A comparative study on potential cytogenetic fingerprints for radiation LET in human lymphocytes

Purpose : To carry out a comparative study on potential cytogenetic fingerprints for radiation LET in human metaphase lymphocytes. Materials and methods : Human lymphocytes were irradiated in vitro with 3.0Gy 60 Co γ-rays, 0.9 Gy 3 H β -rays or 0.2 Gy 2.7Mev neutrons. Detailed chromosome aberrations were analysed by combined FISH with pan-telomere staining and specific wholechromosome painting (1, 2 and 4). Total chromosome translocations and insertions were also analysed by multicolour wholechromosome painting (chromosomes 1, 2 and 4 orange, chromosomes 3, 5 and 6 green). Results : Among the six proposed radiation cytogenetic fingerprints, the ratio of total simple translocations to insertions (I-ratio), showed the largest difference between low-LET 60Co γ-ray and high-LET neutron radiation. The ratios of complete exchanges to incomplete rejoinings [S(I)-ratio] and dicentrics to interstitial deletions (H-ratio), showed a similar significant difference between low- and high-LET radiation. The ratios of centric rings to interstitial deletion (G-ratio) showed a trend of LETrelated difference, but the difference was not significant in this data set. The ratios of dicentrics to centric rings (F-ratio) and apparent complete exchanges to hidden complete exchanges [S(II)-ratio], showed no difference between low- and high-LET radiation. In the 1426 radiation-induced chromosome aberrations observed after 52h culture, evidence for sister-chromatid fusion but not telomere addition was found. Conclusion : Pan-telomere staining plus specific whole chromosome painting allows simultaneous and objective detection of complete or incomplete chromosome exchanges and interstitial or terminal deletions in human peripheral lymphocytes. Of the six proposed cytogenetic ratios, the I-ratio is the most effective cytogenetic fingerprint for distinguishing low-LET from high-LET radiation in human metaphase human lymphocytes.