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The cluster of differentiation (cluster of designation) (often abbreviated as CD) is a protocol used for the identification and investigation of cell surface molecules present on white blood cells. CD molecules can act in numerous ways, often acting as receptors or 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. CD for humans is numbered up to 350 most recently (as of 2009).[1][2]



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 in 1982.[3][4] This system was intended for the classification of the many monoclonal antibodies (mAbs) generated by different laboratories around the world against epitopes on the surface molecules of 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").

Cell markers

CD differentiation

The CD system is commonly used as cell markers, allowing 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. 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 '–' 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, opposed to a fully-differentiated endothelial cell.

Type of cell CD markers
stem cells CD34+,CD31-
all leukocyte groups CD45+
Granulocyte CD45+,CD15+
Monocyte CD45+,CD14+
T lymphocyte CD45+,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 helper and cytotoxic T cells, respectively. 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). Human immunodeficiency virus (HIV) binds CD4 and a chemokine receptor on the surface of a T helper cell to gain entry. The number of CD4 and CD8 T cells in blood is often used to monitor the progression of 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


  1. ^ "HCDM, responsible for HLDA workshop and CD molecules". Human Cell Differentiation Molecules Council (successor to the HLDA Workshops). Retrieved 2009-06-01.  
  2. ^ 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 (2005). "CD molecules 2005: human cell differentiation molecules". Blood 106 (9): 3123–6. doi:10.1182/blood-2005-03-1338. PMID 16020511.  
  3. ^ Bernard A, Boumsell L (1984). "[Human leukocyte differentiation antigens]" (in French). Presse Med 13 (38): 2311–6. PMID 6239187.  
  4. ^ Fiebig H, Behn I, Gruhn R, Typlt H, Kupper H, Ambrosius H (1984). "[Characterization of a series of monoclonal antibodies against human T cells]" (in German). Allerg Immunol (Leipz) 30 (4): 242–50. PMID 6240938.  

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