CD81 is a member of the transmembrane 4 superfamily and it is a cell surface glycoprotein that is known to complex with integrins. CD81 appears to promote muscle cell fusion and support myotube maintenance. Also it may be involved in signal transduction. Moreover, CD81 plays a critical role in Hepatitis C attachment and cell entry by interacting with virus' E1/E2 glycoproteins heterodimer. The large extracellular loop of CD81 binds the hepatitis E2 glycoprotein dimer. It also appears to play a role in liver invasion by Plasmodium species.