Expression of CD26 and DPP IV in T-acute lymphoblastic leukemia: comparison of immunocytochemistry with enzyme cytochemistry.

Tile possible identity ofdipeptidyl peptidase IV (DPP IV) enzymatic activity and CD26 antigen expression in phenotypically defined T-acute lymphoblastic leukemia cells (T-ALL) was examined. For comparative studies, the combination of immunocytochemistry and enzyme cytochemistry methods was used. T he strong correlation between the CD26 antigen expression and DPP IV positivity in the majority of T-lymphoblasts in T-ALL patients was evident. No CD26 antigen was expressed on DPP IV negative T-cells. The variable CD4 and/or CD8 antigen expression, frequent CD5 and CD7 positivity and absence of surface membrane CD3 antigen were the characteristic immunophenotypic features of CD26/DPP IV positive T-lymphoblasts. Moreover, the clear CD71 and CD26/DPP IV coexpression suggested the association of CD26/DPP IV positive cells with proliferation. The immunophenotype of CD26/DPP IV positive T-lymphoblasts seems to be characteristic for the relative immature cell population. In addition, noteworthy was the slight disassociation between the very high CD26 antigen expression and moderate DPP IV activity in cells of some T-ALL patients. The possible existence of enzymatically inactive structures of CD26 antigen or inactive precursors of DPP IV detectable only by immunocytochemistry was discussed. Our study indicates that CD26 antigen expression is tended to identify cells with DPP IV enzymatic activity in T-ALL patients. The results provide some more information of CD26 antigen involvement in the pathology of leukemic cells via its DPP IV enzyme activity.