decreased γH2AX foci caused by X-ray irradiation and accelerated DNA double strand breaks repair. (A) The basic DSB levels of the non-irradiated cells after treatment with PBS, SOD1 or TAT-SOD1, respectively. (B), (C) and (D) Representative images of γH2AX foci of PBS, SOD1 or TAT-SOD1 treated groups after 5 Gy X-ray irradiation at different time points. (E) Kinetics of γH2AX foci loss in different groups of cells after 5Gy X-ray irradiation. HaCaT cells were stained for γH2AX at indicated times and then the mean number of γH2AX foci per cell (foci/cell) was counted.