A basic substance was obtained from calf thymus by acid extraction and further purified by CM-cellulose column chromatography. The material showed a significant prolongation of survival and a promotion of recovery of lymphoid tissues of mice exposed to lethal dose of ionizing radiation, when administered intraperitoneally 10 minutes before irradiation. Furthermore, it was capable of inhibiting the occurrence of radiation-induced leukemia in mice. The most active material (CM3), purified by CM-cellulose column chromatography accelerated the recovery of nucleated cells of bone marrow in irradiated mice. This active fraction, CM-3, was found to be stable after heating at 100°C for 15 minutes and a basic protein with molecular weight of approximately 20, 000.
We also obtained similar fractions from calf liver and spleen by the same extraction procedure. The spleen extract showed the survival effect to some extent in irradiated mice, but the liver extract was ineffective.
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