Activation of host-defense mechanism induced by exposure to a low dose of radiation: an approach to accumulate evidence on the interaction between the whole body and radiation

We found that the effect of a small dose of irradiation on the whole body exists at certain dose level windows which induce delayed radio-protective effects on an animal after a fixed time span depending on its dose levels. The striking increase of survivals against the second mid-lethal irradiation was observed in mice pre-irradiated with 5 cGy eight weeks before, or pre-irradiated with 50 cGy two weeks before. Thymocyte apoptosis was increased six hours after 5 or 50 cGy pre-irradiation. While in spleen plaqueforming cell counts with SRBC immunisation increased at the very time when mice manifested the optimal increase in survival, namely two weeks after 50 cGy pre-irradiation or eight weeks after 5 cGy pre-irradiation. Stress inducing treatment (e.g. administration of a heavy metal salt or irradiation at higher dose etc.) seems to act within a few days stimulating more events at the biochemical level. However, the low-dose irradiation seems to act more at the immune level influencing the cooperation between immune system components in the whole body.