Dendritic cells (DC) are immune cells and form part of the mammalian immune system. They are present in small quantities in tissues that are in contact with the external environment, mainly the skin (where they are often called Langerhans cells) and the inner lining of the nose, lungs, stomach and intestines. They can also be found at an immature state in the blood. Once activated, they migrate to the lymphoid tissues where they interact with T cells and B cells to initiate and shape the immune response. At certain development stages they grow branched projections, the dendrites, that give the cell its name. White Blood Cells is also the name of a White Stripes album. ... Orders Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Australosphenida Ausktribosphenida Monotremata Subclass Eutheria (excludes extinct ancestors) Afrosoricida Anagaloidea (extinct) Arctostylopida (extinct) Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Dinocerata (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Litopterna (extinct) Macroscelidea Mesonychia... The immune system is composed of a complex constellation of cells, organs and tissues, arranged in an elaborate and dynamic communications network and equipped to optimize the response against invasion by pathogenic organisms. ... For alternate meanings see skin (disambiguation). ... Langerhans cells are immature dendritic cells containing large granules called Birbeck granules. ... Human nose in profile A typical bulbous human nose, here used to support a pair of glasses. ... The lungs flank the heart and great vessels in the chest cavity. ... In anatomy, the stomach (in ancient Greek στόμαχος) is an organ in the gastrointestinal tract used to digest food. ... The intestine is the portion of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ...

However, these do not entail any special relation with neurons, which also possess similar appendages. Immature dendritic cells are also called veiled cells, in which case they possess large cytoplasmic 'veils' rather than dendrites. Follicular dendritic cells (FDC) are probably not of hematopoietic origin, but simply look similar to true dendritic cells. In all these cases, as well as in neuron dendrites, the similar morphology results in a very large contact surface to their surroundings compared to overall cell volume. Drawing by Santiago Ramón y Cajal of cells in the pigeon cerebellum. ... Red blood cells (erythrocytes) are present in the blood and help carry oxygen to the rest of the cells in the body Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, platelets). ...

Dendritic cells were discovered in 1973 by Ralph M. Steinman and Zanvil A. Cohn.

Types of dendritic cells

There are two major subsets of dendritic cell in the human system; myeloid and plasmacytoid. Each of these subsets includes numerous sub-populations that reside in different compartments of the body. The exact relationship between these different cell types and the identity of their in vivo precursors 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. Binomial name Macaca mulatta Zimmermann, 1780 The Rhesus Macaque (Macaca mulatta), often called the Rhesus Monkey, is one of the best known species of Old World monkeys. ... Feral mouse A mouse (Plural mice) is a mammal that belongs to one of numerous species of small rodents. ...

In vivo

• Myeloid dendritic cells (MDC) are most similar to monocytes. MDC are made up of at least two subsets:
  • the more common MDC-1, which is a major stimulator of T cells.
  • the extremely rare MDC-2, which may have a function in fighting wound infection
• Plasmacytoid dendritic cells (PDC) look like plasma cells, but have certain characteristics similar to myeloid dendritic cells. They can produce high amounts of interferon-alpha and have thus become known as IPC (interferon-producing cells) before their dendritic cell nature was revealed.

Monocyte A monocyte is a leukocyte, part of the human bodys immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. ... Dendritic cells (DC) are immune cells and form part of the mammalian immune system. ... Plasma cells (also called plasma B cells or plasmocytes) are cells of the immune system that secrete large amounts of antibodies. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

In vitro

In some respects, dendritic cells cultured in vitro do not show the same behavior or capability as dendritic cells isolated ex vivo. Nonetheless, they are often used for research as they are still much more readily available than genuine DCs. Wiktionary has a definition of: In vitro In vitro (Latin: within glass) means within a test tube, or, more generally, outside a living organism or cell. ...

• Mo-DC or MDDC refers to cells matured from monocytes
• HP-DC refers to cells derived from hematopoietic progenitor cells.

Monocyte A monocyte is a leukocyte, part of the human bodys immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. ... Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells or pluripotential hematopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ...

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 viruses and bacteria. This is done through pattern recognition receptors (PRRs) such as the toll-like receptors (TLRs). TLRs recognize specific chemical signatures found on subsets of pathogens. Once they have come into contact with such a pathogen, they become activated into mature dendritic cells. Mature dendritic cells phagocytose pathogens and degrade its proteins into small pieces and upon maturation present those fragments at their cell surface using MHC molecules. Simultaneously, they upregulate cell-surface receptors that act as co-receptors in T-cell activation such as CD80 and CD86, greatly enhancing their ability to activate T-cells. They also upregulate CCR7, a chemotactic receptor that induces the dendritic cell to travel through the blood stream to the spleen or through the lymphatic system to a lymph node. Here they act as antigen-presenting cells: they activate helper T-cells and killer T-cells as well as B-cells by presenting them with antigens derived from the pathogen, alongside non-antigen specific costimulatory signals. A common alternate meaning of virus is computer virus. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Toll-like receptors (TLRs) are type I transmembrane proteins that serve as a key part of the innate immune system. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... It has been suggested that Class I MHC be merged into this article or section. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The spleen is a ductless, vertebrate gland that is not necessary for life but is closely associated with the circulatory system, where it functions in the destruction of old red blood cells in holding a reservoir of blood. ... The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. ... Structure of the lymph node. ... An antigen presenting cell (APC) is a cell that displays foreign antigen complexed with MHC on its surface. ... A helper (or TH) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules found on professional antigen-presenting cells (APCs). ... A K cell (or a killer cell) is a lymphocyte with immunoglobulin Fc receptors, which allow it to bind to and kill antibody-coated cells by antibody-dependent cell-mediated cytotoxicity (ADCC). ... B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response). ...

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 monocytes, white blood cells which circulate in the body and, depending on the right signal, can turn into either dendritic cells or macrophages. 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, used in combination, result in isolation of cells with characteristics unique to DCs. Monocyte A monocyte is a leukocyte, part of the human bodys immune system that protect against blood-borne pathogens and move quickly to sites of infection in the tissues. ... A macrophage of a mouse stretching its arms to engulf two particles, possibly pathogens Macrophages (Greek: big eaters, makros = long, phagein = eat) are white blood cells, more specifically phagocytes, acting in the nonspecific defense as well as the specific defense system of vertebrate animals. ... Grays Anatomy illustration of cells in bone marrow. ...

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. Human immunodeficiency virus (commonly known as HIV, and formerly known as HTLV-III and lymphadenopathy-associated virus[1][2]) is a retrovirus that is the cause of the disease known as AIDS (Acquired Immunodeficiency Syndrome), a syndrome where the immune system begins to fail, leading to many life-threatening opportunistic... Acquired Immunodeficiency Syndrome or Acquired Immune Deficiency Syndrome (AIDS or Aids) is a collection of symptoms and infections in humans resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV). ... A C-type lectin receptor present mainly on myeloid and pre-plasmacytoid dendritic cells that mediates dendritic cell rolling interactions with blood endothelium and activation of CD4+ T cells, as well as recognition of pathogen haptens. ... The term antiretroviral drugs is used to describe drugs used against HIV infection (HIV is an RNA retrovirus). ... Sars may refer to any of the following: Severe acute respiratory syndrome, commonly abbreviated as SARS Michael Sars, a Norwegian biologist, father of Georg Sars Georg Sars, a Norwegian biologist, son of Michael Sars Special Administrative Regions, commonly abbreviated as SARs Sars, Perm Krai, an urban settlement in Perm Krai...

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 the organism's own antigen. An allergy can refer to several kinds of immune reactions including Type I hypersensitivity in which a persons body is hypersensitised and develops IgE type antibodies to typical proteins. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ...

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 rats (but not mice), a subset of dendritic cells exists that displays pronounced killer cell-like activity, apparently through its entire lifespan[[fact}}. However, the principal function of dendritic cells as known to date is always to act as the central command an central encyclopedia of the immune response, or similar to servers in a computer network. They collect and store the immune system's "knowledge", enabling them to instruct and direct the adaptive arms in response to challenges. Binomial name Rattus norvegicus (Berkenhout, 1769) The Brown Rat or Norway Rat (Rattus norvegicus) is one of the best-known and common rats, and also one of the largest. ... In information technology, a server is a computer system that provides services to other computing systems—called clients—over a network. ...

See also

• List of human clusters of differentiation for a list of CD molecules (as CD80 and CD86)

The following is a list of Clusters of Differentiation (or CD) molecules. ...

References

• Banchereau, Jacques (2002): The Long Arm of the Immune System. Scientific American 287(5): 52-59 (summary of dendritic cell knowledge)

• Dzionek, Andrzej; Fuchs,Anja; Schmidt, Petra; Cremer, Sabine; Zysk, Monika; Miltenyi, Stefan; Buck, David W. & Schmitz, Jürgen (2000): BDCA-2, BDCA-3, and BDCA-4: three markers for distinct subsets of dendritic cells in human peripheral blood. Journal of Immuology 165(11): 6037-6046 (detailed description of MDC-1, MDC-2, PDC phenotypes) PDF fulltext

• McKenna, Kelli et al. (2005): Plasmacytoid Dendritic Cells: Linking Innate and Adaptive Immunity. J. Virol. 79(1): 17-27 (summary of knowledge about dendritic cells and PDC in particular)

• Yang, Zhi-Yong et al. (2004): pH-Dependent Entry of Severe Acute Respiratory Syndrome Coronavirus Is Mediated by the Spike Glycoprotein and Enhanced by Dendritic Cell Transfer through DC-SIGN. J. Virol. 78(11): 5642-5650 (dendritic cells in SARS)

• Steinman, Ralph M.; Cohn, Zanvil A. (1973): Identification of a novel cell type in peripheral lymphoid organs of mice: I. Morphology, quantitation, tissue distribution. Journal of Experimental Medicine 137(5): 1142-1162 (First publication).