Neutrophil-mediated endothelial injury in vitro mechanisms of cell detachment

Neutrophil-mediated endothelial injury was assessed in vitro using assays of cell lysis and cell detachment. Activation of human peripheral blood neutrophils adherent to human umbilical vein endothelial cell monolayers by serum-treated zymosan produced dose-dependent endothelial cell detachment without concomitant cell lysis. This injury was inhibited by neutral protease inhibitors, but not by catalase or superoxide dismutase. Neutrophils from a patient with chronic granulomatous disease also produced endothelial cell detachment when activated by serum-treated zymosan similar to normal neutrophils. Endothelial detachment was also produced by cell-free postsecretory media from activated neutrophils or by partially purified human neutrophil granule fraction and was inhibitable by tryptic, elastase, and serine protease inhibitors, but not by an acid protease inhibitor. Analysis of iodinated endothelial cell surface proteins that had been exposed to partially purified neutrophil granule fraction showed complete loss of proteins migrating in the region of fibronectin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This result was prevented in the presence of neutral protease inhibitors. We conclude that neutrophil-derived neutral proteases mediate endothelial cell detachment in vitro through digestion of endothelial cell surface proteins including fibronectin.