Medical Physics and Applied Radiation Sciences Unit, McMaster University, Hamilton, Ontario, Canada.
Dose Response. 2006 Aug 25;4(4):283-90. doi: 10.2203/dose-response.06-111.Mothersill.
This paper reviews our current knowledge of the mechanisms underlying the induction of bystander effects by low dose, low-LET ionizing radiation and discusses how they may be related to observed adaptive responses or other protective effects of low dose exposures. Bystander effects appear to be the result of a generalized stress response in tissues or cells. The signals may be produced by all exposed cells, but the response appears to require a quorum in order to be expressed. The major response involving low LET radiation exposure discussed in the existing literature is a death response. This has many characteristics of apoptosis but is p53 independent. While a death response might appear to be adverse, the position is argued in this paper that it is in fact protective and removes damaged cells from the population. Since many cell populations carry damaged cells without being exposed to radiation, so called "background damage", it is possible that low doses exposures cause removal of cells damaged by agents other than the test dose of radiation. This mechanism would lead to the production of "U-shaped" dose response curves. In this scenario, the level of "adaptive" or beneficial response will be related to the background damage carried by the cell population. This model may be important when attempting to predict the consequences of mixed exposures involving radiation and other environmental stressors.
本文回顾了低剂量、低 LET 电离辐射诱导旁观者效应的机制，并讨论了它们与观察到的适应性反应或低剂量暴露的其他保护效应之间的可能关系。旁观者效应似乎是组织或细胞普遍应激反应的结果。信号可能由所有暴露的细胞产生，但反应似乎需要群体感应才能表达。现有文献中讨论的涉及低 LET 辐射暴露的主要反应是死亡反应。它具有许多细胞凋亡的特征，但不依赖 p53。虽然死亡反应可能看起来是不利的，但本文认为它实际上是保护性的，可将受损细胞从群体中清除。由于许多细胞群体携带未暴露于辐射的受损细胞，即所谓的“背景损伤”，因此低剂量暴露可能会导致除测试剂量辐射外的其他辐射剂引起的细胞损伤清除。这种机制将导致产生“U 形”剂量反应曲线。在这种情况下，“适应性”或有益反应的水平将与细胞群体携带的背景损伤有关。当试图预测涉及辐射和其他环境应激源的混合暴露的后果时，该模型可能很重要。
