The time-profile of the PBMC HSP70 response to in vitro heat shock appears temperature-dependent

Heat shock proteins (HSPs) are synthesised by cells subsequent to a stress exposure and are known to confer protection to the cell in response to a second challenge. HSP induction and decay are correlated to thermotolerance and may therefore be used as a biomarker of thermal history. The current study tested the temperature-dependent nature of the heat shock response and characterised its time profile of induction. Whole blood from 6 healthy males (Age: 26 +/- (SD) 2 yrs; Body mass 74.2 +/- 3.8 kgs; VO(2max): 49.1 +/- 4.0 ml.kg(-1).min(-1)) were isolated and exposed to in vitro heat shock (HS) at 37, 38, 39, 40, and 41 degrees C for a period of 90 min. After HS the temperature was returned to 37 degrees C and intracellular HSP70 was quantified from the leukocytes at 0, 2, 4, and 6 h after heat treatment. The concentration of HSP70 was not different between temperatures (P > 0.05), but the time-profile of HSP70 synthesis appeared temperature-dependent. At control (37 degrees C) and lower temperatures (38-39 degrees C) the mean HSP70 concentration increased up to 4 h post HS (P < 0.05) and then returned towards baseline values by 6 h post HS. With in vitro hyperthermic conditions (40-41 degrees C), the time-profile was characterised by a sharp rise in HSP70 levels immediately after treatment (P < 0.05 for 40 degrees C at 0 h), followed by a progressive decline over time. The results suggest a temperature-dependent time-profile of HSP70 synthesis. In addition, the temperature at which HSP70 is inducted might be lower than 37 degrees C.