Probiotics are live microorganisms that confer health benefits when consumed in adequate amounts. The most commonly used probiotic strains include lactic acid bacteria (LAB) and bifidobacteria. These bacteria have shown significant potential as therapeutic agents for various diseases, but the mechanisms behind their effects are not fully understood. Key mechanisms include modifying the gut microbiota, competitive adhesion to the mucosa and epithelium, strengthening the gut epithelial barrier, and modulating the immune system to benefit the host. Probiotics communicate with the host through pattern recognition receptors like toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-containing proteins (NODs), which modulate signaling pathways such as NF-κB and MAPK to enhance or suppress immune responses. Probiotics enhance the intestinal epithelial barrier by increasing tight junction proteins and modulating gene expression. They also promote mucin secretion, which helps in pathogen exclusion. Adhesion to the intestinal mucosa is crucial for colonization and immune modulation. Probiotics can inhibit pathogen adhesion by competing for receptor sites and producing antimicrobial substances. They also produce antimicrobial peptides and bacteriocins, which inhibit pathogenic bacteria. Probiotics can modulate the immune system by inducing the production of defensins and other antimicrobial peptides, which help in maintaining gut barrier function. Probiotics interact with the immune system through TLRs and NLRs, which are involved in recognizing pathogen-associated molecular patterns (PAMPs). TLRs, such as TLR2 and TLR4, play a role in immune responses, while NLRs are involved in inflammasome formation and activation. Probiotics can also influence the expression of TLRs and NLRs, which affects immune responses. The mechanisms of probiotic action are complex and involve interactions with the host's immune system, gut microbiota, and epithelial cells. Understanding these mechanisms is crucial for selecting appropriate probiotic strains for specific applications and for developing new strategies for the prevention and treatment of gastrointestinal and autoimmune diseases.Probiotics are live microorganisms that confer health benefits when consumed in adequate amounts. The most commonly used probiotic strains include lactic acid bacteria (LAB) and bifidobacteria. These bacteria have shown significant potential as therapeutic agents for various diseases, but the mechanisms behind their effects are not fully understood. Key mechanisms include modifying the gut microbiota, competitive adhesion to the mucosa and epithelium, strengthening the gut epithelial barrier, and modulating the immune system to benefit the host. Probiotics communicate with the host through pattern recognition receptors like toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-containing proteins (NODs), which modulate signaling pathways such as NF-κB and MAPK to enhance or suppress immune responses. Probiotics enhance the intestinal epithelial barrier by increasing tight junction proteins and modulating gene expression. They also promote mucin secretion, which helps in pathogen exclusion. Adhesion to the intestinal mucosa is crucial for colonization and immune modulation. Probiotics can inhibit pathogen adhesion by competing for receptor sites and producing antimicrobial substances. They also produce antimicrobial peptides and bacteriocins, which inhibit pathogenic bacteria. Probiotics can modulate the immune system by inducing the production of defensins and other antimicrobial peptides, which help in maintaining gut barrier function. Probiotics interact with the immune system through TLRs and NLRs, which are involved in recognizing pathogen-associated molecular patterns (PAMPs). TLRs, such as TLR2 and TLR4, play a role in immune responses, while NLRs are involved in inflammasome formation and activation. Probiotics can also influence the expression of TLRs and NLRs, which affects immune responses. The mechanisms of probiotic action are complex and involve interactions with the host's immune system, gut microbiota, and epithelial cells. Understanding these mechanisms is crucial for selecting appropriate probiotic strains for specific applications and for developing new strategies for the prevention and treatment of gastrointestinal and autoimmune diseases.