Activation of the coagulation system in the alveolar space plays an important role in the pathogenesis of
interstitial lung disease (ILD) and
pulmonary fibrosis. The
protein C (PC) pathway is the main modulator of coagulation activation. This study evaluated whether dysfunction of the PC pathway is associated with increased
collagen synthesis in the intraalveolar space of patients with ILD. This study comprised 22 patients with ILD; of these, five had
idiopathic pulmonary fibrosis (IPF), nine had
sarcoidosis-associated ILD, and eight had
collagen vascular disease-associated ILD (CVD-ILD).
Thrombin-antithrombin complex (TAT) was measured as a marker of coagulation activation. As markers of the PC pathway activity, the concentration of activated PC-PC inhibitor (APC-PCI) complex and the APC-PCI/PC ratio were measured and, as a marker of
collagen synthesis, the concentration of aminoterminal propeptide of
type III procollagen (
PIIINP) was measured in bronchoalveolar lavage fluid (BALF) of ILD patients. TAT was significantly increased in BALF from ILD patients as compared to control subjects. The concentrations of
PIIINP were significantly elevated in patients with ILD as compared to healthy subjects. In contrast, the concentration of APC-PCI and the values of APC-PCI/PC ratio were significantly decreased in BALF from patients with ILD. BALF concentration of
PIIINP was significantly and inversely correlated with the concentration of APC-PCI and with the APC-PCI/PC ratio. These findings suggest that dysfunction of the
protein C pathway may have important physiopathologic implications in the development of
pulmonary fibrosis in ILD.