Gut Microbial Secondary Metabolites of Bile Acids and Amino Acids Regulate Th1/Th2 Immune Modulation in Unexplained Infertility: A Multiomics and Cohort Analysis Approach

Unexplained Infertility (UI) is a complex condition of elusive etiology, where the interplay between immune dysregulation and metabolic disturbances remains poorly understood. We hypothesized that gut microbiota-derived metabolites act as central modulators of the systemic immune and metabolic balance in UI patients. We employed an integrated multiomics approach, combining metabolomics, gut microbiome analysis, and immune profiling, in a cross sectional discovery cohort (47 UI patients and 53 healthy controls), and validated key findings in an independent cohort (37 UI patients and 39 healthy controls). Our findings demonstrated that UI patients exhibited a proinflammatory Th1-dominant immune profile, marked by elevated proinflammatory cytokines and reduced anti-inflammatory IL-10. This immune imbalance was accompanied by a deficiency in protective gut-derived secondary metabolites, notably secondary bile acids and phenylpropanoic acid. Furthermore, gut microbiota analysis revealed significant dysbiosis (increased pathogenic taxa and decreased beneficial microbes) and a functional deficiency in the aromatic amino acid metabolism gene cluster, explaining the observed metabolite scarcity. Mechanistically, in vitro assays and network pharmacology indicated that these metabolites directly modulate the Th1/Th2 immune balance by regulating a core host network centered on TNF, PPARG, and PTGS2. In summary, our data reveal the role of a novel gut microbiota-metabolite-immune axis in UI pathophysiology, where a deficiency in protective gut-derived secondary metabolites contributes directly to systemic immune dysregulation and a proinflammatory state. These metabolites serve as potential candidates for future evaluation and represent promising therapeutic targets for interventions to restore immune homeostasis in UI patients.