T-cell surface glycoprotein CD8alpha chain, also known as CD8a, is a single-pass type I membrane protein. TheCD8 glycoprotein is expressed by thymocytes, mature T cells and natural killer(NK) cells and has been implicated in the recognition of monomorphicdeterminants on major histocompatibility complex (MHC) Class I antigens, and insignal transduction during the course of T-cell activation. Both human androdent CD8 antigens are comprised of two distinct polypeptide chains, alpha andbeta. The Ig domains of CD8 alpha are involved in controlling the ability ofCD8 to be expressed. Mutation of B- and F-strand cysteine residues in CD8 alphareduced the ability of the protein to fold properly and, therefore, to beexpressed. Defects in CD8A are a cause of familial CD8 deficiency. Familial CD8deficiency is a novel autosomal recessive immunologic defect characterized byabsence of CD8+ cells, leading to recurrent bacterial infections.

CD8a molecule