Summary Western lifestyle is linked to autoimmune and metabolic diseases, driven by changes in diet and gut microbiota composition. Using a Toll-like receptor 7 (TLR7)-dependent mouse models of lupus, we dissect dietary effects on the gut microbiota and find that Lactobacillus reuteri can drive autoimmunity but is ameliorated via dietary resistant starch (RS). Culture of internal organs and 16S rDNA sequencing revealed TLR7-dependent translocation of Lactobacillus reuteri in mice and fecal enrichment of Lactobacillus in a subset of lupus patients. L. reuteri colonization worsened autoimmune manifestations under specific-pathogen-free and gnotobiotic conditions, notably increasing plasmacytoid dendritic cells (pDCs) and interferon signaling. However, RS suppressed the abundance and translocation of L. reuteri via short-chain fatty acids, which inhibited its growth. Additionally, RS decreased pDCs, interferon pathways, organ involvement and mortality. Thus, RS exerts beneficial effects in lupus-prone hosts through suppressing a pathobiont that mediates interferon pathways implicated in the pathogenesis of human autoimmunity.

Several drugs targeting members of the TNF superfamily or TNF receptor superfamily (TNFRSF) are widely used in medicine or are currently being tested in therapeutic trials. However, their mechanism of action remains poorly understood. Here, we explored the effects of TNFRSF co-stimulation on murine Foxp3 + regulatory T cell (Treg) biology, as they are pivotal modulators of immune responses. We show that engagement of TNFR2, 4-1BB, GITR, and DR3, but not OX40, increases Treg proliferation and survival. Triggering these TNFRSF in Tregs induces similar changes in gene expression patterns, suggesting that they engage common signal transduction pathways. Among them, we identified a major role of canonical NF-κB. Importantly, TNFRSF co-stimulation improves the ability of Tregs to suppress colitis. Our data demonstrate that stimulation of discrete TNFRSF members enhances Treg activation and function through a shared mechanism. Consequently, therapeutic effects of drugs targeting TNFRSF or their ligands may be mediated by their effect on Tregs.