294-OR: Discovery of a Novel Secretory Protein from the Gut Microbiome That Promotes Immune Tolerance and Ameliorates Autoimmunity via Dendritic Cell Induction of IL-10

The human gut microbiota has been associated with diverse autoimmune diseases; however, the underlying mechanisms are largely unknown. To identify gut microbes and derived bioactive molecules that can promote immune tolerance, we systematically investigated the immunoregulatory potential of each member in the Altered Schaedler Flora (ASF) that has demonstrated diverse immune functions in mice. We observed that the eight ASF members presented a division of labor in promoting distinct immunophenotypes of bone marrow-derived dendritic cells, such as the production of IL-10, TNF-a, and TGF-b, and the induction of regulatory T cells. Interestingly, Parabacteroides goldsteinii ASF519 induced strong immune tolerance via novel mechanisms as evidenced by non-pan T cells-mediated promotion of Foxp3⁺ Treg proliferation and reduction of cytotoxic CD8 T cells, as well as TNF-a signaling-independent IL-10 production. Via bioactivity-guided fractionation, ASF519-derived molecules responsible for inducing immune tolerance were identified to be heat-labile secretory proteins with yet-uncharacterized functions. Genome-wide screening additionally identified a complex regulatory network that controls the immunoregulatory potency of ASF519. ASF519 colonization in germ-free mice significantly reduced IL-4 and IL-5 in sera and increased the transcript abundance of ll-10 and ll-17A in colon, suggesting potential roles of ASF519 in modulating both intestinal and systemic immune functions. In mouse immune disease models, oral administration of ASF519 demonstrated a protective role in the development of dextran sodium sulfate-induced colitis and collagen-induced arthritis. Relevant mechanisms are now under investigation. This study has the potential to provide novel therapeutic avenues for the prevention and treatment of autoimmune diseases.