Migration of Neutrophils across Human Pulmonary Endothelial Cells Is Not Blocked by Matrix Metalloproteinase or Serine Protease Inhibitors

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Abstract
It has long been speculated that neutrophils deploy proteases to digest subendothelial matrix as they mi- grate from the bloodstream. Direct evidence for the involvement of proteases in neutrophil transendothe- lial migration is, however, lacking. To address this issue we used transmission electron microscopy to ver- ify the presence of continuous basal lamina beneath pulmonary endothelial cells grown on microporous filters, and then examined the effects of protease inhibitors on neutrophil migration through the endothelial cells and their associated subcellular matrix. Inhibitors of the two major matrix-degrading protease groups present in neutrophils, the matrix metalloproteinases (MMPs) and serine proteases, were assessed for their ability to modulate neutrophil transendothelial migration in response to the chemoattractant n -formyl- methionyl leucylphenylalanine (FMLP). Neither the naturally occurring MMP inhibitor, tissue inhibitor of metalloproteinase-1, nor the hydroxamic acid-based inhibitors GM-6001, BB-3103, or Ro 31-9790 had any significant effect on FMLP-stimulated neutrophil migration across endothelial cells and associated basal lamina, with > 80% of neutrophils migrating through the system, even in the presence of inhibitors, at concentrations that totally inhibited all the gelatinase B (MMP-9) released upon stimulation with FMLP. Similarly, with serine protease inhibitors no significant inhibition of neutrophil migration was observed with a naturally occurring inhibitor, secretory leukocyte protease inhibitor, or a low molecular-weight syn- thetic inhibitor, Pefabloc SC. These results indicate that neither MMP nor serine protease digestion of sub- endothelial matrix is required for successful neutrophil transendothelial migration. Mackarel, A. J., D. C. Cottell, K. J. Russell, M. X. FitzGerald, and C. M. O'Connor. 1999. Migration of neutrophils across human pulmonary endothelial cells is not blocked by matrix metalloproteinase or serine protease in- hibitors. Am. J. Respir. Cell Mol. Biol 20:1209-1219.

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