Cluster of differentiation 267170 222463153 2008-06-29T13:44:20Z DOI bot 6652755 Citation maintenance. Removed redundant parameters. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. The '''cluster of differentiation''' (often abbreviated as '''CD''') is a protocol used for the identification and investigation of [[cell surface molecule]]s present on [[leukocytes]]. CD molecules can act in numerous ways, often acting as [[receptor (biochemistry)|receptors]] or [[ligand (biochemistry)|ligands]] (the molecule that activates a receptor) important to the cell. A signal cascade is usually initiated, altering the behavior of the cell (see [[cell signaling]]). Some CD proteins do not play a role in cell signaling, but have other functions, such as [[cell adhesion]]. There are approximately 250 different proteins.<ref name="pmid16020511">{{cite journal | author = Zola H, Swart B, Nicholson I, Aasted B, Bensussan A, Boumsell L, Buckley C, Clark G, Drbal K, Engel P, Hart D, Horejsí V, Isacke C, Macardle P, Malavasi F, Mason D, Olive D, Saalmueller A, Schlossman SF, Schwartz-Albiez R, Simmons P, Tedder TF, Uguccioni M, Warren H | title = CD molecules 2005: human cell differentiation molecules | journal = Blood | volume = 106 | issue = 9 | pages = 3123–6 | year = 2005 | pmid = 16020511 | doi = 10.1182/blood-2005-03-1338 }}</ref> ==Nomenclature== The '''CD nomenclature''' was proposed and established in the 1st International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA), which was held in [[Paris, France|Paris]] in [[1982]].<ref name="pmid6239187">{{cite journal | author = Bernard A, Boumsell L | title = [Human leukocyte differentiation antigens] | language = French | journal = Presse Med | volume = 13 | issue = 38 | pages = 2311–6 | year = 1984 | pmid = 6239187 | doi = | issn = }}</ref><ref name="pmid6240938">{{cite journal | author = Fiebig H, Behn I, Gruhn R, Typlt H, Kupper H, Ambrosius H | title = [Characterization of a series of monoclonal antibodies against human T cells] | language = German | journal = Allerg Immunol (Leipz) | volume = 30 | issue = 4 | pages = 242–50 | year = 1984 | pmid = 6240938 | doi = | issn = }}</ref> This system was intended for the classification of the many [[monoclonal antibodies]] (mAbs) generated by different laboratories around the world against [[epitope]]s on the surface molecules of [[white blood cell|leukocytes (white blood cells)]]. Since then, its use has expanded to many other cell types, and more than 320 CD unique clusters and subclusters have been identified. The proposed surface molecule is assigned a CD number once two specific [[monoclonal antibodies]] (mAb) are shown to bind to the molecule. If the molecule has not been well-characterized, or has only one mAb, it is usually given the provisional indicator "w" (as in "CDw186"). ==Uses as cell markers== [[Image:Differenzierungsantigene und Lymphozytenreifung.jpg|thumb|300px|CD differentiation. (Captions in German)]] The CD system is commonly used as cell markers; this allows cells to be defined based on what molecules are present on their surface. These markers are often used to associate cells with certain immune functions or properties. While using one CD molecule to define populations is uncommon (though a few examples exist), combining markers has allowed for cell types with very specific definitions within the immune system. CD molecules are utilized in cell-sorting using various methods including [[flow cytometry]]. Cell populations are usually defined using a '+' or a '&ndash;' symbol to indicate whether a certain cell fraction expresses or lacks a CD molecule. For example, a "[[CD34]]+, [[CD31]]&ndash;" cell is one that expresses CD34, but not CD31. This CD combination typically corresponds to a [[stem cell]], opposed to a fully-differentiated [[endothelial cell]]. {| class="wikitable" | '''Type of cell''' || '''CD markers''' |- | [[stem cell]]s || [[CD34]]+,[[CD31]]- |- | all [[leukocyte]] groups || [[CD45]]+ |- | [[Granulocyte]] || CD45+,[[CD15]]+ |- | [[Monocyte]] || CD45+,[[CD14]]+ |- | [[T lymphocyte]] || CD45+,[[CD3 (immunology)|CD3]]+ |- | [[T helper cell]] || CD45+,CD3+,[[CD4]]+ |- | [[Cytotoxic T cell]] || CD45+,CD3+,[[CD8]]+ |- | [[B lymphocyte]] || CD45+,[[CD19]]+ or CD45+,[[CD20]]+ |- | [[Thrombocyte]] || CD45+,[[CD61]]+ |- | [[Natural killer cell]] || [[CD16]]+,[[CD56]]+,CD3- |} Two commonly-used CD molecules are [[CD4]] and [[CD8]], which are, in general, used as markers for [[T helper cell|helper]] and [[cytotoxic T cell|cytotoxic]] T cells, respectively. When defining T cells, these molecules are defined in combination with CD3+, as some other leukocytes also express these CD molecules (some macrophages express low levels of CD4; [[dendritic cells]] express high levels of CD8). CD4 is also an essential receptor during [[HIV]] infection, allowing both the binding of HIV to helper T cells and the destruction of CD4+ T cells. The relative abundance of CD4+ and CD8+ T cells is often used to monitor the progression of an HIV infection. ==Other uses== It is important to note that, while CD molecules are very useful in defining leukocytes, they are ''not merely markers on the cell surface''. While only a fraction of known CD molecules have been thoroughly characterised, most of them have an important function. In the example of CD4 & CD8, these molecules are critical in [[antigen]] recognition. ==See also== *[[List of human clusters of differentiation]] for a list of CD molecules *[[Immune system]] *[[Immune tolerance]] *[[Antibodies]] *[[Leukocytes]] *[[Signal transduction]] ==References== {{reflist}} ==External links== * [http://www.hcdm.org/MoleculeInformation/tabid/54/Default.aspx CD list] maintained by the Human Cell Differentiation Molecules Council (successor to the HLDA Workshops) * [http://www.exactantigen.com/review/cd.html CD Antibody Review] * A [http://www.ebioscience.com/ebioscience/whatsnew/humancdchart.htm list of CD molecules], at ebioscience.com * Another [http://www.expasy.org/cgi-bin/lists?cdlist.txt list of CD molecules], at Expasy.org * Another [http://www.sciencegateway.org/resources/prow/index.html list of CD molecules], at Sciencegateway.org * Yet another [http://pathologyoutlines.com/cdmarkers.html list of CD molecules], at PathologyOutlines.com * [http://www.rndsystems.com/molecule_letter.aspx?l=C Catalogue of some CD-factors], as R&D Systems. *[http://www.ebioscience.com/ebioscience/litreq.asp Wall charts] of CD molecules and other cytokines, with colors, arrows from one cell to another, from [http://ebioscience.com/ eBioscience]. Was supplement to ''Science'' 313(5792) 8 September 2006. {{Clusters of differentiation}} {{Surface antigens}} [[Category:Anatomical pathology]] [[Category:Clusters of differentiation|*]] [[cs:Diferenciační skupina]] [[de:Cluster of differentiation]] [[es:Cúmulo de diferenciación]] [[fr:Cluster of differentiation]] [[ja:CD分類]] [[pt:Grupamento de diferenciação]]