Abstract
Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever (DHF). The mechanisms that cause hemorrhage in DV infections remain poorly understood. Thrombomodulin (TM) is a glycoprotein expressed on the surface of vascular endothelial cells that plays an important role in the thrombin-mediated activation of protein C. Prior studies have shown that the serum levels of soluble TM (sTM) and macrophage migration inhibitory factor (MIF) are significantly increased in DHF patients compared to levels in DF patients or normal controls. In this study, we investigated how MIF and sTM concentrations are enhanced in the plasma of DHF patients and the potential effect of MIF on coagulation through its influence on two factors: thrombomodulin (TM) and intercellular adhesion molecule-1 (ICAM-1) in endothelial cells and monocytes. Recombinant human macrophage migration inhibitory factor (rMIF) was used to treat monocytic THP-1 cells and endothelial HMEC-1 cells or primary HUVEC cells. The subsequent expression of TM and ICAM-1 was assessed by immunofluorescent staining and flow cytometry analysis. Additionally, the co-incubation of THP-1 cells with various cell signaling pathway inhibitors was used to determine the pathways through which MIF mediated its effect. The data provided evidence that severe DV infections induce MIF expression, which in turn stimulates monocytes or endothelial cells to express TM and ICAM-1 via the Erk, JNK MAPK and the PI3K signaling pathways, supporting the idea that MIF may play an important role as a regulator of coagulation.
Highlights
Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) [1]
Our results demonstrated that serum levels of migration inhibitory factor (MIF), as well as of soluble thrombomodulin (sTM), were significantly increased but PC was decreased in the serum of DV patients, and the levels correlated with disease severity (Fig. 1)
The ELISA results and analyses showed that DV2 infection will induce MIF production in THP-1 cells and human umbilical cord vein endothelial cells (HUVECs) but that cells treated with UV-inactivated DV2 (UVDV2) and cells not infected with DV2 (Mock) will not show increased production (Fig. 2A and B)
Summary
Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) [1]. Several studies have suggested that thrombocytopenia and imbalance in the regulation of coagulation and fibrinolysis contribute to the potential for hemorrhage in DHF/DSS [3,4,5,6,7]. Due to the complexity of hemostasis, the mechanisms involved in DVinduced hemorrhaging are still not clearly understood. The thrombin-thrombomodulin complex induces activated protein C (APC). The underlying mechanisms responsible for anticoagulation in acute dengue infections remain poorly understood. DV infection of endothelial cells can enhance platelet adherence and induce tissue plasminogen activator expression, which may contribute to hemorrhaging in DHF/DSS [16,17]. The effect of DV on the expression of molecules involved in the protein C pathway, such as TM, protein S (PS) and endothelial cell protein C receptor (EPCR), in endothelial cells remains unclear
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