Cytochemical distribution of dipeptidylaminopeptidase IV (DAP IV; EC 3.4.14.5) in T-lymphoblastic lymphoma/leukemia characterized with monoclonal antibodies

In human blood and bone marrow, dipeptidylaminopeptidase IV (DAP IV; EC 3.4.14.5) selectively occurs in T lymphocytes bearing Fc receptors for IgM. In the present study 35 cases of lymphoblastic lymphoma and leukemia were analysed for the specificity, incidence and reaction pattern of DAP IV. On the basis of immunohistochemical staining with monoclonal antibodies and enzyme cytochemical staining for acid phosphatase, 12 cases were classified as B-type neoplasms. In 23 cases T-cell properties were expressed to different extents, apparently reflecting different categories of maturation. Whereas B-cell lymphomas were invariably negative for DAP IV, seven of the 23 T-lymphoblastic lymphomas/leukemias showed this enzyme. Thus DAP IV is a highly specific marker for a distinct T-cell subpopulation, apparently irrespective of the stage of differentiation.