Increased Susceptibility of Glutamine-Depleted Monocytes to Fever-Range Hyperthermia

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Abstract
Objective: This study investigates the effect of fever-range hyperthermia on Gln-starving monocytes and the role of the 70-kDa heat shock protein Hsp70. Summary Background Data: Fever is a protective acute-phase response to infection. However, in critically ill patients, the harmful effects of fever seem to be predominant. Critical illness is frequently associated with reduced plasma glutamine (Gln) levels, which contribute to the immune suppression in these patients due to impaired monocyte function. Methods: Isolated monocytes were suspended in Gln-depleted medium and exposed to 41°C. Cell survival was determined by an MTT-based assay, and phagocytosis of Escherichia coli was measured by flow cytometry. Expression of Hsp70 was determined by Western blot. Results: Hyperthermia for 300 minutes strongly decreased the viability of Gln-depleted monocytes (85%), whereas it had only a moderate effect on Gln-supplied cells (45%, P < 0.05). Shorter treatments (45 minutes) of Gln-starving monocytes had almost no effects on viability but decreased the phagocytosis activity by 30.8%. In addition, the expression of Hsp70 was inhibited almost completely. Conclusion: These data show that Gln-starving monocytes have a reduced thermoresistance. This suggests that elevated body temperature damages monocytes in critically ill patients with reduced plasma Gln-levels possibly via an inhibition of the cytoprotective protein Hsp70.