Peyer-Plaques

Johann Conrad Peyer (1653-1712), Swiss anatomist

Peyer's plaques are 10 to 50, organoid aggregated, lymphoid follicles found throughout the small intestine, most commonly in the ileum and appendix. Peyer's plaques are visible from the outside through the intestinal wall as structures about 1 cm in size.

Peyer's plaques belong to the lymphatic system, are part of the so-called MALT system (mucosa-associated lymphoid tissue) or more specifically of the GALT (gut-associated lymphoid tissue) and, as an accumulation of cells of the special, acquired immune system, play an important role in the defense against infection in the intestine and in the initiation of immunological reactions.

Tissue structure/histology: Peyer's plaques are usually located opposite the mesentery in the tela submucosa and the lamina propria of the mucosa (tunica mucosa). The individual follicular aggregates are covered by a zone, the subepithelial dome, in which, depending on the condition, mainly dendritic cells (DCs) as well as B lymphocytes are found. This cell layer interacts directly with the overlying follicle-associated epithelium.

The "follicle-associated surface epithelium" is also a specialized cell layer. It differs in cell composition and its properties from the epithelium of the rest of the intestinal mucosa. A special feature of the follicle-associated epithelium are the so-called M-cells (microfold cells). These M cells are part of the MALT system. They are comparable to the Langerhans cells of the epidermis. Among other things, M cells take up antigens endocytotically and present them to the basally stored lymphocytes and macrophages. Furthermore, they internalize bacteria and transmit them transcytotically to the basally adjacent lymphatic system. Here, depending on the antigen, either an adaptive immune response is triggered or an immunological tolerance is developed, as exists and is necessary, for example, in relation to the commensal intestinal flora.