Lactobacillus johnsonii is a probiotic bacterium that has been investigated for its effects on the gut-associated lymphoid tissue (GALT), including Peyer’s patches. Peyer’s patches are key sites for immune surveillance within the small intestine, and play a role in the initiation of immune responses to antigens present in the gut lumen. Several animal studies have suggested that L. johnsonii can interact with the mucosal immune system, modulating immune cell populations and cytokine production. For example, research in mice has shown that administration of L. johnsonii can increase secretory IgA levels and influence the number and activity of dendritic cells and T lymphocytes in Peyer’s patches (Bunker et al., 2017). Additionally, some studies indicate that L. johnsonii may enhance intestinal barrier function and reduce inflammation, possibly through its effects on Peyer’s patches-mediated immune responses.

However, direct human evidence is limited. Most data come from animal models, with relatively few clinical trials examining specific effects of L. johnsonii on human Peyer’s patches or related immune outcomes. Thus, while there is scientific interest and some preclinical support for its role in modulating the immune system via Peyer’s patches, the overall level of evidence remains modest.