Corynebacterium parvum-Induced Radiosensitivity and Cycling Changes of Hematopoietic Spleen Colony-Forming Units2

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Abstract
Ten days after total-body irradiation with 550 rads of 80Co, spleen colonies were observed in adult C57BL mice. A change in radiosensitivity induced by Corynebacterium parvum, as measured by increased numbers of colony-forming units that survived the 550 rads, began shortly after C. parvum stimulation and extended for at least 7 days before irradiation. C. parvum given 4–24 hours before, followed by high specific activity [3H]thymidine (HSATT) 1 hour before total-body irradiation greatIy reduced survival of the stem cells that formed spleen colonies (CFUs) and CFUs radiosensitivity to control levels. The HSATT sensitivity by “suicide” assay in vivo and the time-response change in radiosensitivity corresponded with the decrease in radiosensitivity, which showed that CFUs were stimulated by C-parvum administration and entered the S-phase shortly after stimulation. The data indicated a resting population close to the S-phase. After stimulation, this population entered S-phase. Syngeneic mouse lymphoma cells injected iv 24 hours earlier did not elicit any effect as a stimulus to CFUs radiosensitivity change.