Dipeptidyl peptidase activity of CD26 in serum and urine as a marker of cholestasis: Experimental and clinical evidence

Dipeptidyl peptidase IV (CD26) is a membrane-associated enzyme that is expr essed on the surface of T cells and on the hepatocyte brush border, In a so luble form it is present in serum, CD26 has been implicated in the regulati on of T cell activation and in the metabolism of hormones and cytokines, Di peptidyl peptidase (DPP) activity is elevated in the urine and serum of pat ients with biliary atresia (BA), To clarify the role of cholestasis in the development of increased serum and urinary DPP/CD26 activity, we studied th e mechanism of activity increase in experimentally induced cholestasis of C D26-deficient and wild-type rats, The clinical utility of serum and urinary DPP/CD26 activity measurements was tested in adult and pediatric patients with hepatobiliary diseases and in liver transplant recipients. The results establish CD26-associated serum DPP activity as a novel, clinically useful marker of cholestasis and demonstrate that in contrast with alkaline phosp hatase levels, DPP levels do not change in metastatic bone disease, Additio nally, DPP activity is useful as a urinary test of cholestasis in infants w ho are not receiving nephrotoxic medication.