Patterns of exogenous and endogenous hematopoietic repopulation following radiation injury.

Patterns of hematopoietic recovery in mice given an LD50/30 radiation exposure were different from those in animals given an LD100/30 exposure and a marrow transplant sufficient to effect 50 per cent 30-day survival. Death occurred later, and recovery of some peripheral blood elements was delayed in the LD50/30 mice. Over the period of study, splenic hematopoiesis and stem cell renewal were insignificant in the LD50/30 mice yet were active in the marrow-transplanted animals. The slow recovery of erythropoiesis in the LD30/30 mice is explained in part by the lack of early splenic hematopoiesis. This effect appeared to be attributable to the splenic microenvironment which, although being suitable for growth of unirradiated hematopoietic cells, was not conducive to repair of radiated splenic hematopoietic cells.