The gut-liver-immune axis: structural basis, cellular architecture, molecular mediators, and disease-specific manifestations.

The gut and liver form an anatomical and functional unit linked by the portal circulation, the biliary tract, lymphatic drainage, and neuroimmune pathways. In recent years, the classical gut-liver axis has expanded from a predominantly microbial and metabolic concept into a broader framework in which immune cells are viewed as central integrators of inter-organ signaling. In health, balanced microbial sensing, intact mucosal and vascular barriers, regulated bile acid signaling, and specialized tissue-resident immune programs preserve tolerance at both intestinal and hepatic interfaces. In disease, dysbiosis, barrier failure, altered bile acid pools, endogenous hepatotoxic metabolites, and aberrant immune-cell trafficking remodel the hepatic immune niche and drive steatohepatitis, alcohol-associated liver injury, cholangiopathy, cirrhosis, acute decompensation, and hepatocellular carcinoma. This review reframes the gut-liver axis as a gut-liver-immune axis and synthesizes current evidence on its structural basis, cellular architecture, molecular mediators, and disease-specific manifestations. We discuss the roles of macrophages, dendritic cells, neutrophils, innate-like T cells, natural killer cells, and adaptive T-cell subsets in translating gut-derived signals into hepatic inflammation, tissue repair, fibrosis, or tumor surveillance. We also highlight the bidirectional role of the liver in shaping intestinal immunity, particularly through bile acids and hepatobiliary-derived mediators. Finally, we examine current therapeutic strategies targeting the microbiota, mucosal barrier, bile acid signaling, and immune-cell trafficking, and we outline major conceptual and translational gaps that should guide the next generation of mechanistic and clinical studies.