Acts as an inhibitory receptor for myeloid cells and mast cells (PubMed:15549731). Positively regulates the phagocytosis of apoptotic cells (efferocytosis) via phosphatidylserine (PS) recognition; recognizes and binds PS as a ligand which is expressed on the surface of apoptotic cells. Plays an important role in the maintenance of immune homeostasis, by promoting macrophage-mediated efferocytosis and by inhibiting dendritic cell-mediated efferocytosis (By similarity). Negatively regulates Fc epsilon receptor-dependent mast cell activation and allergic responses via binding to ceramide and sphingomyelin which act as ligands (PubMed:24035150). May act as a coreceptor for interleukin 4 (IL-4). Associates with and regulates IL-4 receptor alpha-mediated responses by augmenting IL-4- and IL-13-induced signaling (By similarity). Negatively regulates the Toll-like receptor (TLR) signaling mediated by MYD88 and TRIF through activation of PTPN6/SHP-1 and PTPN11/SHP-2 (PubMed:22043923). Inhibits osteoclast formation. Induces macrophage cell death upon engagement (By similarity). Interacts with PTPN6/SHP-1 in a tyrosine phosphorylation dependent manner (PubMed:15184070, PubMed:15549731). Interacts with IL4R (By similarity). Highly expressed in spleen, peripheral blood leukocyte and monocyte, and lung. Weakly expressed in thymus, heart, brain, placenta, liver, skeletal muscle, kidney, pancreas, prostate, testis, ovary, small intestine or colon. Expressed selectively in monocytes and monocyte-related cells. Phosphorylated on tyrosine. Belongs to the CD300 family.