Endothelial Domes Encapsulate Adherent Neutrophils and Minimize Increases in Vascular Permeability in Paracellular and Transcellular Emigration

Abstract

Local edema, a cardinal sign of inflammation associates closely with neutrophil emigration. Neutrophil emigration has been described to occur primarily through endothelial junctions (paracellular) and more rarely directly through endothelial cells (transcellular). Recently, we reported that unlike in wild-type (wt) mice, Mac-1-/- (CD11b) neutrophils predominantly emigrated transcellularly and was significantly delayed taking 20–30 min longer than the paracellular emigration (wt). In the present study we noted significant anatomical disruption of the endothelium and hypothesized that transcellular emigration would greatly increase vascular permeability. Surprisingly, despite profound disruption of the endothelial barrier as the neutrophils moved through the cells, the changes in vascular permeability during transcellular emigration (Mac-1-/-) were not increased more than in wt mice. Instead increased vascular permeability completely tracked the number of emigrated cells and as such, permeability changes were delayed in Mac-1-/- mice. However, by 60 min neutrophils from both sets of mice were emigrating in large numbers. Electron-microscopy and spinning disk multichannel fluorescence confocal microscopy revealed endothelial docking structures that progressed to dome-like structures completely covering wt and Mac-1-/- neutrophils. These domes completely enveloped the emigrating neutrophils in both wt and Mac-1-/- mice making the mode of emigration underneath these structures extraneous to barrier function. In conclusion, predominantly paracellular versus predominantly transcellular emigration does not affect vascular barrier integrity as endothelial dome-like structures retain barrier function.

Reactive Oxygen Species in Inflammation and Tissue Injury

“…These patients suffer from recurrent bacterial infections. b 2 integrin Mac-1 favors paracellular migration of leucocytes and in Mac-1 -/ -(CD11b) mice, neutrophils predominantly emigrate transcellularly (through endothelial cells) and were delayed by 20-30 min compared with the more rapid paracellular emigration route (351). In contrast to b 2 integrins, the b 1 integrin family mediates neutrophil adhesion to extracellular matrix proteins such as fibronectin and VLA4 or a 4 b 1 integrin.…”

Blood cells and endothelial barrier function

“…92,93 This appears to occur despite the fact that endothelial cells can extend projections to envelop the migrating neutrophils, forming endothelial domes, with the leakage response resulting from the transfer of entrapped plasma proteins within the "dome." 83,94 It has also been reported that the endothelial barrier dysruption caused by transmigrating leukocytes are detected by the endothelial cells as a release of isometric tension, which results in protective actin remodeling that is dependent on the production of reactive oxygen species. 95 Furthermore, the results of a recent study reveal that extravasating leukocytes deposit microparticles on the subendothelium during their passage through the junctions and that the microparticle deposition serves to maintain barrier function; inhibition of neutrophil-derived microparticle formation resulted in dramatically increased vascular leakage.…”

Leukocyte transendothelial migration: A local affair

“…transmigratory cups, apical cups, dome structures, ICAM-1-enriched contact areas, or actin dynamic structures. 14,[67][68][69][70][71] The names were based on the hypothesized function or morphology of these structures. Work of Carman and coworkers showed that these structures, that formed both during para-and transcellular diapedesis (Fig.…”