Editing Cluster of differentiation (section)

== Nomenclature ==
The '''CD nomenclature''' was proposed and established in the 1st International Workshop and Conference on Human [[Leukocyte]] Differentiation [[Antigen]]s (HLDA), held in [[Paris, France|Paris]] in 1982.<ref name="pmid6239187">{{Cite journal |vauthors=Bernard A, Boumsell L |year=1984 |title=[Human leukocyte differentiation antigens] |journal=Presse Med |language=fr |volume=13 |issue=38 |pages=2311–6 |pmid=6239187}}</ref><ref name="pmid6240938">{{Cite journal |vauthors=Fiebig H, Behn I, Gruhn R, Typlt H, Kupper H, Ambrosius H |year=1984 |title=Charakterisierung einer Serie von monoklonalen Antikörpern gegen humane T-Zellen |trans-title=Characterization of a series of monoclonal antibodies against human T cells |journal=Allerg Immunol (Leipz) |language=de |volume=30 |issue=4 |pages=242–50 |pmid=6240938}}</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|leukocyte]]s (white blood cells). Since then, its use has expanded to many other cell types, and more than 370 CD unique clusters and subclusters have been identified. The proposed surface molecule is assigned a CD number once two specific monoclonal antibodies 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 "[[CD186|CDw186]]").<ref>{{Cite journal |last=Zola |first=Heddy |last2=Swart |first2=Bernadette |last3=Banham |first3=Alison |last4=Barry |first4=Simon |last5=Beare |first5=Alice |last6=Bensussan |first6=Armand |last7=Boumsell |first7=Laurence |last8=D. Buckley |first8=Chris |last9=Bühring |first9=Hans-Jörg |last10=Clark |first10=Georgina |last11=Engel |first11=Pablo |last12=Fox |first12=David |last13=Jin |first13=Bo-Quan |last14=Macardle |first14=Peter J. |last15=Malavasi |first15=Fabio |date=January 2007 |title=CD molecules 2006 — Human cell differentiation molecules |journal=Journal of Immunological Methods |volume=319 |issue=1-2 |pages=1–5 |doi=10.1016/j.jim.2006.11.001 |quote=Clarify and bring up to date earlier provisional (CDw) designations. |last16=Mason |first16=David |last17=Stockinger |first17=Hannes |last18=Yang |first18=Xifeng}}</ref>

For instance, [[CD2]] mAbs are reagents that react with a 50‐kDa [[transmembrane]] [[glycoprotein]] expressed on [[T cell]]s. The CD designations were used to describe the recognized molecules but had to be clarified by attaching the term antigen or molecule to the designation (e.g., CD2 molecule). Currently, "CD2" is generally used to designate the molecule, and "CD2 [[antibody]]" is used to designate the antibody.<ref name="Monoclonal Antibodies to Human Cell">{{Cite journal |last=Beare |first=Alice |last2=Stockinger |first2=Hannes |last3=Zola |first3=Heddy |last4=Nicholson |first4=Ian |year=2008 |title=Monoclonal Antibodies to Human Cell Surface Antigens |journal=Current Protocols in Immunology |volume=80 |issue=1 |pages=A.4A.1–A.4A.73 |doi=10.1002/0471142735.ima04as80 |pmc=7162157 |pmid=18432634}}</ref>

Cell populations are usually defined using a '+' or a '−' symbol to indicate whether a certain cell fraction expresses or lacks a CD molecule. For example, a "[[CD34]]+, [[CD31]]−" cell is one that expresses CD34 but not CD31. This CD combination typically corresponds to a [[stem cell]], as opposed to a fully differentiated [[endothelial cell]]. Some cell populations can also be defined as <sup>hi</sup>, <sup>mid</sup>, or <sup>low</sup> (alternatively, <sup>bright</sup>, <sup>mid</sup>, or <sup>dim</sup>), indicating an overall [[Expressivity (genetics)|variability]] in CD [[genetic expression|expression]], particularly when compared to other cells being studied. A review of the development of T cells in the [[thymus]] uses this nomenclature to identify cells transitioning from CD4<sup>mid</sup>/CD8<sup>mid</sup> double-positive cells to CD4<sup>hi</sup>/CD8<sup>mid</sup>.<ref name="pmid19151747">{{Cite journal |vauthors=Ho IC, Tai TS, Pai SY |date=February 2009 |title=GATA3 and the T-cell lineage: essential functions before and after T-helper-2-cell differentiation |journal=Nature Reviews Immunology |volume=9 |issue=2 |pages=125–35 |doi=10.1038/nri2476 |pmc=2998182 |pmid=19151747}}</ref>