Activation of human neutrophil by cytokine-activated endothelial cells

Cytokine activation of vascular endothelial cells renders the hyperadhesiveness for neutrophils. During the processes of inflammation and atherosclerosis, the production of reactive oxygen species by neutrophils contributes to endothelial cell (EC) damage and injury. However, the precise mechanisms for neutrophil activation by ECs remain unknown. Thus, we investigated what kinds of pathophysiological factors synthesized by inflammatory cytokine-activated ECs potentiated the activity of neutrophil functions. The magnitude of O(2)(-) release from neutrophils, which is one of pivotal neutrophil functions, was measured as an indicator potentiated by activated ECs. Neutrophils release massive amounts of O(2)(-) on coculture with activated ECs. Anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibody (Ab) or specific platelet-activating factor (PAF)-receptor antagonist suppressed the O(2)(-) release from neutrophils on coculture with the activated ECs by 50% to 70%. The supernatants from activated ECs also induced O(2)(-) release by neutrophils. This stimulatory effect of activated EC supernatants on O(2)(-) release by neutrophils was abolished by anti-GM-CSF Ab or by PAF-receptor antagonist. As we previously reported, we demonstrated the expression of GM-CSF mRNA by Northern blotting and protein synthesis of GM-CSF by ELISA on tumor necrosis factor as well as interleukin-1-activated ECs. Although phosphorylation of mitogen-activated protein kinases was observed in ECs stimulated by tumor necrosis factor and interleukin-1, treatment of ECs with PD98059 (MEK1 inhibitor) and SB203580 (p38 mitogen-activated protein kinase inhibitor) in the presence of the cytokine failed to attenuate the stimulatory effect of activated ECs on neutrophil activation. We found that activated ECs regulated neutrophil function on coculture. We show here for the first time, to our knowledge, that the collaboration between GM-CSF and PAF synthesized by activated ECs markedly potentiated neutrophil activation.