Dipeptidylaminopeptidase IV (DAP IV) in B- and T-cell leukaemias.

A cytochemical study in samples from 100 lymphoid leukaemias, 84 of B-cell type and 16 of T-cell type, was carried out with three acid hydrolases: DAP IV, acid phosphatase (AP) and alpha-naphthyl acetate esterase (ANAE). DAP IV was studied in leukaemic T-cells both by cytochemistry and by a monoclonal antibody with the immunoperoxidase technique. Both methods showed similar results. AP and ANAE gave weak reactions in immature B-cell leukaemias (common-ALL and B-CLL) and were strongly expressed in plasma cell disorders. DAP IV showed no activity in any of the types of B-cell leukaemia studied and was strongly positive in some T-cell leukaemias but with a more restricted distribution than ANAE and AP. T-lymphoblasts (T-ALL) and mature (T8+) leukaemias were DAP IV negative. Within the T4+ malignancies DAP IV was positive in four T-prolymphocytic leukaemias, one of two T-CLL and one of three Sezary syndrome cases. Although DAP IV is strictly T-cell specific it does not appear to aid the differentiation between B- and T-cell disorders or the identification of T-cell subsets as determined by monoclonal antibodies. It remains to be established whether this enzyme will define a functionally distinct T-cell subset.