MAST-CELL TRYPTASE IS A MITOGEN FOR EPITHELIAL-CELLS - STIMULATION OFIL-8 PRODUCTION AND INTERCELLULAR-ADHESION MOLECULE-1 EXPRESSION

Tryptase, a protease unique to the mast cell secretory granule, is rel eased in substantial quantities into the respiratory tract of patients with inflammatory disease of the airways. We have investigated the po tential of tryptase to act as a mitogen for bronchial epithelial cells and to stimulate release of IL-8 and expression of ICAM-1. Tryptase w as isolated from extracts of human lung tissue using ammonium sulphate precipitation, octyl agarose, and heparin agarose chromatography. Pur ified tryptase stimulated DNA synthesis in the human epithelial cell l ine H292, as measured by [H-3]thymidine incorporation. Maximal growth was observed after 24 h using 25 mU/ml of tryptase (where 1 mu m is de fined as that which can hydrolyze 1 mu mol of the peptide substrate N- alpha-benzoyl-DL-arginine p-nitroanilide hydrochloride per minute at 2 5 degrees C), a concentration that is likely to be achieved in vivo. I nhibitors of tryptase activity, including leupeptin and benzamidine hy drochloride, significantly decreased tryptase-induced stimulation of D NA synthesis, indicating the requirement for an active catalytic site. Tryptase stimulated a catalytic site-dependent release of IL-8 from e pithelial cells after 24 h, and this was associated with up-regulation of ICAM-1 expression, as revealed by FACS analysis. Tryptase may play a critical role in epithelial repair and in the recruitment of granul ocytes following mast cell activation.