Radiation-induced bystander effects: Past history and future directions

There has been a recent upsurge of interest in the phenomenon now known as radiation-induced bystander effects. This is largely due to the increased a wareness of the contribution of indirect and delayed effects, such as genom ic instability, to cellular outcomes after low-dose exposures. It is also d ue to the availability of tools such as the microbeam and advanced cell cul ture systems and to the ability to study end points such as gene or protein expression at low doses which were previously difficult to study. This rev iew looks at the history of bystander effects in the earlier literature, in which the clastogenic effect of plasma from irradiated patients was well k nown. The effect was known to persist for several years and to cause transg enerational effects, making it similar to what we now call genomic instabil ity. The review then examines the current data and controversies which are now beginning to resolve, the questions concerning the mechanisms underlyin g the induction and transmission of both bystander effects and genomic inst ability. Finally, the possible impact of data concerning radiation-induced bystander effects on radiotherapy and radiation protection is discussed. (C ) 2001 by Radiation Research Society.