Radiation Sensitivity of New Zealand Black Mice and the Development of Autoimmune Disease and Neoplasia

Young New Zealand Black (NZB) mice manifested extremely high resistance to the lethal effects of acute exposures to ionizing radiation, with a dose necessary to kill 50% of the animals within 30 days, LD(50(30)), of 964 roentgens (R) at 30 days of age and of 856 R for 90-day-old mice. In contrast, Coombs' positive 9-month-old NZB mice (with low primary immune response) were highly susceptible (LD(50(30)) = 543 R), possibly because of anemia-stimulated erythropoiesis leading to a depletion of stem cells. The radiation resistance of young NZB mice, combined with previous observations of their immunologic hyper-responsiveness, support the concept that NZB mice possess an unusually large pool of hematopoietic stem cells, an abnormality which may predispose them to the development of autoimmune disease and neoplasia.