Featured CD Protein Molecules

CD antigens are proteins originally defined as being present on the cell surface of leucocytes but now including some intracellular molecules and molecules present on cells other than leucocytes. Such molecules are assigned a CD number following a consensus reached at regularly held international workshops. CD antigens include a large number of cell surface receptors, signalling molecules and adhesion molecules.

The ‘cluster of differentiation’ antigens that were originally marker antigens found on different classes of lymphocytes using monoclonal antibodies. The CD nomenclature was introduced as a means of bringing consistency because the same CD antigen can be recognized by different monoclonal antibodies; international workshops are run to cross-compare antibodies against standard antigens. The CD antigens are no longer restricted to the immune system and the list covers a wide range of cell surface antigens, some of which are transiently expressed at particular stages of differentiation or following stimulation of cells by particular agents.