Abstract
Summary
In irradiated marrow cultures of nonleukemic cells the ratio of effect of 50 r of irradiation on progranulocytes to the effect on the more susceptible lymphocyte is the same as with a dose of 400 r of irradiation. An increase of 8 times in the amount of irradiation, that is from 50 r to 400 r, produced an increase of only about 1.7 times in the effect on either progranulocytes or lymphocytes. Leukemic progranulocytes showed a greater decrease from a dose of 300 r than nonleukemic progranulocytes from a dose of 400 r, but the character of the curves is similar which suggests that the mechanism of action of irradiation on leukemic cells is probably a prevention of the onset of cell division as was shown to be the case for nonleukemic cells. Leukemic progranulocytes which failed to mature in the patient also failed to mature in cultures in a medium containing normal human cord serum with or without irradiation. All of these observations are explained if the action of irradiation is to prevent the onset of mitotic or amitotic division and not by directly killing cells and if the leukemic process depends on a fundamental change in the cell affecting its rate of division and maturation and not on any alteration in the environment.
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