Cell differentiation and proliferation in the gastrointestinal tract with respect to the local immune system.
Human intestinal lamina propria T cells have a low expression of the CD45RA antigen and a high expression of the CD45RO antigen. This phenotype is characteristic for memory T cells. In addition, T cells in the effector compartment of the mucosa bear surface antigens that are very rarely found in other sites of the immune system. Intestinal T cells also express functional IL-2 receptors, and IL-2 receptor alpha-chain mRNA, and are able to synthesize high amounts of IL-2. However, other markers of memory T cells, as CD29, are not expressed in high density in the lamina propria, indicating that lamina propria T cells differ from "classical" memory T cells. This is supported by functional studies in nonhuman primates infected rectally with Chlamydia trachomatis that show that lamina propria T cells do not proliferate after stimulation with antigen but rather provide helper function for immunoglobulin synthesis. These findings indicate a specific state of differentiation of lamina propria T cells that is adapted to the specific requirements in the gut. In inflammatory bowel disease (IBD) and in celiac disease, an increase in the number of CD25-positive activated T cells is found in involved mucosa. It has been shown that mucosal T-cell activation induces epithelial cell damage and mucosal transformation. Thus, a T cell-mediated damage may contribute to the pathogenesis of IBD. HIV-infected patients have a decreased number of CD4-positive T cells in the intestinal lamina propria. The number of CD25-positive activated T cells is also significantly decreased in the intestine compared to controls. Correlating with the presence of HIV-infected mononuclear cells in the mucosa, mucosal atrophy with hyporegeneration and enterocyte dysmaturation is observed. HIV might thus cause impairment and depletion of activated regulatory T cells in the intestinal lamina propria, which could lead not only to a breakdown of the mucosal immune barrier, resulting in a variety of opportunistic infections, but also to malabsorption, due to mucosal atrophy or enterocyte dysfunction. These findings indicate a close relationship between mucosal T cells and enterocyte proliferation and maturation.
Internal Medicine II, Medical Clinic, University of the Saarland, Humburg/Saar, Germany.
M
M
Zeitz
R
R
Ullrich
T
T
Schneider
H L
HL
Schieferdecker
E O
EO
Riecken
D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D001402:B-Lymphocytes / Q000276:immunology*; D002454:Cell Differentiation; D002455:Cell Division; D004064:Digestive System / Q000166:cytology* / Q000276:immunology*; D015658:HIV Infections / Q000276:immunology; D006801:Humans; D007156:Immunologic Memory; D015212:Inflammatory Bowel Diseases / Q000276:immunology / Q000473:pathology; D007413:Intestinal Mucosa / Q000166:cytology* / Q000276:immunology*; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D015703:Antigens, CD; D011948:Receptors, Antigen, T-Cell