Other Proteins

Leukocyte immunoglobulin-like receptor subfamily A member 3 is also known as CD85 antigen-like family member E, Immunoglobulin-like transcript 6, ILT-6, Leukocyte immunoglobulin-like receptor 4, LIR-4 and Monocyte inhibitory receptor HM43/HM31. In humans, it is encoded by the LILRA3 gene. It acts as soluble receptor for class I MHC antigens. Binds both classical and non-classical HLA class I molecules but with reduced affinities compared to LILRB1 or LILRB2.It is detected in B-cells, natural killer (NK) cells, peripheral blood monocytes and lung.

The cluster of differentiation (CD) system is commonly used as cell markers in Immunophenotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules associating with the immune function of the cell. There are more than 320 CD unique clusters and subclusters have been identified. Some of the CD molecules serve as receptors or ligands important to the cell through initiating a signal cascade which then alter the behavior of the cell. Some CD proteins do not take part in cell signal process but have other functions such as cell adhesion. Cell surface glycoprotein CD200 receptor 1 (CD200R1) is an isoform of CD200 receptors that is expressed on cells of the myeloid lineage. CD200R1 is a receptor for the OX-2 membrane glycoprotein. The receptor-substrate interaction may serve as a myeloid downregulatory signal.

Butyrophilin Subfamily 3 Member A1 (BTN3A1/CD277) is a type I transmembrane glycoprotein member of the Ig superfamily. It is expressed on a wide variety of immune cells. Similar to BTN3A2 and BTN3A3, BTN3A1 is composed of an extracellular N-terminal IgV and a membraneproximal IgC domain followed by a transmembrane domain and a cytoplasmic tail. These Ig domains are also found in B7 family costimulatory molecules, suggesting structural and functional similarities between the two protein families. BTN3A1 acts as a critical protein for the activation of Vγ9Vδ2 T cells following detection of distressed cells. The anti-tumor responses of Vγ9Vδ2 T cells may be enhanced with agonistic anti-BTNA3 antibodies.

CD48 antigen; also known as B-lymphocyte activation marker BLAST-1; BCM1 surface antigen; Leukocyte antigen MEM-102; TCT.1; CD48; BCM1;and BLAST1; CD48 contains one Ig-like C2-type domain and one Ig-like V-type domain; but does not have a transmembrane domain; however; but is held at the cell surface by a GPI anchor via a C-terminal domain which maybe cleaved to yield a soluble form of the receptor. CD48 may facilitate interaction between activated lymphocytes and be involved in regulating T-cell activation. CD48 plays a vital role as an environmental sensor for regulating progenitor cell numbers and inhibiting tumor development. It is suggested that the anti-CD48 mAb has the potential to become an effective therapeutic mAb against multiple myeloma.

CD200 is a transmembrane immunoregulatory protein that belongs to the immunoglobulin superfamily. It contains one Ig like V type domain and one Ig like C2 type domain in its extracelluar domain. CD200 is widely but not ubiquitously expressed. Its receptor (CD200R) is restricted primarily to mast cells; basophils; macrophages; and dendritic cells; which suggests myeloid cell regulation as the major function of CD200. CD200 and CD200R associate via their respective N-terminal Ig-like domains. In myeloid cells; CD200R initiates inhibitory signals following receptor-ligand contact. In T cells; CD200 functions as a co-stimulatory molecule independent of the CD28 pathway. In addition; CD200 also plays an important role in prevention of graft rejection; autoimmune diseases and spontaneous abortion.

The cluster of differentiation (CD) system is commonly used as cell markers in immunophynotyping. Different kinds of cells in the immune system can be identified through the surface CD molecules which associating with the immune function of the cell. The CD155 ligand CD96 is a member of the Ig superfamily. It's a immunoglobulin-like protein tentatively allocated to the repertoire of human NK receptors. NK cells recognize poliovirus receptor (PVR); anectins and nectin-like protein family member serve to mediate cell-cell adhesion; cell migration; with the presence of an additional receptor; CD96. CD96 promotes NK cell adhesion to target cells expressing PVR; stimulates cytotoxicity of activated NK cells; and mediates acquisition of PVR from target cells.

Human Siglec-15 is a transmembrane glycoprotein in the Siglec family. Siglecs are type I transmembrane proteins where the NH3+-terminus is in the extracellular space and the COO?-terminus is cytosolic. Each Siglec contains an N-terminal V-type immunoglobulin domain (Ig domain) which acts as the binding receptor for sialic acid. These lectins are placed into the group of I-type lectins because the lectin domain is an immunoglobulin fold. All Siglecs are extended from the cell surface by C2-type Ig domains which have no binding activity. Siglecs differ in the number of these C2-type domains. Human Siglec-15 consists of a 244 amino acid (aa) extracellular domain (ECD) with two Ig-like domains, a 21 aa transmembrane segment, and a 44 aa cytoplasmic domain. Siglec-15 function is important for osteoclast formation and TRANCE/RANK Ligand signaling in osteoclasts.

CD112 is a type I transmembrane glycoprotein belonging to the Immunoglobulin superfamily. It comprises one Ig-like V-type domain and two Ig-like C2-type domains in the extracellular region. The V domain is believed to mediate nectin binding to its ligands. Nectin2 is known to bind the pseudorabies virus, and herpes simplex virus2 (HSV2), involving in cell to cell spreading of these viruses. It does not bind poliovirus. As a homophilic adhesion molecule, CD112 is found concentrated in adherens junctions, and exists on neurons, endothelial cells,epithelial cells and fibroblasts. CD112 has been identified as the ligand for DNAM-1 (CD226), and the interaction of CD226/CD112 mediates cytotoxicity and cytokine secretion by T and NK cells. The costimulatory responses may be a critical component in allergic reactions and may therefore become targets for anti-allergic therapy.

Tumor necrosis factor ligand superfamily member 4(TNFSF4/OX40L) is a single-pass type II membrane protein. OX40L is expressed on the surface of activated B cells;T cells;dendritic cells and endothelial cells. OX40L binds to OX40(CD134);a member of the TNF receptor superfamily that is expressed predominantly on activated CD4+ T cells. OX40-OX40L co-stimulates signal to promote the survival and proliferation of activated CD4+ T cells and prolong the immune response. It involved in T-cell proliferation and cytokine production. Additional;it has been found association with systemic lupus erythematosus;no association with occurrence of atherosclerosis.