Lactobacillus bulgaricus is a probiotic bacterium commonly used in the fermentation of yogurt and other dairy products. Its potential role in supporting the Peyer’s patches—specialized lymphoid follicles in the small intestine that play a key role in gut-associated immune responses—has been studied to a limited extent. Scientific evidence suggests that certain probiotics, including L. bulgaricus, can influence gut immunity, including modulation of immune cells and cytokine production within the intestinal mucosa. Some animal studies and in vitro experiments have shown that L. bulgaricus may interact with intestinal epithelial cells and immune cells, leading to enhanced production of IgA and stimulation of mucosal immunity, which could involve activation of Peyer’s patch lymphocytes. However, direct, high-quality human studies specifically linking L. bulgaricus supplementation to improved function or health of Peyer’s patches are scarce. The broader category of probiotics has more robust evidence for influencing gut-associated lymphoid tissue, but the evidence is less clear when focusing specifically on L. bulgaricus and its action on Peyer’s patches. Therefore, while there is some mechanistic and preclinical support, clinical evidence in humans remains limited, justifying a low evidence rating.