Lactobacillus casei is a probiotic bacterium that has been studied for its effects on the gut-associated lymphoid tissue (GALT), which includes Peyer’s patches—specialized immune structures in the small intestine. Scientific studies, mostly in animal models and some in vitro human cell models, suggest that L. casei can modulate immune responses by interacting with the cells in Peyer’s patches. Specifically, research indicates that orally administered L. casei can enhance the production of immunoglobulin A (IgA) and stimulate the activity of dendritic cells and T cells within Peyer’s patches, thereby supporting mucosal immunity (Matsuzaki et al., 2007; Matsuzaki et al., 2004).

However, most of the evidence comes from animal studies (especially mice) and in vitro experiments, with fewer robust clinical trials directly demonstrating these effects in humans. Still, the observed immunomodulatory properties in preclinical research provide a plausible scientific rationale for the use of L. casei in supporting the health and function of Peyer’s patches and, by extension, the mucosal immune system. While the evidence is promising, more high-quality human studies are needed to confirm these benefits and determine optimal dosing and strains.