Elevated matrilysin levels in bronchoalveolar lavage fluid do not distinguish idiopathic pulmonary fibrosis from other interstitial lung diseases

Microarray studies have shown that matrilysin or matrix metalloproteinase (MMP)-7 is highly upregulated in the lungs of patients with idiopathic pulmonary fibrosis (IPF), but MMP-7 protein expression has not been systematically compared between IPF and other interstitial lung diseases. MMP-7 levels in bronchoalveolar lavage fluid (BALF) were compared to corresponding samples from nonspecific interstitial pneumonia (NSIP), sarcoidosis, and healthy controls. MMP-7 levels in the BALF were determined by ELISA and localization of MMP-7 in the lung tissue by immunohistochemistry. MMP-7 was similarly elevated in the BALF of all these disorders compared to healthy controls (p=0.007). Even control subjects with prolonged cough displayed a tendency towards elevated MMP-7 expression. There was a negative correlation between BALF MMP-7 levels and forced expiratory vital capacity (r=-0.348, p=0.02, n=42). In IPF lung, MMP-7 immunoreactivity appeared predominantly in the fibrotic parenchyma and arterial wall. In sarcoidosis and NSIP, prominent MMP-7 immunoreactivity was found in areas of inflammation. These results demonstrate that elevated BALF MMP-7 is not restricted to IPF alone but is also observed in other interstitial lung diseases and cannot be used as a differential diagnostic marker for IPF.