Host: The Japan Radiation Research Society
To elucidate the biological effects of low-dose radiation, it is important to study the responses in irradiated cells and in bystander cells. For this purpose, a microbeam irradiation system is a powerful tool, since we can observe individually the cellular responses of both irradiated cells and non-irradiated cells.
We have been studying the differences in lethal effects of V79 cells irradiated with microbeam of different sizes using an X-ray microbeam irradiation system developed at the Photon Factory, KEK. This system can provide an arbitrarily sized X-ray microbeam larger than 5×5 μm².
We reported last year that the low-dose hypersensitivity was more clearly observed in the nucleus-irradiated cell with 10×10 μm² beam than in the whole cell irradiation with 50×50 μm² beam. As the next step, we irradiated 5 cells in the dish with 10×10 μm² beam or with 50×50 μm² beam, and measured the survival of bystander cells. When nuclei only were irradiated, survival fraction of bystander cell decreased down to 90% around 1 Gy and increased back to 96% in higher dose region, whereas in the whole cell irradiation, it decreased monotonously to 92%. Dose-dependent enhancement of cell death was observed in the absence of energy deposition to cytoplasm in both irradiated and bystander cells. We speculate that the energy deposited in the cytoplasm might play an important role in cell killing in the low-dose region. The relationship between cell death (irradiated and bystander cells) and intracellular energy-deposited sites will be discussed.
