<unk>  (cluster of differentiation 8) is a transmembrane glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). Along with the TCR, the<unk>  co-receptor plays a role in T cell signaling and aiding with cytotoxic T cell-antigen interactions. Like the TCR,<unk>  binds to a major histocompatibility complex (MHC) molecule, but is specific for the MHC class I protein. There are two isoforms of the protein, alpha and beta, each encoded by a different gene. In humans, both genes are located on chromosome 2 in position 2p12.
CD8
CD4
CD74
CD137
CD22
CD23
CDV3 
CD44