Human mast cell tryptase, comprises a family of trypsin-like neutral serine proteinases that are predominantly expressed in mast cells. Tryptase has effects on peptides, proteins, cells, and tissues. Many of these effects can ultimately contribute to asthma symptoms. Mast cell tryptase is found in mast-cell granules and has also been reported to be expressed by peripheral blood basophils at low level. Tryptase has been used as a marker of mast cell activation.