Bystander effects induced with inner shell ionization followed by Auger effects

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In low dose region where most of the irradiated cells can survive, biological response to radiation is now known to appear as a result of intra-and/or inter-cell signaling pathway. Purpose of this research project is to investigate the outbreak of original signal induced with energy deposited by radiation from energetic point of view. In order to utilize the tenability of synchrotron X-rays in the microbeain cell irradiation system which had been developed in our previous project funded by scientific research (A) of MIST, we developed an energy-tunable microbeam X-ray irradiation system by aligning all the components along the horizontal beam axis. After overcoming some problems concerning cell irradiation chamber, we succeeded in getting reliable and reproducible biological results. Although these are still preliminary due to the shortage of the beamtime, results are summarized as follows.1. When irradiated with X-rays tuned to Fe K-shell absorption edge, Fe-incorporated cells showed lower bystander cell death than irradiated with below-edge energy X-rays.2. When irradiated with soft X-rays tuned to S K-edge absorption edge, irradiated cells showed less sensitive than cells irradiated with below-edge X-rays. As for the bystander cell death, S K-edge X-rays showed higher lethality than below-edge X-rays.We will continue to study the mechanisms leading to interesting biological phenomena obtained as above.