Microbiota-derived butyrate limits the autoimmune response by promoting the differentiation of follicular regulatory T cells

Background: Rheumatoid arthritis (RA) is a chronic debilitating autoimmune disorder with a high prevalence, especially in industrialized countries. Dysbiosis of the intestinal microbiota has been observed in RA patients. For instance, new-onset untreated RA (NORA) is associated with the underrepresentation of the Clostridium cluster XIVa, including Lachnospiraceae, which are major butyrate producers, although the pathological relevance has remained obscure. Follicular regulatory T (T_FR) cells play critical regulatory roles in the pathogenesis of autoimmune diseases, including RA. Reduced number of circulating T_FR cells has been associated with the elevation of autoantibodies and disease severity in RA. However, the contribution of commensal microbe-derived butyrate in controlling T_FR cell differentiation remains unknown. Methods: We examined the contribution of microbe-derived butyrate in controlling autoimmune arthritis using collagen-induced arthritis (CIA) and SKG arthritis models. We phenotyped autoimmune responses in the gut-associated lymphoid tissues (GALT) in the colon and joint-draining lymph nodes in the CIA model. We developed an in vitro CXCR5⁺Bcl-6⁺Foxp3⁺ T_FR (iT_FR) cell culture system and examined whether butyrate promotes the differentiation of iT_FR cells. Findings: Microbe-derived butyrate suppressed the development of autoimmune arthritis. The immunization of type II collagen (CII) caused hypertrophy of the GALT in the colon by amplifying the GC reaction prior to the onset of the CIA. Butyrate mitigated these pathological events by promoting T_FR cell differentiation. Butyrate directly induced the differentiation of functional T_FR cells in vitro by enhancing histone acetylation in T_FR cell marker genes. This effect was attributed to histone deacetylase (HDAC) inhibition by butyrate, leading to histone hyperacetylation in the promoter region of the T_FR-cell marker genes. The adoptive transfer of the butyrate-treated iT_FR cells reduced CII-specific autoantibody production and thus ameliorated the symptoms of arthritis. Interpretation: Accordingly, microbiota-derived butyrate serves as an environmental cue to enhance T_FR cells, which suppress autoantibody production in the systemic lymphoid tissue, eventually ameliorating RA. Our findings provide mechanistic insights into the link between the gut environment and RA risk. Funding: This work was supported by AMED-Crest (16gm1010004h0101, 17gm1010004h0102, 18gm1010004h0103, and 19gm1010004s0104 to KH), the Japan Society for the Promotion of Science (JP17KT0055, JP16H01369, and JP18H04680 to KH; JP17K15734 to DT), Keio University Special Grant-in-Aid for Innovative Collaborative Research Projects (KH), Keio Gijuku Fukuzawa Memorial Fund for the Advancement of Education and Research (DT), the SECOM Science and Technology Foundation (KH), the Cell Science Research Foundation (KH), the Mochida Memorial Foundation for Medical and Pharmaceutical Research (DT), the Suzuken Memorial Foundation (KH and DT), the Takeda Science Foundation (KH and DT), The Science Research Promotion Fund, and The Promotion and Mutual Aid Corporation for Private Schools of Japan (KH).