Dipeptidyl peptidase IV (CD26) in human leukemia cells: immunological and biochemical data

To study dipeptidyl peptidase IV (DDP-IV), CD26, in various subpopulations of lymphoid cells, a comparison has been made of the immunofluorescence fin dings on the expression of the antigen CD26 on the surface of some leukemia cells and the enzyme activity in lysates of these cells. It was found that monoclonal antibodies (MAb) BA-5b against activation antigen CD26 of human T-lymphocytes react with purified DDP-IV preparations from human kidneys a nd leukemic T-cells. Binding of MAb BA-5b with DDP-IV molecule does not inf luence the enzyme activity. This indicates that they bind outside the zone of active center. MAb BA-Sb react with cells from patients with B-cell chro nic lymphoid leukemia identifying 20-50% of CD26+ cells. This confirms prev ious enzymologic data on the presence of DDP-IV in leukemia B-cells but con tradicts low DDP-IV activity in the above cells. These findings and those o n the cells of T-lymphoblastoid lines Jurkat, GEM, YT show that the percent age of CD26+ cells estimated by binding of MAb BA-5b on cell surface does n ot reflect DDP-IV activity. Thus, immunological and biochemical findings do not coinside which may be explained by the presence of DDP-IV intracellula r pool, of inactive form of this enzyme or existance of several molecular f orms of DDP-IV.