Thermal sensitivity of the murine CFU-S-12: role of environmental cells

The hyperthermic sensitivity of the CFU-S-12 in bone marrow from normal and anaemic mice was determined. The terminal slope of the survival curves, demonstrated by the T0 values, does not significantly differ in the resting and active cycling stem cells. In the active cycling stem cells the initial shoulder region was less dominant compared with the resting stem cells. The difference in heat sensitivity between resting and active proliferating CFU-S-12 might be explained by a difference in the accumulation of damage before lethality becomes manifest. The difference in heat sensitivity appears to be independent of the environmental accessory cells, demonstrated by a similar hyperthermic effect of the purified stem cells from bone marrow and spleen and the stem cells in the total cell suspensions. Therefore the heat sensitivity of the haemopoietic stem cell is not mediated by a release of injurious substances from environmental heat-damaged cells. The heat treatment does not result in a selection of macroscopic detectable colonies 12 days after inoculation, as is demonstrated by the same morphology of the spleen colonies from the stem cells before and after the hyperthermic treatment.