Enzymecytochemical heterogeneity of human chronic T-lymphocytic leukemia as demonstrated by reactivity to dipeptidylaminopeptidase IV (DAP IV; EC 3.4.14.4).

The observation that the dipeptidylaminopeptidase IV (DAP IV; EC 3.4.14.4) occurs exclusively in T mu lymphocytes, stimulated the following study on cases of chronic lymphocytic leukemias. Thirty cases of human chronic lymphocytic leukemia were subjected to the DAP IV reaction in addition to the usually applied cytochemical and immunological tests (acid alpha-naphthyl acetate esterase, acid phosphatase, rosetting with sheep erythrocytes and surface Ig). DAP IV activity was measured directly in normal granulocytes, monocytes, B and T lymphocytes as well as in lymphocyte suspensions of leukemic cases. On a cytochemical level granulocytes, monocytes, B lymphocytes and all 24 cases of B-CLL were found to be DAP IV negative, though some of the latter showed positive reactions for AcE and AcP. From the six cases of T-CLL, five were positive to DAP IV cytochemically. No discrepancies were observed between cytochemical and biochemical results. It is concluded that DAP IV is a reliable and easy to perform marker for T mu lymphocytes and their neoplasias. The results have been interpreted as further evidence for a clonal nature of T-cell neoplasias.