Gut barrier integrity and systemic immunity: Mechanisms linking microbiota, barrier dysfunction, and extra-intestinal disease

The intestinal barrier represents a dynamic interface integrating microbial, epithelial, and immune components to maintain host microbiota symbiosis and systemic immune homeostasis. Beyond its classical protective role, the gut barrier has emerged as a key regulator of extra-intestinal immunity. Structural elements such as epithelial tight junctions and mucus layers, together with biological defenses including antimicrobial peptides, secretory immunoglobulin A, and resident immune cells, coordinate to limit microbial translocation while enabling beneficial microbial signaling. Perturbations in this barrier often driven by microbial dysbiosis, environmental factors, or chronic inflammation can permit the systemic dissemination of microbial products and metabolites, thereby reshaping immune signaling networks. Increasing evidence links such barrier dysfunction to the pathogenesis of diverse extra-intestinal conditions, including autoimmune and inflammatory diseases, infections, and cancer. This review synthesizes emerging mechanistic insights into microbiota barrier immune interactions and highlights therapeutic strategies aimed at restoring gut barrier integrity to recalibrate systemic immune responses.