GAMMA-RAY-INDUCED AND FISSION NEUTRON-INDUCED MICRONUCLEI IN PHA STIMULATED AND UNSTIMULATED HUMAN-LYMPHOCYTES

Two groups of normal human blood cells, one stimulated with phytohaemaglutinin (PHA) for 24 hr (G1-S phase of the cell cycle) and one unstimulated (G0 phase), were irradiated with Co-60 gamma rays or Cf-252 radiation. A comparison of radiation-induced micronucleus frequencies showed that the high-dose-rate gamma rays were more effective in inducing micronuclei than low-dose-rate gamma rays. In the cells exposed to low-dose-rate irradiation, there was little difference between the frequency of micronuclei in the G0 phase and the G1-S phase. However, cells in the G1-S phase were more sensitive than G0-phase cells to high-dose-rate gamma rays. The relative biological effectiveness of Cf-252 neutron irradiation measured in micronucleus assays was consistent with the value obtained for the lethal effect of Cf-252 on cultured cells.