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Special features of the intestinal lymphocytic system
G Köhne1, T Schneider, M Zeitz
1Department of Internal Medicine II, University of Saarland, Homburg/Saar, Germany.
Insights
The gastrointestinal immune system involves Peyer's patches and gut-resident lymphocytes. Specialized adhesion molecules guide lymphocytes, including lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (IEL), for gut immunity.
Area of Science:
- Immunology
- Gastroenterology
- Cell Biology
Background:
- The gastrointestinal immune system comprises organized lymphoid tissues like Peyer's patches and diffuse mucosal lymphocytes.
- Antigen entry into the gut-associated lymphoid tissue (GALT) occurs via M cells in Peyer's patches.
- Primed lymphocytes migrate from the gut, recirculate, and return to mucosal tissues to perform immune functions.
Purpose of the Study:
- To describe the functional compartments of the gastrointestinal lymphocytic system.
- To highlight the role of adhesion molecules in lymphocyte homing to the gut.
- To differentiate gut-resident lymphocytes from peripheral blood lymphocytes.
Main Methods:
- Analysis of lymphocyte populations within the gastrointestinal tract.
- Characterization of adhesion molecule expression on lymphocytes.
- Comparison of surface markers and functional features of gut lymphocytes versus peripheral lymphocytes.
Main Results:
- Gut lymphocytes, including lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (IEL), exhibit distinct adhesion molecule profiles compared to peripheral blood lymphocytes.
- Specific integrins like alpha 4 beta 7 and alpha E beta 7 (HML-1) are crucial for lymphocyte homing to the gut mucosa.
- Gut-resident lymphocytes possess unique functional characteristics and contribute to specialized humoral defense through IgA secretion.
Conclusions:
- The gastrointestinal immune system relies on specialized lymphocyte populations and homing mechanisms for effective immune surveillance.
- Adhesion molecules play a critical role in directing lymphocytes to their functional sites within the gut.
- Gut-resident lymphocytes, particularly plasma cells secreting IgA, are essential for mucosal immunity.
Abstract:
The gastrointestinal lymphocytic system can be divided in two functional compartments, the organized lymphoid tissue, for example, the Peyer's patches, and the lymphocytes located diffusely in the mucosa, the lamina propria lymphocytes (LPL), and the intra-epithelial lymphocytes (IEL). Antigens enter the Peyer's patches as the afferent part of the GALT via specialized epithelial cells called M cells. After the initiation of the immune response by antigen processing and presentation to B and T cells in Peyer's patches, primed lymphocytes leave the mucosa via the thoracic duct. Finally they migrate back to the mucosa where they exert effector functions. Adhesion molecules, including integrins, especially alpha 4 beta 7 and alpha E beta 7 (HML-1) are involved in these homing and adhesion processes. LPL and LEL differ from peripheral blood lymphocytes in their expression of adhesion molecules and other surface and activation markers. Additionally, they exhibit functional features different from those of other lymphocyte compartments. In the mucosal immune system, plasma cells mainly secrete IgA, which is part of the specialized humoral defence in the gut.