Long term radiation effects on the bone marrow stem cells of C3H mice

This study investigated the radiation effects for up to eighteen months on the bone marrow stem cells in mice. To distinguish any effects due to aging, time course changes were also studied in control animals. In totally irradiated animals, in spite of continuous pluripotential (CFU-S) haemopoietic stem cell proliferation associated with the increase of bone marrow nucleated cells, leukopaenia appeared at eighteen months which suggested a persistent defect of haemopoiesis. After sub-total irradiation (one leg protected), incomplete recovery of the medullary stem cell compartment persisted but ineffective haemopoiesis did not occur. After local irradiation of one leg, no stimulation of CFU-S proliferation was observed in the irradiated leg nor in the protected leg, and there was no recovery of CFU-S number in the irradiated marrow; the number of white blood cells and nucleated cells were also not different from the controls. After fractionated partial body irradiation (one leg protected), the peripheral blood count returned to normal at six months. This contrasted with the high CFU-S proliferative activity and the increased numbers of unipotential (CFU-G) stem cells which suggested the existence of ineffective haemopoiesis; the CFU-S proliferation persisted in both the protected and irradiated areas during the observation period. (U.K.)