Project Summary Long-term heavy drinking causes multiple organ injury with the liver as the most impacted organ. Alcoholic liver disease (ALD) covers a spectrum of liver lesions, including simple steatosis, alcoholic hepatitis and cirrhosis. Unfortunately, FDA approved medication is not available for any stage of ALD. Thus, there is an urgent need to investigate the mechanisms of disease pathogenesis and explore therapeutic strategies for ALD. Increasing evidence support that translocation of pathogen associated molecular patterns (PAMP) from the intestine to the liver triggers hepatic inflammation. During the past funding period, we investigated the role of type 1 conventional dendritic cells (cDC1s) in alcohol-induced defects at the gut-liver axis. We observed that Chronic alcohol feeding reduced intestinal cDC1s and IL-12. In accordance, Th1 cells and their INF- expression were also reduced. Batf3 knockout mice (cDC1 deficient) showed that cDC1 deficiency exaggerated alcohol- reduced Th1/IFN- and worsened alcohol-induced dysbiosis, gut barrier dysfunction, PAMP translocation and hepatic inflammation. Adaptive transfer of cDC1s reversed alcohol-decreased intestinal defects and amelioration of ALD. We also found that IFN-γ administration restored intestinal STAT1 and STAT3, upregulated AMPs, orchestrated gut microbiota, and reversed alcohol-induced endotoxemia and hepatic inflammation. These results suggest that dysregulation of dendritic cell-T cell axis represents a novel mechanism in alcohol-induced pathogenesis at the gut-liver axis. Our preliminary studies further demonstrated that chronic alcohol feeding increased type 2 conventional dendritic cells (cDC2s) in the intestine, suggesting an imbalance between cDC1 and cDC2 responses. cDC2s after antigen acquisition in the lamina propria migrate to lymph tissues and induce Th17 cell differentiation. Indeed, we observed that CD4+IL-17+ T cells (Th17 cells) were increased in the lymph tissues after alcohol exposure. We also found that alcohol increased the dendritic cell surface succinate receptor, GPR91, in association with increased intestinal succinate. These results suggest a novel host immunity-microbiota crosstalk mechanism in activation of cDC2s-Th17 cells circuit in alcohol-induced pathogenesis at the gut-liver axis. This renewal project plans to investigate the role of DC2 activation and induction of Th17 response and the mechanism of how alcohol activate cDC2s in the pathogenesis of ALD. The project will carry out three aims. Aim 1 is to determine the causal role of intestinal cDC2 cell activation in alcohol-induced pathogenesis at the gut-liver axis. Aim 2 is to investigate a succinate- activated GPR91 signaling pathway in alcohol-induced intestinal DC2 activation and migration. Aim 3 is to determine the mechanisms by which alcohol elicits an intestinal succinate signal.