Fecal virome transplantation attenuates arthritis in mice by remodeling gut ecology, systemic tryptophan metabolism, and innate immune responses.

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by chronic joint inflammation and systemic immune dysregulation. Emerging evidence suggests that the gut microbiome plays an important role in immune modulation in RA, yet the role of the gut virome remains poorly understood. Here, using the K/BxN serum-transfer arthritis model, we systematically evaluated the potential role of fecal virome transplantation (FVT) in modulating gut ecology and innate inflammatory responses. Arthritic mice exhibited marked alterations in gut virome composition compared with healthy controls. Administration of purified virus-like particles (VLPs) from healthy donors correlated with reductions in paw swelling, histopathological inflammation, bone erosion, circulating proinflammatory cytokines, and myeloid cell infiltration in inflamed tissues. In parallel, 16S rRNA sequencing showed that FVT remodeled the gut bacterial community toward a composition more similar to that of healthy controls. Targeted serum metabolomics revealed increased levels of microbiota-derived tryptophan metabolites, including indole-3-lactic acid and related indole derivatives, suggesting a link between gut microbial remodeling and systemic immunometabolic regulation. Collectively, these findings indicate that FVT may attenuate inflammatory arthritis by remodeling gut microbial ecology, potentially involving virome-bacteriome interactions and immunometabolic pathways.