Heterophilic receptor of the signaling lymphocytic activation molecule (SLAM) family; its ligand is CD48. SLAM receptors triggered by homo- or heterotypic cell-cell interactions are modulating the activation and differentiation of a wide variety of immune cells and thus are involved in the regulation and interconnection of both innate and adaptive immune response. Activities are controlled by presence or absence of small cytoplasmic adapter proteins, SH2D1A/SAP and/or SH2D1B/EAT-2. Acts as activating natural killer (NK) cell receptor (PubMed:10359122, PubMed:8376943, PubMed:11714776). Activating function implicates association with SH2D1A and FYN (PubMed:15713798). Downstreaming signaling involves predominantly VAV1, and, to a lesser degree, INPP5D/SHIP1 and CBL. Signal attenuation in the absence of SH2D1A is proposed to be dependent on INPP5D and to a lesser extent PTPN6/SHP-1 and PTPN11/SHP-2 (PubMed:10934222, PubMed:15713798). Stimulates NK cell cytotoxicity, production of IFN-gamma and granule exocytosis (PubMed:8376943, PubMed:11714776). Optimal expansion and activation of NK cells seems to be dependent on the engagement of CD244 with CD48 expressed on neighboring NK cells (By similarity). Acts as costimulator in NK activation by enhancing signals by other NK receptors such as NCR3 and NCR1 (PubMed:10741393). At early stages of NK cell differentiation may function as an inhibitory receptor possibly ensuring the self-tolerance of developing NK cells (PubMed:11917118). Involved in the regulation of CD8(+) T-cell proliferation; expression on activated T-cells and binding to CD488 provides costimulatory-like function for neighboring T-cells (By similarity). Inhibits inflammatory responses in dendritic cells (DCs) (By similarity). Interacts with CD48 (PubMed:9841922,PubMed:27249817). Interacts (via phosphorylated ITSM 1-4) with SH2D1A (via SH2 domain); SH2D1A probably mediates association with FYN. Interacts (via phosphorylated ITSM 3) with PTPN11/SHP-2, INPP5D/SHIP1, PTPN6/SHP-1 and CSK; binding of SH2D1A/SAP prevents association with PTPN11, PTPN6 and CSK; conflictingly a similar association has been described for phosphorylated ITSM 1 also including GRB2 and PLCG1. Interacts weakly (via phosphorylated ITSM 2) with PTPN11/SHP-2 and CSK (PubMed:10358138, PubMed:10934222, PubMed:12458214, PubMed:24642916, PubMed:26221972, PubMed:15713798). Interacts with SH2D1B (PubMed:12458214, PubMed:24642916). Interacts with PIK3R1; PI3K recruits SH2D1A (PubMed:11815622). Interacts with MHC class I proteins; the interaction is proposed to prevent self-killing of NK cells. Receptor engagement results in a recruitment to lipid drafts essential for the subsequent tyrosine phosphorylation of the ITSMs. Expressed in spleen, PBL, followed by lung, liver, testis and small intestine. Expressed in all natural killer (NK) cells, monocytes and basophils, TCR-gamma/delta+ T-cells, monocytes, basophils, and on a subset of CD8(+) T-cells. The ITSMs (immunoreceptor tyrosine-based switch motifs) with the consensus sequence T-X-Y-X-X-[VI] present in SLAM family receptors have overlapping specificity for activating and inhibitory SH2 domain-containing binding partners. Especially they mediate the interaction with the SH2 domain of SH2D1A and SH2D1B. A 'three-pronged' mechanism is proposed involving threonine (position -2), phosphorylated tyrosine (position 0) and valine/isoleucine (position +3). N-linked glycosylation is essential for the binding to its ligand CD48. Also O-glycosylated, in contrast, O-linked sialylation has a negative impact on ligand binding. Phosphorylated by FYN and CSK on tyrosine residues following activation. Coligation with inhibitory receptors such as KIR2DL1 inhibits phosphorylation upon contact of NK cells with sensitive target cells. Binds to CD48 with a sronger affinity than isoform 1, and interactions induces greater cytotoxicity and intracellular calcium release.