[1] They are an important part of gut associated lymphoid tissue usually found in humans in the lowest portion of the small intestine, mainly in the distal jejunum and the ileum, but also could be detected in the duodenum.

It was not until 1850 that the Swiss physician Rudolph Oskar Ziegler (1828–1881) suggested, after careful microscopic examination, that Peyer's patches were actually lymph glands.

[11] Finally, follicle-associated epithelium is less permeable for ions and macromolecules, basically due to higher expression of tight junction proteins.

Pathogenic microorganisms and other antigens entering the intestinal tract encounter macrophages, dendritic cells, B-lymphocytes, and T-lymphocytes found in Peyer's patches and other sites of gut-associated lymphoid tissue (GALT).

Peyer's patches have adaptive immune capabilities through inducing selective apoptosis of B cells due CD122-targeted interleukin-2 (IL-2) signaling.

[14][15] At the same time the paracellular pathway of follicle-associated epithelium is closed tightly to prevent penetration of antigens and continuous contact with immune cells.

Activated lymphocytes pass into the blood stream via the thoracic duct and travel to the gut where they carry out their final effector functions.