Neutrophil-mediated increased permeability of microcarrier-cultured endothelial monolayers: a model for the in vitro study of neutrophil-dependent mediators of vasopermeability.

Changes in the permeability of human endothelial monolayers in response to activated human neutrophils were examined in a novel, in vitro model of vasopermeability changes. Microcarrier-cultured human umbilical vein endothelial monolayers were used in a system that responds to histamine. Human neutrophils did not increase Evans Blue staining of the endothelium-covered microcarriers if added alone or if added with the neutrophil-dependent mediator of vasopermeability, formyl-methionyl-leucyl-phenylalanine (FMLP, 0.1 microM). In contrast, neutrophils, added to the endothelial cells in a ratio as low as 2.5:1 caused time-dependent increases in microcarrier staining if pretreated with cytochalasin B (5 micrograms/mL) before addition with FMLP. Neutrophil cell-free releasate and purified human sputum elastase also caused concentration-related increases in Evans Blue staining of the endothelial-covered microcarriers and these effects were inhibited by the elastase inhibitor methoxysuccinyl-alanyl-alanyl-prolyl-valyl chloromethyl ketone. This compound also inhibited neutrophil-mediated endothelial permeability increases. The microcarrier-cultured human endothelial monolayer system rapidly detects permeability alterations of endothelial monolayers in response to activated human neutrophils. This model is a potentially useful screening assay for the development of therapeutic agents, directed at neutrophil degranulation or degranulation products, for the control of inflammatory vasopermeability abnormalities.