MUTANT FREQUENCY AT THE HPRT LOCUS IN PERIPHERAL-BLOOD T-LYMPHOCYTES OF ATOMIC-BOMB SURVIVORS

The mutant frequency at the hypoxanthine-guanine phosphoribosyltransferase locus in peripheral blood lymphocytes was measured for 254 atomic bomb survivors (171 exposed and 83 control survivors) by a colony assay using recombinant human interleukin-2. Weak but significant effects were detected for atomic bomb radiation dose and smoking status at the time of examination but not for age and sex. However, the slope of the dose-response curve is quite small, and the smoking effect would not have been significant without the inclusion of data from just three individuals with extremely high mutant frequencies. The weakness of the dose response is at least partly due to the time lapse of 50 years since radiation exposure. Among the 254 survivors, 23 had chromosome aberration data in lymphocytes and the dose response was highly significant. However, the correlation between the mutant frequency and the proportion of cells with aberrations was not significant. It was concluded that the lymphocyte mutation assay is presently not sensitive enough for biological dosimetry of radiation exposure in the survivors.