Abstract

The capacity of cytokines to modulate neutrophil apoptosis is thought to be a major factor influencing the resolution of granulocytic inflammation. We have previously shown that the late survival effect of TNF-alpha in human neutrophils involves activation of both NF-kappa B and phosphoinositide 3-kinase (PI3-kinase) pathways. In this study, we address how these pathways integrate to prevent cell death. In human neutrophils, TNF-alpha (200 U/ml) induced rapid I kappa B-alpha degradation, NF-kappa B activation and IL-8 release (31.8+/-5.4 pg/10(5) cells/2 h), whereas GM-CSF (10 ng/ml) stimulated an equivalent IL-8 release (26.5+/-4.5 pg/10(5) cells/2 h) without enhanced I kappa B-alpha degradation or NF-kappa B activation compared to control. Importantly, inhibition of PI3-kinase did not modify TNF-alpha -induced I kappa B-alpha degradation, yet fully inhibited the survival effect of both cytokines. Inhibition of I kappa B-alpha phosphorylation, PI3-kinase or ERK1/2 activation blocked IL-8 release by both cytokines. Blocking IL-8 activity by inhibiting its synthesis or by using a neutralizing antibody enhanced the early pro-apoptotic effect of TNF-alpha and inhibited its late survival effect without affecting GM-CSF-induced survival. These data suggest that cross-talk between NF-kappa B and PI3-kinase pathways in TNF-alpha -stimulated neutrophils results from NF-kappa B/ERK1/2-dependent IL-8 production which acts in an autocrine manner to drive PI3-kinase-dependent survival. In contrast, GM-CSF-mediated survival does not involve NF-kappa B activation or IL-8 release.