Outer Membrane Vesicles Derived From Escherichia coli Regulate Neutrophil Migration by Induction of Endothelial IL-8

Abstract

Outer membrane vesicles (OMVs) are spherical, proteolipid nanostructures that are constitutively released by Gram-negative bacteria including <i>Escherichia coli</i>. Although it has been shown that administration of <i>E. coli</i> OMVs stimulates a strong pulmonary inflammatory response with infiltration of neutrophils into the lungs <i>in vivo</i>, the mechanism of <i>E. coli</i> OMV-mediated neutrophil recruitment is poorly characterized. In this study, we observed significant infiltration of neutrophils into the mouse lung tissues <i>in vivo</i>, with increased expression of the neutrophil chemoattractant CXCL1, a murine functional homolog of human IL-8, on intraperitoneal administration of <i>E. coli</i> OMVs. In addition, OMVs and CD31-positive endothelial cells colocalized in the mouse lungs. Moreover, <i>in vitro</i> results showed that <i>E. coli</i> OMVs significantly increased IL-8 release from human microvascular endothelial cells and toll-like receptor (TLR)4 was found to be the main component for recognizing <i>E. coli</i> OMVs among human endothelial cell-associated TLRs. Furthermore, the transmigration of neutrophils was suppressed in the lung tissues obtained from TLR4 knockout mice treated with <i>E. coli</i> OMVs. Taken together, our data demonstrated that <i>E. coli</i> OMVs potently recruit neutrophils into the lung via the release of IL-8/CXCL1 from endothelial cells in TLR4- and NF-κB-dependent manners.