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Human mast cell tryptase stimulates the release of an IL‐8‐dependent neutrophil chemotactic activity from human umbilical vein endothelial cells (HUVEC)

Tryptase, the major product of human mast cell activation, is a potent stimulus of vascular leakage and neutrophil accumulation in vivo in animal studies, but the mechanisms of action remain unclear. Using HUVEC cultures we have sought to investigate the potential of tryptase to alter monolayer permeability or induce the release of neutrophil chemotactic activity. Tryptase (1–100 mU/ml) failed to alter the permeability of endothelial cell monolayers as assessed by albumin flux over 1 h. However, supernatants from endothelial cells treated with tryptase (1–50 mU/ml) for a 24‐h period induced neutrophil migration across Transwell filters, with maximal migration observed at 10 mU/ml tryptase. Pretreatment of tryptase with the protease inhibitor leupeptin abolished the chemotactic activity, indicating a dependence on the catalytic site. Moreover, this effect was abolished by addition of an IL‐8 neutralizing antibody, suggesting that IL‐8 release makes an important contribution to the chemotactic activity. The interaction of mast cell tryptase with endothelial cells could be important in stimulating the ingress of neutrophils following mast cell activation in inflammatory disease.