Bacillus species, particularly Bacillus subtilis and related strains, are spore-forming probiotic bacteria that have been studied for their effects on the immune system, including the gut-associated lymphoid tissue (GALT) such as Peyer’s patches. Peyer’s patches are critical components of the intestinal immune system, sampling antigens from the gut and initiating immune responses.

Preclinical studies—mainly in rodent models—have shown that certain Bacillus strains can stimulate the proliferation and activation of immune cells within Peyer’s patches. For example, oral administration of Bacillus subtilis has been reported to increase the number of IgA-producing cells and to enhance both local (intestinal) and systemic immune responses. The mechanism involves the interaction of Bacillus spores with M cells in Peyer’s patches, leading to antigen presentation and modulation of immune cell activity.

Human clinical evidence remains limited, but some studies on multi-strain probiotics containing Bacillus species suggest possible immunomodulatory effects, though these are not always directly linked to Peyer’s patches. The scientific validation comes primarily from animal studies and mechanistic research, rather than large-scale human trials.

In summary, while there is a plausible scientific basis for Bacillus supporting the Peyer’s patches and mucosal immunity, current evidence is moderate and primarily preclinical. More rigorous human studies are needed to confirm these effects.