We recently discovered that a ubiquitous protein, high mobility group box 1 protein (HMGB1), is released by activated macrophages, and functions as a late mediator of lethal systemic inflammation. To elucidate mechanisms underlying the regulation of HMGB1 release, we examined the roles of other cytokines in induction of HMGB1 release in macrophage cell cultures. Macrophage migration inhibitory factor, macrophage-inflammatory protein 1β, and IL-6 each failed to significantly induce the release of HMGB1 even at supraphysiological levels (up to 200 ng/ml). IFN-γ, an immunoregulatory cytokine known to mediate the innate immune response, dose-dependently induced the release of HMGB1, TNF, and NO, but not other cytokines such as IL-1α, IL-1β, or IL-6. Pharmacological suppression of TNF activity with neutralizing Abs, or genetic disruption of TNF expression (TNF knockout) partially (50–60%) inhibited IFN-γ-mediated HMGB1 release. AG490, a specific inhibitor for Janus kinase 2 of the IFN-γ signaling pathway, dose-dependently attenuated IFN-γ-induced HMGB1 release. These data suggest that IFN-γ plays an important role in the regulation of HMGB1 release through a TNF- and Janus kinase 2-dependent mechanism.

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Apnea-induced hypoxia and reoxygenation, which generates reactive oxygen species, may activate the oxidant-sensitive, proinflammatory transcription factor nuclear factor kappaB (NF-kappaB), increasing systemic inflammation in obstructive sleep apnea. We measured NF-kappaB activity in circulating neutrophils and plasma levels of NF-kappaB-controlled gene products, soluble E (sE)-selectin and soluble vascular cell adhesion molecule-1 (sVCAM-1) in control subjects and in obstructive sleep apnea (OSA) patients. To confirm a causal link with OSA, we reassessed these parameters after nasal continuous positive airway pressure (CPAP) therapy. Twenty-two subjects undergoing evaluation for symptoms of sleep-disordered breathing were grouped by apnea hypopnea index: control, less than 5/h; mild to moderate OSA, 11-40/h; severe OSA, more than 40/h. A morning venous blood sample was obtained. Neutrophils were isolated, and NF-kappaB activity was determined by electrophoretic mobility shift assay. Plasma sE-selectin and sVCAM-1 were assayed by enzyme-linked immunosorbent assay. Neutrophils in mild to moderate and severe OSA patients showed 4.8- and 7.9-fold greater NF-kappaB binding activity compared with control subjects (p<0.0001). The degree of NF-kappaB activation was positively correlated with indices of apnea severity. In five severe OSA patients, 1 month of CPAP therapy decreased neutrophil NF-kappaB activation to control levels. sE-selectin and sVCAM concentrations were reduced by CPAP in four of these five subjects. OSA leads to NF-kappaB activation, which may constitute an important pathway linking OSA with systemic inflammation and cardiovascular disease.