All studies on human subjects were approved by the Ethics Committee of Tongji Medical College of Huazhong University of Science and Technology (permit number: TJ-C20170924), and all participants provided informed consent in compliance with the Helsinki Declaration revised in 1983.

The animal experiments were approved by the Institutional Animal Care and Use Committee of Tongji Hospital (permit number: TJ-A20171008) and were conducted in accordance with state guidelines from the Ministry of Science and Technology of China.

Seven patients with ACLF, as defined by the Asian Pacific Association for Study of the Liver (APASL) guidelines[18], who were undergoing liver transplantation were included in the study; liver samples were obtained during the surgery. The clinical features of the patients are summarized in Table 1. Control samples (n = 3) were obtained from a healthy liver donor and from the paratumor tissues of a patient with hepatic hemangioma and a patient with hepatocellular carcinoma without cirrhosis.

Female BALB/c mice (HFK Bioscience Company Ltd., Beijing, China) at 6-8 weeks of age were used in all animal experiments. The mice were housed in a controlled environment (specific pathogen-free, 12 h light/dark cycle, 21 ± 2 °C, humidity 50 ± 10%) and had free access to food and water. Fgl2-/- mice were generated by introducing a deletion at the N-terminal of the open reading frame of the Fgl2 locus using CRISPR/Cas9 technology. WT BALB/c mice were used as controls. To establish the fulminant hepatitis model, 100 plaque-forming unit (PFUs) of MHV-3 (American Type Culture Collection, Manassas, VA, USA) dissolved in 200 µL saline was injected into the WT and Fgl2-/- mice intraperitoneally. To deplete macrophages, mice were intravenously injected with 200 µL clodronate liposomes or phosphate-buffered saline (PBS)-liposomes as a control (Liposome B.V., the Netherlands) 24 h prior to MHV-3 injection. To inhibit MoMF infiltration, a chemokine receptor-2 (CCR2) inhibitor (cenicriviroc; 10 mg/kg) was intraperitoneally injected 24 h prior to MHV-3 infection. WT or Fgl2-/- mice were randomly selected to be sacrificed at 0, 24, 48, and 72 h following MHV-3 injection, and liver and blood samples were harvested for analysis.

Hepatic mononuclear non-parenchymal cells from WT and Fgl2-/- mice were isolated via liver perfusion, enzymatic digestion, and differential centrifugation, as described previously[19]. Peritoneal exudate macrophages (PEMs) were isolated from the mice 3 d after intraperitoneal injection of 3% starch broth (1 mL/mice). Bone marrow-derived macrophages (BMDMs) were differentiated from hematopoietic stem cells isolated from the femurs cultured in Dulbecco’s modified Eagle medium (DMEM) containing 10% fetal bovine serum (FBS) and macrophage-colony stimulating factor (30 μg/mL, Peprotech) for 7 days. BMDMs or PEMs were maintained in DMEM supplemented with 10% FBS and treated with LPS (100 ng/mL), interleukin (IL)-4 (20 ng/mL), or MHV-3 (5 × 10⁵ PFU/mL).

KCs are the largest population of hepatic resident non-parenchymal cells and the first line of defense against pathogens and toxins[6]. The priming of KCs may therefore be involved in initiation of the hepatic immune response, a critical step for subsequent exacerbation of inflammatory accumulation. Accordingly, we also assessed liver damage following MHV-3 infection with depletion of macrophages by clodronate liposomes. WT mice were treated with 200 µL clodronate liposomes or PBS-liposomes as a control to deplete macrophages, which then served as the recipient mice for adoptive transfer. Harvested BMDMs from WT and Fgl2-/- mice were intravenously injected into the recipient mice at 5 × 10⁵ cells/mouse. MHV-3 (100 PFU/mouse) injection was performed 24 h later. Liver and blood samples were harvested at 48 h post MHV-3 infection for further analyses.

Single-cell suspensions were blocked with 2 μg/mL anti-CD16/CD32, followed by staining with fluorescence-conjugated antibody cocktails. For intracellular staining, surface-stained cells were fixed and permeabilized using Cytofix/Cytoperm Fixation/Permeabilization Kit (No. 554714, BD Pharmingen) prior to incubation with target antibodies. Data were acquired on a BD FACS Canto II flow cytometer (BD Bioscience, San Jose, CA) and analyzed using FACS Diva software.

Detailed procedures and other materials are described in the supporting information.

Statistical testing was performed using GraphPad Prism 5.0 software (GraphPad Software Inc., San Diego, CA, United States). Comparisons between WT and Fgl2^−/− mice (or other situations where only two groups are compared) were performed using Student’s unpaired t-test; one-way analysis of variance with Tukey’s post-hoc test or Mann-Whitney U test was used for multiple comparisons (unless otherwise indicated). Data are presented as mean ± standard deviation; P < 0.05 was considered to indicate a statistically significant difference.

Marked infiltration of leukocytes was observed in samples of the patients with ACLF, along with massive necrosis in the parenchymal lobules (Figure 1A). CD68+ macrophages markedly accumulated in the periportal areas (Figure 1B, Supplementary Figure 1), suggesting widespread liver damage[20]. Furthermore, macrophages were polarized to proinflammatory macrophages, as confirmed by the expression of S100A9 (Figure 1C), an alarmin molecule expressed in proinflammatory macrophages, activated neutrophils, and granulocytes, which is often used as a biomarker of inflammation[21]. Interestingly, the majority of S100A-positive activated proinflammatory macrophages also expressed FGL2 in consecutive sections of liver samples from patients with HBV-related liver failure (Figure 1D). These data suggest that a high expression level of FGL2 could be an important molecular event of hepatic macrophage polarization during viral liver failure.

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Figure 1 Fibrinogen-like protein 2 was expressed on proinflammatory macrophages in patients with hepatitis B virus-associated liver failure. A: Representative image of liver sections (200×) subjected to Hematoxylin and eosin staining (H&E); Black circles point to transparent necrosis, red circles point to infiltrating leukocytes; B: Calculation of CD68+ macrophages at periportal and lobular areas; C: Immunofluorescence against CD68, S100A9 on liver sections (200×) from patients of hepatitis B virus-associated acute chronic-on liver failure (acute-on-chronic liver failure (ACLF), n = 7) and healthy controls (n = 3); D: Immunofluorescence against S100A9 and fibrinogen-like protein 2 on liver sections (200×) from ACLF patients (n = 7) and healthy controls (n = 3), representative images on the left and statistical columns on the right. Data are expressed as mean ± SD.

In the experimental fulminant hepatitis mouse model, pathogenesis was divided into an early stage without global liver damage at 24 h post-infection of MHV-3, a progression phase with continuous enlargement of block necrosis and increased transaminase levels, and an end stage defined at 72 h post-infection when the animals were near death (Figure 2A and B). At the early stage of infection, hematoxylin and eosin staining showed that the hepatic architecture was intact and no obvious macrophages infiltration was noted (Figure 2A). Aggregating plots of the CD11b F4/80-expressing flow cytometry panel[22] showed a continuous increase in the number of hepatic MoMFs (CD11b^high F4/80^int) and a decline in the number of KCs (CD11b^low F4/80^high) over the course of infection, accompanied by enlarged lesions until confluent necrosis of the liver lobules occurred at the later stage (Figure 2A and C). Notably, KCs constituted the dominant hepatic macrophage population at the early stage of infection, with an increased M1 macrophage subset [induced nitric oxide synthase (iNOS+) KCs] (Figure 2D, Supplementary Figure 2A and C). However, MoMFs subsequently dominated the hepatic macrophage population, characterized by an increased ratio of Ly6C^high cells; however, the Ly6C^high/Ly6C^low ratio decreased at the end stage of the disease (Figure 2E, Supplementary Figure 2A), implying a transition from Ly6C^high MoMFs to Ly6C^low MoMFs. The dynamic alterations in hepatic macrophage populations were also revealed by an increase in the levels of proinflammatory cytokines TNF-α and IL-6 during progression, which then decreased at the end stage, along with a continued decrease in transforming growth factor (TGF)-β levels in macrophages (Supplementary Figure 2D). Consistent with the reconstitution of hepatic macrophage populations in which Ly6C^high MoMFs are more inflammatory with an expanded spectrum of cytokine and chemokine expression compared with M1 macrophages[23], the serum MCP-1 level was remarkably increased during infection-induced liver failure progression (Supplementary Figure 2B).

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Figure 2 Dynamic alteration of macrophage subsets during viral fulminant hepatitis progression. A: Time-course H&E staining on liver sections of mice after murine hepatitis virus strain 3 infection. Arrowheads indicated hepatocyte cytoplasmic destruction, Circles pointed to necrosis; B: ALT and AST levels from serum of mice post-viral infection; C: Flow cytometry of KCs (CD45+ F4/80high), MoMFs (CD45+ Ly6C+ F4/80int) of cells (left), and their percentage in the liver at various time point after viral infection; D: Flow cytometry of KCs (left) and frequency of M1 (iNOS+), M2 (CD206+) macrophages in KCs (right); E: Representative image of MoMFs (left) and frequency of Ly6Chigh and Ly6Clow MoMFs at different time point after viral infection. Data are presented as mean ± SD (n = 5). These experiments were repeated at least three times. KCs: Kuffer cells; MoMFs: Monocyte derived macrophages.

As shown in Figure 3A, over 90% of FGL2-positive KCs were found in iNOS+ macrophages based on flow cytometry. Moreover, Ly6C^high MoMFs constituted the major population of FGL2-positive MoMFs, and the expression level of FGL2 was remarkably higher in Ly6C^high MoMFs than in Ly6C^low MoMFs (Figure 3B). After viral infection, sequential induction of FGL2 expression was observed in both polarized M1 KCs and Ly6C^high MoMFs during disease progression, although a slight decrease in the expression level was observed when the KC and MoMF populations were somewhat exhausted at 48 and 72 h post viral infection, respectively (Figure 3C and D). However, FGL2 expression was maintained at low levels in Ly6C^low populations (Figure 3D). Together, these data suggested that FGL2 is markedly induced in proinflammatory macrophages upon viral infection.

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Figure 3 Fibrinogen-like protein 2 expression was robustly inducted upon proinflammatory macrophage activation. A: Flow cytometry of fibrinogen-like protein 2 (Fgl2) +KCs expressing iNOS and CD206 under homeostatic conditions (left), and frequency of iNOS+ and CD206+ cells subsets (right); B: Representative image of Fgl2+MoMFs expressing Ly6C (left), and relative expression level of Fgl2 in Ly6ChiMoMFs and Ly6Clo MoMFs under physiological conditions (right); C: Time course-presentation of Fgl2 expression in M1 polarized KCs (left), and expression level of Fgl2 in Ly6ChiMoMFs and Ly6Clow MoMFs, respectively (right); D: Cell counts of Fgl2+ MoMFs (left), and relative level of Fgl2 expression on both MoMFs subset (right) following viral infection. Data are presented as mean ± SD (n = 5). These experiments were repeated at least three times. MFI: Mean fluorescence intensity.

In Fgl2-/- mice (Supplementary Figure 3A), liver damage following MHV-3 infection was significantly attenuated, as revealed by narrowed necrosis foci and lower alanine transaminase (ALT) and aspartate transaminase (AST) levels compared with those in WT mice (Figure 4A and B). In addition, viral titers were reduced in Flg2^-/- mice compared with those in their WT counterparts (Supplementary Figure 3B). Consistent with the pathology results, monocyte infiltration was significantly reduced in Flg2^-/- mice, whereas a large number of KCs was maintained during VFH progression (Figure 4C). To determine whether Fgl2 was required for proinflammatory macrophage activation, we investigated the polarization of KCs at the early stage of VFH when KC populations were reserved. We found a decrease in the M1 KC subset and an increase in the M2 KC numbers in FGL2-deficient mice before and after MHV-3 infection (Figure 4D), suggesting that FGL2 depletion impaired inflammatory macrophage activation and favored the M2 phenotype. As expected, a small Ly6C^high subset was also observed in the MoMF population in FGL2-deficient mice after viral infection, implying that Fgl2 loss predisposed MoMFs to the Ly6C^low phenotype (Figure 4E). This interpretation was further supported by the reduced levels of TNF-α and IL-6 and the increased levels of TGF-β on KCs from Fgl2-/- mice after viral infection compared with those in WT mice (Supplementary Figure 3C).

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Figure 4 Fibrinogen-like protein 2 promotes pro-inflammatory macrophage polarization following murine hepatitis virus strain 3 infection. A: H&E staining on liver sections from wild type (WT) and fibrinogen-like protein 2 (Fgl2-/-) mice at 48 and 72 h post viral infection. Circled field represented bulk necrosis. Arrows point to necrotic cells; B: Serum alanine transaminase and aspartate transaminase levels at 0, 24, 48, and 72 h post viral infection in WT and Fgl2-/- mice; C: Flow cytometry of KCs and MoMFs in hepatic CD45+ leukocytes at steady condition and 48 h following viral fulminant hepatitis in WT and Fgl2-/- mice (left); and respective frequency at 48 h post infection; D: Frequency of polarized M1 (iNOS+), M2 (CD206+) KCs at 0 and 24 h post murine hepatitis virus strain 3 (MHV-3) infection; E: Frequency of Ly6Chi and Ly6Clow MoMFs at 0 and 48 h post MHV-3 infection. Data are presented as mean ± SD (n = 5). These experiments were repeated at least three times.

Macrophage depletion by clodronate liposomes significantly relieved liver injury, as shown by decreased necrosis foci and ALT/AST levels, in both WT and FGL2-deficient mice (Figure 5A and B). Notably, further reduction in liver ALT/AST levels and fewer necrotic hepatocytes were observed in FGL2-deficient mice after viral infection, suggesting the requirement of FGL2 for macrophage polarization and disease progression. To determine whether FGL2 regulates macrophage polarization directly, BMDMs from WT and Fgl2-/- mice were transferred into WT recipient mice with self-BMDMs depleted in advance in the VFH model. Interestingly, Fgl2-/- BMDMs exhibited reduced numbers of inflammatory polarized macrophages and increased numbers of anti-inflammatory macrophages (Figure 5D and E). Moreover, recipient mice adoptively transferred with Fgl2-/- BMDMs exhibited reduced liver injury, as revealed by histological analysis (Figure 5A) and ALT/AST levels (Figure 5C), when compared with that in recipients transferred with WT BMDMs.

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Figure 5 Depletion of macrophages in fibrinogen-like protein 2 synergically attenuated liver damage after viral infection. A: H&E staining on liver sections from mice administered with either clodronate liposomes (CL) (b and d on the right) or PBS-liposomes (PBS) (a and c on the left) at 48 h post murine hepatitis virus strain 3 (MHV-3) infection; e-f, liver sections from bone marrow-derived macrophages (BMDMs) adoptive transferred mice at 48 h post MHV-3 infection (e: WT BMDM donor; f: Fibrinogen-like protein 2 (Fgl2-/-) BMDM donor); B: Serum ALT and AST levels from clodronate liposomes-treated WT and Fgl2-/- mice at 48 h post MHV-3 infection; C: Serum AST and ALT levels from WT and Fgl2-/- BMDM chimeric mice; D: representative F4/80+ iNOS+ and F4/80+ CD206+ donor macrophages from WT and Fgl2-/- BMDM chimeric mice at 48 h post infection; E: statistical analysis of iNOS+ and CD206+ donor macrophages in chimeric mice at 48 h post infection; F: H&E-stained liver section from mice which were treated with Cenicriviroc (CVC) in advance and subjected to MHV-3 infection for 48 h. Arrows represented necrotic cells, circles represent areas of hepatocyte necrosis. Image magnificence: 200×; G: aminotransferase levels of CVC treated viral fulminant hepatitis mice and its control. Data were presented as mean ± SD (n = 5). These experiments were repeated at least three times. BMDM: Bone marrow derived macrophages.

As depicted in Supplementary Figure 3D and E, smaller numbers of MPO^high myeloid cells, which are considered to be neutrophils, were observed in liver sections from mice with macrophage depletion or in FGL2-deficient mice compared with those from untreated WT mice following MHV-3 infection. However, no significant difference in neutrophil abundance was observed between WT and Fgl2-/- mice with macrophage depletion.

Because MoMFs formed the largest component of myeloid cells during the acute stage and CCR2 is mainly expressed in proinflammatory monocytes (Ly6C^high)[24], we speculated that MoMF-derived inflammation is a major source of hepatic inflammation. Indeed, treatment with the CCR2 inhibitor cenicriviroc significantly reduced the virus-induced liver damage (Figure 5F and G). Collectively, these data suggest that FGL2 directly regulates proinflammatory macrophage polarization and that infiltrated MoMFs are the major source of hepatic inflammation during acute liver injury.

To further determine whether FGL2 regulates macrophage polarization directly in vitro, we examined its regulatory effect on BMDMs and PEMs by LPS stimulation or MHV-3 infection. As expected, in WT BMDMs, robust production of cytokines and chemokines, such as IL-1β, TNF-α, IL-6, IL-12, and MCP-1, and reactive species, such as the NO-derived nitrite product (NO₂^-), were observed in response to either LPS treatment or MHV-3 infection. In contrast, the levels of such products were markedly reduced in BMDMs from Fgl2-/- mice under the same condition (Figure 6A). Consistently, the transcription levels of M1 indicators, such as NOS2, TNF-α, IL-6, IL-1β, IL-12, and Marco, were significantly reduced in BMDMs of Fgl2-/- mice compared with those in BMDMs from WT mice in response to either LPS stimulation or MHV-3 infection (Figure 6B and C). In contrast, both IL-10 production and the transcriptional levels of M2 markers were significantly higher in Fgl2-/- BMDMs than in WT BMDMs in response to IL-4 treatment (Figure 6D and E). Similar results were also obtained in Fgl2-/- PEMs in response to LPS treatment (Supplementary Figure 4). Taken together, these data suggest that FGL2 deficiency impairs the proinflammatory polarization of macrophages and promotes an alternative activated phenotype in response to IL-4 stimulation.

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Figure 6 Fibrinogen-like protein 2 promoted bone marrow-derived macrophages M1 polarization in vitro. A: Supernatant concentration of NO2-, IL-1β, TNF-α, IL -6, IL-12 and MCP-1 released by bone marrow-derived macrophages (BMDMs) after LPS (100 ng/mL) treatment or murine hepatitis virus strain 3 (MHV-3) infection for 24 h; B: Relative transcriptional level of M1 markers (NOS2, IL-6, IL-12, IL-1β, TNF-α and marco) of WT and fibrinogen-like protein 2 (Fgl2-/-) BMDMs after the stimulation of LPS for 6 hours; C: Relative transcriptional level of M1 markers of WT and Fgl2-/- BMDMs after MHV-3 infection for 8 hours; D: Supernatant IL-10 concentration of BMDMs culture after the IL-4 stimulation (20 ng/mL) for 72 h; E: mRNA expression of M2 markers (Fizz1, ARG1, YM-1, MRC1, IL-10 and TGF-β) of WT and Fgl2 -/- BMDMs after of IL-4 treatment for 72 h. All data are presented as mean ± SD (n > 3). These experiments were repeated at least three times.

A critical function of hepatic macrophages during homeostasis maintenance is to engulf pathogens, endotoxins, and debris of dead cells via a process called phagocytosis, followed by antigen presentation by major histocompatibility complex (MHC) II for T cells. We therefore cultured E. coli labeled with red fluorescence together with peritoneal macrophages to examine their phagocytic capabilities. The number of engulfed bacteria was notably smaller in macrophages from FGL2-deficient mice than in macrophages from WT mice, although more macrophages were detected in Fgl2-/- mice (Figure 7A and B). Furthermore, surface expression of MHC II was more severely impaired in FGL2-deficient macrophages than in WT macrophages under normal conditions or after viral stimulation (Figure 7C), whereas expression of CD80, CD86, or MHC I was not altered (data not shown). These data suggest that FGL2 deficiency attenuates both the phagocytic capacity and antigen presentation potential of macrophages.

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Figure 7 Fibrinogen-like protein 2 deficiency resulted in low expression of major histocompatibility complex II and impaired phagocytosis of macrophage. A: Absolute number of PEMs under the stimulation of 3% starch broth or murine hepatitis virus strain 3 (MHV-3) extracted from wild-type (WT) and fibrinogen-like protein 2 (Fgl2-/-) mice; B: MFI of FITC+ phagocyted E.Coli by PEMs from WT and Fgl2-/- mice at different time points; C: Expression of major histocompatibility complex II on WT and Fgl2-/- PEMs under the stimulation of 3% starch broth or MHV-3 infection. All data are presented as mean ± SD. These experiments were repeated at least three times. PEMs: Peritoneal exudate macrophages.

To explore how FGL2 modulates inflammatory cascades, we examined the serial components of inflammatory signaling pathways in BMDMs by mimicking invading pathogen infections in vitro. Consistent with the results from MoMFs in the VFH model, FGL2 was robustly induced in BMDMs following LPS treatment and MHV-3 infection (Figure 8A). In addition, phosphorylation of IκBα, p65, IRF3, and IRF7, which are critical modulators of NF-κB activation and IFN expression, was remarkably impaired in Fgl2-/- BMDMs in response to LPS treatment and viral infection (Figure 8B, Supplementary Figure 5). However, the expression of adaptor proteins such as TRIF and MyD88 was not altered under the same conditions (Figure 8B). Among mitogen-activated protein kinases (MAPKs), the level of phosphorylated p38 was reduced, whereas the levels of activated (phosphorylated) JNK and ERK were not affected in Fgl2-/- BMDMs compared with those in WT BMDMs following LPS treatment and viral infection (Figure 8C, Supplementary Figure 5), suggesting that FGL2 induces a positive feedback proinflammatory loop through p38 activation. Phosphorylation of p65 at Ser276 by c-Raf1 enables the recruitment of acetyltransferase CREB-binding protein (CBP) and p300, which leads to the acetylation of p65 and thus an enhanced NF-κB transcription rate[16]. Interestingly, phosphorylation of c-Raf1 and p65 (Ser276) and acetylation of p65 were reduced in Fgl2-/- BMDMs compared with those in WT BMDMs following either LPS stimulation or viral infection (Figure 8D). Phosphorylation of TBK, a modulator downstream of SYK that is involved in C-type lectin receptor (CLR)/Toll-like receptor (TLR) signaling-mediated innate immunity[25], did not differ between WT and Fgl2-/- BMDMs following LPS and MHV-3 challenge (Figure 8E). Taken together, our data suggest that induction of FGL2 in macrophages regulates inflammatory signaling by modulating p38, IRF3, IRF7, and p65 phosphorylation.

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Figure 8 Fibrinogen-like protein 2 deficiency impaired inflammatory cascade in response to lipopolysaccharide treatment of viral infection. A: Immunoblot for fibrinogen-like protein 2 (Fgl2) and β-actin expression in wild-type (WT) BMDMs in response lipopolysaccharide (LPS) stimulation and murine hepatitis virus strain 3 (MHV-3) infection. B-E: Immunoblot for proteins panels from lysates of WT and Fgl2-/- BMDMs in response to LPS treatment and MHV-3 infection; B: MyD88, TRIF, IκBα, phosphorylated IκBα, phosphorylated p65 (S468) and IRF3, phosphorylated IRF3, and IRF7; C: p38, JNK, ERK and phosphorylated p38, JNK, ERK; D: Phosphorylated c-Raf, phosphorylated p65 (S276), acetyl p65 (lys310); E: BTK, and phosphorylated BTK (Y223), BTK (Tyr550). These experiments were repeated at least three times.

Viral fulminant hepatitis (VFH) is a devastating syndrome that pathologically caused by excessive activation of both innate and adaptive immunity. However, the extent of contribution of innate immunity in VFH is not well defined. Macrophage polarization have been implicated in host defense and the pathogenesis of various hepatic diseases. Fibrinogen-like protein 2 (FGL2) can be induced robustly and exclusively in macrophages in response to cytokines or viral infection. Exploring their roles in VFH can greatly improve our understanding of the disease and thus seek the therapeutic approaches.

Hepatic macrophages are attractive therapeutic targets because their functions can be inhibited or augmented to alter disease outcomes. A better understanding of their biological properties and immunologic function in liver homeostasis and pathology may pave the way for new diagnostic and therapeutic approaches for liver failure or other liver diseases.

To evaluate the role of Fgl2 in the reconstitution of hepatic macrophages during VFH progression by the VFH mouse model.

Liver sections of liver failure patients and controls were immuno-stained for macrophages examination. Murine hepatitis virus strain 3 (MHV-3) was used to induce VFH experimental model in wild type and Fgl2-/- mice. Adoptive transfer or depletion of macrophages were employed to assess liver damage and hepatic macrophages alteration. Signal cascade induced by LPS or MHV-3 were detected in macrophages.

Infiltrated MoMFs is a major source of hepatic inflammation during VFH progression. Fgl2 expression on macrophages prompts and enhances the inflammatory phenotype of hepatic macrophages, which breaks the previous understanding that the mechanism of Fgl2 during VFH is generally considered to be procoagulant activity.

We revealed for the first time that pro-inflammatory monocyte-derived macrophages (MoMFs) infiltration is critical event for hepatic inflammatory accumulation and subsequent liver damage during virus-induced hepatitis progression and Fgl2 is required for maintaining the pro-inflammatory hepatic macrophages phenotype.

Macrophages are ‘keystones’ of liver architecture in both homeostasis and disease. The development of potential therapies highly depends on a fundamental knowledge about the mechanisms that trigger the polarization and control the fate of hepatic macrophages. We believe that a better understanding of the specific mechanisms underlying macrophages participation in diseases will definitely result in the increased efficacy of these therapies.