Radiation-induced Bystander Effects: Are They Good, Bad or Both?

Abstract

Our current knowledge of the mechanisms underlying the induction of bystander effects by low dose–low linear-energy-transfer ionising radiation is reviewed, and the question of how bystander effects may be related to observed adaptive responses, systemic genomic instability or other effects of low doses exposures is considered. Bystander effects appear to be the result of a generalised stress response in tissues or cells. The signals may be produced by all exposed cells but the response may require a quoram in order to be expressed. The major response involving low LET radiation exposure discussed in the existing literature is a death response, which has many characteristics of apoptosis but may be detected in cell lines without p53 expression. While a death response might appear to be adverse, it can in fact be protective and remove damaged cells from the population. Since many cell populations carry damaged cells without being exposed to radiation (‘background damage’) low doses exposures might cause removal of cells damaged by agents other than the test dose of radiation, which would lead to the production of ‘u- or n-shaped’ dose–response curves. The level of harmful or beneficial response would then be related to the background damage carried by the cell population and the genetic programme determining response to damage. This model may be important when attempting to predict the consequences of mixed exposures involving radiation and other environmental stressors.

Keywords:

• Adaptive response 
• Bystander effect 
• Genomic instability 
• Low-level radiation

Acknowledgements

We acknowledge support from The Canadian Canada Research Chair programme and from the National Science and Engineering Research Council (NSERC).

Notes

Carmel Mothersill holds a senior Canada Research Chair at McMaster University. Her research interests include the study of the effects of low doses of radiation in humans and on the environment, in particular the bystander effects. She has published widely in the research literature and is an author of several reviews concerning low-level radiation effects.

Colin Seymour is a senior member of the Faculty at McMaster University. He has similar research interests to his wife, Carmel Mothersill, and has published extensively in these fields.

Additional information

Notes on contributors

Carmel Mothersill

Carmel Mothersill holds a senior Canada Research Chair at McMaster University. Her research interests include the study of the effects of low doses of radiation in humans and on the environment, in particular the bystander effects. She has published widely in the research literature and is an author of several reviews concerning low-level radiation effects. Colin Seymour is a senior member of the Faculty at McMaster University. He has similar research interests to his wife, Carmel Mothersill, and has published extensively in these fields.