Cytochemistry of dipeptidylaminopeptidase IV in T lymphoblastic leukaemia-lymphoma

The cytochemical distribution of dipeptidylaminopeptidase IV (DAP IV) was studied in 5 cases of T lymphoblastic leukaemic lymphoma and 12 cases of acute T lymphoblastic leukaemia, in order to ascertain differences between the enzyme positivity patterns of T cells at different stages of differentiation. Early thymic phenotype cases were almost completely negative; those of intermediate and mature thymic phenotype showed positivity in various percentages of blasts: either a single coarse granule or many coarse and small granules were detected. In mature phenotype cells a particularly intense DAP IV reaction was observed. In conclusion, our findings suggest that DAP IV reaction could be a useful tool for the cytochemical characterization of T acute leukaemia subtypes.