RADIATION QUALITY AFFECTS THE EFFICIENCY OF INDUCTION AND THE MOLECULAR-SPECTRUM OF HPRT MUTATIONS IN HUMAN T-CELLS

Human T lymphocytes can be used to determine the frequency and molecul ar spectrum of somatic cell gene mutations induced by ionizing radiati ons both in vivo and in vitro. In vitro exposure of these G(0) cells t o low-LET Cs-137 gamma rays results in the induction of HPRT mutations and a predominant molecular spectrum of DNA deletions and rearrangeme nts, particularly total gene deletions (11-12%), Similar results are f ound in samples from humans exposed to low-LET radiation from I-131. T he doubling dose for mutation induction is calculated to be 0.8 and 1. 0 Gy from these exposures performed in vitro and in vivo, respectively , In vitro studies of the effects of high-LET radiation from exposure to Rn-222 also showed an induction of HPRT mutations, with a doubling dose of approximately 0.2 Gy. With this radiation, the predominant mut ations were small partial deletions, with less than 2% total gene dele tions. Studies of humans exposed to high-LET radiation from Pu-239 sho wed an increased HPRT mutant frequency for the group, although no sign ificant dosimetry could be defined. In contrast to the humans exposed to I-131, no increase in the frequency of total gene deletions was fou nd. This is consistent with the results for Rn-222 in vitro. The avail able data show that radiation quality affects both the efficiency of i nduction and the molecular spectrum of HPRT mutations in human T lymph ocytes both in vitro and in vivo. The mutational spectrum may be relat ively specific for radiations of different quality and thus allow a mo re precise measurement of the induction of somatic gene mutations resu lting from individual exposures to radiation, and thereby provide more sensitive assessments of health risks. (C) 1997 by Radiation Research Society.