Changes in the Number of Residual γH2AX Foci in Ki-67-Positive and Ki-67-Negative Human Fibroblasts Irradiated with X-Rays in Doses of 2-10 Gy.

We studied changes in the number of residual γH2AX foci in cultured human fibroblasts with different expression of the cell proliferation marker protein Ki-67 24, 48, and 72 h after exposure to X-ray radiation in doses of 2-10 Gy. It was shown that, regardless of the expression of Ki-67, the number of residual γH2AX foci in irradiated cells linearly depends on the absorbed dose of X-ray radiation. However, the quantitative yield of residual γH2AX foci per unit of the absorbed dose in Ki-67 cells 24 and 48 h after irradiation was higher than in Ki-67 cells by 1.8 and 2.0 times, respectively. In Ki-67 cells, the quantitative yield of residual γH2AX foci per unit of absorbed dose decreases by ~1.7 times with increasing the time after irradiation from 24 to 72 h. For the purposes of practical radiation biodosimetry, it can be recommended to quantify residual γH2AX foci in non-proliferating cells at least 72 h after irradiation.