Peyer’s patches are specialized immune structures found within the digestive system. They serve as a component of the gut-associated lymphoid tissue (GALT). These patches are organized centers for immune responses in the intestinal tract. Their presence underscores the intricate connection between the digestive system and the immune system’s function.
Anatomy and Location
Peyer’s patches are aggregates of lymphoid tissue, primarily situated in the ileum, which is the final section of the small intestine. They appear as oval, dome-like structures protruding into the intestinal lumen. These patches are not merely simple collections of cells but rather highly organized immune microenvironments.
They contain various immune cells. B cells and T cells are abundant, forming distinct follicular and interfollicular regions, respectively. Macrophages and dendritic cells are also present, positioned to interact with antigens. A unique feature on their surface are specialized M (microfold) cells, flattened epithelial cells lacking typical microvilli. These M cells directly sample antigens from the gut lumen.
Role in Gut Immunity
Peyer’s patches are immune surveillance stations within the intestinal wall. The specialized M cells on their surface transcytose antigens (e.g., bacteria, viruses, toxins, or harmless food particles) from the gut lumen across the epithelial barrier. These transported antigens are then delivered to the underlying lymphoid tissue, where they encounter antigen-presenting cells.
Dendritic cells and macrophages within the patch capture and process these antigens, presenting them to naïve B and T lymphocytes to initiate adaptive immune responses. Once activated, these lymphocytes proliferate and differentiate, migrating through the lymphatic system to other mucosal sites throughout the body. This migration leads to the production of secretory IgA antibodies in the lamina propria and other mucosal secretions, which neutralize pathogens and maintain immune balance in the gut lumen. Peyer’s patches thus play an important role in distinguishing between beneficial commensal bacteria and harmful pathogens, tailoring the immune response accordingly.
Involvement in Health and Disease
Peyer’s patches maintain gut homeostasis and protect against intestinal infections. Their proper functioning helps in developing tolerance to harmless food antigens and commensal bacteria, preventing inappropriate immune reactions. Alterations in the immune responses within these patches can contribute to the development of inflammatory bowel diseases, such as Crohn’s disease, where there is often a dysregulated immune response to gut contents.
Certain pathogens exploit Peyer’s patches as entry points into the host’s system. For instance, Salmonella typhi, which causes typhoid fever, utilizes M cells to breach the intestinal barrier and gain access to the underlying lymphatic system, leading to systemic infection. Similarly, prions, which cause Creutzfeldt-Jakob disease, can also enter the body through Peyer’s patches. Understanding these entry mechanisms informs the development of oral vaccines, which deliver antigens directly to Peyer’s patches to elicit mucosal and systemic immune responses.