CD300A is a single-pass type I membrane protein that belongs to the CD300 family. CD300A consists of a 163 amino acid (aa) extracellular domain (ECD) with one Ig-like V- type domain, a 21 amino acid transmembrane segment, and a 98 amino acid cytoplasmic domain with tyrosine residues. CD300A is expressed not only by natural killer (NK) cells but also by T-cell subsets, B-cells, dendritic cells, mast cells, granulocytes and monocytes. CD300A 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.