Tryptase, a mediator of human mast cells.

Tryptase, a mediator secreted by human mast cells during immediate reactions, has demonstrated effects on several pathways in vitro. This enzyme can rapidly inactivate fibrinogen and, as a complex with heparin, may prevent coagulation that may otherwise occur when plasma enters tissues at sites of immediate reactions. Tryptase may also activate prostromelysin, which in turn activates latent collagenase. When canine pulmonary smooth muscle is incubated with canine tryptase, the contractile response to histamine is increased. Tryptase, quantifiable in complex biologic fluids by immunoassay, can serve as a specific indicator of mast cell involvement in certain clinical settings. For example, after bee sting--induced anaphylaxis, tryptase levels in the blood peak at approximately 1 hour, then decline with a half-life of approximately 2 hours. Additionally, elevated tryptase levels in bronchoalveolar lavage fluid of asymptomatic, atopic persons with asthma suggest ongoing mast cell activation, which may relate to adenosine hyperresponsiveness and a persistence of bronchial hyperreactivity. Tryptase levels in bronchial lavage fluid of atopic patients with asthma rise markedly after endobronchial allergen challenge but not after an exercise challenge, suggesting a lack of mast cell involvement in the latter condition.