THE NATURE OF HIGH-FREQUENCY SISTER-CHROMATID EXCHANGE CELLS (HFCS)

We employed the three-way differential staining technique (TWD), which allows SCEs to be distinguished on a per generation basis by scoring third metaphases (M3), in order to study the spontaneous levels of SCE s in normal and high frequency cells (HFCs) that occurred in the first (S1), second (S2) and third (S3) S phases, Fifty one of 900 lymphocyt es from 37 healthy donors were defined as HFCs by calculating the 95th percentile of the distribution of SCEs in S1 + S2. 'Normal' cells pre sented almost the same number of SCEs after the first, second and thir d cell cycles (SCE averages of 2.43, 2.04 and 3.53 respectively), In c ontrast, HFCs showed a higher SCE count in S1, which decreased rapidly through the cycles and reached baseline level at S3 (SCE averages of 7.18, 4.29 and 3.45 respectively), This would suggest that the lesions responsible for the higher SCE frequency in HFCs were effectively rem oved after two cell cycles and strongly support the hypothesis that HF Cs are lymphocytes which accumulate higher levels of DNA lesions throu gh time.