Induction and quantification of γ-H2AX foci following low and high LET-irradiation

Purpose: To investigate quantitatively the induction and rejoining of DNA double strand breaks (DSB) in V79-4 and xrs-5 Chinese hamster cells and HF19 human fibroblast cells, using the phosphorylation of the histone protein H2AX (gamma-H2AX) as an indicator of DSB, exposed to low doses of either low linear energy transfer (LET) Co-60 gamma-rays or high LET alpha-particles. Materials and methods: Cells were irradiated with low or high LET ( 20 - 2000 mGy). The gamma-H2AX foci were detected using immunohistochemistry and quantified by image analysis. Results: The number of DSB determined 30 min post gamma-irradiation at 37 degrees C is 12.2 (+/- 1.5), 13.5 (+/- 1.6) and 19.1 (+/- 1.7) foci/cell/ Gy for V79-4, xrs- 5 and HF19 cells respectively, comparable with levels detected in V79-4 cells using pulse field gel electrophoresis. 6 h post gamma-irradiation, gamma-H2AX foci levels in V79-4 and HF19 cells approach control levels but remain higher in DSB repair deficient xrs- 5 cells. gamma-H2AX foci levels remain significantly higher than controls at 6 h in alpha-irradiated cells. Conclusions: gamma-radiation and alpha-radiation induced the phosphorylation of H2AX in response to DSB at low doses; the variation in the rate of dephosphorylation of induced foci are dependent both on radiation quality and cell characteristics.