DIRECT ASSOCIATION OF ADENOSINE-DEAMINASE WITH A T-CELL ACTIVATION ANTIGEN, CD26

CD26, the T cell activation molecule dipeptidyl peptidase IV (DPPIV), associates with a 43-kilodalton protein. Amino acid sequence analysis and immunoprecipitation studies demonstrated that this 43-kilodalton p rotein was adenosine deaminase (ADA). ADA was coexpressed with CD26 on the Jurkat T cell lines, and an in vitro binding assay showed that th e binding was through the extracellular domain of CD26. ADA deficiency causes severe combined immunodeficiency disease (SCID) in humans. Thu s, ADA and CD26 (DPPIV) interact on the T cell surface, and this inter action may provide a clue to the pathophysiology of SCID caused by ADA deficiency.