Gut microbial metabolites in inflammatory bowel disease: immunological mechanisms regulating Treg/Th17 balance and therapeutic potential.

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder resulting from a combination of genetic susceptibility, environmental factors, and an abnormal immune response of the intestinal immune system to commensal microorganisms. The gut microbiota and its metabolites play a pivotal role in maintaining intestinal immune homeostasis. Recent advances indicate that dysbiosis of the microbiota is accompanied by alterations in its metabolic functions. Abnormal levels of key metabolites, particularly short-chain fatty acids (SCFAs), tryptophan derivatives, and secondary bile acids, are closely associated with the pathogenesis of IBD. These metabolites act as G protein-coupled receptor ligands, nuclear receptor ligands, or epigenetic modifiers, deeply involved in the differentiation, function, and dynamic balance between regulatory T cells (Tregs) and T helper 17 cells (Th17). Disruption of the Treg/Th17 balance is a central driver of intestinal immune inflammation in IBD. This review systematically explores the molecular networks through which major microbial metabolites regulate the differentiation and function of Treg and Th17 cells, including their profound effects on cellular metabolic reprogramming, the epigenetic landscape, and the local immune microenvironment. Furthermore, it analyzes how the disturbance of the microbial metabolome in the pathological state of IBD leads to the attenuation of beneficial immunoregulatory signals and the generation of potential pro-inflammatory signals, thereby contributing to a vicious cycle of immune tolerance deficiency and chronic inflammation. Based on these mechanisms, this article evaluates therapeutic strategies targeting the microbiota-metabolism-immune axis, such as dietary interventions, probiotics/prebiotics, postbiotics, engineered bacterial therapies, fecal microbiota transplantation, and small-molecule receptor modulators, discussing their current status and challenges. Finally, the limitations of current research are outlined, and future directions are proposed, including the use of integrated multi-omics analyses, spatial biology technologies, and organoid models to advance the development of personalized precision medicine.