FUNCTION: Functions as an inhibitory receptor that plays a constitutive negative regulatory role on cytolytic function of natural killer (NK) cells, B-cells and T-cells. Activation by Tyr phosphorylation results in recruitment and activation of the phosphatases PTPN6 and PTPN11. It also reduces the increase of intracellular calcium evoked by B-cell receptor ligation. May also play its inhibitory role independently of SH2-containing phosphatases. Modulates cytokine production in CD4+ T-cells, down-regulating IL2 and IFNG production while inducing secretion of transforming growth factor beta. Also down-regulates IgG and IgE production in B-cells as well as IL8, IL10 and TNF secretion. Inhibits proliferation and induces apoptosis in myeloid leukemia cell lines as well as prevents nuclear translocation of NF-kappa-B p65 subunit/RELA and phosphorylation of I-kappa-B alpha/CHUK in these cells. Inhibits the differentiation of peripheral blood precursors towards dendritic cells. {ECO:0000269|PubMed:10229813, ECO:0000269|PubMed:10764762, ECO:0000269|PubMed:11069054, ECO:0000269|PubMed:11160222, ECO:0000269|PubMed:12072189, ECO:0000269|PubMed:15939744, ECO:0000269|PubMed:15950745, ECO:0000269|PubMed:16380958, ECO:0000269|PubMed:9285412, ECO:0000269|PubMed:9692876}.