Mast Cells at the Crossroad of Gut-Derived Signals Through Aryl Hydrocarbon Receptor Activation: A Microbial–Immune Dialogue in Liver Inflammation with Therapeutic Perspectives

Highlights: What are the main findings? Aryl hydrocarbon receptor (AhR) signaling may act as a mechanistic bridge linking gut-derived tryptophan metabolites to mast cell (MC) activation, potentially shaping hepatic inflammation and fibrogenesis. MCs may represent an underexplored node in the gut–liver axis, where the existing evidence on the roles of AhR in liver disease and MCs in liver pathology has rarely been integrated into a unified framework. What are the implications of the main findings? Modulating microbial or dietary sources of endogenous AhR ligands, alongside selective AhR-targeting strategies, could help recalibrate MC-driven hepatic inflammation. Pending the validation of MC-specific AhR programs and disease-context outputs, AhR modulation may evolve into predictive or precision approaches for autoimmune and cholestatic liver diseases. Mast cells (MCs) are multifunctional innate immune cells that regulate inflammation, tissue repair, and immune responses, and they are increasingly recognized as contributors to chronic liver disease. In parallel, the aryl hydrocarbon receptor (AhR) has emerged as a key environmental sensor activated by gut-derived tryptophan metabolites such as kynurenine and microbial indoles. The current literature separately describes the role of AhR in MC signaling, as well as the contributions of MCs to liver pathology and the disrupted gut–liver axis, which drives immune dysfunction in chronic liver disease. However, these aspects have been rarely considered together. This review aims to bridge these fragmented areas, providing an integrated framework where AhR-driven MC responses are examined within the gut–liver axis along with their impacts on liver inflammation and fibrosis. We discuss how this microbial–immune dialogue shapes autoimmune and cholestatic liver diseases, including autoimmune hepatitis, primary sclerosing cholangitis, and primary biliary cholangitis. Finally, we highlight translational perspectives, from microbiota modulation to AhR-targeting approaches, as potential strategies to control MC-driven hepatic inflammation. By integrating these currently separate concepts, this review offers a novel perspective on the role of MCs as important mediators at the interface of gut-derived signals and liver pathology via AhR signaling, while highlighting innovative therapeutic avenues through the modulation of the microbiota, targeting of AhR, and regulation of MC responses.