LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

CHAPTER 1
INTRODUCTION
is provided by low-dose cancer risk, which up to now has generally been estimated by
assuming a linear, no-threshold dose-response.
Fig. 1.6: Radiation induced bystander effect. Irradiation of target cells leads to
elicitation of response from unirradiated bystander cells. This takes place through the
transduction of the signal from the irradiated cell to the bystander cell via gap junctions
or through the release of the signaling molecules into the surrounding medium.
A large amount of data on bystander effects has been obtained with the so-called ICM
(Irradiated conditioned medium) treatment [216-219]. This technique consists in
replacing the culture medium of non-irradiated cells with medium taken from cell
cultures previously exposed to radiation. The main finding of these studies, lie in the fact
that such treatment can reduce survival of unexposed cells. This suggests that, as a result
of a radiation insult, certain cell types can release factors in the medium, which therefore
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