| Dendritic Cell |
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Information AboutDendritic Cell |
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| SHOPPER'S DELIGHT | |
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Dendritic cells were discovered in 1973 by Ralph M. Steinman and Zanvil A. Cohn . TYPES OF DENDRITIC CELLS Unfortunately, there are at least two different types of cells involved with immunity that are called dendritic cells. The exact relationship of these types to each other, as well as the identity of their parent cells in vivo, remains controversial. While humans and non-human primates such as Rhesus Macaques appear to have DCs divided into these groups, other species (such as the Mouse ) have different subdivisions of DCs. In vivo
In vitro In some respects, dendritic cells cultured In Vitro do not show the same behavior or capability as dendritic cells isolated ''ex vitro'', but they are often used for research, as they are still much more readily available than genuine DCs.
LIFE CYCLE Dendritic cells start out as immature dendritic cells. These cells are characterized by high endocytic activity and low T-cell activation potential. Dendritic cells constantly sample the surroundings for pathogens such as s and Killer T-cell s as well as B-cell s by presenting them with antigens derived from the pathogen, alongside non-antigen specific costimulatory signals. Every helper T-cell is specific to one particular antigen. Only professional antigen-presenting cells (macrophages, B lymphocytes, and dendritic cells) are able to activate a helper T-cell which has never encountered its antigen before. Dendritic cells are the most potent of all the antigen-presenting cells. As mentioned above, MDC probably form from Monocyte s, white blood cells which circulate in the body and, depending on the right signal, can turn into either dendritic cells or Macrophage s. Activated macrophages have a lifespan of only a few days. The lifespan of activated dendritic cells, while somewhat varying according to type and origin, is of a similar order of magnitude, but immature dendritic cells seem to be able to exist in an unactivated state for much longer. The monocytes in turn are formed from stem cells in the Bone Marrow . However, the exact genesis and development of the different types and subsets of dendritic cells and their interrelationship is only marginally understood at the moment, as dendritic cells are so rare and difficult to isolate that only in recent years they have become subject of focused research. Distinct surface antigens that characterize dendritic cells have only become known from 2000 on; before that, researchers had to work with a 'cocktail' of several antigens which, in combination, are unique to DCs. RELATIONSHIP TO HIV, ALLERGY, AND AUTOIMMUNE DISEASES HIV , which causes AIDS , can bind to dendritic cells via various receptors expressed on the cell. The best studied example is DC-SIGN (usually on MDC subset 1, but other subsets under certain conditions; since not all dendritic cell subsets expresss DC-SIGN, its exact role in sexual HIV-1 transmission is not clear). When the dendritic cell takes up HIV and then travels to the lymph node, the virus is able to move to helper T-cells, and this infection of helper T-cells is the major cause of disease. This knowledge has vastly altered our understanding of the infectious cycle of HIV since the mid-1990s, since in the infected dendritic cells, the virus possesses a reservoir which also would have to be targeted by a therapy. This infection of dendritic cells by HIV explains one mechanisms by which the virus could persist after prolonged HAART . Many other viruses, such as the SARS virus seems to use DC-SIGN to 'hitchhike' to its target cells. However, most work with virus binding to DC-SIGN expressing cells has been conducted using in vitro derived cells such as moDCs. The physiological role of DC-SIGN in vivo is more difficult to ascertain. Altered function of dendritic cells is also known to play a major or even key role in Allergy and Autoimmune Diseases like Lupus Erythematosus . Allergy is a pathologically overblown reaction to an outside allergen, autoimmune diseases are erroneous immune reactions to self-antigen. DENDRITIC CELLS IN ANIMALS OTHER THAN HUMANS The above applies to humans. In other organisms, the function of dendritic cells can differ slightly. For example, in Brown Rat s (but not mice), a subset of dendritic cells exists that displays strong killer cell-like activity. However, the principal function of dendritic cells as known to date is always to act as the generals or an "central encyclopedia" of the immune response, collecting and storing immunological knowledge, enabling them to instruct the adaptive arms to respond invading pathogens and telling the adaptive immune system what the most effective type of response is. EXTERNAL LINKS REFERENCES
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