CD8 is a cell surface glycoprotein, member of immunoglobulin superfamily; at 2p12CD8 molecule consists of two chains, termed alpha and beta chain, which are expressed as a disulphide-linked alpha/beta heterodimer 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 heterodimer. CD8 functions as a co-receptor 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). MHC class I restricted receptor; binds to nonpolymorphic region of class I molecules and may increase avidity of interactions between cytotoxic T-cell and target cell during antigen-specific activation. CD8 stains cortical thymocytes (70-80%), T-cells (25-35% of mature peripheral T-cells, mostly cytotoxic T-cells); NK cells (30%, which are also CD3 negative). CD8 has been shown to be an important marker to analyze T-cell mediated inflammatory dermatoses and useful for analysis of mycosis fungoides.