[en] In order to detect injury to stem cells which neither kills them nor inhibits their reproductive integrity, an assay method was used which measures the proliferative ability of irradiated bone marrow relative to unirradiated bone marrow, following transfusion into lethally irradiated recipient mice. Neither the proliferation factor nor the CFU-S number per femur recovered completely within one year after 5 Gy, and the number of CFU-S per femur was more suppressed than the PF. (UK)

[en] In order to study radiation induced residual injury in hemopoietic stem cells the number and size of spleen colonies were compared to the incorporation of ¹²⁵I-labeled iododeoxyuridine (¹²⁵IUdR) in the spleen after transfusion of irradiated bone marrow cells in the lethally irradiated mouse. Bone marrow cells from non-irradiated or from mice that had been given 3,000 rad in daily 50 rad increments 5 days per week were used 3 months after termination of irradiation. Marrow cells from donor mice given 50 rad immediately prior to the experiment were comparably used to study acute radiation effect. The splenic proliferation factor (PF) (ratio of 5th to 3rd day-¹²⁵IUdR incorporation) of 7.3 +- 0.2 for the 3,000 rad irradiated bone marrow is 44.2% of the control value (16.5 +- 0.9). Spleen colonies produced by stem cells from 3,000 rad mice are 40-50% of the size of colonies produced by nonirradiated stem cells. An acute dose of 50 rad reduced the PF from 20.7 +- 0.9 for controls to 8.0 +- 0.7 for the irradiated bone marrow. This reduction is compatible with the reduction in size and number of the spleen colonies. The cytological appearance of spleen colonies formed from the 3,000 rad and 50 rad irradiated bone marrow was different. The colonies produced by bone marrow from mice given 50 rad immediately before preparing the BM showed extensive karyorrhexis, so called apoptosis, not seen in the colonies produced by BM cells taken from mice 3 months after receiving 3,000 rad in 50 rad increments 5 days per week for 12 weeks. (author)