Bacillus subtilis natto is a probiotic bacterium commonly found in the traditional Japanese fermented food "natto." There is emerging scientific evidence that B. subtilis natto can positively influence the immune system, particularly through interactions with Peyer's patches, which are lymphoid tissues in the small intestine that play a critical role in mucosal immunity. Animal and in vitro studies have shown that B. subtilis spores can survive gastrointestinal transit, reach the gut-associated lymphoid tissue (GALT), and stimulate immune responses. Specifically, research indicates that exposure to B. subtilis can enhance the production of immunoglobulin A (IgA) and promote the maturation of dendritic cells in Peyer's patches, thereby strengthening mucosal immunity (Hong et al., 2018; Tam et al., 2011).

While these findings are promising, most of the direct evidence comes from animal models or laboratory experiments. Human clinical data are more limited but suggest that fermented foods containing B. subtilis natto may support gut health and immunity. Therefore, the use of B. subtilis natto to support the Peyer's patches and mucosal immunity is based on a foundation of preliminary scientific evidence, justifying a moderate evidence rating.