The mechanisms driving idiopathic pulmonary fibrosis (IPF) remain undefined, however it is postulated that coagulation imbalances may play a role. The impact of blood-derived clotting factors, including factor XII (FXII) has not been investigated in the context of IPF. Plasma levels of FXII were measured by ELISA in patients with IPF and in age-matched healthy donors. Expression of FXII in human lung tissue was quantified using multiplex immunohistochemistry and Western blotting. Mechanistic investigation of FXII activity was assessed in vitro on primary lung fibroblasts using qPCR and specific receptor/FXII inhibition. The functional outcome of FXII on fibroblast migration was examined by high-content image analysis. Compared with 35 healthy donors, plasma levels of FXII were not higher in patients with IPF (n = 27, P > 0.05). Tissue FXII was elevated in IPF (n = 11) and increased numbers of FXII+ cells were found in IPF (n = 8) lung tissue compared with nondiseased controls (n = 6, P < 0.0001). Activated FXII induced IL6 mRNA and IL-6 protein in fibroblasts that was blocked by anti-FXII antibody, CSL312. FXII induced IL-6 production via PAR-1 and NF-κB. FXII induced migration of fibroblasts in a concentration-dependent manner. FXII is normally confined to the circulation but it leaks from damaged vessels into the lung interstitium in IPF where it 1) induces IL-6 production and 2) enhances migration of resident fibroblasts, critical events that drive chronic inflammation and therefore, contribute to fibrotic disease progression. Targeting FXII-induced fibroblastic processes in IPF may ameliorate pulmonary fibrosis.
Keywords: FXII; IL-6; fibroblasts; interstitial lung disease; pulmonary fibrosis.