Cytochemical demonstration of dihydrofolate reductase in leukaemia and other haematological diseases.

The dihydrofolate reductase activity has been studied cytochemically in various haematological diseases. The variation between normal controls, Hodgkin's disease, myeloma, polycythaemia vera, chronic lymphocytic leukaemia and chronic myeloid leukamia was not significant, comparing the same type of cells. In acute myeloid leukaemia and acute lymphoblastic leukaemia the blast cells were weakly positive or negative. This finding is very interesting as the blast cells are capable of division. Probably the dihydrofolate reductase appears in the blast cells in some stage of mitosis. Lymphocytes stimulated by phytohaemagglutinin showed increased enzyme activity compared with normal non-stimulated lymphocytes. The "blast like" cells were more strongly positive than the blast cells of leukaemic patients. The patients with acute lymphoblastic leukaemia or acute myeloid leukaemia treated with methotrexate showed increased dihydrofolate reductase activity cytochemically.