The gut microbiota-bile acid axis: a crucial regulator of immune function and metabolic health.

The gut microbiota and bile acid metabolism are intricately linked, playing a crucial role in immune regulation, metabolic processes, and overall health. The gut microbiome, consisting of diverse bacterial genera such as Bacteroides, Clostridium, Lactobacillus, Bifidobacterium, and Eubacterium, facilitates the conversion of primary bile acids into secondary bile acids through enzymatic modifications. Bile acids, synthesized in the liver and modified by gut microbiota, act as signaling molecules that regulate immune responses via bile acid receptors, including the farnesoid X receptor (FXR), G protein-coupled bile acid receptor 1 (GPBAR1), pregnane X receptor (PXR), vitamin D receptor (VDR), and sphingosine-1-phosphate receptor 2 (S1PR2). Dysbiosis-an imbalance in gut microbial composition-disrupts bile acid metabolism, leading to impaired activation of bile acid receptors and contributing to various diseases. These include inflammatory bowel disease, metabolic disorders such as obesity and type 2 diabetes, autoimmune diseases like multiple sclerosis, and liver conditions such as cholestasis and non-alcoholic fatty liver disease. Dysfunctional bile acid receptor signaling further promotes chronic inflammation, metabolic dysregulation, and disturbances in gut-liver-immune homeostasis. Emerging therapeutic strategies targeting bile acid receptors, restoring microbiota balance, and implementing dietary interventions offer promising avenues for disease prevention and management. This review explores the pivotal role of gut microbiota in modulating immune responses through bile acid receptors and highlights their therapeutic potential in improving treatment outcomes.