Anti-TAPA-1 (CD81) Antibody, clone 5A6 clone 5A6, from mouse

CD81 antigen (UniProt: P60033; also known as 26 kDa cell surface protein TAPA-1, Target of the antiproliferative antibody 1, Tetraspanin-28, Tspan-28, CD81) is encoded by the CD81 (also known as TAPA1, TSPAN28) gene (Gene ID: 975) in human. TAPA-1 is a nonglycosylated, homodimeric, multi-pass membrane protein of the tetraspanin (TM4SF) family. It is expressed in a wide range of cells, including hematolymphoid, neuroectodermal, and mesenchymal tumor cell lines and is reported to play a role in the regulation of lymphoma cell growth. It contains four transmembrane domains, two extracellular loops, and short amino and carboxyl termini that are intracellular. TAPA-1 is shown to affect cell adhesion, morphology, activation, proliferation, and differentiation of B, T, and other cells. On B cells it is a part of a complex involving CD21, CD19, and Leu13 and this complex is reported to reduce the threshold for B cell activation via the B cell receptor by bridging antigen specific recognition and CD21-mediated complement recognition. On T cells, it is shown to associate with CD4 and CD8 and provides a costimulatory signal with CD3. It is also reported to act as a receptor for hepatitis C virus (HCV) in hepatocytes. Mutations in CD81 gene cause common variable immunodeficiency 6 (CVID6) that is characterized by antibody deficiency, hypogammaglobulinemia, recurrent bacterial infections, and an inability to mount an antibody response to antigen. (Levy S., et al. (1998). Annu. Rev. Immunol.16; 89-109; Oren, R., et al. (1990). Mol. Cell Biol. 10(8); 4007-15).