Cell surface antigens of leukocytes are called CD antigens. The term CD refers a cluster of differentiation (also known as cluster of designation or classification determinant), which is a protocol for the identification of cell surface molecules for immunophenotyping. The CD nomenclature was established in 1982 at the International Workshop and Conference on Human Leukocyte Differentiation Antigens (HLDA). CD of humans is numbered up to 371 as of 2016.
While CD molecules are very useful in defining leukocytes, they are not merely markers on the cell surface. In some cell types, CD antigens are expressed only at certain stages of development or under certain conditions such as cell activation or disease conditions. In many cases, the expression of CD antigens is influenced by cytokines, such as binding of ligands to CD antigens which has shown to modulate the expression of cytokines.
Most CD antigens have an important function, while only a fraction of them have been thoroughly studied. For instances, CD4 and CD8, which are markers for T-helper and T-suppressor cells, respectively, are critical in antigen recognition. Many CD molecules are involved in immunotherapies, such as CD34 which is involved in T-cell activation signaling and regulation of TCR expression, CD19 and CD20 that regulate B-cell activation and proliferation.
EUPROTEIN offers the following high-quality recombinant CD antigens. Click the names of the molecules to learn more.