Assays demonstrate the interferon-gamma suppresses infection-stimulated hepatic fibrin deposition by promoting fibrinolysis

Abstract

Background: Inflammatory cytokines potently impact hemostatic pathways during infection, but the tissue-specific regulation of coagulation and fibrinolysis complicates studies of the underlying mechanisms. Methods and results: Here, we describe assays that quantitatively measuring prothrombinase (PTase), protein C-ase (PCase) and plasminogen activator (PA) activities in situ, thereby facilitating studies of tissue-specific hemostasis. Using these assays, we investigate the mechanisms regulating hepatic fibrin deposition during murine toxoplasmosis and the means by which interferon-gamma (IFN-c) suppresses infection-stimulated fibrin deposition. We demonstrate that Toxoplasma infection upregulates hepatic PTase, PCase, and PA activity. Wild type and gene-targeted IFN-c-deficient mice exhibit similar levels of infection-stimulated PTase activity. By contrast, IFN-c-deficiency is associated with increased PCase activity and reduced PA activity during infection. Parallel analyses of hepatic gene expression reveal that IFN-c-deficiency is associated with increased expression of thrombomodulin (TM), a key component of the PCase, increased expression of thrombinactivatable fibrinolysis inhibitor (TAFI), a PC substrate, and reduced expression of urokinase PA (u-PA). Conclusions: These findings suggest that IFN-c suppresses infection-stimulated hepatic fibrin deposition by suppressing TM-mediated activation of TAFI, thereby destabilizing fibrin deposits, and concomitantly increasing hepatic u-PA activity, thereby promoting fibrinolysis. We anticipate that further application of these in situ assays will improve our understanding of tissuespecific hemostasis, its regulation by cytokines, and its dysregulation during coagulopathy. © 2006 International Society on Thrombosis and Haemostasis.