The OKT8 monoclonal antibody specifically reacts with human CD8α molecule, a tyPEI transmembrane glycoprotein of 32-34 kDa. CD8α is a member of the Ig superfamily, expressed as a homodimer (CD8αα) or as a heterodimer (CD8αβ). CD8+ αβ T lymphocytes express both CD8αα and CD8αβ, while some T lymphocytes and the natural killer cells express only the homodimers. CD8 binds to MHC class I and influences the development and the activation of T lymphocytes.

OKT8, RPA-T8, and HIT8a antibodies do not compete with each other for binding to peripheral leukocytes, meaning that that they do not recognize the same epitoPEor block each other by steric hindrance.