10. Direct and Reverse Bystander Effect Between Irradiated and Unirradiated Organisms: The Modulating Role of Chemosignalling in Ecology

It was shown that mice or rats exposed to sublethal dose of ionizing radiation are able to decrease the immune reactivity of intact animals when them kept together in the same cage. Even one individual can cause such a disturbances of immunity in a group of intact animals. The data indicate that at early stage after exposure to sublethal doses of ionizing radiation mice secrete volatile components (VC) in urine which decreased thymus dependent humoral immune response in intact animals (to 60–70% relative control). The stable effect observed as a result of 1-day exposure allowed us to study the time course of secretion of immunosuppressive VC by irradiated animals. These VC possess attractive properties for the intact individuals. The irradiated mice showed an increased attractiveness to intact individuals. The biological significance of a combination of the immunosuppressive and attractive effects of VC is unclear. It is supposed, that mammals possess of the distant immunomodulating chemosignal system, aimed at the immunoreactivity of individuals with immunodeficiency state.

It was established that VC of intact mice restored the humoral immune response and other parameters of immunity in irradiated with a dose of 1 Gy animals. In this case, the irradiated recipients demonstrated an increase of humoral immune response to 140–170%. These VC of intact mice activated at irradiation mice phagocytic activity peritoneal macrophages. Exposure of rats for the third day after irradiation (1 Gy) to the VC of intact animals significantly increased the number of red blood cells, lymphocytes and granulocytes in the bloodstream.

Thus, direct and reverse bystander chemosignaling between the irradiated and intact, irradiated and irradiated animals mediate the modification of immunity and behavioral reactions of recipients. Apparently these untargeted effects of radiation spreading from one individual to another can have a significant impact on the viability of the entire population of animals.