CD81 is widely expressed and is involved in a variety of biological processes. In the brain it is expressed on astrocytes, oligodendrocytes, microglia, and endothelial cells. The CD81 antigen is a 26 kDa cell surface glycoprotein, also known as TAPA-1, and a member of the tetraspanin family, characterised by the presence of four hydrophobic domains. CD81 is known to complex with integrins, and mediates signal transduction events in the regulation of muscle cell fusion, myotube maintenance, signal transduction, cell development, activation, growth, and motility. The CD81 gene is localized in the tumor suppressor gene region and thus it is a candidate gene for malignancies.
