The effect of neutrophil migration on epithelial permeability.

Abstract

Abstract. To reach an inflammatory lesion, neutrophils must frequently traverse the epithelium of an infected organ. Whether the actual migration of neutrophils alters the epithelial permeability is unknown. Through the use of an in vitro model system it was possible to directly determine the effect of neutrophil emigration on the transepithelial electrical resistance of the monolayer. Human neutrophils (5 x 106 cells/ml) were placed in the upper compartment of a combined chemotaxis/resistance chamber and stimulated for 40 min by a gradient of 10 -7 M n-formylmethionyl-leucyl-phenylalanine to traverse a confluent monolayer of canine kidney epithelial cells grown on micropore filters. Neither the chemoattractant alone (10-5-10 -9 M) nor the accumulation of an average of eight neutrophils per millimeter of epithelium lowered the transepithelial electrical resistance. However, under certain conditions the migration of neutrophils temporarily increased the permeability of the monolayer.The resistance fell ~48 % within 5 min if the migratory cells were stimulated to reverse their migration across the same monolayer. As re-migration continued, the resistance returned to its initial levels within 60 min. Doubling the initial neutrophil concentration to 10 x 106 cells/ml resulted in the accumulation of an average of 66 neutrophils per millimeter of epithelium and an average fall in resistance of 46% (r = 0.98; P < 0.001) in 40 min. If the resistance had fallen <45 %, removal of the neutrophils remaining in the upper compartment resulted in a return of the transepithelial electrical resistance to its initial level within 65 min. However, when the fall was >45 %, the resistance only recovered to 23.5 % of its initial levels within the same time frame. Thus, these results suggest that the integrity of an epithelium can, under certain conditions, be affected by the emigration of neutrophils, but that this effect is either completely or partially reversible within 65 min.T HE accumulation of leukocytes is an important part of the inflammatory response. To reach the site of inflammation, leukocytes must be able to traverse the endothelium lining blood vessels and the epithelium lining an infected organ (i.e., transitional epithelium during a bladder infection or tubular epithelium in pyelonephritis; 9, 24, 40, 41). While many in vivo studies have examined the effect of leukocyte migration on the permeability of the vascular endothelium (1, 18-22, 26-28, 34, 39, 42, 44, 46), relatively few studies (8, 36,43,45) have determined the effect of inflammatory mediators or neutrophil migration on the permeability of organ epithelia.The paracellular or intercellular permeability of the epithelium is regulated by the zonulae occludentes (tight or occluding junctions; 5, 11). Ultrastructurally, these junctions appear as regions of fusion between the outer leaflets of the plasma membrane of adjacent epithelial cells and are thought to form an occluding belt around the circumference of each cell (3, 10). The tightness of these junctions ...

Disruption of the subendothelial basement membrane during neutrophil diapedesis in an in vitro construct of a blood vessel wall.

“…Since these results predict that the basement membrane of venules surrounding an inflamed site are undergoing active perforation, it is tempting to speculate that the leakage of lipoproteins, fibrinogen, and erythrocytes into inflamed sites in vivo reflects the imperfect masking of matrix defects by the overlying endothelium (72,73). Finally, it should be stressed that conclusions regarding the status of the subendothelial basement membrane are quite distinct from recent reports demonstrating the ability of migrating neutrophils to alter transcellular electrical resistance (74,75). The electrical measurements only reflect the "tightness" of intercellular occluding junctions to small ions, and changes in electrical resistance occur independently of alterations in basement membrane integrity (13).…”

Transepithelial Migration of Neutrophils

“…Small numbers of neutrophils can transmigrate without any change in permeability, as measured by electrical resistance and macromolecular flux (6,15,94,120), and although larger numbers of transmigrating neutrophils (especially if activated) induce increased epithelial permeability, this can be transient and reversible (24,93,120,122). This suggests that there are mechanisms by which tight junctions are opened and closed to allow for paracellular neutrophil transmigration without marked and permanent increased permeability or damage to the epithelium.…”

Neutrophil migration across cultured intestinal epithelial monolayers is modulated by epithelial exposure to IFN-gamma in a highly polarized fashion.

“…Studies of PMN transepithelial migration have largely focused on this nonphysiologically directed migration for technical reasons (Evans et al, 1983;Cramer et al, 1986;Milks et al, 1986;Nash et al, 1987;Migliorisi et al, 1988;Parkos et al, 1991). However, we have also recently shown that, while the efficiency of transmigration does vary depending on the direction in which PMN cross monolayers, in several qualitative ways transmigration is similar in both directions (i.e., ability of transmigration to proceed, specific chemotactic gradients required, and CDllb/18 dependence) .…”