Lactococcus casei is a probiotic bacterium that has been studied for its effects on the immune system, including potential actions within the gut-associated lymphoid tissue (GALT) such as Peyer’s patches. Peyer’s patches are important sites in the small intestine where immune responses to gut antigens are initiated. Several animal studies and some in vitro experiments have demonstrated that administration of L. casei can increase the number or activity of immune cells in Peyer’s patches, including IgA-producing cells and dendritic cells. These effects are thought to be mediated by the interaction of probiotic bacteria with the intestinal mucosa, leading to modulation of local and systemic immune responses.

For example, studies in mice have shown that oral administration of L. casei can enhance mucosal immune responses and stimulate production of secretory IgA, which is critical for intestinal immunity. Some research suggests that L. casei can influence cytokine production and may help maintain intestinal barrier function. However, most of the evidence comes from preclinical models, and direct human evidence regarding specific effects on Peyer’s patches is limited. There is modest but growing support for the idea that L. casei can support gut immune function via mechanisms involving Peyer’s patches, but more robust clinical studies are needed to confirm these effects in humans.