Lactobacillus brevis is a probiotic bacterium that has been studied for its effects on the gut-associated lymphoid tissue (GALT), including the Peyer’s patches, which are important components of the intestinal immune system. Scientific studies, primarily in animal models and a limited number of human cell culture experiments, suggest that L. brevis may influence immune responses by interacting with the mucosal immune system. For example, research indicates that certain strains of L. brevis can stimulate the production of immunoglobulin A (IgA) and modulate cytokine production in the intestinal mucosa, processes in which Peyer’s patches play a central role (Kato et al., 2009).

However, direct evidence in humans is limited. Most findings come from in vitro studies or animal experiments where L. brevis is shown to enhance or modulate immune responses associated with Peyer’s patches. These findings provide some scientific rationale for the use of L. brevis in supporting the gut immune system, but well-controlled human clinical studies specifically linking L. brevis supplementation to improved function of Peyer’s patches are lacking. Therefore, while there is a scientific basis, the current evidence is preliminary and not robust, resulting in a moderate rating.