M cell

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In M cells ( M eng. For microfold ; fold = "fold", micro = "small") is specialized epithelial cells , which in the wall of the small intestine (ileum), a part of the small intestine , and the tonsils occur. They play an important role in the functioning of the immune system .

Occurrence

The M cells are part of the so-called follicle-associated epithelium (FAE), which covers the Peyer's plaques and the tonsils. About 10-15% of the surface of the follicle-associated epithelium is made up of M cells. The rest of the FAE is mainly slime forming goblet cells and columnar epithelial dominated. Like the rest of the intestinal epithelium, the M cells presumably arise from stem cells in the crypts. Cell-cell contacts with B lymphocytes, among others , probably play a role in the differentiation . Other M cells occur together with Langerhans cells in the FAE of all tonsils.

morphology

M cells differ morphologically from the rest of the epithelium of the ileum and from the follicle-associated epithelium (FAE). On the apical side (towards the intestinal lumen ) they have only a small number of microvilli which, in contrast to those of other cells, are shorter and partially branched. The apical side is characterized by many small folds that give the M cells their name. The basal side of the M cells (away from the intestinal lumen) is marked by several indentations. The T and B lymphocytes of the Peyer's plaques as well as dendritic cells and macrophages are in close contact with the M cells via these indentations .

function

The M cells play an important role in the function of the MALT system ( Mucosa Associated Lymphoid Tissue ), which also includes Peyer's plaques, and thus also for the immune system . The M cells take up antigens on their apical side via endocytosis. The antigens that M cells can take up include macromolecules as well as bacteria, viruses and smaller parasites. The antigens are delivered to the cells of the adaptive immune system on the basal side . The exact mechanism has not yet been clarified. It is also unclear whether the antigens are processed in the M cells and whether and how the antigens are presented to the effector cells of the immune system. Apparently a large part of the antigens taken up apically is transported unprocessed via vesicular transport to the basal and released by exocytosis . The orally administered vaccines are also absorbed into the body via the M cells .

swell

  • Thomas Heinzeller, Carl M. Büsing: Histology, Histopathology and Cytology for an introduction . Georg Thieme Verlag, 2001, ISBN 3-13-126831-X , p. 152.
  • Georg A. Holländer (Ed.): Immunology: Basics for clinics and practice. 1st edition. Elsevier, 2005, ISBN 3-437-21301-6 , p. 215 ff.
  • Detlev Ganten, Klaus Ruckpaul: Manual of molecular medicine. Volume 4: Immune System and Infectious Diseases. 12 volumes. 1st edition. Springer-Verlag, 1999, ISBN 3-540-62464-3 , p. 107 ff.