A Late Effect of Radiation on the Haemopoietic Stem Cells of the Mouse

SummaryThe number of nucleated cells and the proportion of colony-forming units (CFU) were estimated in the femoral marrow of (C57Bl × C3H)F1 male mice aged 20 months or more, and of mice of the same age surviving a mid-lethal dose of x-rays delivered when young adults. Both total cellularity and CFU's were found to be decreased by previous irradiation compared with controls of comparable age. These parameters were also found to be slightly age-dependent in normal mice but not those that had been irradiated. Particular attention was paid to the histopathology of haemopoietic organs of the ageing mice; donor animals in which reticular tissue tumours were found, even in early stages, were excluded. Results are discussed mainly in terms of residual radiation injury.