DIFFERENT SENSITIVITY TO CELL-KILLING AND CHROMOSOME MUTATION-INDUCTION BY GAMMA-RAYS IN 2 HUMAN LYMPHOBLASTOID CELL-LINES DERIVED FROM A SINGLE-DONOR - POSSIBLE ROLE OF APOPTOSIS

The gamma-ray sensitivity of two human lymphoblastoid cell lines, TK6 and WI-L2-NS, was studied; both cell lines are derived from the same p arent, WI-L2 TK6 was more sensitive to the cytotoxic effects of gamma rays, but showed fewer induced chromosome aberrations. There was no di fference between the two cell lines in their capacity to rejoin DNA do uble-strand breaks or in the kinetics of the rejoining process. The ki netics of cell cycle progression following radiation exposure was also similar in TK6 and WI-L2-NS. However, while TK6 cells were very sensi tive to apoptosis induction, showing high levels of apoptotic cells wi thin 24 h of exposure, no evidence for any significant levels of apopt osis was found for WI-L2-NS within 30 h of irradiation, when chromosom e aberration frequency was determined. Evidence of apoptosis were seen at later times in WI-L2-NS cells, but the levels were significantly l ower than comparably treated TK6 cells. The results support a hypothes is that the lower survival and induced aberration frequencies in TK6 c ells are due to selective removal of damaged cells by apoptotic proces ses prior to analysis of chromosome aberration frequencies in mitosis.