Analysis of H2AX phosphorylation. a) Immunofluorescence analysis of NHDF cells transfected with pBabepuro alone (control) or in combination with pCMV-Int (integrase). Blue color is DAPI-staining, visualizing nuclear DNA. Red color is staining of phosphorylated H2AX using anti-γ-H2AX antibodies. b) Quantitation of the percentage of cells with upregulated H2AX phosphorylation. Each experiment was repeated 3 times, and 100 cells were counted in each sample. Error bars indicate standard error of the mean. Only in day 3 there is a significant difference between the three treatments (p < 0.05).