Effects of Lactobacillus helveticus 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 Lactobacillus helveticus 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.