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 which 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. CD300 is a glycoprotein family of cell surface molecules that regulate a diverse array of cellular processes via their triggering and inhibitory receptor functions. The CD300 family of myeloid immunoglobulin receptors includes activating(CD300b, CD300e) and inhibitory members(CD300a, CD300f), as well as CD300c and CD300d, whose function is uncertain.

CD300C is a single-pass type I membrane protein which belongs to the immunoregulatory signaling (IRS) family. CD300C contains one Ig-like V-type domain and is present on the surface of natural killer cells, granulocytes, most myeloid cells, dendritic cells, and a subpopulation of T and B lymphocytes. The CD300C (CMRF-35A) and CD300A (CMRF-35H) molecules are homologous leukocyte surface proteins. CD300a and CD300C play an important role in the cross-regulation of TNF-alpha and IFN-alpha secretion from pDCs. CD300A and CD300C are indistinguishable on the surface of NK cells. The ligand for CD300C is presently unknown.