Studies on the Protective Effect of Allogeneic Marrow Grafts in the Rat following Whole-body Irradiation at Different Dose-rates

In rats exposed to large doses of whole-body radiation at three different dose-rates, transplantation of syngeneic and allogeneic marrow was used as a means of determining the dose levels at which the immune response to the foreign graft was suppressed. This was compared with the dose levels at which haemorrhagic death and intestinal death occurred. A dose of 800 r of X rays at 29 r/minute suppressed the immune response sufficiently to prevent haemorrhagic death in rats given allogeneic marrow. At a dose-rate of 1·4 r/minute and a dose of 1,600 r (γ rays), the largest dose that could be given without causing intestinal failure, allogeneic marrow was rejected. When the dose-rate was reduced to 0·28 r/minute, after a total dose of 2,870 r neither suppression of the immune response nor intestinal failure occurred.