Antibodies to CD Antigens

Cluster of Differentiation (CD) antigen are cell surface markers expressed by leukocytes and used to distinguish cell lineages, developmental stages, and functional subsets; such markers can be identified by specific monoclonal antibodies and are numbered CD1, CD2, CD3, etc. (table of CD antigen designations). CD designations are not related to biological function, thus CD antigens include receptors, glycans, adhesion molecules, membrane-bound enzymes, etc.

The arguably best known CD antigens are CD4 and CD8 which are lineage markers for T-helper and T-suppressor cells, respectively. CD4 binds to relatively invariant sites on class II major histocompatibility complex molecules outside the peptide-binding groove, which interacts with the T-cell receptor. CD4 is also the main docking receptor for human immunodeficiency virus. CD8 binds to relatively invariant sites on class I major histocompatibility complex molecules outside the peptide-binding groove. CD8 is also expressed on a subset of dendritic cells. Other more important CD antigens include the leukocytes integrins (CD11/CD18) and the hematopoietic stem cell marker CD34.

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