CD8 molecule consists of two chains, termed alpha and Beta chain, which are expressed as a disulphide-linked alpha/Beta heterdimer or as an alpha/alpha homodimer on T cell subset, thymocytes and NK cells. The majority of CD8+ T cells express CD8 as alpha/Beta heterdimer. CD8 functions as a coreceptor in concert with TCR for binding the MHC class I/peptide complex. The HIV-2 envelope glycoprotein binds CD8 alpha chain (but not Beta chain).