Glycylprolyl-diaminopeptidase in human leukocytes: selective occurrence in T lymphocytes and influence on the total serum enzyme activity.

Using biochemical methods glycylprolyl-diaminopeptidase (GP-DAP, EC 3.4.14.5) was measured in purified leukocyte subpopulations and found selectively in T lymphocytes. In 129 subjects with normal hepatic function a significant correlation was observed between the serum GP-DAP activity and the peripheral blood lymphocyte count. In four patients suffering from rheumatoid arthritis, four weeks of thoracic duct drainage resulted in a reduction of the peripheral blood lymphocyte count and a concomitant decrease of the serum GP-DAP activity. These observations suggest that lymphocytic GP-DAP may contribute to the total serum GP-DAP activity.