Interleukin-8 and Leukotriene-B4, but not formylmethionyl leucylphenylalanine, stimulate CD18-independent migration of neutrophils across human pulmonary endothelial cells in vitro

Although neutrophil migration from the systemic circulation involves the beta 2- (or CD18) integrin family, the existence of an alternative, CD18-independent route of neutrophil extravasation to tissues has been demonstrated in animal models. The molecular interactions involved in this alternative migratory route have not yet been characterized. The objective of this study was to assess the CD18-dependency of neutrophil migration across human endothelial cells from an organ known to support CD18-independent migration, the lung, with a view to establishing an in vitro model to facilitate study of CD18-independent migration. Neutrophil migration across human pulmonary artery endothelial cells (HPAECs) in response to three different chemoattractants, formylmethionyl leucylphenylalanine (FMLP), interleukin (IL)-8, and leukotriene (LT) B-4, was examined. Results demonstrated that a function-blocking antibody to CD18 decreased FMLP-stimulated migration by 71.7 +/- 4.4% (P < 0.001). In contrast, migration in response to LTB4 was decreased by only 20.5 +/- 10.2% (P < 0.01), and no significant decrease was observed with migration to IL-8, Neutrophils that migrated to FMLP had 1.7-fold more surface CD11b/CD18 compared with nonmigrated neutrophils (P 0.01), whereas this integrin complex was not significantly upregulated on neutrophils that had migrated to IL-8 or LTB4. Further investigation of this migratory route indicated that it did not involve the beta 1 integrins (CD29) or the endothelial selectins, E- or P-selectin, nor did it require the activity of either metalloproteinases or neutrophil elastase. These results indicate that neutrophil migration across HPAECs in vitro to IL-8 and LTB4 is predominantly CD18-independent and provides a much-needed in vitro system for examination of the neutrophil-endothelial interactions involved in this alternative migratory route.