CD81 molecule (also called CD81 antigen or Tetraspanin-28) (CD81)

CD81 molecule (CD81 antigen, Tetraspanin-28) is a cell surface protein belonging to the tetraspanin family, characterized by four transmembrane domains and a large extracellular loop containing a conserved cysteine motif[1][3][4][5]. CD81 is widely expressed in immune cells including B cells, T cells, monocytes, and macrophages, where it functions as a protein scaffold regulating cell signaling, adhesion, migration, and development[1][3][5]. CD81 associates with partner proteins such as CD19 (critical for B cell receptor signaling), CD21, integrins, and is well-known as a required entry receptor for Hepatitis C virus in hepatocytes[2][3][5]. The protein's dynamic extracellular domain enables conformational adaptability for binding diverse ligands, including viral envelope proteins and immune partners; this underlies its role in viral infection, immune signaling, and cancer biology[2][5]. CD81 is also an established exosome marker. Its structural features—including a cholesterol-binding intramembrane cavity—are typical of tetraspanins and may influence membrane organization and cell signaling[5][6]. While no approved drugs directly target CD81, anti-CD81 antibodies are used experimentally, and it is of high interest as a marker, therapeutic candidate, and research tool in immunology, virology, and oncology[4][3][5].

Other names

CD81 antigenTAPA1TSPAN28Tspan-28TAPA-1S5.726 kDa cell surface protein TAPA-1Target of the antiproliferative antibody 1Tetraspanin-28CVID6

Antibody binding (blocking or modulating receptor function, e.g. anti-CD81 mAbs); Potential inhibition of HCV binding and entry (antiviral candidates); Modulation of B cell activation by regulating CD19 trafficking.