Abstract
DNA double-strand breaks (DSBs) induced by ionizing radiation represent the most serious damage in cells. Immediately after the formation of DSB, histone H2AX is phosphorylated at the site of DSB. The phosphorylated H2AX (γH2AX) foci can be observed with an immunohistochemical staining. In this research, we examined that γH2AX serves to an index for existence of DSBs which are unrejoined for a long time participating in the radiation susceptibility. 2Gy X-rays were irradiated cells with varying radiosensitivity and the change in the number of foci were observed with time. In all cell lines, foci formation was seen immediately after irradiation, and the number of foci reached a peak at 30 to 60 minutes. At 12 hours, many foci were remained in sensitive cells but having almost disappeared in resistant cells. That is, compared with resistant cells, it was suggested that the rejoining activity of DSBs in sensitive cells is descended. Our result has suggested that the quantity of residual γH2AX serves as an index of radiation susceptibility. [J Radiat Res 44:411 (2003)]
