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. Cluster of differentiation 36 (CD36), also known as FAT, SCARB3, GP88, glycoprotein IV (gpIV) and glycoprotein IIIb (gpIIIb), is a member of the CD system as well as the class B scavenger receptor family of cell surface proteins. CD36 can be found on the surface of many cell types in vertebrate animals and it consists of 472 amino acids and is extensively glycosylated. It is an integral membrane protein primarily serving as receptors for thrombospondin and collagen and by the erythrocytes infected with the human malaria parasite. The role of CD36 as a cell surface receptor has been extended to that of a signal transduction molecule.
CD38, also known as ADP-ribosyl cyclase, is a Type II integral membrane protein. The enzyme is able to transform NAD(P)+ into three different products with calcium mobilizing ability, cyclic ADP-ribose, NAADP+, and ADP-ribose . CD38 is expressed in B and T lymphocytes, osteoclasts, and in cardiac, pancreatic, liver and kidney cells . Through its production of cyclic ADP-ribose, CD38 modulates calcium-mediated signal transduction in many types of cells, including neutrophils and pancreatic beta cells.
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. Cluster of differentiation 38 (CD38), also known as ADP-ribosyl cyclase, is a glycoprotein found on the surface of many immune cells (white blood cells), including CD4+, CD8+, B and natural killer cells. It shares several characteristics with ADP-ribosyl cyclase 2 CD157. CD38 is a multifunctional ectoenzyme that catalyzes the synthesis and hydrolysis of cyclic ADP-ribose (cADPR) from NAD+ to ADP-ribose. It also functions in cell adhesion, signal transduction and calcium signaling. CD38 has been used as a prognostic marker in leukemia. It can also be used to identify plasma cells.
The protein encoded by this gene is a non-lineage-restricted, type II transmembrane glycoprotein that synthesizes and hydrolyzes cyclic adenosine 5'-diphosphate-ribose, an intracellular calcium ion mobilizing messenger. The release of soluble protein and the ability of membrane-bound protein to become internalized indicate both extracellular and intracellular functions for the protein. This protein has an N-terminal cytoplasmic tail, a single membrane-spanning domain, and a C-terminal extracellular region with four N-glycosylation sites. Crystal structure analysis demonstrates that the functional molecule is a dimer, with the central portion containing the catalytic site. It is used as a prognostic marker for patients with chronic lymphocytic leukemia. Alternative splicing results in multiple transcript variants.
CD39,also known as ectonucleoside triphosphate diphosphohydrolase 1 (NTPDase 1), is a multi-pass membrane ectoenzyme that metabolizes adenosine-5'-triphosphate (ATP) to regulate purinergic signaling. Purinergic signaling by extracellular ATP and its metabolites regulate many biological processes, including vascular tone, digestion, neuronal function, and inflammation in both normal and diseased states. CD39 is expressed in endothelial cells in the vasculature to regulate local platelet purinergic signaling via metabolism of ATP to adenosine. Accordingly, CD39 regulates platelet activation aggregation and contributes to the antithrombotic properties of endothelial cells. ATP and its metabolites also finely modulate the activity of T cells and macrophages. Immunomodulation is regulated, in part, by the availability of extracellular ATP and adenosine, suggesting that CD39 may play an immunosuppressive role in the tumor microenvironment.
The protein encoded by this gene is part of the T-cell receptor/CD3 complex (TCR/CD3 complex) and is involved in T-cell development and signal transduction. The encoded membrane protein represents the delta subunit of the CD3 complex, and along with four other CD3 subunits, binds either TCR alpha/beta or TCR gamma/delta to form the TCR/CD0 complex on the surface of T-cells. Defects in this gene are a cause of severe combined immunodeficiency autosomal recessive T-cell-negative/B-cell-positive/NK-cell-positive (SCIDBNK). Two transcript variants encoding different isoforms have been found for this gene. Other variants may also exist, but the full-length natures of their transcripts has yet to be defined.
The CD3 complex, composed of gamma, delta, epsilon, and zeta subunits, is essential for the assembly, trafficking, and surface expression of the T cell receptor (TCR) complex. These subunits are structurally related members of the immunoglobulin superfamily and are encoded by closely linked genes on human chromosome 11. CD3 is expressed by thymocytes in a developmentally regulated manner and by all mature T cells, but not on B or NK cells. The CD3 subunits play a crucial role in transducing antigen-recognition signals into the cytoplasm of T cells. The cytoplasmic tails of CD3 subunits contain a double tyrosine-based motif that associates with cytoplasmic signal transduction molecules, mediating T cell activation through the TCR. Crosslinking of the TCR initiates intracellular biochemical pathways that result in cellular activation, proliferation, and potentially growth arrest and cell survival. CD3 is present on 68-82% of normal peripheral blood lymphocytes, 65-85% of thymocytes, and Purkinje cells in the cerebellum. Decreased percentages of T lymphocytes may be observed in some autoimmune diseases. Defects in the CD3 gene are associated with CD3 immunodeficiency, highlighting its importance in immune function and regulation.
CD3D is a component of the TCR-CD3 complex, which is present on T-lymphocyte cell surface that plays an essential role in adaptive immune response. When antigen presenting cells (APCs) activate T-cell receptor (TCR), TCR-mediated signals are transmitted across the cell membrane by the CD3 chains CD3D, CD3E, CD3G and CD3Z. All CD3 chains contain immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic domain. Upon TCR engagement, these motifs become phosphorylated by Src family protein tyrosine kinases LCK and FYN, resulting in the activation of downstream signaling pathways. In addition, CD3D plays an essential role in thymocyte differentiation. It participates in correct intracellular TCR-CD3 complex assembly and surface expression. In absence of a functional TCR-CD3 complex, thymocytes are unable to differentiate properly. It interacts with CD4 and CD8 and thus serves to establish a functional link between the TCR and coreceptors CD4 and CD8, which is needed for activation and positive selection of CD4 or CD8 T-cells.
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