Peyer's patches or aggregated lymphoid nodules are organized lymphoid follicles, named after the 17th-century Swiss anatomist Johann Conrad Peyer. * Reprinted as: * Peyer referred to Peyer's patches as ''plexus'' or ''agmina glandularum'' (clusters of glands). From (Peyer, 1681), p. 7: ''"Tenui a perfectiorum animalium Intestina accuratius perlustranti, crebra hinc inde, variis intervallis, corpusculorum glandulosorum Agmina sive Plexus se produnt, diversae Magnitudinis atque Figurae."'' (I knew from careful study of more advanced animals, the intestines bear — often here and there, at various intervals — clusters of glandular small bodies or "plexuses" of diverse size and shape.) From p. 15: ''"(has Plexus seu agmina Glandularum voco)"'' (I call them "plexuses" or clusters of glands) He described their appearance. From p. 8: ''"Horum vero Plexuum facies modo in orbem concinnata; modo in Ovi aut Olivae oblongam, aliamve angulosam ac magis anomalam disposita figuram cernitur."'' (But the configurations of these "plexuses" are arranged at one time in a circle; at another time, it is seen in an egg

hape High-altitude pulmonary edema (HAPE) is a life-threatening form of non-cardiogenic pulmonary edema that occurs in otherwise healthy people at altitudes typically above . HAPE is a severe presentation of altitude sickness. Cases have also been r ...

or an oblong olive

or other faceted and more irregularly arranged shape.) Drawings of Peyer's patches appear after pages 22 and 24. They are an important part of gut associated lymphoid tissue usually found in humans in the lowest portion of the

small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...

, mainly in the distal

jejunum The jejunum is the second part of the small intestine in humans and most higher vertebrates, including mammals, reptiles, and birds. Its lining is specialized for the absorption by enterocytes of small nutrient molecules which have been pr ...

and the

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may ...

, but also could be detected in the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

History

Peyer's patches had been observed and described by several anatomists during the 17th century, but in 1677 Swiss anatomist Johann Conrad Peyer (1653–1712) described the patches so clearly that they were eventually named after him. However, Peyer believed they were glands that secreted something into the small intestine to facilitate digestion. 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.

Structure

Peyer's patches are observable as elongated thickenings of the intestinal mucosa measuring a few centimeters in length. About 100 are found in humans. Microscopically, Peyer's patches appear as oval or round lymphoid follicles (similar to

lymph nodes A lymph node, or lymph gland, is a kidney-shaped Organ (anatomy), organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphoc ...

) located in the

mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It ...

layer of the

and extend into the

submucosa The submucosa (or tela submucosa) is a thin layer of tissue in various organs of the gastrointestinal, respiratory, and genitourinary tracts. It is the layer of dense irregular connective tissue that supports the mucosa (mucous membrane) an ...

layer. The number of Peyer's patches peaks at age 15–25 and then declines during adulthood. In the distal ileum, they are numerous and they form a lymphoid ring. At least 46% of Peyer's patches are concentrated in the distal 25 cm of ileum in humans. It is important to note that there are large variations in size, shape, and distribution of Peyer's patches from one individual to another one. In adults, B lymphocytes are seen to dominate the follicles' germinal centers. T lymphocytes are found in the zones between follicles. Among the mononuclear cells, CD4+/CD25+ (10%) cells and CD8+/CD25+ (5%) cells are more abundant in Peyer's patches than in the peripheral blood. Peyer's patches are characterized by the follicle-associated epithelium (FAE), which covers all lymphoid follicles. FAE differs from typical small

intestinal villus Intestinal villi (: villus) are small, finger-like projections that extend into the lumen of the small intestine. Each villus is approximately 0.5–1.6 mm in length (in humans), and has many microvilli projecting from the enterocytes of i ...

epithelium: it has fewer goblet cells therefore mucus layer is thinner, and it is also characterized by the presence of specialized M cells or microfold cells, which provide uptake and transport of antigens from lumen. Moreover,

basal lamina The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often incorrectly referred to as the basement membrane, though it does constitute a portion of the basement membrane. The b ...

of follicle-associated epithelium is more porous compared to intestinal villus. Finally, follicle-associated epithelium is less permeable for ions and macromolecules, basically due to higher expression of

tight junction Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein Cell junction, junctional complexes between epithelial cells, sealing and preventing leakage of solutes and water. Th ...

proteins.

Function

Because the lumen of the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

is exposed to the external environment, much of it is populated with potentially

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

microorganism A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...

s. Peyer's patches thus establish their importance in the immune surveillance of the intestinal lumen and in facilitating production of the immune response within the

. Pathogenic microorganisms and other

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

s entering the intestinal tract encounter

macrophages Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

dendritic cell A dendritic cell (DC) is an antigen-presenting cell (also known as an ''accessory cell'') of the mammalian immune system. A DC's main function is to process antigen material and present it on the cell surface to the T cells of the immune system ...

s, B-lymphocytes, and T-lymphocytes found in Peyer's patches and other sites of gut-associated lymphoid tissue (GALT). Peyer's patches thus act for the gastrointestinal system much as the tonsils act for the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

, trapping foreign particles, surveilling them, and destroying them. Peyer's patches have adaptive immune capabilities through inducing selective apoptosis of B cells due CD122-targeted interleukin-2 (IL-2) signaling. Additionally, the B cell population can be restored. Peyer's patches are covered by a special follicle-associated epithelium that contains specialized cells called microfold cells ( M cells) which sample antigen directly from the lumen and deliver it to

antigen-presenting cells An antigen-presenting cell (APC) or accessory cell is a cell that displays an antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation. T cells may recognize these complexes u ...

(located in a unique pocket-like structure on their basolateral side). Dendritic cells and macrophages can also directly sample the lumen by extending dendrites through transcellular M cell-specific pores. 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.

T cells T cells (also known as T lymphocytes) are an important part of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their ce ...

, B-cells and memory cells are stimulated upon encountering

in Peyer's patches. These cells then pass to the mesenteric lymph nodes where the immune response is amplified. Activated lymphocytes pass into the blood stream via the

thoracic duct In human anatomy, the thoracic duct (also known as the ''left lymphatic duct'', ''alimentary duct'', ''chyliferous duct'', and ''Van Hoorne's canal'') is the larger of the two lymph ducts of the lymphatic system (the other being the right lymph ...

and travel to the gut where they carry out their final effector functions. The maturation of B-lymphocytes takes place in the Peyer's patch.

Clinical significance

Although important in the immune response, excessive growth of lymphoid tissue in Peyer's patches is pathologic, as

hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number. Although hypertro ...

of Peyer's patches has been closely associated with idiopathic intussusception. Having too many or larger than normal Peyer's patches is associated with an increased risk of prion diseases, and intussusception in children. A history of viral illness is a risk factor for enlarged or inflamed Peyer's patches. '' Salmonella typhi'' and poliovirus also target this section of the intestine. Disturbances in the gut microbiota and immune regulation within Peyer's patches are implicated in the pathogenesis of autoimmune diseases, such as Crohn's disease, where chronic inflammation can arise due to overactive immune responses. As Peyer's patches are packed with immune cells and produce protective proteins such as secretory IgA to maintain gut balance, their dysfunction can trigger inappropriate immune responses, driving the inflammation and tissue damage characteristic of autoimmune diseases.

References

External links