Quantitative and qualitative studies of leukaemic cell dipeptidylpeptidases II and IV

Abstract

Cellular concentrations of dipeptidylpeptidases (DAP) II and IV were determined by fluorimetric assay in 152 cases of leukaemia and 24 permanent T-cell lines. Whilst its estimation appears to have few diagnostic applications, it was found that DAPII levels were generally higher in prolymphocytoid CLL variants (CLL-Pro) compared with “typical” CLL cases. Qualitatively, DAPII extracted from leukaemic B- and T-cells did not differ significantly with respect to molecular weight ( M r 82 kD: FPLC gel filtration) or substrate affinity ( K m). Similarly, a single molecular weight species ( M r 189 kD) of DAPIV was also detected in all leukaemic sonicates examined although, in quantitative terms, increased DAPIV levels were primarily associated with a subgroup of CD4-positive post-thymic malignancies. Studies of immature T-cell proliferations however indicated that DAPIV expression was unrelated to either stage of immunological differentiation or CD4 expression. No evidence of lineage restriction was found for either enzyme and it is concluded that variations in DAP cytochemical staining patterns reflect quantitative rather than qualitative differences.