For the viewing of γ-H2AX immunofluorescence foci, an epifluorescence microscope (ProvisAX70, Olympus) was used. Fields were initially selected at 10x on the basis of DAPI counterstained nuclei. Acquired DAPI image was used to define the focusing area and the detection of foci was performed using 40x objectives at optimized detection parameters. Scoring of foci was carried out manually in double blinded manner.