Early Repair Processes in Marrow Cells Irradiated and Proliferating in Vivo

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Abstract
Survival of the colony-forming ability of cells of the mouse hematopietic system was studied following exposure of the cells to fractionated doses of Co60 gamma-rays. It was demonstrated that early repair of sublethal damage in surviving cells, similar to that described by Elkind and Sutton for mammalian cells in tissue culture occurred under physiological conditions in vivo. The relationship between the extent of repair and the time interval between dose fractions was qualitatively similar to that reported by Elkind and Sutton, with the kinetic curve of the repair process showing an initial maximum followed by an intermediate minimum. The initial maximum occurred 5 hours after the first dose fraction, and showed a twofold increase in survival. The intermediate minimum occurred at 11 hours and showed little or no increase in survival. Similar results were obtained for colony-forming cells derived from bone-marrow transplants and for endogenous spleen-colonizing cells irradiated in situ.