Neutrophil-mediated inflammation is usually self-limiting, because neutrophils have a remarkably short life span. Prolonged neutrophil survival, which is caused by decreased spontaneous apoptosis, leads to persistent inflammation in sepsis. Because many inflammatory cytokines, which generate signals that delay apoptosis, are regulated by nuclear factor-κB transcription factor, we hypothesized that nuclear factor-κB might be related to the reduced neutrophil apoptosis observed in sepsis.

Neutrophils of healthy volunteers and sepsis patients were freshly isolated from venous blood. Neutrophil apoptosis was assayed with two approaches: by counting apoptotic cells under a microscope and by flow cytometry using Annexin V. The activity of nuclear factor-κB was assessed by immunofluorescent staining or electrophoretic mobility shift assay. Expression of X-linked inhibitor of apoptosis was measured by western blot assay.

We confirmed reduced spontaneous neutrophil apoptosis in patients with sepsis. The number of apoptotic neutrophils in patients with sepsis increased to the level of that in healthy controls after cycloheximide treatment, suggesting that decreased spontaneous neutrophil apoptosis is dependent on de novo protein synthesis. In patients with sepsis, basal neutrophil nuclear factor-κB was activated compared to the level in healthy controls. Moreover, a blockade of nuclear factor-κB activity reversed the decreased spontaneous neutrophil apoptosis in sepsis patients. Meanwhile, X-linked inhibition of apoptosis expression, which is regulated by nuclear factor-κB, decreased 24 hours after incubation in healthy persons, but persisted for 24 hours in patients with sepsis.

These observations suggest that the reduced spontaneous neutrophil apoptosis observed in patients with sepsis may be related to the induction of survival protein by nuclear factor-κB.