Immune-mediated Liver Injury Research Articles

CEACAM1 controls immune-mediated liver injury by promoting IL-2-dependent Treg induction

CEACAM1 controls immune-mediated liver injury by promoting IL-2-dependent Treg induction

1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG) reduces hepatic injury in concanavalin A-treated mice.

1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG), a chemically synthesized monoacetyldiaglyceride, is one of the constituents in Sika deer antlers and has been known traditionally as having immunomodulatory effects. However, the mechanism by which PLAG controls neutrophil migration, which evokes liver injury in the hepatitis animal model, remains largely unknown. This study was designed to evaluate the immunomodulatory effects of PLAG on cytokine secretion and neutrophil migration in vivo and in vitro. Concanavalin A (Con A) induced leukocyte infiltration in the liver and increased plasma cytokine levels. Pretreatment with PLAG reduced the levels of interleukin (IL)-4, IL-6, IL-10, and CXCL2, but maintained interferon (IFN)-γ levels and modulated neutrophil recruitment toward the liver. Furthermore, the mRNA and protein levels of IL-4 and CXCL2 in liver tissue were also decreased in the Con A-treated mice. Liver histology analyses showed that PLAG reduced Con A-induced hepatic necrosis, which was accompanied by leukocyte infiltration. The in vitro studies revealed that PLAG reduced IL-4 secretion in Con A stimulated T cell and blocked signal transducer and activator of transcription 6 (STAT6) Con A induced hepatocyte. PLAG attenuated IL-4 induced activation of atypical protein kinase C (PKC)/STAT6 in hepatocytes and inhibited neutrophil migration toward the liver tissue through suppression of IL-8/vascular cell adhesion molecule (VCAM) expression. These results suggest that PLAG could mitigate excess neutrophil migration into liver tissue and potentially have a therapeutic effect on immune-mediated liver injury.

Protective Effect of Akkermansia muciniphila against Immune-Mediated Liver Injury in a Mouse Model.

Accumulating evidence indicates that gut microbiota participates in the pathogenesis and progression of liver diseases. The severity of immune-mediated liver injury is associated with different microbial communities. Akkermansia muciniphila can regulate immunologic and metabolic functions. However, little is known about its effects on gut microbiota structure and function. This study investigated the effect of A. muciniphila on immune-mediated liver injury and potential underlying mechanisms. Twenty-two C57BL/6 mice were assigned to three groups (N = 7–8 per group) and continuously administrated A. muciniphila MucT or PBS by oral gavage for 14 days. Mouse feces were collected for gut microbiota analysis on the 15th day, and acute liver injury was induced by Concanavalin A (Con A, 15 mg/kg) injection through the tail vein. Samples (blood, liver, ileum, colon) were assessed for liver injury, systemic inflammation, and intestinal barrier function. We found that oral administration of A. muciniphila decreased serum ALT and AST and alleviated liver histopathological damage induced by Con A. Serum levels of pro-inflammatory cytokines and chemokines (IL-2, IFN-γ, IL-12p40, MCP-1, MIP-1a, MIP-1b) were substantially attenuated. A. muciniphila significantly decreased hepatocellular apoptosis; Bcl-2 expression increased, but Fas and DR5 decreased. Further investigation showed that A. muciniphila enhanced expression of Occludin and Tjp-1 and inhibited CB1 receptor, which strengthened intestinal barriers and reduced systemic LPS level. Fecal 16S rRNA sequence analysis indicated that A. muciniphila increased microbial richness and diversity. The community structure of the Akk group clustered distinctly from that of mice pretreated with PBS. Relative abundance of Firmicutes increased, and Bacteroidetes abundance decreased. Correlation analysis showed that injury-related factors (IL-12p40, IFN-γ, DR5) were negatively associated with specific genera (Ruminococcaceae_UCG_009, Lachnospiraceae_UCG_001, Akkermansia), which were enriched in mice pretreated with A. muciniphila. Our results suggested that A. muciniphila MucT had beneficial effects on immune-mediated liver injury by alleviating inflammation and hepatocellular death. These effects may be driven by the protective profile of the intestinal community induced by the bacteria. The results provide a new perspective on the immune function of gut microbiota in host diseases.

Immunomodulatory Therapy of Inflammatory Liver Disease Using Selectin-Binding Glycopolymers.

Immunotherapies have the potential to significantly advance treatment of inflammatory disease and cancer, which are in large part driven by immune cells. Selectins control the first step in immune cell adhesion and extravasation, thereby guiding leukocyte trafficking to tissue lesions. We analyzed four different highly specific selectin-binding glycopolymers, based on linear poly(2-hydroxypropyl)-methacrylamide (PHPMA) polymers. These glycopolymers contain either the tetrasaccharide sialyl-LewisX (SLeX) or the individual carbohydrates fucose, galactose, and sialic acids mimicking the complex SLeX binding motive. The glycopolymers strongly bind to primary human macrophages, without activating them, and also to primary human blood leukocytes, but poorly to fibroblasts and endothelial cells in vitro. After intravenous injection in mice, all glycopolymers accumulated in the liver without causing hepatotoxicity. The glycosylated binder most potently targeted resident hepatic macrophages (Kupffer cells) and protected mice from acute toxic liver injury in the two different experimental models, carbon tetrachloride (CCl4) or Concanavalin A (ConA)-based hepatitis. Its sulfated counterpart, on the other hand, induced a decrease in infiltrating and resident macrophages, increased T helper cells, and aggravated immune-mediated liver injury. We demonstrate that, in the context of selectin-binding glycopolymers, minor modifications strongly impact leukocyte influx and macrophage activation, thereby ameliorating or aggravating liver inflammation depending on the underlying immunopathology. The nonsulfated random glycopolymer is a promising candidate for the treatment of inflammatory disease. The modulation of hepatic immune cells by selectin-binding glycopolymers might breach the immunosuppressive hepatic microenvironment and could improve efficacy of immunotherapies for inflammatory disease and cancer.

Challenges and difficulties in pathological diagnosis of autoimmune hepatitis.

Autoimmune hepatitis (AIH) with acute presentation is widely recognized as a distinct clinical entity, and its clinicopathology has been extensively studied. In most cases, AIH with acute presentation is merely acute exacerbation of classical chronic AIH, but pure acute-onset AIH without previous symptoms of chronic liver disease is also encountered. Rapid diagnosis and initiation of immunosuppressive treatment are necessary for both acute exacerbation and acute-onset to prevent fatal liver failure. The diagnostic criteria commonly used for classical AIH are generally applicable to acute exacerbation, but acute-onset AIH may present with additional pathological features. These features include an acute hepatitis phase characterized by centrilobular necrosis. However, centrilobular necrosis is also a feature of drug-induced liver injury, and there are no known histological characteristics exclusive to acute-onset AIH. Moreover, the possibilities of drug-induced AIH and immune-mediated drug-induced liver injury make diagnosis even more difficult. At present, liver biopsy is mandatory for the diagnosis of AIH with acute presentation, but careful consideration of all clinicopathological signs is necessary for differential diagnosis.

Differences in Genetic Background Contribute to Pseudomonas Exotoxin A-Induced Hepatotoxicity in Rats

Pseudomonas aeruginosa exotoxin A (PEA) causes severe hepatotoxicity in experimental animals and is useful in investigations of immune-mediated liver injury. However, strain differences in the sensitivity to PEA-induced hepatotoxicity in rats remains be elucidated. In this study, we determined the severity of PEA-induced hepatotoxicity in six genetically different rat strains. Male LE (Long Evans), Wistar, F344, WKY, BN/SsN and LEW rats were administered a single intravenous injection of PEA (20 μg/kg). Significantly elevated serum ALT and AST levels, massive necrosis and hemorrhage, and numerous TUNEL-positive hepatocytes were observed in BN/SsN rats. In contrast, low levels of ALT and AST as well as mild changes in liver histopathology were observed in Wistar and F344 rats. Moderate levels of hepatic injuries were observed in LE, WKY, and LEW rats. Pro-inflammatory cytokines including TNF-α, IL-2 and IL-6 serum levels were markedly increased in BN/SsN rats compared to Wistar and F344 rats. However, the hepatic levels of low density lipoprotein receptor-related protein (LRP), which functions as the PEA receptor, were not significantly different in each strain. Taken together, we suggest that BN/SsN is the most sensitive rat strain, whereas Wistar and F344 were the most resistant rat strains to PEA-induced liver damage. The different genetic background of rat strains plays an important role in the susceptibility to PEA-induced epatotoxicity that may depend on immune-regulation but not LRP receptor levels.

The inhibition of NLRP3 signaling attenuates liver injury in an α-galactosylceramide-induced hepatitis model

Inflammasomes are involved in innate immune responses. Several NOD-Like receptors (NLRs) participate in the formation of inflammasomes. NACHT, LRR and PYD domains-containing protein 3 (NALP3) belongs to the NLR family and recognizes adenosine triphosphate (ATP), crystals, and Reactive Oxygen Species (ROS). This study examined the effect of inflammasomes on alpha-galactosylceramide (GalCer)-induced liver injury using NALP3-knockout (KO) mice. GalCer administration induced inflammasome activation and IL-1β-maturation. In NALP3-KO mice treated with GalCer, serum ALT levels were significantly reduced compared with those in GalCer-treated WT mice. Histological examination revealed decreased necrosis in NALP3-KO mice compared with WT mice, consistent with ALT levels. Expression of proinflammatory cytokines (such as IL-6, and TNF-α) and chemokines was also significantly suppressed in NALP3-KO mice. Moreover, flow cytometry analysis revealed fewer infiltrating immune cells in the livers of GalCer-treated NALP3-KO mice. Inportantly, the frequency of MDSCs (CD11b+Gr-1int cells), which suppress the immune response, was significantly increased in GalCer-treated NALP3-KO mice. In conclusion, NALP3 inhibition attenuated liver injury in GalCer-induced hepatitis. The inhibition of NALP3 signaling coused be a therapeutic target in immune-mediated liver injury.

Effect of preventive treatment in EAE mouse model transplanted with DN T cells transformed from CD4 T cells

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) has long served as an animal model for human MS. Both diseases are characterized by inflammation and demyelination of the CNS. Lots of study confirmed that Th1 and Th17 cells could aggravate the illness, while Foxp3+ regulatory T cells (Treg cells) could inhibit the autoimmune reaction and limit disease progression. However, it has been studied that both the number and immune suppression function of Treg cells were reduced in EAE mice, and although myelin specific Treg cells accumulated in the CNS, it failed to control autoimmune inflammation. Based on that, promoting immune regulation by other regulatory cells may be a new strategy to restore immune homeostasis and control EAE. Many studies have demonstrated that in peripheral lymphoid tissues of normal mice and healthy humans, 1% to 3% of T cell receptor positive T cells are double negative T cells (DN T cells), which capable of down regulating immune responses. We have identified a new differentiation pathway for the conversion of CD4 T cells to DN T cells, which could large amount DN T cells in vitro in a short time. We have showed that the converted DN T cells retained a stable phenotype and expressed a unique set of cell surface markers and gene profiles. These cells were highly potent in suppressing allo- and auto-immune responses both in vitro and in vivo in an antigen specific manner. Adoptive cell therapy using these antigen specific DN T cells could prevent and cure autoimmune diabetes and promote islet allograft survival in NOD mice. In a ConA mediated liver injury model, CD4 T cell converted DN T cells exerted significant protection against immune mediated liver injury and maintained the homeostasis of the immune system. Up to now, there is no report on the role of these converted DNT cells in mouse EAE model. In this study, we further explored the protection and its mechanism of DN T cells on EAE. CD4 T cells were converted to antigen specific DN T cells in vitro with MOG35–55 stimulation. Then we adoptive transferred these antigen specific DN T cells to mice before EAE immunization. Time of disease onset, EAE score, mouse weight, lymphocyte infiltration were compared between EAE control group and DNT pre-treatment group, the inhibitory function of DN T cells on pathogenic CD4 T cells from EAE model were further explored. Our data showed that a single adoptive transfer of MOG35–55 primed DN T cells significantly lowered the EAE score, prevented the weight loss and reduced lymphocytes infiltration in brain tissue. DN T cells pre-treatment group contained lower plasma IL-2 and IL-4 levels compared to EAE control group. In vitro suppression assays showed DN T cells significantly suppressed the proliferation of inflammatory CD4 T cells from EAE mice. Our data suggests that DN T cells can significantly reduce the EAE severity. This preventive effect is partly due to DN T cells’ suppression on the proliferation and cytokine production of inflammatory CD4 T cells. DN T cells may have a potential clinical application in the prevention and treatment of MS.

Pregnenolone 16α-carbonitrile ameliorates concanavalin A-induced liver injury in mice independent of the nuclear receptor PXR activation

The pregnane X receptor (PXR) is well-known as a key regulator of drug/xenobiotic clearance. Upon activation by ligand, PXR transcriptionally upregulates the expression of drug-metabolizing enzymes and drug transporters. Recent studies have revealed that PXR also plays a role in regulating immune/inflammatory responses. Specific PXR activators, including synthetic ligands and phytochemicals, have been shown to ameliorate chemically induced colitis in mice. In this study, we investigated an anti-inflammatory effect of pregnenolone 16α-carbonitrile (PCN), a prototypical activator for rodent PXR, in concanavalin A (Con A)-induced liver injury, a model of immune-mediated liver injury, using wild-type and Pxr−/− mice. Unexpectedly, pretreatment with PCN significantly ameliorated Con A-induced liver injury in not only wild-type but Pxr−/− mice as well, accompanied with lowered plasma ALT levels and histological improvements. Pretreatment with PCN was found to significantly repress the induction of Cxcl2 and Ccl2 mRNA expression and neutrophil infiltration into the liver of both wild-type and Pxr−/− mice at the early time point of Con A-induced liver injury. Our results indicate that PCN has unexpected immunosuppressive activity independent of PXR activation to protect mice from immune-mediated liver injury induced by Con A.

Bone Marrow-Derived Mesenchymal Stem Cells Attenuate Immune-Mediated Liver Injury and Compromise Virus Control During Acute Hepatitis B Virus Infection in Mice.

Mesenchymal stem cells (MSCs) have been used as therapeutic tools not only for their ability to differentiate toward different cells, but also for their unique immunomodulatory properties. However, it is still unknown how MSCs may affect immunity during hepatitis B virus (HBV) infection. This study was designed to explore the effect of bone marrow-derived MSCs (BM-MSCs) on hepatic natural killer (NK) cells in a mouse model of acute HBV infection. Mice were injected with 1 × 106 BM-MSCs, which stained with chloromethyl derivatives of fluorescein diacetate fluorescent probe, 24 h before hydrodynamic injection of viral DNA (pHBV1.3) through the tail vein. In vivo imaging system revealed that BM-MSCs were accumulated in the injured liver, and they attenuated immune-mediated liver injury during HBV infection, as shown by lower alanine aminotransferase levels, reduced proinflammatory cytokine production, and decreased inflammatory cell infiltration in the liver. Importantly, administration of BM-MSCs restrained the increased expression of natural-killer group 2, member D (NKG2D), an important receptor required for NK cell activation in the liver from HBV-infected mice. BM-MSCs also reduced NKG2D expression on NK cells and suppressed the cytotoxicity of NK cells in vitro. Furthermore, BM-MSC-derived transforming growth factor-β1 suppressed NKG2D expression on NK cells. As a consequence, BM-MSC treatment enhanced HBV gene expression and replication in vivo. These results demonstrate that adoptive transfer of BM-MSCs influences innate immunity and limits immune-mediated liver injury during acute HBV infection by suppressing NK cell activity. Meanwhile, the effect of BM-MSCs on prolonging virus clearance needs to be considered in the future.

Salecan protected against concanavalin A-induced acute liver injury by modulating T cell immune responses and NMR-based metabolic profiles

Salecan, a water-soluble extracellular β-glucan produced by Agrobacterium sp. ZX09, has been reported to exhibit a wide range of biological effects. The aims of the present study were to investigate the protective effect of salecan against Concanavalin A (ConA)-induced hepatitis, a well-established animal model of immune-mediated liver injury, and to search for possible mechanisms. C57BL/6 mice were pretreated with salecan followed by ConA injection. Salecan treatment significantly reduced ConA-induced acute liver injury, and suppressed the expression and secretion of inflammatory cytokines including interferon (IFN)-γ, interleukin (IL)-6 and IL-1β in ConA-induced liver injury model. The high expression levels of chemokines and adhesion molecules such as MIP-1α, MIP-1β, ICAM-1, MCP-1 and RANTES in the liver induced by ConA were also down-regulated after salecan treatment. Salecan inhibited the infiltration and activation of inflammatory cells, especially T cells, in the liver induced by ConA. Moreover, salecan reversed the metabolic profiles of ConA-treated mice towards the control group by partly recovering the metabolic perturbations induced by ConA. Our results suggest the preventive and therapeutic potential of salecan in immune-mediated hepatitis.

The impact of sterile inflammation in acute liver injury.

The liver has a number of functions in innate immunity. These functions predispose the liver to innate immune-mediated liver injury when inflammation goes unchecked. Significant progress has been made in the last 25 years on sterile inflammatory liver injury in a number of models; however, a great deal of controversy and many questions about the nature of sterile inflammation still exist. The goal of this article is to review sterile inflammatory liver injury using both a basic approach to what constitutes the inflammatory injury, and through examination of current models of liver injury and inflammation. This information will be tied to human patient conditions when appropriate. Inflammation is one of the most critical factors for managing in-patient liver disease in a number of scenarios. More information is needed for both scientists and clinicians to develop rational treatments.

RORγt-Mediated TNF-α Production from Human FoxP3+ Regulatory T Cells Contributes to Tissue Inflammation in Acute Viral Infection

CD4+CD25+Foxp3+regulatory T (Treg) cells control immune responses, thereby preventing excessive inflammation and homeostasis of the immune system. Paradoxically, in several autoimmune disorders, it has been suggested that Treg cells undergo inflammatory conversion to produce effector cytokines promoting tissue inflammation. However, such inflammatory changes have not been reported so far in human acute viral infection. Herein, we investigated the production of inflammatory cytokines from Treg cells of acute hepatitis A (AHA) patients. We also studied a cellular mechanism for production of effector cytokines by Treg cells and clinical significance of inflammatory conversion of Treg cells.First, we examined the production of a variety of inflammatory cytokines from Treg cells following T cell receptor (TCR) stimulation of peripheral blood lymphocytes with anti-CD3/CD28 antibody, using intracellular cytokine staining. As a result, we found that a remarkable proportion of CD4+CD25+Foxp3+Treg cells of AHA patients produced TNF-α upon TCR stimulation, particularly at the acute phase. TNF-α production by Treg cells was dramatically diminished at convalescent phase of AHA.Next, we investigated the expression of Th cell type-specific transcription factors and chemokine receptors in TNF-α-producing Treg cells of AHA patients, using multicolor flow cytometry. TNF-α-producing Treg cells expressed substantially higher level of RORγt and CCR6 than the TNF-α-counterpart, suggesting that they share various immunophenotypes of helper 17 T (Th17) cells. More strikingly, the TNF-α production was significantly reduced by RORγt inhibition, indicating that TNF-α production from Treg cells of AHA patients is controlled by Th17-specific transcription factor RORγt.We further examined the suppressive activity of TNF-α-producing CD4+CD25+Foxp3+ Treg cells of AHA patients. TNF-α+CD4+CD25+Foxp3+ Treg cells of AHA patients expressed lower level of Foxp3 than the TNF-α- counterpart. Similarly, the percentage of CD39+ cells was lower in TNF-α+CD4+CD25+Foxp3+ Treg cells than in the TNF-α- counterpart. In fact, Treg suppressive activity of AHA patients was significantly reduced compared with that of healthy controls when non-Treg CD4+ T cells or CD8+T cells were used as responder cells.Finally, we examined the clinical significance of TNF-α-producing CD4+CD25+Foxp3+ Treg cells in AHA patients. In particular, we focused on the liver injury, which is mediated by effector T cells during AHA. Intriguingly, the frequency of TNF-α+ cells among circulating Treg cells significantly correlated with the serum ALT level whereas the frequency of IFN-γ+ or IL-17A+cells did not. This result indicates that the pathologic conversion of Treg cells to produce TNF-α contributes to severe immune-mediated liver injury in AHA patients.Taken together, Treg cells undergo functional alteration to produce TNF-α during AHA. TNF-α-producing CD4+CD25+Foxp3+ Treg cells of AHA patients exhibit a Th17-like feature and produce TNF-α in a RORγt-dependent manner. TNF-α-producing Treg cells show reduced suppressive activity and are associated with severe liver injury in AHA. Importantly, we provide new insight into immunopathologic mechanisms in human acute viral infection, by demonstrating inflammatory conversion of Treg cells and its association with immune-mediated liver injury in AHA. DisclosuresNo relevant conflicts of interest to declare.

A plant cell-expressed recombinant anti-TNF fusion protein is biologically active in the gut and alleviates immune-mediated hepatitis and colitis

The orally administered BY-2 plant cell-expressed recombinant anti-TNF fusion protein (PRX-106) (n=6) consists of the soluble form of the human TNF receptor (TNFR) fused to the Fc component of a human antibody IgG1 domain. AimTo evaluate the immune modulatory effect of the oral administration of plant cells expressing PRX-106. MethodsMice treated with Concanavalin A (ConA) to induce immune hepatitis was orally treated with cells expressing PRX-106 containing 0.5 or 5μg PRX 106. In the colitis model, TNBS-colitis was induced in mice followed by the oral administration of plant cells expressing PRX-106. The immune modulatory effect was determined through follow-up to assess the clinical effect, histology, and serum cytokine levels and by FACS analysis for lymphocyte subsets. ResultsThe oral administration of BY-2 cells expressing PRX-106 alleviated immune-mediated liver injury. Serum AST and ALT levels decreased and were comparable to those of mice that had received high-dose steroids. The beneficial effect was also observed as a marked decrease in hepatic necrosis. In the colitis model, the oral administration of BY-2 plant cells expressing PRX-106 alleviated weight loss associated with immune-mediated colitis and improved bowel histology. A reduction in I-IkB-alpha phosphorylation in treated mice was also observed. These effects were associated with a significant alteration in the distribution of CD4+CD25+FOXP3+ cells. ConclusionsPlant cells expressing recombinant anti-TNF fusion protein show biological activity when orally administered, exerting an immune modulatory effect through the alleviation of immune-mediated hepatitis and immune-mediated colitis.

A murder mystery in the liver: who done it and how?

Hepatocyte death, which can be apoptosis or necrosis depending on the context, is a prominent feature of liver disease. The lectin concanavalin A (ConA) activates immune cells, resulting in inflammatory liver injury and hepatocyte necrosis. In this issue of the JCI, Günther et al. demonstrate that the pseudokinase mixed lineage kinase domain-like protein (MLKL) participates in hepatocyte death in ConA injury and that MLKL-mediated death is independent of the receptor-interacting protein kinase RIPK3. RIPK3 was absent in hepatocytes, and MLKL-deficient mice, but not RIPK3-deficient mice, were protected from ConA-induced liver injury. The authors also present evidence that an unidentified kinase activates MLKL, as RIPK1 bound MLKL but did not phosphorylate it. Moreover, ConA rapidly induced MLKL, mediated by the IFN-γ/STAT1 pathway, while activation and translocation to the plasma membrane required TNF. Increased phospho-MLKL staining in liver biopsies from patients with autoimmune hepatitis suggests a role for MLKL in this disease. This study describes a previously unrecognized form of cell death in the liver that should be further explored as a potential therapeutic target in immune-mediated liver injury.

Knockdown of RIPK1 Markedly Exacerbates Murine Immune-Mediated Liver Injury through Massive Apoptosis of Hepatocytes, Independent of Necroptosis and Inhibition of NF-κB.

Receptor-interacting protein kinase (RIPK)1 has an essential role in the signaling pathways triggered by death receptors through activation of NF-κB and regulation of caspase-dependent apoptosis and RIPK3/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis. We examined the effect of RIPK1 antisense knockdown on immune-mediated liver injury in C57BL/6 mice caused by α-galactosylceramide (αGalCer), a specific activator for invariant NKT cells. We found that knockdown of RIPK1 markedly exacerbated αGalCer-mediated liver injury and induced lethality. This was associated with increased hepatic inflammation and massive apoptotic death of hepatocytes, as indicated by TUNEL staining and caspase-3 activation. Pretreatment with zVAD.fmk, a pan-caspase inhibitor, or neutralizing Abs against TNF, almost completely protected against the exacerbated liver injury and lethality. Primary hepatocytes isolated from RIPK1-knockdown mice were sensitized to TNF-induced cell death that was completely inhibited by adding zVAD.fmk. The exacerbated liver injury was not due to impaired hepatic NF-κB activation in terms of IκBα phosphorylation and degradation in in vivo and in vitro studies. Lack of RIPK1 kinase activity by pretreatment with necrostatin-1, a RIPK1 kinase inhibitor, or in the RIPK1 kinase-dead knock-in (RIPK1D138N) mice did not exacerbate αGalCer-mediated liver injury. Furthermore, RIPK3-knockout and MLKL-knockout mice behaved similarly as wild-type control mice in response to αGalCer, with or without knockdown of RIPK1, excluding a switch to RIPK3/MLKL-mediated necroptosis. Our findings reveal a critical kinase-independent platform role for RIPK1 in protecting against TNF/caspase-dependent apoptosis of hepatocytes in immune-mediated liver injury.

Endogenous n-3 Polyunsaturated Fatty Acids Attenuate T Cell-Mediated Hepatitis via Autophagy Activation.

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert anti-inflammatory effects in several liver disorders, including cirrhosis, acute liver failure, and fatty liver disease. To date, little is known about their role in immune-mediated liver diseases. In this study, we used fat-1 transgenic mice rich in endogenous n-3 PUFAs to examine the role of n-3 PUFAs in immune-mediated liver injury. Concanavalin A (Con A) was administered intravenously to wild-type (WT) and fat-1 transgenic mice to induce T cell-mediated hepatitis. Reduced liver damage was shown in Con A-administrated fat-1 transgenic mice, as evidenced by decreased mortality, attenuated hepatic necrosis, lessened serum alanine aminotransferase activity, and inhibited production of pro-inflammatory cytokines (e.g., TNF-α, IL-6, IL-17A, and IFN-γ). In vivo and in vitro studies demonstrated that n-3 PUFAs significantly inhibited the activation of hepatic T cells and the differentiation of Th1 cells after Con A challenge. Further studies showed that n-3 PUFAs markedly increased autophagy level in Con A-treated fat-1 T cells compared with the WT counterparts. Blocking hepatic autophagy activity with chloroquine diminished the differences in T cell activation and liver injury between Con A-injected WT and fat-1 transgenic mice. We conclude that n-3 PUFAs limit Con A-induced hepatitis via an autophagy-dependent mechanism and could be exploited as a new therapeutic approach for autoimmune hepatitis.

PGAM5-mediated programmed necrosis of hepatocytes drives acute liver injury

ObjectivesAutoimmune hepatitis (AIH) is a severe necroinflammatory liver disease associated with significant mortality. Although loss of hepatocytes is generally recognised as a key trigger of liver inflammation and liver failure,...

Hepatic NK cell-mediated hypersensitivity to ConA-induced liver injury in mouse liver expressing hepatitis C virus polyprotein.

The role of hepatic NK cells in the pathogenesis of HCV-associated hepatic failure is incompletely understood. In this study, we investigated the effect of HCV on ConA-induced immunological hepatic injury and the influence of HCV on hepatic NK cell activation in the liver after ConA administration. An immunocompetent HCV mouse model that encodes the entire viral polyprotein in a liver-specific manner based on hydrodynamic injection and φC31o integrase was used to study the role of hepatic NK cells. Interestingly, the frequency of hepatic NK cells was reduced in HCV mice, whereas the levels of other intrahepatic lymphocytes remained unaltered. Next, we investigated whether the reduction in NK cells within HCV mouse livers might elicit an effect on immune-mediated liver injury. HCV mice were subjected to acute liver injury models upon ConA administration. We observed that HCV mice developed more severe ConA-induced immune-mediated hepatitis, which was dependent on the accumulated intrahepatic NK cells. Our results indicated that after the administration of ConA, NK cells not only mediated liver injury through the production of immunoregulatory cytokines (IFN-γ, TNF-α and perforin) with direct antiviral activity, but they also killed target cells directly through the TRAIL/DR5 and NKG2D/NKG2D ligand signaling pathway in HCV mice. Our findings suggest a critical role for NK cells in oversensitive liver injury during chronic HCV infection.

Anti-4-1BB monoclonal antibodies attenuate concanavalin A-induced immune-mediated liver injury in mice.

Effective therapies for the treatment of immune-mediated liver disease are currently lacking. As a member of the tumor necrosis factor receptor superfamily, 4-1BB has a key role in T-cell activation and has been implicated in the development of autoimmune disorders. The purpose of the present study was to evaluate the potential therapeutic or preventive function of an anti-4-1BB monoclonal antibody (mAb) in a mouse model of concanavalin (Con) A-induced immune-mediated liver injury. A mouse model of immune-mediated liver injury was established by tail vein injection of Con A (20 mg/kg). 4-1BB mAb (100 µg), with or without methylprednisolone (MEP; 3 mg/kg), was intraperitoneally injected into the tail vein 2 h prior to or 2 h following Con A injection. Con A induced marked hepatocyte necrosis, significantly reduced CD 4+/CD25+ T-cell levels, and increased the serum levels of aspartate transaminase (AST) and alanine transaminase (ALT), in addition to the percentage of 4-1BB+ T-cells, compared with the control (all P<0.05). The administration of 4-1BB mAb prior to or following Con A injection was able to attenuate Con A-induced liver tissue damage and significantly reduce serum AST and ALT levels (P<0.05). A combination of MEP and 4-1BB mAb further reduced serum AST and ALT levels, compared with either treatment alone. In addition, administration of 4-1BB mAb and MEP alone or in combination significantly increased CD4+/CD25+ T-cell levels, compared with the control (P<0.05). These results suggested that 4-1BB mAb was able to attenuate liver injury and preserve liver function in a mouse model of Con A-induced immune-mediated liver injury by promoting the expansion of CD4+/CD25+ T-cells. Furthermore, a combination of 4-1BB mAb with MEP was associated with greater beneficial effects than either treatment alone. The clinical significance of 4-1BB mAb in immune-mediated liver disease remains to be elucidated in future studies.