Abstract
Extracellular nucleotides can function as paracrine and autocrine mediators that signal through P2Y nucleotide receptors. Human polymorphonuclear (PMN) cells express P2Y receptors on the cell surface but the role of these G protein-coupled receptors in human neutrophils is not well established. Interleukin-8 (IL-8), which is a CXC-chemokine that induces adherence of neutrophils to vascular endothelium and extravasation into tissue, is produced by macrophages and endothelium. Additionally, neutrophils can synthesize and release interleukin-8 upon stimulation with lipopolisacharides (LPS) but the intracellular signaling pathways involved in this process are not clearly understood. LPS is a potent activator of macrophages and is responsible for the initiation the septic shock, increasing the secretion of various cytokines. Here we present evidence that LPS (1 ng/ml to 100 ng/ml) causes IL-8 production in a dose- and time- dependent manner and demonstrate that LPS itself is responsible for mitogen-activated protein kinase (MAPK) ERK1/2 phosphorylation. We used an enzyme immunosorbent-linked assay (ELISA) to determinate the amount of IL-8 released by isolated human neutrophils and present evidence that extracellular nucleotide uridine triphosphate (UTP) (1 μM/ml to 100 μM/ml) can inhibit IL-8 production in human neutrophils in a dose- and time- dependent manner. The addition of ATP had a similar inhibitory effect suggesting that nucleotides act on neutrophils via the P2Y2 receptor, which is equally activated by UTP and ATP. A cytokine array was used to detect the release of 42 different cytokines in the extracellular medium. IL-8 and IL-6 ere the major cytokines detected in the medium, though other cytokines were detected in lower concentrations. In the current study, we demonstrated that extracellular nucleotides may have an important role in regulating IL-8 production in neutrophils and potentially modulating the inflammatory response.
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