Cluster of Differentiation (CD) Proteins

The CD antigens / Cluster of Differentiation mainly act as receptors and ligands to start a signal cascade and alter the cell behavior. Some CD proteins have cell adhesion function. The CD system is commonly used as cell markers in immunophenotyping, allowing cells to be defined based on what molecules are present on their surface. These markers are often used to associate cells with certain immune functions, for example CD4 and CD8 are common T cell markers.