Peyer Patches – Function and Role in Gut Immunity
Peyer patches are specialized lymphoid tissue structures in the small intestine that play a central role in intestinal immune defense and the recognition of pathogens.
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Peyer patches are specialized lymphoid tissue structures in the small intestine that play a central role in intestinal immune defense and the recognition of pathogens.
What are Peyer Patches?
Peyer patches are organized clusters of lymphoid tissue located primarily in the mucosa of the ileum – the final segment of the small intestine. They are named after the Swiss anatomist Johann Conrad Peyer, who first described them in the 17th century. Peyer patches belong to the so-called gut-associated lymphoid tissue (GALT) and are a key component of the intestinal immune system.
Structure and Anatomy
Peyer patches consist of aggregated lymphoid follicles covered by a specialized epithelium. This epithelial layer contains M cells (microfold cells), which are capable of sampling antigens – foreign substances such as bacteria or viruses – from the intestinal lumen and delivering them to underlying immune cells. Within the Peyer patches, several types of immune cells can be found:
- B lymphocytes (located in the germinal centers of the follicles)
- T lymphocytes (in the interfollicular regions)
- Dendritic cells and macrophages (acting as antigen-presenting cells)
In humans, there are typically 30 to 40 Peyer patches. Their number is highest during childhood and adolescence and decreases with age.
Function in the Immune System
The primary role of Peyer patches is to monitor intestinal contents and initiate targeted immune responses. They serve several important functions:
- Antigen sampling: M cells transport antigens from the gut lumen into the lymphoid tissue, where they are recognized and processed by immune cells.
- Immune response: B cells are activated and differentiate into antibody-producing plasma cells, primarily secreting immunoglobulin A (IgA). IgA is released into the intestinal lumen, where it neutralizes pathogens.
- Immune tolerance: Peyer patches are also involved in the development of oral tolerance – the ability of the immune system to recognize and not attack harmless dietary components and beneficial gut bacteria.
- Immunological memory: After initial exposure to a pathogen, memory cells are generated within the Peyer patches, enabling a faster immune response upon subsequent encounters.
Clinical Relevance
Peyer patches play an important role in several medical conditions:
Infectious Diseases
Certain pathogens exploit the M cells of Peyer patches as an entry point into the body. Well-known examples include Salmonella typhi (the causative agent of typhoid fever), Yersinia species, and certain viruses. Inflammation of the Peyer patches in typhoid fever can lead to intestinal ulcers and, in severe cases, intestinal perforation.
Inflammatory Bowel Disease
In Crohn disease and other inflammatory bowel diseases (IBD), dysfunction of the gut-associated immune system – including the Peyer patches – is considered a potential contributing factor in disease development. Impaired immune tolerance may lead to exaggerated inflammatory responses against the body's own intestinal microbiota.
Prion Diseases
In the context of prion diseases such as variant Creutzfeldt-Jakob disease (vCJD), Peyer patches have been shown to play a role in the early replication of prions within the gut before they reach the central nervous system.
Diagnostics
Peyer patches can occasionally be visualized during ileocolonoscopy or through imaging procedures. In histopathological examinations of intestinal biopsies, they can be identified microscopically. Specific diagnostic assessment of Peyer patches is generally carried out only when there is a clinical indication, such as suspected infectious disease or intestinal pathology.
References
- Neutra MR, Pringault E, Kraehenbuhl JP. Antigen sampling across epithelial barriers and induction of mucosal immune responses. Annual Review of Immunology. 1996;14:275-300.
- Mowat AM, Agace WW. Regional specialization within the intestinal immune system. Nature Reviews Immunology. 2014;14(10):667-685.
- World Health Organization (WHO). Typhoid fever – Fact Sheet. Available at: https://www.who.int/news-room/fact-sheets/detail/typhoid
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