The radiation-induced bystander effect (bystander effect) is the phenomenon in which unirradiated cells exhibit irradiated effects as a result of signals received from nearby irradiated cells. In November 1992, Hatsumi Nagasawa and John B. Little first reported this radiobiological phenomenon.[1]
There is evidence that targeted cytoplasmic irradiation results in mutation in the nucleus of the hit cells.[2][3] Cells that are not directly hit by an alpha particle, but are in the vicinity of one that is hit, also contribute to the genotoxic response of the cell population.[4][5] Similarly, when cells are irradiated, and the medium is transferred to unirradiated cells, these unirradiated cells show bystander responses when assayed for clonogenic survival and oncogenic transformation.[6][7] This is also attributed to the bystander effect.
The demonstration of a bystander effect in 3D human tissues[8] and, more recently, in whole organisms[9] have clear implication of the potential relevance of the non-targeted response to human health.
This effect may also contribute to the final biological consequences of exposure to low doses of radiation.[10][11] However, there is currently insufficient evidence to suggest that the bystander effect promotes carcinogenesis in humans at low doses.[12]