The
cluster of differentiation (
cluster of designation) (often abbreviated as
CD) is a protocol used for the identification and investigation of
cell surface moleculeCell surface molecules are molecules located in biological cells. An extraordinary array of specialized cells have evolved to accomplish many different tasks required in organisms in their environments. In order for specialized cells to interact with each other and their environments, they must...
s present on White blood cells. CD molecules can act in numerous ways, often acting as
receptorsIn biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach...
or
ligandsIn biochemistry and pharmacology, a ligand is a substance that is able to bind to and form a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as...
(the molecule that activates a receptor) important to the cell. A signal cascade is usually initiated, altering the behavior of the cell (see
cell signalingCell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...
).
The
cluster of differentiation (
cluster of designation) (often abbreviated as
CD) is a protocol used for the identification and investigation of
cell surface moleculeCell surface molecules are molecules located in biological cells. An extraordinary array of specialized cells have evolved to accomplish many different tasks required in organisms in their environments. In order for specialized cells to interact with each other and their environments, they must...
s present on White blood cells. CD molecules can act in numerous ways, often acting as
receptorsIn biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach...
or
ligandsIn biochemistry and pharmacology, a ligand is a substance that is able to bind to and form a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as...
(the molecule that activates a receptor) important to the cell. A signal cascade is usually initiated, altering the behavior of the cell (see
cell signalingCell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...
). Some CD proteins do not play a role in cell signaling, but have other functions, such as
cell adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins.- Process :...
.
CD for humans is numbered up to 350 most recently (as of 2009).
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 in 1982. This system was intended for the classification of the many
monoclonal antibodiesMonoclonal antibodies are monospecific antibodies that are identical because they are produced by one type of immune cell that are all clones of a single parent cell. Given almost any substance, it is possible to create monoclonal antibodies that specifically bind to that substance; they can then...
(mAbs) generated by different laboratories around the world against
epitopeAn epitope, also known as antigenic determinant, is the part of a macromolecule that is recognized by the immune system, specifically by antibodies, B cells, or T cells. The part of an antibody that recognizes the epitope is called a paratope...
s on the surface molecules of
leukocytes (white blood cells)White blood cells , or leukocytes , are cells of the immune system defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a...
. 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 antibodiesMonoclonal antibodies are monospecific antibodies that are identical because they are produced by one type of immune cell that are all clones of a single parent cell. Given almost any substance, it is possible to create monoclonal antibodies that specifically bind to that substance; they can then...
(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
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 cytometryFlow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
. 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 "
CD34CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+,
CD31CD31 is a cluster of differentiation molecule. It is also called PECAM-1 for platelet endothelial cell adhesion molecule. It plays a key role in removing aged neutrophils from the body...
–" cell is one that expresses CD34, but not CD31. This CD combination typically corresponds to a
stem cellStem cells are cells found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian...
, opposed to a fully-differentiated endothelial cell.
| Type of cell |
CD markers
>-
| stem cellStem cells are cells found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic cell division and differentiating into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian...
s |
CD34 CD34 molecule is a cluster of differentiation molecule present on certain cells within the human body. It is a cell surface glycoprotein and functions as a cell-cell adhesion factor. It may also mediate the attachment of stem cells to bone marrow extracellular matrix or directly to stromal cells...
+,CD31CD31 is a cluster of differentiation molecule. It is also called PECAM-1 for platelet endothelial cell adhesion molecule. It plays a key role in removing aged neutrophils from the body...
-
>-
| all leukocyte groups |
CD45 Protein tyrosine phosphatase, receptor type, C also known as PTPRC is an enzyme which in humans is encoded by the PTPRC gene. PTPRC is also known as CD45 antigen which was originally called leukocyte common antigen.- Function :The protein encoded by this gene is a member of the protein tyrosine...
+
>-
| GranulocyteGranulocytes are a category of white blood cells characterised by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
|
CD15 CD15 is a cluster of differentiation antigen - an immunologically significant molecule. CD15 is a carbohydrate adhesion molecule that can be expressed on glycoproteins, glycolipids and proteoglycans.- Function :...
+
>-
| MonocyteMonocyte is a type of white blood cell, part of the human body's immune system. Monocytes have two main functions in the immune system: replenish resident macrophages and dendritic cells under normal states, and in response to inflammation signals, monocytes can move quickly Monocyte is a type of...
|
CD14Cluster of differentiation 14 also known as CD14 is a human gene.The protein encoded by this gene is a component of the innate immune system. CD14 exists in two forms. It is either anchored into the membrane by a glycosylphosphatidylinositol tail or it appears in a soluble form...
+
>-
| T lymphocyte |
|
>-
| T helper cellT helper cells are a sub-group of lymphocytes that play an important role in establishing and maximizing the capabilities of the immune system...
CD4 CD4 is a glycoprotein expressed on the surface of T helper cells, regulatory T cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
+
>-
| Cytotoxic T cellA cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or dysfunctional...
|
CD8CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...
+
>-
| B lymphocyte |
CD19 CD19 , is a human protein encoded by the gene.CD19 is expressed on follicular dendritic cells and B cells...
+ or CD45+,CD20CD20 is a non-glycosylated phosphoprotein expressed on the surface of all mature B-cells.B-lymphocyte antigen CD20 is a protein that in humans is encoded by the MS4A1 gene.-Function:...
+
>-
| ThrombocyteThrombocytes are cells that play a key role in blood clotting. In mammals, thrombocytes are anucleated cell fragments called platelets. Nucleated thrombocytes of nonmammalian vertebrates differ from the mammalian thrombocytes not only in having a nucleus and thus resembling B lymphocytes, but also...
|
CD61 Integrin beta-3 is a protein that in humans is encoded by the ITGB3 gene. CD61 is a cluster of differentiation found on thrombocytes.-Interactions:CD61 has been shown to interact with PTK2, ITGB3BP, TLN1 and CIB1.-Further reading:...
+
>-
| Natural killer cellNatural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...
|
CD16 CD16 is an Fc receptor.It is a cluster of differentiation found on the surface of natural killer cells, neutrophil polymorphonuclear leukocytes, monocytes and macrophages...
+,CD56+,CD3- |
Two commonly-used CD molecules are
CD4CD4 is a glycoprotein expressed on the surface of T helper cells, regulatory T cells, monocytes, macrophages, and dendritic cells. It was discovered in the late 1970s and was originally known as leu-3 and T4 before being named CD4 in 1984...
and
CD8CD8 is a transmembrane glycoprotein that serves as a co-receptor for the T cell receptor . Like the TCR, CD8 binds to a major histocompatibility complex molecule, but is specific for the class I MHC protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene...
, which are, in general, used as markers for
helperT helper cells are a sub-group of lymphocytes that play an important role in establishing and maximizing the capabilities of the immune system...
and
cytotoxicA cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or dysfunctional...
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
antigenAn antigen is a substance that prompts the generation of antibodies and can cause an immune response. "Self" antigens are usually tolerated by the immune system; whereas "Non-self" antigens are identified as intruders and attacked by the immune system...
recognition.
See also
- List of human clusters of differentiation for a list of CD molecules
- Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumour cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
- Immune tolerance
Immune tolerance or 'immunological tolerance' can be either 'natural' or 'self tolerance', where the body does not mount an immune response to self antigens, or 'induced tolerance', where tolerance to external antigens can be created by manipulating the immune system...
- Antibodies
- Leukocytes
- Signal transduction
In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another. Most processes of signal transduction involve ordered sequences of biochemical reactions inside the cell, which are carried out by enzymes and activated by second messengers,...
External links