Specificity: CD8 is a 68 kDa transmembrane glycoprotein expressed as a heterodimer by a majority of thymocytes, and by major histocompatibility complex (MHC) class I restricted, mature, suppressor/cytotoxic T-cells. Immunogen: A 13 amino acid peptide from C-terminal cytoplasmic domain of alpha chain of human CD8 molecule.