Antigen-presenting cell

Antigen presenting cells allow the detection of invading pathogens or altered body cells and thus derive their effective removal by a specific immune response a. Although almost all body cells have the ability of antigen presentation, are thus described only generally the so-called "professional" antigen presenting cells of the immune system - ie, dendritic cells, monocytes, macrophages and B lymphocytes - meant. "Professional" means here that antigen presentation is an essential function of these cells and that only they can trigger an activation of T - lymphocytes, which are not previously come into contact with the corresponding antigen. In this case, the antigen presentation by MHC class II complexes called runs. In contrast, most other body cells present antigens on MHC I, to be detected even in case of infection or tumor-like changes in the immune system.

Dendritic cells

Dendritic cells have a large repertoire of molecules that can trigger and influence the activation of T- lymphocyte. This gives them in particularly the ability to set a fast and effective immune response against invading pathogens in motion, especially when it is a primary infection. Since they can perform multiple inflammatory signals from the surrounding tissue and send it to T lymphocytes in addition, they decisively influence whether the developing immune response takes a humoral or cell-mediated course.

Dendritic cells are present in all body tissues. The so-called immature state they constantly take antigen in different forms: Dead cells by phagocytosis, contained in the body fluid and specifically selected molecules via pinocytosis substances via receptor-mediated endocytosis. Infection and inflammatory reaction associated trigger a maturation in dendritic cells, during which they lose the ability to raise new antigen. The previously recorded antigen is, however, now being presented effectively and in high density on the cell surface. During inflammation many signals act on the dendritic cells, be it from the tissue or bacterial substances released inflammatory mediators. These dendritic cells stimulate the production of other factors, so that the presented antigen is involved in a complex pattern of activating and inhibitory signals, which allows an accurate adjustment of the immune response to the found infection. With the onset of maturation, dendritic cells migrate from the body tissues to the nearest lymphatic organ in which it comes into contact with T lymphocytes. Recognizes a T lymphocyte, with its T cell receptor, the presented antigen, there is a strong and long-lasting binding of the dendritic cell and a variety of signal exchange which assures that the ensuing immune response which occurred infection as effectively as possible can eliminate.

Monocytes and macrophages

Macrophages and its cellular precursor monocytes, remove damaged tissue and phagocytose invading pathogens. The case captured antigen is then presented directly in the same tissue, the cells migrate normally not in lymphoid organs. Since the occurring in the tissues T lymphocytes have ever had contact with most antigen, macrophages are mainly involved in the maintenance of an already tarnished immune response or to fight infection with a previously known pathogens. A unique type phagozitierender cells represent the microglial cells of the CNS, whose peculiarity is that it is both to glial cells of the nervous tissue as well as by mononuclear phagocytes with them.

B-lymphocytes

B lymphocytes take antigen receptor- mediated endocytosis in B- cells through its receptor. Is the so- recorded and then presented antigen recognized by T lymphocytes, there is a reciprocal activation of B - and T-lymphocytes. B lymphocytes then either pour large amounts of antibodies, which bind to the same antigen as the B -cell receptor, or they change their antibodies at random, so that some cells can produce antibodies with increased efficacy. Antigen presentation by B cells thus serves mainly to control one's own antibody production.

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