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 (PubMed:10746781, PubMed:16339535, PubMed:9701027). Negatively regulates the Toll-like receptor (TLR) signaling mediated by MYD88 but not TRIF through activation of PTPN6 (PubMed:22043923). Upon tyrosine-phosphorylation, interacts with PTN6/SHP-1 and PTPN11/SHP-2 and INPP5D. Expressed not only by natural killer (NK) cells but also by T-cell subsets, B-cells, dendritic cells, mast cells, granulocytes and monocytes. Phosphorylated on tyrosine. N-glycosylated. Belongs to the CD300 family. Extended N-terminus.