Cytochemistry of dipeptidylaminopeptidase IV and II in normal and neoplastic lymphoid cells

Summary Cytochemical methods were used to determine the distribution of dipeptidylaminopeptidase IV (DAP IV) and II (DAP II) in lymphoid cell populations from patients with lymphoproliferative diseases. Special attention was paid to unusual intracellular distribution patterns which might correlate with the presence of various membrane markers. In healthy patients, about 50% of the circulating lymphocytes were found to be positive to both reactions, the intracellular distribution patterns being variable. The DAP IV reaction was negative in all B-CLL cases. In 2 cases of T-CLL with phenotype E⁺ OKT₃⁺T₄^–T₈⁺one was negative and one was weakly positive, while two cases of T-CLL with phenotype E⁺ OKT₃⁺T₄⁺T₈^–were both strongly positive. The other non-T lymphoproliferative diseases studied were negative for DAP IV, while one T-ALL and three T-lymphoma cases showed a strong granular or diffuse distribution. The DAP II reaction was strongly positive in all the T lymphoproliferative diseases studied, irrespective of their immunological phenotype. This reaction was also weakly positive in some cases of plasmocytoma and lymphoplasmocytoid lymphoma.