Human mucosal T-lymphocyte and macrophage subpopulations in normal and inflamed intestine

Antigen presentation in the intestine

The intestinal mucosa is the largest surface area in the body which is continually exposed to an enormous amount of food antigens, viruses, bacteria, parasites or the by-products of these organisms. In such an antigen-loaded environment, specialized defence mechanisms must exist. There is clear evidence that the function of lymphocytes in the intestinal mucosa (IELs or LPLs) is different from that of lymphocytes of the peripheral blood, lymph node or spleen (these are antigen-free organs). The basic processes of these reactions are not completely understood. The role of differential antigen handling and presentation, and the non-random distribution of responsibilities between the professional and non-professional APC in this regard, have not been characterized. Thus, much remains to be learned about the basic mechanisms of antigen uptake, processing and presentation in the intestine which are necessary to induce an immune response. Diversity in APC function is a natural requirement for the maintenance of homeostasis in the intestine. Subpopulations of professional and non-professional APC may have been programmed to function in such a way that non-professional APCs may play a dominant role. It is anticipated that in vivo model systems will be developed and that eventually a clearer understanding will be gained in this rapidly evolving field.

Phenotypic and functional assessment of intraepithelial lymphocytes (IEL) isolated from rat colon and small bowel

We have compared the proliferative potential of IELs isolated from rat colon (CIEL) and small bowel (SBIEL), and compared this with that observed using spleen lymphocytes. Unless additional irradiated spleen cells were added as a source of accessory cells, both IEL populations show poor proliferation in response to Con A stimulation. The CD4/CD8 ratio in spleen, SBIEL and CIEL was markedly different (3:1, 1:3, and 1:1, respectively). Cells expressing surface markers characteristic of macrophages were not routinely found in SBIELs. Both IEL preparations inhibited spleen cell proliferation in response to Con A or immobilized anti-CD3, and produced a soluble factor(s) capable of causing similar inhibition. For CIEL this inhibition was dependent upon a proliferation-independent but cell-cell contact dependent event.

M cells in Peyer's patches of the intestine

M cells are specialized epithelial cells of the mucosa-associated lymphoid tissues. A characteristic of M cells is that they transport antigens from the lumen to cells of the immune system, thereby initiating an immune response or tolerance. Soluble macromolecules, small particles, and also entire microorganisms are transported by M cells. The interactions of these substances with the M cell surface, their transcytosis, and the role of associated lymphoid cells are reviewed in detail. The ultrastructure and several immuno- and lectin-histochemical properties of M cells vary according to species and location along the intestine. We present updated reports on these variations, on identification markers, and on the origin and differentiation of M cells. The immunological significance of M cells and their functional relationship to lymphocytes and antigenpresenting cells are critically reviewed. The current knowledge on M cells in mucosa-associated lymphoid tissues outside the gut is briefly outlined. Clinical implications for drug deliver, infection, and vaccine development are discussed.

Lymphoid and non-lymphoid cells in the epithelium and lamina propria of intestinal mucosa of pigs

The jejunum and ileum of 5 day old and adult normal pigs and of 45 day old germ free pigs were used to study the lymphocyte pools in the epithelium and lamina propria by sequential treatments with EDTA, four hours, and 12 hours of collagenase treatment. In adult animals the incubation of the jejunal wall with EDTA resulted in mean (SD) 26.8 (10.9) x 10(6) intraepithelial lymphocytes per g of tissue. The ileal wall gave lower cell yields. After complete digestion of the lamina propria by collagenase a further yield of 35.2 (10.2) x 10(6)/g lymphocytes was achieved. The separation of the gut wall from 5 day old pigs resulted in a 10-fold lower total lymphocyte yield, and the tissue was totally digested after four hours of collagenase treatment. Many eosinophils and mast cells were found in the suspensions from adult animal tissues after the collagenase treatment; 4.7 x 10(6)/g and 4.8 x 10(6)/g, respectively. The suspensions after 12 hour collagenase incubation contained up to 30% plasma cells. Almost all cells isolated by EDTA incubation were CD8+ T cells. After collagenase incubation CD4+ and CD8+ T lymphocytes were found in all animal groups, and in adult animals up to 20% surface Ig+ cells were harvested. When the incorporation of the thymidine analogue bromodesoxyuridine was used to study the lymphocyte production in vivo 3 to 7% lymphocytes in the epithelium were labelled 24 hours later (lamina propria T lymphocytes about 1%). In this study lymphoid as well as non-lymphoid cells have been analysed in mucosal cell suspensions. The absolute cell yield per gram of mucosal tissue is a basis to estimate the pool sizes of intraepithelial and lamina propria lymphocytes.

Interleukin 1 is released by murine macrophages during apoptosis induced by Shigella flexneri

Peritoneal macrophages undergoing apoptosis induced by Shigella flexneri infection release the inflammatory cytokine interleukin 1 (IL-1), but not IL-6 or tumor necrosis factor alpha (TNF alpha). Wild type shigella causes a very fast and significant release of IL-1 from prestimulated peritoneal macrophages, before the cell's integrity is compromised. Both IL-1 alpha and IL-1 beta are released, IL-1 beta in its mature processed form. IL-1 is released from presynthesized cytoplasmic pools. These results demonstrate that bacteria-induced apoptosis of macrophages may play an active role in vivo by releasing IL-1, which in turn mediates an early inflammatory response in epithelial tissues.

Characterization of macrophage-like cells in the external layers of human small and large intestine

In the external layers of human small and large intestine macrophage-like cells were characterized by immunohistochemical, histochemical and electron-microscopical methods. Using immunohistochemistry and a number of monoclonal antibodies, the presence and distribution of phenotypic subpopulations of macrophages were evaluated. In all locations macrophage-like cells were identified with antibody EBM11, which recognizes CD68 antigen, C3bi which recognizes CD11b, and partly with an antibody which recognizes protein 150,95 (CD11c). Macrophage-like cells in the external muscle layer were HLA-DR-positive (expressing the MHC class-II antigen), in contrast to macrophage-like cells in the subserosa and submucosa. Macrophage-like cells in the external muscle layer were mostly acid phosphatase-negative, and at the electron-microscopic level they were found to have features of macrophages: primary lysosomes, coated vesicles and pits. However, very few secondary lysosomes were present. Birbeck granules were not observed. It is concluded that in the external muscle layer of human small and large intestine numerous macrophages of a special type are present. It is discussed whether this cell type plays a role in gastrointestinal motility and/or has an immunological function.