Tryptase

Tryptase is a serine protease (an enzyme that cuts proteins) and one of the most abundant pre-formed mediators stored in mast cell granules. It’s clinically important primarily as a laboratory marker of mast cell activation and mast cell burden.

What It Does

Tryptase degrades extracellular matrix proteins (fibronectin, fibrinogen, pro-urokinase), activates other protease cascades (complement, matrix metalloproteinases), and stimulates fibroblast proliferation (contributing to tissue remodeling and fibrosis in chronic activation).

It also activates PAR-2 (Protease-Activated Receptor 2) on various cell types — neurons (pain signaling), epithelial cells (barrier function), and smooth muscle cells (contraction). PAR-2 activation on enteric neurons contributes to the visceral pain and hypersensitivity in GI-predominant MCAS.

As a Diagnostic Marker

See Serum Tryptase. Tryptase is the primary laboratory marker used in the stricter MCAS diagnostic criteria. However, it has significant limitations — it may be normal during piecemeal Degranulation, which is the predominant mode in chronic MCAS. Baseline tryptase is more useful for detecting mastocytosis (elevated mast cell numbers) than MCAS (normal numbers, abnormal behavior).