Heat Sensitivity, Thermotolerance, and Profile of Protein Synthesis of Human Bone Marrow Progenitors1

Hyperthermic sensitivity, kinetics of thermotolerance induction and decay, and profile of heat shock protein synthesis were studied in human granulocyte-macrophage progenitors and nucleated bone marrow cells, respectively. The I),, of the heat survival curves of human granulocytemacrophage colony-forming cells at 43°C,44°C,and 45°Cwere 23, 12, and 5 min, respectively. The kinetics of thermotolerance induction was measured with a trig gering dose of 44°C/20min, 4S°C/10min, 41°C/2h, and 42°C/1and 4 h. The cells were then challenged with 44 ( or 45°Cafter incubation for 2, 4, 6, 24, and 48 h at 37°C. In all cases, except for 41°C/2h, thermotoler ance was maximum at 2 to 6 h, began to decay at 24 h, and decayed completely by 48 h. At the 41°C/2-htriggering dose, the thermotolerance decayed completely by 24 h. The heat shock protein synthesis was measured after a triggering dose of 44°C/20min or 45°C/10min. Synthe sis of M, 70,000 and 87,000 heat shock proteins in the total nucleated bone marrow cells was evident at least for 8 h after the initial heating.