CD antigens are protocol used for the identification and investigation of cell surface molecules providing targets for immunophenotyping of cells. In terms of physiology, CD antigens 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. Some CD antigens do not play a role in cell signaling, but have other functions, such as cell adhesion, cell activation, and cell inhibition.
Cells interact with each other, and their substrate, throughout their lifetime. The adhesion complex that interacts with the cellular substrate, or extracellular matrix, and one that interacts with another cell. These complex cellular structures involve many proteins, such as CD antigens. Cell adhesions are mediated by either transmembrane cell-adhesion molecules, or adhesion receptors.