NAC treatment abolishes the non-linear characteristics of γH2AX induction in EA.hy926 EC following low-dose X-irradiation. EA.hy926 EC were stimulated with TNF-α (20 ng/ml) or mock-treated and were irradiated in the presence of NAC (10 mM, applied 4 h before irradiation). At 24 h after irradiation relative DCF-fluorescence (A) and γH2AX foci induction (B) were analysed as described before. Data represent means ± SD from at least three independent experiments. *p < 0.05 vs. 0.3 Gy and 0.7 Gy irradiated EC. **p < 0.01 vs. relative DCF controls.