The cluster of differentiation (CD) system is commonly used as cell markers in immunophynotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules which associating with the immune function of the cell. There are more than 32 CD unique clusters and subclusters have been identified. Some of the CD molecules serve as receptors or ligands important to the cell through initiating a signal cascade which then alter the behavior of the cell. Some CD proteins do not take part in cell signal process but have other functions such as cell adhesion. CD3 is a glycoprotein family of cell surface molecules that regulate a diverse array of cell processes via their triggering and inhibitory receptor functions. The CD3 family of myeloid immunoglobulin receptors includes activating(CD3b, CD3e) and inhibitory members(CD3a, CD3f), as well as CD3c and CD3d, whose function is uncertain.