Abstract
Postbiotics defined as soluble factors (products or metabolic byproducts) that are released after bacterial lysis or secreted by live bacteria, have attracted considerable attention because of their long shelf life, safety, and beneficial effects. In this study, we investigated the immune-enhancing activities of squid jeotgal (a traditional Korean fermented seafood)-derived Bacillus velezensis Kh2-2 (Kh2-2) postbiotics in vitro, ex vivo, and in vivo. Cell lysates of four Bacillus species were prepared by sonication. In particular, Kh2-2 lysates induced NO production by upregulating iNOS expression in RAW264.7 cells compared with the lysates of B. subtilis Kh2-1, B. vallismortis Kh8-3, and B. amyloliquefaciens Kh3-1. Furthermore, Kh2-2 lysates stimulated immune activation of macrophages by upregulating the NF-κB and MAPK signaling pathways and promoting immune-related cytokine secretion. In the ex vivo study, Kh2-2 lysates stimulated proliferation and polarized Th1 response by inducing the production of IL-2 and IFN-γ and inhibiting IL-10 expression in splenocytes. The in vivo immune-enhancing effects of Kh2-2 lysates and Kh2-2 were further evaluated using a cyclophosphamide (CTX)-induced immunosuppression mouse model. The results showed that oral administration of Kh2-2 lysates improved CTX-induced immunosuppression by enhancing innate and adaptive immunity, stimulating immune-related cytokine secretion, and modulating gut microbiota dysbiosis in mice. Thus, we concluded that Kh2-2 lysates have potential as a functional material for postbiotics with immune-enhancing effects.