Dose Responses of Bystander Cell Death are Modified by Sites of Energy Deposition within Cells Irradiated with a Synchrotron X-Ray Microbeam

Introduction The bystander response is a phenomenon whereby biological responses occur in cells that are located nearby cells that have been traversed by charged particles, but which themselves have not been traversed. Therefore, microbeam irradiation system, which enables the observation of cellular responses of individual nonirradiated and irradiated cells, has become a powerful tool to elucidate the mechanisms underlying the bystander responses. Using a synchrotron X-ray microbeam irradiation system with a changeable beam size developed at the Photon Factory, KEK [1, 2], we recently demonstrated that cell death is more prevalent in cells irradiated with low doses of radiation when only nuclei are irradiated than when whole cells are irradiated [3]. In this study we examined the relationship between bystander cell death and intracellular energy-deposited sites.