CD81 (also known as TAPA1 or TSPAN28) is a membrane protein in the tetraspanin superfamily, characterized by the presence of four conserved transmembrane regions. Many members of this superfamily are expressed on white blood cells and play important roles in signal transduction, intercellular interactions, cell activation and development, as well as regulation of growth and movement. CD81 is involved in signal transduction and cell adhesion in the immune system, and has been identified as an essential receptor for hepatitis C virus (HCV). This protein can form complexes with integrins. This protein is considered a candidate gene for malignant tumors because its gene is located in the tumor suppressor gene region.
