CorpusHuman Anatomy
Lymphatic & ImmuneLymphoid organ

Peyer patches

Noduli lymphoidei aggregati

Also known as: Peyer's patches, aggregated lymphoid follicles, aggregated lymphoid nodules

Oval clusters of lymphoid follicles in the mucosa and submucosa of the small intestine, most numerous in the distal ileum on the antimesenteric border, covered by an epithelium containing M cells that sample gut antigens.

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Overview

NumberPeaks at ≈ 15–25 years (≈ 30 macroscopic patches in the distal ileum in autopsy series), declining with age
PositionAntimesenteric border, distal ileum

Peyer patches are the organised inductive sites of the gut immune system. Each is an elongated, oval aggregate of a few to several hundred lymphoid follicles (with germinal centres) lying in the lamina propria and extending through the muscularis mucosae into the submucosa, on the antimesenteric border of the bowel. They are most numerous and largest in the distal ileum, where they are visible to the naked eye as slightly raised, velvety patches a few centimetres long. Their number rises through childhood, peaks between about 15 and 25 years (autopsy counts of ≈ 30 in the distal ileum; estimates for the whole small intestine are higher) and then declines.

Each follicle bulges into the lumen as a dome, where the villi are absent and the surface is a follicle-associated epithelium with few goblet cells and many M (microfold) cells. M cells take up antigens, microbes and particles by endocytosis and deliver them intact into a basolateral pocket occupied by B cells, T cells and dendritic cells. Dendritic cells of the subepithelial dome process the antigen and present it to T cells in the interfollicular T-cell zones (which contain HEVs) and to B cells in the follicles, where class switching to IgA predominates.

There are no afferent lymphatics. Activated lymphocytes leave via efferent lymphatics to the mesenteric lymph nodes, enter the blood through the thoracic duct and home back to the intestinal lamina propria as IgA-secreting plasma cells and effector T cells.

Location

Mucosa and submucosa of the small intestine on the antimesenteric border, concentrated in the distal ileum.

Parts & subdivisions

  1. Follicle-associated epithelium and M cells
    Dome epithelium with few goblet cells and specialised antigen-transporting microfold (M) cells.
  2. Subepithelial dome
    Region rich in dendritic cells and macrophages beneath the dome epithelium.
  3. Lymphoid follicles
    B-cell follicles with germinal centres; IgA class switching.
  4. Interfollicular T-cell zones
    T-cell areas containing high endothelial venules (MAdCAM-1⁺).

Anatomy

Arterial supply

Ileal branches of the superior mesenteric artery; HEVs in the interfollicular areas.

Lymphatic drainage

Efferent lymphatics → mesenteric lymph nodes → intestinal trunk → cisterna chyli.

Histology

On a section of ileum: large lymphoid follicles with pale germinal centres in the lamina propria and submucosa, interrupting the muscularis mucosae; overlying villi absent or blunted over the domes. Their presence identifies the ileum histologically.

Function

  • Sample luminal antigens through M cells.
  • Induce IgA-producing B cells and gut-homing T cells.
  • Contribute to oral tolerance to food and commensal bacteria.

Clinical significance

Typhoid fever

Salmonella Typhi invades via M cells and multiplies in Peyer patch macrophages; hyperplasia and necrosis produce oval ulcers along the long axis of the bowel on the antimesenteric border, which can bleed or perforate (typically in the third week). Other pathogens using M cells include Yersinia, Shigella, poliovirus and prions.

Intussusception

In infants (≈ 6–36 months), hypertrophied Peyer patches after viral infection act as a lead point, telescoping the terminal ileum into the colon (ileocolic intussusception): colicky pain with drawing up of the legs, a sausage-shaped mass, vomiting and "redcurrant jelly" stool. Usually reduced by air or contrast enema.

Crohn disease

The earliest lesions are aphthous ulcers over lymphoid follicles, including Peyer patches of the terminal ileum — the most commonly affected segment.

Test yourself

Microfold (M) cells, which transport luminal antigens to underlying lymphoid follicles, are found in the…
  1. Follicle-associated epithelium over Peyer patches
  2. Germinal centres of lymph nodes
  3. Splenic red pulp
  4. Thymic medulla

Answer: Follicle-associated epithelium over Peyer patches

M cells in the follicle-associated epithelium of Peyer patches (and other MALT) lack a thick glycocalyx and microvilli and transcytose antigens to dendritic cells and lymphocytes in the subepithelial dome. Salmonella Typhi and poliovirus exploit them.

More lymphatic & immune system questions

Compiled from standard anatomy and physiology references — see the Lymphatic & Immune System sources. For education only; not medical advice.