A second subunit of CD8 is expressed in human T cells
Norment, A.M.; Littman, D.R.
EMBO Journal 7(11): 3433-3439
1988
ISSN/ISBN: 0261-4189 PMID: 3145195 Document Number: 311948
The CD8 glycoprotein plays important functions in T cell development and in T cell activation. In rodents, CD8 is a heterodimer, consisting of an .alpha.-chain (Lyt2) and a .beta.-chain (Lyt3). In humans, only the .alpha.-chain has been detected, and it has been thought that CD8 consists of homodimers of this protein. We have isolated functional cDNA clones encoding human CD8.beta., and show that the CD8.beta. protein is expressed on the surface of CD8+ human T cells. cDNA clones encoding multiple forms of the human CD8.beta.-chain have been isolated and characterized. These structural variants, which are likely to arise by alternative splicing, differ in the sequences encoding the cytoplasmic domain, which can consist of 19, 30 or 52 amino acids. One of the cDNAs lacks nucleotide sequences corresponding to a hydrophobic transmembrane domain, and may encode a secreted CD8.beta. protein. The protein product of the human CD8.beta. gene can be detected by a recently described anti-CD8 monoclonal antibody, 597. Expression of the epitope recognized by this antibody requires co-expression of the CD8.alpha. and CD8.beta. gene products. About 90% of human CD8.alpha. positive thymocytes and peripheral blood lymphocytes express CD8.beta. at the cell surface. Expression of the CD8.beta. chain is thus conserved between human and rodents, and the variant CD8.beta. polypeptides may have distinct roles in T cell function and development.