– 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.