A ROLE FOR TRYPTASE IN THE ACTIVATION OF HUMAN MAST-CELLS - MODULATION OF HISTAMINE-RELEASE BY TRYPTASE AND INHIBITORS OF TRYPTASE

Tryptase, the most abundant protein product of human mast cells is eme rging as an important mediator and target for therapeutic intervention in allergic disease. We have investigated the potential of tryptase a nd inhibitors of tryptase to modulate histamine release from human mas t cells. Addition of purified human tryptase in concentrations ranging from 1 to 100 mU/ml stimulated a concentration-dependent release of h istamine from cells dispersed from tonsil, although not from skin tiss ue. The reaction depended on an intact catalytic site being inhibited by heat inactivation of the enzyme, or by preincubating with the trypt ase inhibitors APC366 or leupeptin or the tryptic substrate N-benzoyl- DL-arginine-p-nitroanilide (BAPNA). Tryptase-induced histamine release took approximately 6 min to reach completion, appeared to require exo genous calcium and magnesium, and on the basis of inhibition by antimy cin A and 2-deoxy-D-glucose, seemed to be a noncytotoxic process. Prei ncubation of cells with tryptase at concentrations that were suboptima l for histamine release had little effect on their responsiveness to a nti-immunoglobulin (Ig) E or to calcium ionophore A23187, but at highe r concentrations their subsequent activation was inhibited. APC366 sig nificantly inhibited histamine release induced by anti-IgE or calcium ionophore from both tonsil and skin cells, with up to 90% inhibition b eing observed at a concentration of 100 mu M with skin. IgE-dependent histamine release was inhibited also by leupeptin, benzamidine and BAP NA. Tryptase may act as an amplification signal for mast cell activati on, and this could account at least partly for the potent mast cell st abilizing properties of tryptase inhibitors.