Background: Tryptase, the most abundant protease of the human mast cell, has been
implicated as a key mediator of allergic inflammation that acts through activation of PAR2.
Objectives: To investigate the contribution of PAR2 in the pro-inflammatory actions
mediated by tryptase in a mice model.
Methods: We have injected recombinant human bII-tryptase into the peritoneum of
PAR2-deficient and wild-type C57BL/6 mice. After 6, 12 and 24 hours, mice were
killed, peritoneal lavage performed and inflammatory changes investigated.
Results: Tryptase stimulated an increase in neutrophil numbers in the peritoneum,
but responses did not differ between PAR2-deficient and wild-type mice. Heat inactivation
of trypta... More
Background: Tryptase, the most abundant protease of the human mast cell, has been
implicated as a key mediator of allergic inflammation that acts through activation of PAR2.
Objectives: To investigate the contribution of PAR2 in the pro-inflammatory actions
mediated by tryptase in a mice model.
Methods: We have injected recombinant human bII-tryptase into the peritoneum of
PAR2-deficient and wild-type C57BL/6 mice. After 6, 12 and 24 hours, mice were
killed, peritoneal lavage performed and inflammatory changes investigated.
Results: Tryptase stimulated an increase in neutrophil numbers in the peritoneum,
but responses did not differ between PAR2-deficient and wild-type mice. Heat inactivation
of tryptase or pre-incubation with a selective tryptase inhibitor reduced
neutrophilia, but neutrophil accumulation was not elicited with a peptide agonist of
PAR2 (SLIGRL-NH2). Zymography indicated that tryptase stimulated the release of
matrix metalloproteinases (MMP) 2 and 9 in the peritoneum of both mouse strains.
Studies involving immunomagnetic isolation of neutrophils suggested that neutrophils
represent the major cellular source of tryptase-induced MMP2 and MMP9.
At 24 hours after tryptase injection, there was increased microvascular leakage as
indicated by high levels of albumin in peritoneal lavage fluid, and this appeared to
be partially abolished by heat-inactivating tryptase or addition of a protease inhibitor.
There was no corresponding increase in levels of histamine or total protein. The
extent of tryptase-induced microvascular leakage or gelatinase release into the peritoneum
did not differ between PAR2-deficient and wild-type mice.
Conclusions: Our findings indicate that tryptase is a potent stimulus for neutrophil
accumulation, MMP release and microvascular leakage. Although these actions
required an intact catalytic site, the primary mechanism of tryptase in vivo would
appear to involve processes independent of PAR2.
