Inhibitory receptor involved in the down-regulation of the immune response and the development of immune tolerance (PubMed:11875462). Receptor for FN1 (PubMed:34089617). Receptor for apolipoprotein APOE (PubMed:30333625). Receptor for ALCAM/CD166 (PubMed:29263213). Inhibits receptor-mediated phosphorylation of cellular proteins and mobilization of intracellular calcium ions (PubMed:9151699). Inhibits FCGR1A/CD64-mediated monocyte activation by inducing phosphatase-mediated down-regulation of the phosphorylation of multiple proteins including LCK, SYK, LAT and ERK, leading to a reduction in TNF production (PubMed:19833736). This inhibition of monocyte activation occurs at least in part via binding to FN1 (PubMed:34089617). Inhibits T cell proliferation, inducing anergy, suppressing the differentiation of IFNG-producing CD8+ cytoxic T cells and enhancing the generation of CD8+ T suppressor cells (PubMed:16493035, PubMed:19833736, PubMed:29263213). Induces up-regulation of CD86 on dendritic cells (PubMed:19860908). Interferes with TNFRSF5-signaling and NF-kappa-B up-regulation (PubMed:11875462). Interacts with PTPN6. Ligand binding leads to internalization and translocation to an antigen-processing compartment. Detected on monocytes, macrophages, dendritic cells, natural killer cells and B-cells (at protein level). Expressed in the lung. Induced on monocyte-derived macrophages by S.typhimurium infection (PubMed:19860908). Induced on monocytes and dendritic cells upon contact with CD8(+)CD28(-) alloantigen-specific T suppressor (Ts) cells (PubMed:11875462). Contains 3 copies of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). This motif is involved in modulation of cellular responses. The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases. Activated by APOE on acute myeloid leukemia (AML) cells which leads to suppression of T cell proliferation and promotion of AML cell migration and infiltration (PubMed:30333625). LILRB4 signaling on AML cells is mediated by PTPN11/SHP-2 (PubMed:30333625). Alternative use of an acceptor site.