Lactobacillus gasseri is a probiotic bacterium that has been studied for its effects on the immune system, including its interaction with Peyer's patches—specialized lymphoid tissues in the small intestine that play a critical role in mucosal immunity. Scientific research, primarily in animal models and in vitro studies, has shown that certain strains of L. gasseri can modulate immune responses by interacting with gut-associated lymphoid tissue (GALT), which includes Peyer’s patches. Some studies suggest that L. gasseri may enhance the production of immunoglobulin A (IgA), influence the balance of T-helper cells, and support the maturation of immune cells in the gut.

However, direct evidence in humans for L. gasseri specifically supporting Peyer's patches is limited. Most of the clinical evidence focuses on general gut health, modulation of inflammation, and support of the overall immune system rather than explicit, targeted effects on Peyer’s patches. Thus, while the biological plausibility exists and some preclinical data support an immune-modulating role, the evidence is not robust or specific enough for a higher rating.

In summary, there is some scientific validation—mainly from preclinical research—that L. gasseri can influence gut immune tissues like Peyer’s patches, but human data are lacking and the evidence is still emerging.