Acts as an inhibitory receptor for myeloid cells and mast cells (PubMed:17438331). 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 (PubMed:21865548). Plays an important role in the maintenance of immune homeostasis, by promoting macrophage-mediated efferocytosis and by inhibiting dendritic cell-mediated efferocytosis (PubMed:26768664). Negatively regulates Fc epsilon receptor-dependent mast cell activation and allergic responses via binding to ceramide which acts as a ligand (PubMed:23123064). 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 (PubMed:26124135). Negatively regulates the Toll-like receptor (TLR) signaling mediated by MYD88 and TRIF through activation of PTPN6/SHP-1 and PTPN11/SHP-2 (By similarity). Inhibits osteoclast formation (PubMed:14662855). Induces macrophage cell death upon engagement (PubMed:18097021). (Microbial infection) Acts as a functional murine norovirus (MNV) receptor that mediates binding to the cell surface and is both necessary and sufficient for viral entry and replication. Primary determinant of MNV species tropism and is sufficient to render cells permissive to infection by MNV. Can render nonmurine mammalian cells susceptible to MNV infection (PubMed:27681626, PubMed:27540007). Interacts with PTPN6/SHP-1 in a tyrosine phosphorylation dependent manner (PubMed:14662855). Interacts with IL4R (PubMed:26124135). Expressed in myeloid cells. Present on the surface of macrophages (at protein level). Highly expressed by alveolar, splenic macrophages and bone marrow-derived dendritic cells. Expression is increased following aeroallergen challenge in macrophages, mast cells, and eosinophils. Up-regulated by interleukin-4/IL-4. Phosphorylated on tyrosine. Belongs to the CD300 family.