Effect of Bacillus Subtilis BN Strain on M1 Macrophage Antiviral Response

M1 macrophages play an important role in pathogenic microorganism infection. Natto, a traditional fermented food from Japan, has long been thought to prevent infection by pathogenic microorganisms. Bacillus subtilis BN strain, which has been isolated from natto, is used in animal feed, health food products, and pharmaceuticals as a probiotic capable of regulating intestinal flora and immunomodulates. The purpose of this study is to investigate the effects of B. subtilis BN strain on the antiviral immune function of human M1 macrophages. The M1 macrophages studied here were derived from a human monocytic cell line (THP-1). Overall, we found that B. subtilis BN strain enhanced gene expressions of antiviral and anti-inflammatory cytokines in M1 macrophages and M1 macrophages stimulated with resiquimod in a cell culture model that mimics single-stranded RNA virus infection. In M1 macrophages, B. subtilis BN strain was also found to promote the gene expression and phosphorylation of key molecules in the toll-like receptor signaling pathways. Furthermore, the BN strain induced the expression of some cytokine mRNA was reduced by the knockdown of NFκB in M1 macrophages. Taken together, these results suggest that toll-like receptor signal pathways are involved in the regulation of antiviral and anti-inflammatory cytokine gene expressions induced by the BN strain in M1 macrophages.