Abscopal Effects of X-Irradiation on Mouse Bone Marrow

Abstract

X-Irradiation of the rest of the body with the spleen shielded has been observed to cause reduction in cell number and increase in acid deoxyribonuclease (DNase) activity per average remaining cell in the protected spleen (1). The mechanism of this of X-irradiation remains unclear. Shift in cell population probably plays a role but is not likely to account for the entire phenomenon. Whereas loss of cells low in DNase, leaving behind a population high in DNase, could account for an increase in DNase content per average remaining cell, it could not account for the transitory increase in total DNase activity observed. The short life of active radicals makes it improbable that the circulation of such products of X-irradiation could mediate the indirect effects. However, other breakdown products which might have a toxic effect on the spleen could mediate the effect. It would be expected that such a mechanism would be influenced by the volume of tissue irradiated and possibly also by the X-irradiation sensitivity of the irradiated organs. Finally, the possibility that irradiation of endocrine organs might produce the distant effects was also considered (1). It is the purpose of this paper to report on experiments designed to detect local and abscopal effects of X-irradiation on bone marrow. Since bone marrow cells are very radiosensitive, the abscopal effect might be expected to be a function of the volume of bone marrow irradiated, whether the mechanism involved primarily shift in cell population (interchange between irradiated and protected marrow sites) or toxic effects. Beyond the lethal dose for the cells low in DNase activity in the irradiated tissue, approximately 800 r (2), increase in radiation dose would not be expected to produce increase in acid DNase activity per average remaining cell.