Le CD8 (cluster of differentiation 8) est une Glycoprotéine qui sert de co-récepteur s'exprimant à la surface des cellules TC. Les CD8 comportent une chaîne α et une chaîne ß, qui toutes deux ressemblent à immunoglobulin-like domain that is connected to the membrane by a thin stalk. It is attracted to the α₃ portion of the Class I MHC molecule. This affinity keeps the T cell receptor of the cytotoxic T cell and the target cell bound closely together during antigen-specific activation. Cytotoxic T cells with CD8 surface protein are called CD8+ T cells. -->