G-CSF, but not corticosterone, mediates circulating neutrophilia induced by febrile-range hyperthermia.

We previously showed that sustained exposure to febrile-range hyperthermia (FRH) for 24 h caused an increase in circulating granulocyte colony-stimulating factor (G-CSF) levels and a peripheral neutrophilia in mice (Hasday J, Garrison A, Singh I, Standiford T, Ellis G, Rao S, He JR, Rice P, Frank M, Goldblum S, and Viscardi R. Am J Pathol 162: 2005-2017, 2003). In this study, we utilized a conscious temperature-clamped mouse model to analyze the kinetics of G-CSF expression and peripheral neutrophil expansion and the contributions of FRH-induced G-CSF expression, glucocorticoid generation, and catecholamine-induced neutrophil demargination. In conscious mice housed at an ambient temperature of 34.5 degrees C, core temperature rapidly equilibrated at 39.5-40 degrees C. Peripheral neutrophil counts increased 2-fold after 24-h exposure to hyperthermia, peaked at 3.6-fold baseline levels after 36-h exposure to FRH, and returned to baseline levels after 42 h of sustained hyperthermia. Plasma G-CSF levels were increased by 6.8-fold after 24 h and peaked at 40-fold baseline levels after 36 h in the hyperthermic mice. Plasma corticosterone levels peaked at 3.3-fold baseline levels after 30-h sustained hyperthermia and returned to baseline by 42 h. Immunoneutralization of G-CSF blocked FRH-induced peripheral neutrophilia, but blockade of the glucocorticoid receptor with mifepristone failed to modify FRH-induced neutrophilia. Epinephrine induced similar increases in peripheral blood absolute neutrophil counts in euthermic mice (2.2-fold increase) and mice exposed to FRH for 36 h (1.8-fold increase). Collectively, these data suggest that FRH-induced expression of G-CSF drives the sustained peripheral neutrophilia that occurs during sustained (36 h) hyperthermia, whereas glucocorticoid generation and catecholamine-induced demargination play little role in this response.

Febrile-range hyperthermia augments pulmonary neutrophil recruitment and amplifies pulmonary oxygen toxicity.

Febrile-range hyperthermia (FRH) improves survival in experimental infections by accelerating pathogen clearance, but may also increase collateral tissue injury. We hypothesized that FRH would worsen the outcome of inflammation stimulated by a non-replicating agonist and tested this hypothesis in a murine model of pulmonary oxygen toxicity. Using a conscious, temperature-controlled mouse model, we showed that maintaining a core temperature at FRH (39 degrees C to 40 degrees C) rather than at euthermic levels (36.5 degrees C to 37 degrees C) during hyperoxia exposure accelerated lethal pulmonary vascular endothelial injury, reduced the inspired oxygen threshold for lethality, induced expression of granulocyte-colony stimulating factor, and expanded the circulating neutrophil pool. In these same mice, FRH augmented pulmonary expression of the ELR(+) CXC chemokines, KC and LPS-induced CXC chemokine, enhanced recruitment of neutrophils, and changed the histological pattern of lung injury to a neutrophilic interstitial pneumonitis. Immunoblockade of CXC receptor-2 abrogated neutrophil recruitment, reduced pulmonary vascular injury, and delayed death. These combined data demonstrate that FRH may enlist distinct mediators and effector cells to profoundly shift the host response to a defined injurious stimulus, in part by augmenting delivery of neutrophils to sites of inflammation, such as may occur in infections. In certain conditions, such as in the hyperoxic lung, this process may be deleterious.