The role of tryptase and activation of protease activated receptor-2 (PAR-2) in human airways disease

Levels of expression of PAR-1 in bronchial and nasal tissue from subjects with asthma and allergic rhinitis respectively were studied. Bronchial biopsies embedded in GMA resin from eight mild asthmatic subjects, from eight severe asthmatic subjects and from 15 non-asthmatic subjects were used. In addition, bronchial biopsies were also taken from six mild asthmatic subjects six hours following exposure to saline or house dust mite allergen. For a study of rhinitis nasal biopsies from eight perennial rhinitic subjects and six non-rhinitic subjects were used. Nasal biopsies were also collected from six patients with seasonal allergic rhinitis (out-of-season) and six hours following saline or grass pollen allergen treatment. Two micron sections were strained with P2A or an antibody raised against a peptide fragment of rat PAR-2 (B5 antiserum), and PAR-2 staining intensity quantified using computerised image analysis. PAR-2 expression was detect mainly on epithelial cells and found to be significantly higher in the bronchial epithelium of severe asthmatics compared to non-asthmatic subjects (Mann Whitney U test, P < 0.05). Although PAR-2 expression in the bronchial epithelium of mild asthmatics did not differ from that in subjects with asthma, expression was significantly increased following allergen provocation (Wilcoxon’s test, P < 0.05). There was no change in the expression of PAR-2 in the nasal epithelium of perennial rhinitic subjects compared to those without rhinitis. However, expression was significantly reduced following allergen challenge (Mann Whitney U test, P < 0.05). The difference in expression of PAR-2 in the upper and lower airways suggest that its expression may be regulated by separate elements in the nose and the bronchi in rhinitis and asthma. The expression of PAR-2 on eosinophils and the activation by tryptase on the function of these cells were investigated, using eosinophils purified from human peripheral blood. PAR-2 expression was assessed by flow cytometry using P2A and the B5 antiserum. PAR-2 was detected both at the surface and intracellularly on eosinophils using P2A. These studies demonstrate that tryptase activities eosinophils by a PAR-2 independent mechanism, and could involve activation of an as yet unidentified PAR. We have also shown that PAR-2 expression may be up-regulated in asthma. Thus, tryptase and PAR-2 could play key roles in allergic airways diseases, and as such can be considered as potential targets for therapeutic intervention.