Signaling via β2 Integrins Triggers Neutrophil-Dependent Alteration in Endothelial Barrier Function

Abstract

Activation of polymorphonuclear leukocytes (PMNs) and adhesion to the endothelial lining is a major cause of edema formation. Although known to be dependent on the function of β2 integrins (CD11/CD18), the precise mechanisms by which adherent PMNs may impair endothelial barrier capacity remain unclear. Here, the role of transmembrane signaling by β2 integrins in PMN-induced alterations in tight junctional permeability of cultured endothelial cell (EC) monolayers was investigated. PMN activation, in the absence of proinflammatory stimuli, was accomplished through antibody cross-linking of CD11b/CD18, mimicking adhesion-dependent receptor engagement. CD18 cross-linking in PMNs added to the EC monolayer provoked a prompt increase in EC permeability that coincided with a rise in EC cytosolic free Ca2+ and rearrangement of actin filaments, events similar to those evoked by chemoattractant PMN activation. Cell-free supernatant obtained after CD18 cross-linking in suspended PMNs triggered an EC response indistinguishable from that induced by direct PMN activation, and caused clear-cut venular plasma leakage when added to the hamster cheek pouch in vivo preparation. The PMN-evoked EC response was specific to β2 integrin engagement inasmuch as antibody cross-linking of l-selectin or CD44 was without effect on EC function. Our data demonstrate a causal link between outside-in signaling by β2 integrins and the capacity of PMNs to induce alterations in vascular permeability, and suggest a paracrine mechanism that involves PMN-derived cationic protein(s) in the cellular crosstalk between PMNs and ECs.

Eoxins are proinflammatory arachidonic acid metabolites produced via the 15-lipoxygenase-1 pathway in human eosinophils and mast cells

“…In this study, we used an in vitro model system for analysis of mediator-induced perturbation of EC monolayer barrier function. Continuous measurement of TEER permits detection of rapid changes in EC permeability and has been shown previously to be a sensitive measure of the barrier capacity of cultured EC monolayers and to mimic changes in vascular permeability in vivo (27,32). The permeability-increasing activity of inflammatory mediators such as histamine and the cysteinyl LTs has long been known.…”

Neutrophil-derived azurocidin alarms the immune system

“…Adhesion of the PMN to the EC induces rapid intracellular Ca 2ϩ mobilization in both cell types, leading to granule exocytosis in the PMN and rearrangement of the EC cytoskeleton. Blockage of ␤ 2 -integrin function abrogated these responses completely [66]. More recently, it was shown that azurocidin is released upon ␤ 2 -integrin ligation and that this protein has a central role in the PMN-evoked permeability change.…”

“…Previous studies clearly indicate that emigration of PMN is accompanied by efflux of plasma from the vasculature and that these cells are in a position to trigger permeability changes themselves [64,65]. Of critical importance in a PMN-evoked permeability increase is the PMN adhesion and activation via ␤ 2 -integrins [66]. Adhesion of the PMN to the EC induces rapid intracellular Ca 2ϩ mobilization in both cell types, leading to granule exocytosis in the PMN and rearrangement of the EC cytoskeleton.…”

Neutrophil-Derived Heparin-Binding Protein (HBP/CAP37) Deposited on Endothelium Enhances Monocyte Arrest under Flow Conditions

“…PMN activation and secretion was induced through Ab cross-linking of integrin ␤ 2 -chain CD18 as previously described (21). In brief, isolated PMN were incubated with mAb IB4 against CD18 (3 g of IB4 per 10 6 neutrophils), washed and subjected to CD18 receptor cross-linking through addition of goat anti-mouse F(abЈ) 2 (diluted 1/20; Jackson ImmunoResearch Laboratories).…”