Effect of H₂O₂. The L-clone and HeLa cells transfected with L-siRNA (A) and H-siRNA (B) for 40 hours were plated (10⁴ for well) and incubated for 2 hours with the indicated concentration of H₂O₂ in serum free-medium. After washing, the cellular vitality was measured by MTT assay. Values were plotted as percentage of the absorbance of the untreated control cells. Data are the means ± SD of 3 independent experiments, each in 8 replicates.