Local microvascular leakage promotes trafficking of activated neutrophils to remote organs.

Charlotte Owen-Woods,Monja Stein,Sussan Nourshargh,Bin Ma,Anna Barkaway,Dietmar Vestweber,Régis Joulia,David O Bates,Mathieu-Benoit Voisin,Kenton P Arkill,Astrid Fee Nottebaum,Matthew Golding,Loïc Rolas,Tamara Girbl

doi:10.1172/jci133661

Abstract

Increased microvascular permeability to plasma proteins and neutrophil emigration are hallmarks of innate immunity and key features of numerous inflammatory disorders. Although neutrophils can promote microvascular leakage, the impact of vascular permeability on neutrophil trafficking is unknown. Here, through the application of confocal intravital microscopy, we report that vascular permeability–enhancing stimuli caused a significant frequency of neutrophil reverse transendothelial cell migration (rTEM). Furthermore, mice with a selective defect in microvascular permeability enhancement (VEC-Y685F-ki) showed reduced incidence of neutrophil rTEM. Mechanistically, elevated vascular leakage promoted movement of interstitial chemokines into the bloodstream, a response that supported abluminal-to-luminal neutrophil TEM. Through development of an in vivo cell labeling method we provide direct evidence for the systemic dissemination of rTEM neutrophils, and showed them to exhibit an activated phenotype and be capable of trafficking to the lungs where their presence was aligned with regions of vascular injury. Collectively, we demonstrate that increased microvascular leakage reverses the localization of directional cues across venular walls, thus causing neutrophils engaged in diapedesis to reenter the systemic circulation. This cascade of events offers a mechanism to explain how local tissue inflammation and vascular permeability can induce downstream pathological effects in remote organs, most notably in the lungs.

Highlights

IntroductionAcute inflammation is a critically important pathophysiological response to a local stimulus (e.g., bacterial infection) characterized by local tissue infiltration of neutrophils and tissue swelling (edema)
Acute inflammation is a critically important pathophysiological response to a local stimulus characterized by local tissue infiltration of neutrophils and tissue swelling
To directly investigate potential associations between neutrophil trafficking and microvascular permeability, inflamed mouse cremaster muscles were analyzed for neutrophil breaching of endothelial cells (ECs) junctions and microvascular leakage in real time and in 3D (i.e., 4D) by confocal intravital microscopy (IVM)

Summary

Introduction

Acute inflammation is a critically important pathophysiological response to a local stimulus (e.g., bacterial infection) characterized by local tissue infiltration of neutrophils and tissue swelling (edema). These responses typically begin within minutes after a stimulus and collectively support the activation of essential immunoregulatory, proinflammatory, and proresolution pathways required for effective host defense and tissue repair. Neutrophil trafficking, ECs provide critical proadhesive and other effector molecules that facilitate a cascade of neutrophil-EC interactions, such as neutrophil rolling, firm arrest, and luminal crawling. These events that are generally considered to be prerequisite to breaching of the endothelium [3]. We recently demonstrated the importance of retaining directional cues within EC junctions in facilitating luminal-toabluminal neutrophil breaching of the endothelium [6]

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Conclusion