On the role of haemopoietic tissue in interstrain differences in radiosensitivity of mice.

Mice of three different strains were classified according to the percentage of survival after a whole-body exposure of 600R as radioresistant (strain C57BL/10), radiosensitive (strain BALB/c) and intermediate (strain BFU). Haemopoietic recovery after a whole-body exposure of 200R was followed in the three groups. It was found that the radiosensitivity of bone marrow and spleen haemopoietic stem cells was equal in all the mouse strains tested. The extent of radiation damage to haemopoiesis, assessed by the changes in nucleated cell counts in bone marrow and spleen, as well as by bone marrow and spleen 59Fe uptake, was smaller and the rate of recovery higher in strain C57BL/10 than in strains BALB/c or BFU. An analogical difference among the strains was also observed during realimentation in the recovery of bone marrow and spleen haemopoiesis inhibited by fasting. The role of the capacity of haemopoietic cell population to repair the induqed haemopoietic damage is discussed and its decrease in BALB/c mice is held responsible for their higher radiosensitivity.