Trichostatin A enhances radiation-induced γH2AX foci formation in K562 cells. Cells were pre-treated with the indicated concentrations of Trichostatin A for 24 hours prior to irradiation (2 Gy, 137Cs). Cells were fixed and stained for γH2AX analysis 1 hour after irradiation. Images were acquired with a Zeiss LSM 510 meta confocal microscope using 0.5 μm z‐sectioning (63x oil immersion objective). The number of γH2AX foci per nucleus was quantitated using ImageJ (Fiji). Mean ± standard deviations are indicated, *** p < 0.001 (A). Images were exported as TIFF files using Metamorph software for immunofluorescence visualization of nuclei (TO-PRO-3, blue) and γH2AX foci (green). For comparison cells treated with 2 Gy alone (i and ii) and cells exposed to 0.5 μM Trichostatin A prior to 2 Gy irradiation (iii and iv) are shown (B).