Expression of and functional responses to protease-activated receptors on human eosinophils

Abstract: Eosinophil recruitment to airway tissue is a key feature of asthma, and release of a wide variety of toxic mediators from eosinophils leads to the tissue damage that is a hallmark of asthma pathology. Factors that control the release of these toxic mediators are targets for potential therapeu-tic intervention. Protease-activated receptors (PARs) are a novel class of receptors that are ac-tivated by cleavage of the N terminus of the recep-tor by proteases such as thrombin or trypsin-like enzymes. To date, PAR1–4 have been identified, and there are several studies that have demon-strated the expression of PARs in airway tissue, particularly the respiratory epithelium. We have investigated whether eosinophils express PARs and if activation of these receptors will then trigger a functional response. Using a combination of re-verse transcriptase-polymerase chain reaction, Western blotting, and flow cytometry analysis, we have demonstrated that eosinophils express PAR1 and PAR2. FACS analysis showed that PAR1 could be clearly detected on the surface of the cells, whereas PAR2 appeared to be primarily intracel-lular. Trypsin and the PAR2 agonist peptide were seen in trigger shape change, release of cysteinyl leukotrienes, and most obviously, generation of reactive oxygen species. In contrast, thrombin had no effect on eosinophil function. The PAR1 agonist peptide did have a minor effect on eosinophil func-tion, but this was most likely down to its ability to activate PAR1 and PAR2. These results demon-strate that PAR2 is the major PAR receptor that is capable of modulating eosinophil function. J. Leu-koc. Biol. 74: 60–68; 2003