Thrombin-Mediated Release of Lipids From Pulmonary Artery Endothelial Cells Promotes Neutrophil Adherence

We previously have described the ability of α-thrombin (the native procoagulant enzyme) to stimulate adherence of neutrophils to pulmonary artery endothelial cells. In the present study, we observed that conditioned medium factors released by α-thrombin (10 M) treatment of cultured ovine pulmonary artery endothelial cells increased neutrophil adherence to naive pulmonary artery endothelial monolayers. This effect was independent of any residual aothrombin present in the medium. In contrast to thrombin-induced neutrophil adherence, adherence of neutrophils mediated by the conditioned medium was not inhibited by the anti-CD18 monoclonal antibody 60.3, indicating a CD18-independent mechanism. The factors generated by the action of α-thrombin on endothelial cells also resulted in concentration-dependent neutrophil migration. The neutrophil adherence- and migration-promoting activities were isolated in the ether portion after extraction of the conditioned medium. Chromato-graphic analysis showed that the active components (which resolved into two peaks by reversed-phase high-performance liquid chromatography) were relatively hydrophilic low molecular weight lipids without phosphorus or amino acids. Reconstitution of these peaks indicated that they mediated neutrophil adhesion and migration responses. The results indicate that lipid factors promoting neutrophil adhesion and migration are generated by the action of thrombin on pulmonary artery endothelial cells. The generation of these factors may contribute to the amplification of the lung inflammatory response after pulmonary intravas-cular coagulation induced by thrombin.