Mechanisms and biological importance of photon-induced bystander responses: Do they have an impact on low-dose radiation responses

Elucidating the biological effect of low linear energy transfer (let),low-dose and/or low-dose-rate ionizing radiation is essential in ensuring radiation safety. over the past two decades,non-targeted effects,which are not only a direct consequence of radiation-induced initial lesions produced in cellular dna but also of intraand inter-cellular communications involving both targeted and non-targeted cells,have been reported and are currently defining a new paradigm in radiation biology. these effects include radiation-induced adaptive response,low-dose hypersensitivity,genomic instability,and radiation-induced bystander response (ribr). ribr is generally defined as a cellular response that is induced in non-irradiated cells that receive bystander signals from directly irradiated cells. ribr could thus play an important biological role in low-dose irradiation conditions. however,this suggestion was mainly based on findings obtained using high-let charged-particle radiations. the human population (especially the japanese,who are exposed to lower doses of radon than the world average) is more frequently exposed to low-let photons (x-rays or γ-rays) than to high-let charged particle radiation on a daily basis. there are currently a growing number of reports describing a distinguishing feature between photon-induced bystander response and high-let ribr. in particular,photon-induced bystander response is strongly influenced by irradiation dose,the irradiated region of the targeted cells,and p53 status. the present review focuses on the photon-induced bystander response,and discusses its impact on the low-dose radiation effect. © the author 2014.