Extracellular nucleotides mediate LPS-induced neutrophil migration in vitro and in vivo

Extracellular nucleotides are emerging as important inflammatory mediators. Here, we demonstrate that these molecules mediate LPS-induced neutrophil migration in vitro and in vivo. Apyrase, a nucleotide scavenger, reduced the ability of LPS-stimulated monocytes to recruit neutrophils, as assayed using a modified Boyden chamber. This effect resulted from the inhibition of IL-8 release from monocytes. Furthermore, LPS-induced IL-8 release by monocytes was attenuated significantly by P2Y6 receptor antagonists, RB-2 and MRS2578. Reciprocally, UDP, the selective P2Y6 agonist, induced IL-8 release by monocytes. As for LPS, the media of UDP-stimulated monocytes were chemotactic for neutrophils; IL-8 accounted for approximately 50% of neutrophil migration induced by the media of LPS- or UDP-treated monocytes in transendothelial migration assays. It is important that in the murine air-pouch model, extracellular nucleotides were instrumental in LPS-induced neutrophil migration. Altogether, these data imply that LPS induces the release of nucleotides from monocytes and that by autocrine stimulation, the latter molecules regulate neutrophil migration caused by Gram-negative bacteria, suggesting a proinflammatory role of extracellular nucleotides in innate immunity.