Severe alcoholic hepatitis (SAH) is the most severe form of the alcoholic liver diseases (ALD) caused by acute and chronic alcohol abuse. ALD is associated with increased susceptibility to pneumonia, viral infections (e.g., HIV and HCV), and infection with Mycobacterium tuberculosis. Current therapies are largely ineffective – 40% of patients do not respond to corticosteroid therapy with high resultant short term mortality. Therefore, the development of novel targeted therapies will be dependent on delineating the molecular mechanisms of SAH. Studies in the past thirty years in both humans and animal models have revealed that acute and chronic alcohol consumption cause leaky gut via inflammation, gut microbiome dysbiosis, tight junction disruption, decreased mucus and antimicrobial peptides. The advance of bacterial 16S rRNA revealed that in alcoholics with dysbiosis Bacteroidacea have been found to be decreased while Proteobacteria and Fusobacteria were increased. It is now clear that a gut-liver axis is causatively linked to progression of alcohol-induced liver disease. Our long-term goal is to identify novel therapeutic targets and develop novel therapy for intervention and prevention of SAH. During the current funding period, the Zhu and Sun groups discovered a massive deposition of antibodies in SAH livers, and that these antibodies exhibited hepatocyte killing efficacy, while the corresponding serum antibodies did not. We further showed that antibodies from SAH livers cross-react with both human and E. coli proteins. Finally, large amounts of B and plasma cells are found infiltrating SAH livers. Based on these results and the literature, we hypothesize that B and plasma cells infiltrated in SAH livers produce anti-gut bacteria antibodies that can cross-react with human proteins and cause liver damage. Identification of the origin of gut bacteria that elicit the cross-reacting antibodies in SAH is a crucial step towards understanding the etiology of SAH. Equally important is to isolate the B and plasma cells infiltrated in SAH livers and characterize their roles in liver damage. The goal of this proposal is to determine the origins of these cross-reacting antibodies in SAH and characterize their function and contribution to liver damage. To test our hypothesis, we propose three Specific Aims: 1) Identify gut bacteria that elicit cross-reactive antibodies specific in patients with SAH; 2) Determine cross-reactive antibody signatures in patients with SAH; and 3) Characterize B/plasma cells infiltrated in SAH livers that produce cross-reactive antibodies. The success of this project will allow us to further elucidate the molecular mechanism of the gut-liver axis in liver injury.