Radiosensitivity of the Immune Response to Sheep Red Cells in the Mouse, as Measured by the Hemolytic Plaque Method

Summary γ-Ray survival curves have been obtained for the capacity of adult male mice to respond to the injection of sheep erythrocytes by the production of hemolytic plaque-forming cells (11, 12). When antigen was given within 2 hr after irradiation of the mice, the survival curve was found to be a simple negative exponential, with a D37 of 80 rads. No significant change in this curve was found when an interval of 10 days separated radiation and antigen injection, indicating that radiation-induced damage to the immune system was not repaired during this interval. The capacity of plaque-forming cells to form plaques was found to be much less sensitive to radiation than was the capacity of the animals to produce plaque-forming cells. No decrease in the capacity of plaque-forming cells to form plaques was found for doses of radiation up to 2 kilorads. On the basis of these survival curves, it is suggested that the spleens of normal mice contain a minimum of 103 cells which do not themselves produce hemolysin, but respond to the injection of antigen by proliferation and differentiation into hemolysin-producing cells. Further, when these cells, which may be termed antigen-sensitive cells, are rendered incapable of proliferation by radiation they are not replaced to a significant degree for a period of at least 10 days.