Cluster of differentiation

The concept of cluster of differentiation ( " distinctive groups " ), abbreviated as CD, refers to groups of immunophenotypic surface features of cells that can be classified according to biochemical or functional criteria. The CD molecules are mostly to membrane-bound glycoproteins that are partly expressed in a cell -specific and can have a variety of functions: Some CDs have receptor or signal function while could be detected in other enzymatic activity; In addition, some cluster molecules ( see also cell contact ) is a central role in intercellular communication attributed.

History

After it was Georges Köhler and César Milstein end of the 1970s succeeded in producing monoclonal antibodies hundreds of different clones were generated with mostly different, but partly overlapping specificities within a few years. Here, however, the molecular and genetic identity of the detected feature was mostly unknown. To bring order out of chaos, 1981, for the first time antibodies that recognize the same feature, grouped together.

According to the latest Human Leukocyte Differentiation Antigen ( HLDA ) conference in 2004 included the CD nomenclature than 300 cluster (CD1 - CD339, with some gaps), some of which are further divided (about CD3γ, CD3δ, CD3ε or CD8a, CD8b ). The pooling in a cluster does not mean that the antibodies must necessarily recognize the same epitope of the protein.

Furthermore, also some overlap in the detection range of the antibody possible. This shows well the example of the tyrosine phosphatase CD45. This is - expressed by almost all cells of the hematopoietic system - with the exception of erythrocytes. However, cell type- dependent different splice and Glykosylierungsvarienten are formed here. Antibodies which all will recognize these variants clustered as CD45, whereas antibodies which (restricted german) spectrum will recognize as CD45R, CD45RO, CD45RA, CD45RB or CD45RC clustered only limited. In the mouse CD45R is commonly used as a B- cell marker, where it is referred to as " B220 " (this name is derived from the molar mass (220 kDa ) of the corresponding tyrosine variant fro).

The CD nomenclature refers originally to humans, but the orthologous proteins in other species (mainly mouse but also others ) assigned to the corresponding cluster. To avoid confusion, in unclear cases the CDxx a species abbreviation is prefixed (about hCD4: human CD4 or mCD25: mouse CD25 ).

Also note that the protein and gene name does not have to be identical to the CD cluster: mCD161c (CD) - NKR - P1C (protein) - Ly55c ( gene).

Diagnostic significance

Since various CD molecules are specific for a certain type or level of development of cells, they can be used as a marker that can be recognized by monoclonal antibodies and detected in this way. The analysis of the expression pattern of CD- molecules ( immunophenotyping ) on leukemia cells plays a role in the diagnosis and classification of leukemias. It is also of critical importance, particularly in the classification and treatment planning in acute lymphoblastic leukemia.

Therapeutic significance

Due to the cell-specificity of various CD molecules attempting to use these as targets for pharmacological therapy of various diseases.

An example of a therapeutic monoclonal antibody to a CD antigen is rituximab. This antibody specifically binds to CD20 and may thus an immune response against CD20 -positive cells, such as non-Hodgkin's lymphoma that trigger.