May act as receptor for class I MHC antigens. Becomes activated upon coligation of LILRB3 and immune receptors, such as FCGR2B and the B-cell receptor. Down-regulates antigen-induced B-cell activation by recruiting phosphatases to its immunoreceptor tyrosine-based inhibitor motifs (ITIM).
The leukocyte immunoglobulin-like receptor (LILR) B4 belongs to a family of cell surface receptors that possesses cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). LILRB4 is believed to down-regulate activation signals mediated by non-receptor tyrosine kinase cascades through the recruitment of SHP-1. LILRB4 is associated with the pathological processes of various inflammatory diseases.The LILRB4 is a central inhibitory receptor in uterine dendritic cells (uDCs) that plays essential immune-regulatory roles at the maternal-fetal interface.
Mouse Leukocyte Immunoglobulin-like Receptor Subfamily B Member 4 (LILRB4/CD85k/ILT3) is an approximately transmembrane glycoprotein that negatively regulates immune cell activation. Mouse LILRB4 consists of a 215 amino acid (aa) extracellular domain with two Ig-like domains; a 22 aa transmembrane segment; and a 75 aa cytoplasmic domain with 3 immunoreceptor tyrosine-based inhibitory motifs (ITIM). Within the ECD; mouse LILRB4 shares 45% and 77% aa sequence identity with human and rat LILRB4; respectively. Alternative splicing of mouse LILRB4 generates a potentially soluble isoform that lacks the transmembrane segment. LILRB4 is expressed on dendritic cells (DC); monocytes; macrophages; and vascular endothelial cells (EC). Ligation of LILRB4 triggers ITIM-mediated inhibition of cellactivating signaling; leading to enhanced immune tolerance and reduced allogeneic graft rejection. Soluble LILRB4 induces the differentiation of CD8+ T suppressor cells (Ts) that can inhibit the effector functions of CD4+ Th cells and CD8+ CTL. In turn; CD8+ Ts cells induce LILRB4 up-regulation and a tolerogenic phenotype in monocytes; DC; and EC.
Human Leukocyte Immunoglobulin-like Receptor Subfamily B Member 5 (LILRB5/CD85c/LIR-8) belongs to a family of transmembrane glycoproteins that negatively regulate immune cell activation. Mature human LIR-8 consists of a 435 amino acid (aa) extracellular domain with four Iglike domains, a 21 aa transmembrane segment, and a 111 aa cytoplasmic domain with two immunoreceptor tyrosine-based inhibitory motifs (ITIM). Alternative splicing of human LIR-8 generates an isoform that lacks the second Ig-like domain. LIR-8 is expressed on NK cells and in the tryptic granules of mast cells. Following cell activation and degranulation, it is present on the mast cell surface. Activated mast cells may also release soluble forms of LIR-8.
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