Gut Microbiota as a Biomarker and Target in Biologic Therapy for Autoimmune and Immune-Mediated Arthritis: A Systematic Review

Objective Gut microbiota dysbiosis has been implicated in the pathogenesis of autoimmune and immune-mediated arthritis. Biologics may influence gut microbiota composition; however, it is uncertain whether biologics act directly on microbial communities or indirectly through disease modulation and restoration of immune homeostasis. This systematic review explores how biologic therapies modulate gut microbiota in autoimmune arthritis and their potential as biomarkers for treatment response and disease activity. Methods We searched PubMed, Scopus, Cochrane Library, and Web of Science for studies assessing gut microbiota changes induced by any biologic therapy in immune-mediated or autoimmune arthritis. The outcomes included changes in microbiota and the potential for microbiota as predictive biomarkers for treatment response and disease activity. Results A total of 12 studies were included. Biologic agents, predominantly tumor necrosis factor inhibitors and interleukin 17 inhibitors, significantly altered gut microbiota composition and diversity, with most studies showing increased α-diversity and normalization of β-diversity post therapy; however, these effects were not uniformly consistent. Treatment restored beneficial short-chain fatty acid–producing taxa, including Faecalibacterium prausnitzii , Megamonas , Lachnoclostridium , and Blautia , while reducing inflammatory genera such as Escherichia - Shigella and Klebsiella . Certain taxa, notably Lachnospiraceae and Megamonas , correlated with clinical improvement and reduced disease activity. Conclusion Biologic therapy modulates gut microbiota composition in autoimmune and immune-mediated arthritis, promoting a shift toward eubiosis. Specific microbial taxa, including Lachnospiraceae , Blautia , and F. prausnitzii , show potential as noninvasive biomarkers for treatment response and disease activity. These findings guide further longitudinal and interventional studies to validate microbial signatures and their clinical applicability.