Transendothelial Migration Enables Subsequent Transmigration of Neutrophils through Underlying Pericytes

Chantal E Ayres-Sander,Anjelica L Gonzalez,Parid Sava,Cheryl L Maier,Holly Lauridsen,Jordan S Pober,Rajesh Mohanraj

doi:10.1371/journal.pone.0060025

Abstract

During acute inflammation, neutrophil recruitment into extravascular tissue requires neutrophil tethering and rolling on cytokine-activated endothelial cells (ECs), tight adhesion, crawling towards EC junctions and transendothelial migration (TEM). Following TEM, neutrophils must still traverse the subendothelial basement membrane and network of pericytes (PCs). Until recently, the contribution of the PC layer to neutrophil recruitment was largely ignored. Here we analyze human neutrophil interactions with interleukin (IL)-1β-activated human EC monolayers, PC monolayers and EC/PC bilayers in vitro. Compared to EC, PC support much lower levels of neutrophil binding (54.6% vs. 7.1%, respectively) and transmigration (63.7 vs. 8.8%, respectively) despite comparable levels of IL-8 (CXCL8) synthesis and display. Remarkably, EC/PC bilayers support intermediate levels of transmigration (37.7%). Neutrophil adhesion to both cell types is Mac-1-dependent and while ICAM-1 transduction of PCs increases neutrophil adhesion to (41.4%), it does not increase transmigration through PC monolayers. TEM, which increases neutrophil Mac-1 surface expression, concomitantly increases the ability of neutrophils to traverse PCs (19.2%). These data indicate that contributions from both PCs and ECs must be considered in evaluation of microvasculature function in acute inflammation.

Highlights

Neutrophil recruitment from the blood to the tissue is a central component of the acute inflammatory response
We have compared the interactions of neutrophils with human umbilical vein endothelial cells (ECs) with interactions of human Thy-1+ NG2+ PCs isolated from placental microvessels
The vast majority of leukocyte extravasation from the blood into infected tissue occurs through post-capillary venules where the EC lining of the vessel is invested by a network of PCs embedded within a shared basement membrane; neutrophils must diapedese through two distinct cell layers, EC and PC, in order to reach perivascular tissue [33,34]

Summary

Introduction

Neutrophil recruitment from the blood to the tissue is a central component of the acute inflammatory response. This process begins with changes in the endothelial cell (EC) lining of postcapillary venules, notably increased expression of leukocyte adhesion molecules (LAMs) and increased display of neutrophilactivating chemokines. Rolling leukocytes encounter and respond to the surface-bound chemokines, principally interleukin-8 (IL-8 or CXCL8) in humans, triggering firm attachment via integrin-mediated adhesion to other endothelial LAMs, most significantly to intercellular adhesion molecule-1 (ICAM-1 or CD54) by neutrophil Mac-1 (CD11b/CD18) [1,2]. EC chemokines and ICAM-1 contribute to neutrophil crawling along the EC surface and eventually to initiation of transendothelial migration (TEM) that occurs at or near inter-EC junctions. While the details of capture and traversing the EC lining of the venule have been extensively studied for several decades using in vitro models, as well as in situ observations, much less attention has been paid to the final events involving neutrophil interactions with PCs [1,4,5,6,7]

Methods

Results

Conclusion