C5aR, TNF-α, and FGL2 contribute to coagulation and complement activation in virus-induced fulminant hepatitis

Background & Aims Viral fulminant hepatitis (FH) is a disease with a high mortality rate. Activation of the complement system correlates with the development of FH. However, the key factors mediating complement activation in FH remain elusive. Methods Liver tissues were isolated from FH patients infected by hepatitis B virus (HBV) and from mice infected with murine hepatitis virus strain 3 (MHV-3). Wild type mice were treated with or without antagonists of C5aR or TNF-α, and mice deficient for C5aR (C5aR−/−), Fgl2 (Fgl2−/−), and Tnfα (Tnfα−/−) mice were not treated with the antagonists. C5b-9, C5aR, FGL2, CD31, CD11b, fibrin, TNF-α, and complement C3 cleavage products were detected by immunohistochemistry, immunofluorescence, or ELISA. Sorted liver sinusoidal endothelial cells (LSECs) or myeloid-derived (CD11b+) cells were stimulated with C5a, TNF-α or MHV-3 in vitro. The mRNA expressions levels of Fgl2 and Tnfα were determined by qRT-PCR analyses. Results We observed that complement activation, coagulation and pro-inflammatory cytokine production were upregulated in the HBV+ patients with FH. Similar observations were made in the murine FH models. Complement activation and coagulation were significantly reduced in MHV-3 infected mice in the absence of C5aR, Tnfα or Fgl2. The MHV-3 infected C5aR−/− mice exhibited reduced numbers of infiltrated inflammatory CD11b+ cells and a reduced expression of TNF-α and FGL2. Moreover, C5a administration stimulated TNF-α production by CD11b+ cells, which in turn promoted the expression of FGL2 in CD31+ LSEC-like cells in vitro. Administration of antagonists against C5aR or TNF-α ameliorated MHV-3-induced FH. Conclusions Our results demonstrate that C5aR, TNF-α, and FGL2 form an integral network that contributes to coagulation and complement activation, and suggest that those are potential therapeutic targets in viral FH intervention. Viral fulminant hepatitis (FH) is a disease with a high mortality rate. Activation of the complement system correlates with the development of FH. However, the key factors mediating complement activation in FH remain elusive. Liver tissues were isolated from FH patients infected by hepatitis B virus (HBV) and from mice infected with murine hepatitis virus strain 3 (MHV-3). Wild type mice were treated with or without antagonists of C5aR or TNF-α, and mice deficient for C5aR (C5aR−/−), Fgl2 (Fgl2−/−), and Tnfα (Tnfα−/−) mice were not treated with the antagonists. C5b-9, C5aR, FGL2, CD31, CD11b, fibrin, TNF-α, and complement C3 cleavage products were detected by immunohistochemistry, immunofluorescence, or ELISA. Sorted liver sinusoidal endothelial cells (LSECs) or myeloid-derived (CD11b+) cells were stimulated with C5a, TNF-α or MHV-3 in vitro. The mRNA expressions levels of Fgl2 and Tnfα were determined by qRT-PCR analyses. We observed that complement activation, coagulation and pro-inflammatory cytokine production were upregulated in the HBV+ patients with FH. Similar observations were made in the murine FH models. Complement activation and coagulation were significantly reduced in MHV-3 infected mice in the absence of C5aR, Tnfα or Fgl2. The MHV-3 infected C5aR−/− mice exhibited reduced numbers of infiltrated inflammatory CD11b+ cells and a reduced expression of TNF-α and FGL2. Moreover, C5a administration stimulated TNF-α production by CD11b+ cells, which in turn promoted the expression of FGL2 in CD31+ LSEC-like cells in vitro. Administration of antagonists against C5aR or TNF-α ameliorated MHV-3-induced FH. Our results demonstrate that C5aR, TNF-α, and FGL2 form an integral network that contributes to coagulation and complement activation, and suggest that those are potential therapeutic targets in viral FH intervention.