CMRF35-like molecule 8, also known as CD3 antigen-like family member A, CMRF35-H9, Immunoglobulin superfamily member 12, Inhibitory receptor protein 6, NK inhibitory receptor, CD3a and CMRF35H, is a single-pass type I membrane protein which belongs to theCD3 family. The CD3 family of myeloid immunoglobulin receptors includes activating ( CD3b, CD3e ) and inhibitory members ( CD3a, CD3f ), as well as molecules presenting a negative charge within their transmembrane domain ( CD3c, CD3d ). CD3A / IGSF12 is expressed not only by natural killer (NK) cells but also by T-cell subsets, B-cells, dendritic cells, mast cells, granulocytes and monocytes.It contains oneIg-like V-type ( immunoglobulin-like ) domain. CD3A / IGSF12 is an inhibitory receptor which may contribute to the down-regulation of cytolytic activity in natural killer (NK) cells, and to the down-regulation of mast cell degranulation. CD3c is a functional immune receptor able to deliver activating signals upon ligation in RBL-2H3 mast cells. CD3c signaling is partially mediated by a direct association with the immune receptor tyrosine-based activation motif-bearing adaptor FcεRγ. CD3a and CD3c play an important role in the cross-regulation of TNF-alpha and IFN-alpha secretion from plasmacytoid dendritic cells (pDCs).