Constitutive expression of CD26/dipeptidylpeptidase IV on peripheral bloodB lymphocytes of patients with B chronic lymphocytic leukaemia

We have investigated the expression of the ectoenzyme dipeptidylpeptidase I V (DPP IV)/CD26 on lymphocytes obtained from patients with B chronic lympho cytic leukaemia (B-CLL) and compared it with healthy subjects. Using two-co lour immunofluorescence analysis with CD26 and CD20 or CD23 monoclonal anti bodies, CD26 was found undetectable on peripheral resting B-cells (CD20(+) CD23(-)) from normal donors whereas it was expressed on B-cells activated i n vitro with interleukin (IL)-4 and Staphylococcus aureus strain cowan I (C D20(+) CD23(+)). The expression of CD26 on leukaemic B-cells (CD20(+) CD23( +)) was clearly induced in 22 out of 25 patients examined. Consequently, in duced levels of CD26 cell surface expression on either normal activated and malignant B-cells coincided with the enhancement of DPP IV activity detect ed on the surface of these cells. Reverse transcription polymerase chain re action analyses showed that the transcript levels of the CD26 gene was high er in normal activated B-cells and B-CLL cells than in resting B-cells, sug gesting that CD26 was expressed at the level of transcriptional activation. These observations provide evidence of the abnormal expression of DPPIV/CD 26 in B-CLL which, therefore, may be considered as a novel marker for B-CLL . Further investigation in relation to CD26 expression and other B malignan cies needs to he defined.