Lactococcus lactis (L. lactis) is a lactic acid bacterium commonly used in dairy fermentation. Its relevance to the Peyer’s patches—the immune tissue in the small intestine—has been explored in several scientific studies, particularly in the context of mucosal immunity. Peyer’s patches are crucial for initiating immune responses to antigens present in the gut. Some animal studies have demonstrated that oral administration of L. lactis can stimulate immune responses in the gut, including increased production of secretory IgA and enhanced activity of immune cells within Peyer’s patches. For example, recombinant L. lactis engineered to express specific antigens has been used as a delivery vehicle in vaccine research, leading to localized immune activation in Peyer’s patches in mice (Steidler et al., 2014). However, evidence in humans is limited, and most data come from preclinical models rather than clinical trials. The use of L. lactis in dietary supplements or functional foods for the purpose of modulating Peyer’s patches or mucosal immunity is therefore scientifically plausible, but not robustly validated in humans. There is little traditional use of L. lactis specifically for immune health, as its primary traditional role has been as a starter culture in food. In summary, there is some scientific basis, largely from animal studies, but not strong clinical evidence for its use in supporting Peyer’s patches in humans.