Cytochemical demonstration of 5-formyl-tetrahydrofolate cyclodehydrase activity in leucocytes of patients with acute leukaemia.

The activity of 5-formyl-tetrahydrofolate cyclodehydrase has been studied cytochemically in leucocytes of children with acute leukaemia. Comparison of enzymatic activity in the same types of cells showed no significant variation between normal controls and the patients with acute leukaemia. The blast cells were weakly positive or negative. This finding is of very interest as the blast cells are capable of division. Probably the enzyme appears in the blast cells at some stage of the cell cycle. 2 populations of lymphocytes were observed, 1 positive with a few granules and 1 negative. A reduction of enzyme activity was observed after prophylactic cranial irradiation and methotrexate decreased enzyme activity in some patients.