Clinical implication of protease-activated receptor-2 in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lethal pulmonary disease which is characterized by progressive fibrosis. In general, the exaggerated activation of the coagulation cascade has been observed during initiation or maintenance of the fibrotic disease. In a recent study, protease-activated receptor (PAR)-2, which plays a key role in coagulation cascade, was up-regulated in IPF patients, however, its clinical implications have not been understood. The objective of the present study was to evaluate the clinical significance of PAR-2 expression in the alveolar epithelial cells of IPF patients. PAR-2 expression was evaluated by immunohistochemical method in formalin-fixed and paraffin-embedded tissues of surgical lung biopsies from patients with IPF. Fibrosis scores from hematoxylin and eosin-stained lung sections and honeycombing scores in chest CT were calculated. Medical records were retrospectively reviewed and the correlation between the expression of PAR-2 and clinical profiles were assessed. Among thirty-three IPF patients, PAR-2 expression was observed in 25 (75.8%). The lymphocyte counts in peripheral blood (2317 vs. 1753, p = 0.044) and honeycombing scores in chest CT (4.0 vs. 3.0 p = 0.046) were higher in PAR-2 positive group compared with PAR-2 negative group. During a follow-up duration of median 40.3 months, 7 (21.2%) patients died and they were all included in the PAR-2 positive group (p = 0.113). We conclude that PAR-2 is expressed in the alveolar epithelial cells of a substantial number of IPF patients, and the expression of PAR-2 significantly correlates with the extent of honeycombing shown in chest CT.