Proteinase-activated receptor 2 activation in the airways enhances antigen-mediated airway inflammation and airway hyperresponsiveness through different pathways

Background: Serine proteinases such as mast cell tryptase, trypsin-like enzymes, and certain allergens are important in the pathogenesis of asthma. These proteinases can activate the proteinase-activated receptor (PAR)-2, which has been shown to be upregulated in the airways of patients with asthma. Objective: The purpose of this study was to investigate PAR-2 activation in the airways during allergen challenge and its effects on the 2 principle features of asthma, airway inflammation and airway hyperresponsiveness (AHR). Methods: Proteinase-activated receptor 2 activating peptide SLIGRL-NH2 (PAR-2 activating peptide [ap]) or control peptide LSIGRL-NH2 (PAR-2 control peptide [cp]) was administered alone or in conjunction with ovalbumin intranasally to mice, and AHR and airway inflammation were evaluated. Results: PAR2ap did not induce AHR or airway inflammation in ovalbumin-sensitized mice that had not been challenged with ovalbumin. When administered with ovalbumin, PAR-2ap enhanced AHR and airway inflammation compared with ovalbumin administered alone or with PAR-2cp. The enhanced AHR persisted for 5 days, whereas the enhancement to airway inflammation dissipated. Mice administered PAR-2ap alone during the 5 days after the final antigen challenge demonstrated an additional enhancement to airway inflammation compared with the control animals. PAR-2ap administered with allergen increased TNF and IL-5 mRNA in lung tissue and IL-13 and TNF in bronchoalveolar lavage fluid. Conclusion: Exogenous PAR-2 activation in parallel with allergen challenge enhances allergen-mediated AHR and airway inflammation through distinct mechanisms. PAR-2 activation can also enhance established airway inflammation even when dissociated from exposure to allergen. Therefore, PAR-2 activation may play a pathogenic role in the development of AHR and airway inflammation.