The cluster of differentiation (CD) system is commonly used as cell markers in Immunophenotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules associating with the immune function of the cell. There are more than 320 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. CD83 is considered as a marker of mature dendritic cells as well as an adhesion receptor that binds to resting monocytes and a subset of activated CD8+ T cells. In certain conditions, CD83 tended to dimerize or even multimerize through its aberrant intermolecular disulfide bonds. The injection of CD83-Ig can significantly enhance the rate of tumor growth and inhibit the T cell growth.