Role of CD26-adenosine deaminase interaction in T cell-mediated immunity

CD26 is a 110 kDa surface-bound ectopeptidase with intrinsic dipeptidyl peptidase IV (DPP IV) activity, which binds adenosine deaminase (ADA) on the surface of T cells. ADA is an enzyme of the purine metabolism that has been the object of considerable interest mainly because the congenital defect causes severe combined immunodeficiency (SCID). This review focuses on work demonstrating that CD26-ADA interaction has a key role in T cell mediated immunity. The enzymatic and extra-enzymatic roles of ADA and CD26 in the immune context are discussed. Furthermore, the structure of the CD26-ADA complex, the signal transduction pathway triggered by the co-stimulatory ADA-CD26 interaction and the cytokine pattern induced during the immunosynapse are analyzed. In this context, the implications of the impairment of CD26-ADA interaction and its catalytic activities in the pathophysiology of AIDS are discussed.