Peyer’s patches are specialized immune structures in the digestive system. They act as surveillance sites within the gut, monitoring the intestinal environment and contributing to defense against foreign invaders.
What Peyer’s Patches Are
Peyer’s patches are organized clusters of lymphatic tissue, also known as aggregated lymphoid nodules. They are primarily found in the lowest portion of the small intestine, specifically the ileum, though they can also appear in the jejunum and duodenum. These patches are visible to the naked eye as elongated thickenings in the intestinal lining, typically numbering 30 to 40 in humans, with the highest concentration in young adults.
These structures are a significant part of the gut-associated lymphoid tissue (GALT), which represents a substantial portion of the body’s immune cells. Unlike encapsulated lymph nodes, Peyer’s patches are not surrounded by a connective tissue capsule. They are composed of various immune cells, including B lymphocytes, T lymphocytes, macrophages, dendritic cells, and plasma cells. The B lymphocytes are mainly located in the central follicles, while T lymphocytes are found in the surrounding areas.
A specialized layer of cells, known as the follicle-associated epithelium (FAE), covers Peyer’s patches. This FAE contains unique cells called Microfold cells, or M cells. M cells have a specific structure and function involving direct interaction with the gut lumen contents.
How Peyer’s Patches Function
Peyer’s patches function as sites for immune surveillance within the intestinal lumen. Their primary function involves detecting and responding to potentially harmful substances. Specialized M cells on their surface actively sample antigens from the gut.
M cells take up foreign particles, such as bacteria or viruses, through processes like endocytosis, phagocytosis, or transcytosis. Once sampled, these antigens are transported across the M cell and released into a unique pocket-like structure on their basolateral side. This strategic location allows the antigens to be presented to a variety of underlying immune cells, including dendritic cells, macrophages, and lymphocytes.
Dendritic cells then present these antigens to T and B lymphocytes, initiating immune responses. Activated lymphocytes can then migrate to regional lymph nodes, where the immune response is amplified. This activation leads to the production of antibodies, such as immunoglobulin A (IgA), and the development of immune cells that neutralize and clear pathogens.
Peyer’s Patches and Gut Health
Peyer’s patches contribute to maintaining a balanced gut environment and overall systemic immunity. By monitoring microbial populations within the intestines, they prevent harmful bacteria overgrowth and pathogen entry. This surveillance safeguards gastrointestinal tract integrity.
These lymphoid structures also play a role in distinguishing between potential threats and beneficial substances. They contribute to oral immune tolerance, a process where the immune system learns to not overreact to harmless antigens from food or the commensal (beneficial) gut microbiota. This balanced response prevents unnecessary inflammation and promotes a healthy gut ecosystem.
Immune responses initiated within Peyer’s patches are part of adaptive immunity, enabling defense against specific invaders. The production of IgA antibodies, facilitated by these patches, forms a protective layer in the gut lumen, which prevents pathogens from adhering to intestinal surfaces. Their function supports the digestive system’s immune response.