Effects of <i>Lactobacillus helveticus</i> KLDS 1.1105 Postbiotics and Their Exopolysaccharides on Immune Function and Gut Microbiota in Immunosuppressed Mice

Postbiotics are inactive probiotics and their metabolites. In this study, a cyclophosphamide (CTX)-induced immunosuppression mouse model was established to systematically evaluate the effects of <i>Lactobacillus helveticus</i> KLDS 1.1105 postbiotics (LHPs) and their exopolysaccharides (EPS) on host immune function and gut microbiota composition. The results showed that high-dose postbiotics (1200 mg/kg) and EPS (200 mg/kg) significantly restored immune organ indexes, increased activities of splenic lymphocytes and natural killer (NK) cells, and improved intestinal barrier integrity. Both postbiotics and EPS restored the Th17/Treg balance and activated the TLR4/NF-κB signaling pathway. Additionally, treatment restored the balance of the gut microbiota, which promoted short-chain fatty acid (SCFAs) production. These findings indicated that LHPs and their EPS possess immunomodulatory and gut microbiota-regulating functions. Comparative analysis of the overall effects of postbiotics and those of EPS alone suggested that EPS is a key bioactive component responsible for the immunoregulatory activity of the postbiotic formulation.