Sequential migration of neutrophils across monolayers of endothelial and epithelial cells.

In the course of granulocyte-dominated lung inflammation, granulocytes migrate across the endothelium and epithelium of the lung and cause severe tissue damage. To study this process in more detail, we developed a bilayer transmigration model composed of primary human endothelial and lung epithelial cells, simultaneously cultured on opposite sides of Transwell filters. Electron microscopical analysis showed that the morphology of the cells and the expression of junctional proteins remained unaltered and that matrix components were deposited onto the filter. Intriguingly, neutrophil migration was more efficient across the bilayers than across single epithelial monolayers and did not differ from migration across single endothelial monolayers. Coculture experiments showed that endothelial cells stimulated epithelial cells to release IL-6 and that epithelial cells enhanced release of IL-8 from endothelial cells. Together these data reveal bidirectional signaling and enhanced neutrophil migration in a transmigration model of primary human epithelial and endothelial cells.