Mouse CMRF35-like molecule 8, also known as CD300 antigen-like family member A, CMRF35-H9, Immunoglobulin superfamily member 12, Inhibitory receptor protein 60, NK inhibitory receptor, CD300a and CMRF35H, is a single-pass type I membrane protein which belongs to the CD300 family. The CD300 family of myeloid immunoglobulin receptors includes activating ( CD300b, CD300e ) and inhibitory members ( CD300a, CD300f ), as well as molecules presenting a negative charge within their transmembrane domain ( CD300c, CD300d ). CD300A / 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 one Ig-like V-type ( immunoglobulin-like ) domain. CD300A / 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. CD300c is a functional immune receptor able to deliver activating signals upon ligation in RBL-2H3 mast cells. CD300c signaling is partially mediated by a direct association with the immune receptor tyrosine-based activation motif-bearing adaptor FcεRγ. CD300a and CD300c play an important role in the cross-regulation of TNF-alpha and IFN-alpha secretion from plasmacytoid dendritic cells (pDCs).