Probiotics as modulators of intestinal barrier integrity and immune homeostasis: a comprehensive review.

The gastrointestinal tract is the largest interface between the human body and external agents and hosts a vast community of microorganisms that confer diverse health benefits. Among these microorganisms are probiotics, which, when consumed in adequate amounts, provide benefits beyond basic nutrition. Through membrane-associated glycoproteins and the secretion of metabolites, probiotics can: (1) enhance intestinal epithelial barrier integrity by reinforcing tight junction expression; (2) stimulate mucin production, strengthening the mucus layer and promoting mucosal adhesion; (3) prevent pathogen and toxin adhesion to the intestinal epithelium; (4) inhibit pathogenic microorganisms by competing directly for environmental nutrients and producing antimicrobial metabolites (e.g., bacteriocins and organic acids); and (5) stimulate the intestinal immune system through membrane components that activate immune cells such as macrophages, neutrophils, and epithelial cells, thereby eliciting an effective immune response. This review describes the intestinal barrier and its function, the role of probiotics, and the most extensively studied mechanisms by which they benefit the intestinal immune system. © 2025 Society of Chemical Industry.