lachno/Rumino and joint derived antigens by AR and early RA PB-derived mAbs, and induction of joint inflammation by such bacteria in mono-colonized mice, suggests that bacterial antigens and/or arthritogenic factors derived from these families drive a breach in tolerance during human preclinical RA and contribute centrally to the development of arthritis and classified RA.

« Back to ACR Convergence 2020

ACR Meeting Abstracts - https://acrabstracts.org/abstract/bacterial-families-lachnospiraceae-ruminococcaceae-are-immunologically-targeted-in-individuals-at-risk-for-ra-and-a-specific-strain-is-arthritogenic-in-monocultured-gnotobiotic-mice/