Lack of Development of Thermotolerance in Early Progenitors of Murine Bone Marrow Cells1

We have studied the sensitivities of four hematopoietic stem cell types to heat stress as well as their abilities to develop thermotolerance. Granulocyte-macrophage colony forming units were the most heat resistant bone marrow progenitors tested. Of the erythroid progenitors tested, erythrocyte colony forming units were more resistant than the two more primitive erythrocyte burst forming units. To determine their ability to develop thermotolerance, hematopoietic precursors were heated in vivo at 43°C for 30 min. At various times thereafter the hematopoietic stem cells were flushed from female C3Hf/Sed mouse preheated tibia. The bone marrow cell suspensions were then heated in vitro and plated for colony formation. The four stem cell precursors differed markedly in their abilities to develop thermotolerance. The ther motolerance induced in granulocyte-macrophage colony forming units reached a maximum at 3-6 h after heating and disappeared by 24-48 h. The thermotolerance in erythrocyte colony forming units (0.5 units erythropoietin/ml media) reached a maximum at 3-6 h and disappeared by 48-72 h. The maximum level of thermotolerance reached by granulocyte-macrophage colony forming units and erythrocyte colony forming units was approx imately the same. On the contrary, the two more primi tive erythrocyte precursors which were grown by the addition of 2.5 and 5 units erythropoietin/ml of media do not develop thermotolerance.