Activated neutrophils disrupt endothelial monolayer integrity by an oxygen radical-independent mechanism.

We have measured the effect of activated neutrophils on endothelial monolayer integrity in vitro by assessing the capacity of endothelial monolayers on polycarbonate filters to exclude 125I-albumin. Although formylmethionyl-leucyl-phenylalanine (FMLP)-activated neutrophils failed to induce 51Cr-release or detachment after 4 hours of incubation with endothelial monolayers cultured in polystyrene wells, FMLP-activated neutrophils produced a marked increase in the passage of 125I-albumin across bovine aortic or pulmonary artery endothelial monolayers on polycarbonate filters. This effect was evident as early as 30 minutes following the addition of FMLP-activated neutrophils to the monolayer and reached 180% over control values at 2 hours (p = 0.001). Light and transmission electron microscopic examination of the polycarbonate filters exposed to FMLP-activated neutrophils revealed focal disruption of the endothelial monolayers. Chronic granulomatous disease neutrophils produced similar disruption of the endothelial monolayer at 2 hours. Moreover, catalase and superoxide dismutase failed to reduce significantly the neutrophil-mediated increase in 125I-albumin passage at 2 hours. Cell-free postsecretory supernatants of FMLP-activated neutrophils, leukotriene C4, and platelet activating factor did not induce a significant increase in 125I-albumin passage across the endothelial monolayers. Of note, FMLP-activated neutrophils from a patient with a congenital abnormality of neutrophil adhesion and chemotaxis did not induce disruption of the monolayer or increase 125I-albumin passage. We conclude that activated neutrophils mediate rapid, nonlytic disruption of endothelial monolayer integrity by an oxygen radical-independent mechanism that requires neutrophil-endothelial contact.