The Gut Microbiota in Rheumatoid Arthritis: Evaluation of Microbial Profiles, Disease Activity, Biomarkers, and Treatment Response.

OBJECTIVES: Rheumatoid arthritis (RA) is a chronic autoimmune disease with complex etiopathogenesis, and variable clinical course. The human gastrointestinal (GI) tract is a dynamic ecosystem in which micro-organisms influence metabolism, immune signalling, and pathogen resistance. Understanding these interactions is key to exploring the microbiota's role in RA. This review examines how intestinal and oral microbiota differ in RA patients and influence disease activity and treatment response. METHOD: A literature search was conducted using PubMed, from inception until January 3, 2025. Studies were selected based on the inclusion of original research involving human subjects diagnosed with RA. Exclusion criteria comprised reviews, case reports, animal studies, and studies with insufficient data. Of the 329 records identified, 72 were included in this review. RESULTS: Most studies have implicated changes in bacterial composition involving specific phyla in RA-associated dysbiosis. The imbalance is primarily driven by alterations in the phyla Bacillota, Pseudomonadota, and Bacteroidota, with Bacillota and Pseudomonadota accounting for 70% of increased taxa, and Bacillota and Bacteroidota for 83% of decreased intestinal taxa. Other findings include reduced α-diversity in seronegative patients and associations between decreased Prevotella taxa and higher disease activity, inflammation biomarkers, and autoantibodies. Smaller studies have also reported elevated serum zonulin-a marker of intestinal permeability-in RF-positive patients. CONCLUSION: This review highlights key bacterial phyla linked to RA and emphasises the potential of probing gut micro-biota-immune system interactions to improve diagnosis and treatment.