INDUCTION BY CHEMOKINES OF LIPID MEDIATOR SYNTHESIS IN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-TREATED HUMAN NEUTROPHILS

In recent years, there has been a growing body of evidence suggesting that IL-8 and granulocyte-macrophage CSF (GM-CSF) play an important ro le in inflammatory processes. We show that after GM-CSF treatment, the exposure of human neutrophils to IL-8 results in the synthesis of leu kotriene (LT)B4 and platelet-activating factor. In GM-CSF-treated cell s, IL-8 induced a concentration-dependent synthesis of both lipid medi ators, with a threshold at 10 to 30 nM, suggesting that IL-8 could sti mulate phospholipase A2 activity, an enzyme essential for both synthes es. Accordingly, IL-8 induced a substantial release of H-3-arachidonic acid in GM-CSF-treated PMN. It was also found that IL-8 activates the neutrophil 5-lipoxygenase (5-LO), the other key enzyme in LT biosynth esis. IL-8 induced 5-LO activation in a time- and concentration-depend ent manner, with a threshold at 1 nM, and prior treatment of neutrophi ls with GM-CSF enhanced this effect of IL-8 over the 1 to 300 nM range . Neutrophil-activating peptide-2 and the melanoma growth-stimulatory activity, two peptides that are closely related to IL-8, also had the ability to activate the 5-LO and stimulate LT synthesis, albeit less p otently than IL-8. Finally, pertussis toxin and the 5-LO translocation inhibitor, MK-886, both blocked the IL-8-elicited 5-LO activation. Ta ken together, our results raise the possibility that the combined pres ence of IL-8 and of GM-CSF at inflammatory foci could result in the sy nthesis of platelet-activating factor and LTB4 by neutrophils, thereby contributing to the amplification of the inflammatory response.