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

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

Surface Mol (CD11b/CD18) glycoprotein is up-modulated by neutrophils recruited to sites of inflammation in vivo

Inasmuch as the recruitment of polymorphonuclear leukocytes (PMNs) to inflammatory foci in vivo involves adhesion-dependent events (e.g., margination, diapedesis, and directed migration), we sought to characterize the relationship between the local accumulation of PMNs in sterile peritonitis and their surface expression of the adhesion-promoting plasma membrane glycoprotein. Mol (CD11b/ CD18). In an immunofluorescence analysis of PMNs isolated from rats injected intraperitoneally with sterile 1% glycogen solution, we detected a significant enhancement of surface Mol expression by exudative peritoneal PMNs. In contrast, no significant rise in Mol expression was noted over time by circulating intravascular PMNs (isolated simultaneously). However, these intravascular PMNs had the capacity to increase their surface Mol density upon exposure to peritoneal fiuid supernatant at 37°C. These results demonstrate that PMNs at sites of inflammation in vivo do up-modulate their surface expression of the adhesion-promoting Mol glycoprotein during their recruitment from the circulating, intravascular leukocyte pool.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44502/1/10753_2004_Article_BF00916757.pd