The function of LILRB4 (leukocyte immunoglobulin like receptor B4, Ensembl gene identifier ENSG00000186818) is as follows. 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+ cytotoxic 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). {ECO:0000269|PubMed:11875462, ECO:0000269|PubMed:16493035, ECO:0000269|PubMed:19833736, ECO:0000269|PubMed:19860908, ECO:0000269|PubMed:29263213, ECO:0000269|PubMed:30333625, ECO:0000269|PubMed:34089617, ECO:0000269|PubMed:9151699}.