Abstract: Objective To determine the change of clotting activation-thrombin-antithrombin Ⅲ complex(TAT) and collagen metabolism-procollagen Ⅲ(PCⅢ),and investigate the correlation between TAT and PCⅢ in bronchoalveolar lavage fluid(BALF) of patients with idiopathic pulmonary fibrosis(IPF).To determine the change of protein C(PC),protein S(PS),thrombomodulin(TM) and TAT levels in BALF and plasma of the patients with IPF,and to investigate the correlation between the change of Protein C anticoagulant system and the procoagulant activity as well as the pulmonary fibrosis.Methods 16 patients with IPF and 16 healthy individuals were inrolled and investigated.The bronchoalveolar lavage was performed to all patients with IPF and 8 healthy ones of control.Plasma was collected at the same time.The levels of TM,PC,PS,PCⅢ and TAT in the BALF and plasma also PCⅢ in BALF were measured using ELISA assays.Results The levels of PCⅢ and TM in BALF were significantly higher in patients with IPF than control subjects(P<0.01,P<0.05),the levels of PS in BALF were decreased as compared with the control subjects(P<0.05).The levels of TAT in plasma were significantly higher in patients with IPF than control subjects(P<0.01),the levels of PC were decreased as compared with the control subjects(P<0.05).The BALF concentration of PCⅢ was proportionally correlated with concentration of TAT in BALF(r=0.52,P<0.05).Conclusion Excessive procoagulant activity exists in patients with IPF.Excessive procoagulant activity in the alveolar space and lung interstitium may play a relevant role in the pathogenesis of IPF.Decreased PC,PS level and increased thrombomodulin level were observed in patient with IPF,and impairment of PC pathway was the reason for the excessive procoagulant activity of IPF and may promote lung fibrosis.

Key words: idiopathic pulmonary fibrosis, protein C, protein S, thrombomodulin