Invariant natural killer T-cell-deficient mice display increased CCl4-induced hepatitis associated with CXCL1 over-expression and neutrophil infiltration

Type 1 invariant natural killer T cells in chronic inflammation and tissue fibrosis

Chronic tissue inflammation often results in fibrosis characterized by the accumulation of extracellular matrix components remodeling normal tissue architecture and function. Recent studies have suggested common immune mechanisms despite the complexity of the interactions between tissue-specific fibroblasts, macrophages, and distinct immune cell populations that mediate fibrosis in various tissues. Natural killer T (NKT) cells recognizing lipid antigens bound to CD1d molecules have been shown to play an important role in chronic inflammation and fibrosis. Here we review recent data in both experimental models and in humans that suggest a key role of type 1 invariant NKT (iNKT) cell activation in the progression of inflammatory cascades leading to recruitment of neutrophils and activation of the inflammasome, macrophages, fibroblasts, and, ultimately, fibrosis. Emerging evidence suggests that iNKT-associated mechanisms contribute to type 1, type 2 and type 3 immune pathways mediating tissue fibrosis, including idiopathic pulmonary fibrosis (IPF). Thus, targeting a pathway upstream of these immune mechanisms, such as the inhibition of iNKT activation, may be important in modulating various fibrotic conditions.

Receptor-interacting protein kinase-1 ablation in liver parenchymal cells promotes liver fibrosis in murine NASH without affecting other symptoms

Non-alcoholic steatohepatitis (NASH), a chronic liver disease that emerged in industrialized countries, can further progress into liver fibrosis, cirrhosis, and hepatocellular carcinoma. In the next decade, NASH is predicted to become the leading cause of liver transplantation, the only current interventional therapeutic option. Hepatocyte death, triggered by different death ligands, plays key role in its progression. Previously, we showed that the receptor-interacting protein kinase-1 (RIPK1) in hepatocytes exhibits a protective role in ligand-induced death. Now, to decipher the role of RIPK1 in NASH, Ripk1^LPC-KO mice, deficient for RIPK1 only in liver parenchymal cells, and their wild-type littermates (Ripk1^fl/fl) were fed for 3, 5, or 12 weeks with high-fat high-cholesterol diet (HFHCD). The main clinical signs of NASH were analyzed to compare the pathophysiological state established in mice. Most of the symptoms evolved similarly whatever the genotype, whether it was the increase in liver to body weight ratio, the steatosis grade or the worsening of liver damage revealed by serum transaminase levels. In parallel, inflammation markers followed the same kinetics with significant equivalent inductions of cytokines (hepatic mRNA levels and blood cytokine concentrations) and a main peak of hepatic infiltration of immune cells at 3 weeks of HFHCD. Despite this identical inflammatory response, more hepatic fibrosis was significantly evidenced at week 12 in Ripk1^LPC-KO mice. This coincided with over-induced rates of transcripts of genes implied in fibrosis development (Tgfb1, Tgfbi, Timp1, and Timp2) in Ripk1^LPC-KO animals. In conclusion, our results show that RIPK1 in hepatocyte limits the progression of liver fibrosis during NASH.

Activation of iNKT Cells Facilitates Liver Repair After Hepatic Ischemia Reperfusion Injury Through Acceleration of Macrophage Polarization

Macrophage polarization is critical for liver tissue repair following acute liver injury. However, the underlying mechanisms of macrophage phenotype switching are not well defined. Invariant natural killer T (iNKT) cells orchestrate tissue inflammation and tissue repair by regulating cytokine production. Herein, we examined whether iNKT cells played an important role in liver repair after hepatic ischemia-reperfusion (I/R) injury by affecting macrophage polarization. To this end, we subjected male C57BL/6 mice to hepatic I/R injury, and mice received an intraperitoneal (ip) injection of α-galactosylceramide (α-GalCer) or vehicle. Compared with that of the vehicle, α-GalCer administration resulted in the promotion of liver repair accompanied by acceleration of macrophage differentiation and by increases in the numbers of Ly6C^high pro-inflammatory macrophages and Ly6C^low reparative macrophages. iNKT cells activated with α-GalCer produced interleukin (IL)-4 and interferon (IFN)-γ. Treatment with anti-IL-4 antibodies delayed liver repair, which was associated with an increased number of Ly6C^high macrophages and a decreased number of Ly6C^low macrophages. Treatment with anti-IFN-γ antibodies promoted liver repair, associated with reduced the number of Ly6C^high macrophages, but did not change the number of Ly6C^low macrophages. Bone marrow-derived macrophages up-regulated the expression of genes related to both a pro-inflammatory and a reparative phenotype when co-cultured with activated iNKT cells. Anti-IL-4 antibodies increased the levels of pro-inflammatory macrophage-related genes and decreased those of reparative macrophage-related genes in cultured macrophages, while anti-IFN-γ antibodies reversed the polarization of macrophages. Cd1d-deficient mice showed delayed liver repair and suppressed macrophage switching, compared with that in wild-type mice. These results suggest that the activation of iNKT cells by α-GalCer facilitated liver repair after hepatic I/R injury by both IL-4-and IFN-γ-mediated acceleration of macrophage polarization. Therefore, the activation of iNKT cells may represent a therapeutic tool for liver repair after hepatic I/R injury.

Effects of Nintedanib in an Animal Model of Liver Fibrosis

Systemic sclerosis can affect multiple internal organs, including the liver and lungs. Nintedanib, an antifibrotic approved for treatment of interstitial lung disease associated with systemic sclerosis, may have activity outside of the lungs. This study explored the effect of preventive and therapeutic nintedanib treatment in a 3-week carbon tetrachloride (CCL₄)-induced (500 mg/kg/day twice weekly for 3 weeks) model of hepatic inflammation and fibrosis in C57Bl/6 mice (aged 8 weeks, n = 5 per group). Mice also received nintedanib (30 or 60 mg/kg/day) either each day for 21 days (preventive treatment) or from day 7 or day 14 (therapeutic treatment). Preventive nintedanib treatment at both doses significantly reduced CCL₄-induced increases in myeloperoxidase (p < 0.01), hepatic collagen (p < 0.001), and interleukin (IL)-6 (p < 0.01) in the liver. Nintedanib also significantly reduced hepatic necrosis (p < 0.01 and p < 0.05), inflammation (p < 0.001 and p < 0.05), fibrosis (p < 0.001 and p < 0.05) and IL-1β (p < 0.05 and p < 0.001) at both 30 and 60 mg/kg/day, respectively. Therapeutic treatment with nintedanib at 30 and 60 mg/kg/day significantly reduced CCL₄-induced serum alanine aminotransferase from day 7 (p < 0.05 and p < 0.001) and day 14 (p < 0.01 and p < 0.05), respectively. Increases in tissue inhibitor of metalloproteinase-1 were significantly reduced by nintedanib at 60 mg/kg/day from day 7 only (p < 0.001), and nintedanib completely blocked elevation of IL-6 and IL-1β levels regardless of dose or start of treatment (p < 0.05-p < 0.001). In both the preventive and therapeutic treatment schedules of the study, nintedanib treatment was beneficial in attenuating CCL₄-induced pathology and reducing hepatic injury, inflammation, and fibrosis, demonstrating that nintedanib has antifibrotic and anti-inflammatory activity outside of the lungs.

Endogenous IL-33 has no effect on the progression of fibrosis during experimental steatohepatitis

Interleukin (IL)-33 has been recently reported to be strongly pro-fibrogenic in various models of liver disease. Our aim was to study the role of endogenous IL-33 in a diet-induced model of steatohepatitis. IL-33 deficient mice and wild type (WT) littermates received a high-fat diet (HFD), or a standard diet for 12 weeks. The HFD-induced steatohepatitis was associated with an upregulation of IL-33 transcripts and protein. An insulin tolerance test revealed lower systemic insulin sensitivity in IL-33-/—HFD mice than in WT-HFD mice. Nevertheless, IL-33 deficiency did not affect the severity of liver inflammation by histological and transcriptomic analyses, nor the quantity of liver fibrosis. Livers from HFD mice had more myeloid populations, markedly fewer NKT cells and higher proportion of ST2+ Treg cells and ST2+ type 2 innate lymphoid cells (ILC2), all unaffected by IL-33 deficiency. In conclusion, deficiency of endogenous IL-33 does not affect the evolution of experimental diet-induced steatohepatitis towards liver fibrosis.

Invariant NKT cells promote skin wound healing by preventing a prolonged neutrophilic inflammatory response

The wound-healing process consists of the inflammation, proliferation, and remodeling phases. In chronic wounds, the inflammation phase is prolonged with persistent neutrophil infiltration. The inflammatory response is critically regulated by cytokines and chemokines that are secreted from various immune cells. Recently, we showed that skin wound healing was delayed and the healing process was impaired under conditions lacking invariant natural killer T (iNKT) cells, an innate immune lymphocyte with potent immuno-regulatory activity. In the present study, we investigated the effect of iNKT cell deficiency on the neutrophilic inflammatory response during the wound healing process. Neutrophil infiltration was prolonged in wound tissue in mice genetically lacking iNKT cells (Jα18KO mice) than in wild-type (WT) control mice on days 1 and 3 after wounding. MIP-2, KC, and IL-17A were produced at a significantly higher level in Jα18KO mice than in WT mice. In addition, neutrophil apoptosis was significantly reduced in the wound tissue in Jα18KO mice than in WT mice. Treatment with anti-IL-17A mAb, anti-Gr-1 mAb, or neutrophil elastase inhibitor reversed the impaired wound healing in Jα18KO mice. These results suggest that iNKT cells may promote the wound healing process through preventing the prolonged inflammatory response mediated by neutrophils.

Crosstalk of liver immune cells and cell death mechanisms in different murine models of liver injury and its clinical relevance

BACKGROUND

Liver inflammation or hepatitis is a result of pluripotent interactions of cell death molecules, cytokines, chemokines and the resident immune cells collectively called as microenvironment. The interplay of these inflammatory mediators and switching of immune responses during hepatotoxic, viral, drug-induced and immune cell-mediated hepatitis decide the fate of liver pathology. The present review aimed to describe the mechanisms of liver injury, its relevance to human liver pathology and insights for the future therapeutic interventions.

DATA SOURCES

The data of mouse hepatic models and relevant human liver diseases presented in this review are systematically collected from PubMed, ScienceDirect and the Web of Science databases published in English.

RESULTS

The hepatotoxic liver injury in mice induced by the metabolites of CCl₄, acetaminophen or alcohol represent necrotic cell death with activation of cytochrome pathway, formation of reactive oxygen species (ROS) and mitochondrial damage. The Fas or TNF-alpha induced apoptotic liver injury was dependent on activation of caspases, release of cytochrome c and apoptosome formation. The ConA-hepatitis demonstrated the involvement of TRAIL-dependent necrotic/necroptotic cell death with activation of RIPK1/3. The alpha-GalCer-induced liver injury was mediated by TNF-alpha. The LPS-induced hepatitis involved TNF-alpha, Fas/FasL, and perforin/granzyme cell death pathways. The MHV3 or Poly(I:C) induced liver injury was mediated by natural killer cells and TNF-alpha signaling. The necrotic ischemia-reperfusion liver injury was mediated by hypoxia, ROS, and pro-inflammatory cytokines; however, necroptotic cell death was found in partial hepatectomy. The crucial role of immune cells and cell death mediators in viral hepatitis (HBV, HCV), drug-induced liver injury, non-alcoholic fatty liver disease and alcoholic liver disease in human were discussed.

CONCLUSIONS

The mouse animal models of hepatitis provide a parallel approach for the study of human liver pathology. Blocking or stimulating the pathways associated with liver cell death could unveil the novel therapeutic strategies in the management of liver diseases.

Expression of a hepatitis B virus pre-S2 deletion mutant in the liver results in hepatomegaly and hepatocellular carcinoma in mice

Hepatocellular carcinoma (HCC) is the most common form of liver cancer and has a poor prognosis and a low survival rate; its incidence is on the rise. Hepatitis B virus (HBV) infection is one of the main causes of HCC. A high prevalence of pre-S deletions of HBV surface antigen, which encompass T-cell and/or B-cell epitopes, is found in HBV carriers; antiviral therapy and viral immune escape may cause and select for these HBV mutants. In particular, the presence of pre-S2 deletion mutants is an important risk factor associated with cirrhosis and HCC. We generated Alb-preΔS2 transgenic mice that express a naturally occurring pre-S2 mutant protein containing a 33-nucleotide deletion (preΔS2); the aim was to investigate its effect on hepatocarcinogenesis. After 30 months of follow-up, the liver pathology of the mice fell into four groups: G1, chronic inflammation solely; G2, chronic inflammation and fibrosis; G3, inflammation, fibrosis, and hepatomegaly accompanied by rectal prolapse (4-12%); and G4, hepatomegaly and spontaneous HCC (12-15%). Striking degeneration of the endoplasmic reticulum (ER) was present in the mouse livers at an early stage (4 months old). At 8 months, overt ER stress and the Atf6 pathway of the unfolded protein response (UPR) were induced; at the same time, metabolic pathways associated with mevalonate and cholesterol biogenesis, involving the peroxisomes and the ER, were disturbed. At 20 months and older, the protein kinase RNA-like endoplasmic reticulum kinase (PERK) pathway of the UPR was induced and the Hippo transducer Yap was activated. Together, these ultrastructural aberrations and metabolic disturbance all seem to contribute to the molecular pathogenesis and hepatocarcinogenesis present in the Alb-preΔS2 mice. These findings may contribute to the development of therapies for the liver disorders and HCC associated with pre-S2 deletion mutations among HBV carriers. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Ablation of interaction between IL-33 and ST2+ regulatory T cells increases immune cell-mediated hepatitis and activated NK cell liver infiltration

The IL-33/ST2 axis plays a protective role in T-cell-mediated hepatitis, but little is known about the functional impact of endogenous IL-33 on liver immunopathology. We used IL-33-deficient mice to investigate the functional effect of endogenous IL-33 in concanavalin A (Con A)-hepatitis. IL-33(-/-) mice displayed more severe Con A liver injury than wild-type (WT) mice, consistent with a hepatoprotective effect of IL-33. The more severe hepatic injury in IL-33(-/-) mice was associated with significantly higher levels of TNF-α and IL-1β and a larger number of NK cells infiltrating the liver. The expression of Th2 cytokines (IL-4, IL-10) and IL-17 was not significantly varied between WT and IL-33(-/-) mice following Con A-hepatitis. The percentage of CD25(+) NK cells was significantly higher in the livers of IL-33(-/-) mice than in WT mice in association with upregulated expression of CXCR3 in the liver. Regulatory T cells (Treg cells) strongly infiltrated the liver in both WT and IL-33(-/-) mice, but Con A treatment increased their membrane expression of ST2 and CD25 only in WT mice. In vitro, IL-33 had a significant survival effect, increasing the total number of splenocytes, including B cells, CD4(+) and CD8(+) T cells, and the frequency of ST2(+) Treg cells. In conclusion, IL-33 acts as a potent immune modulator protecting the liver through activation of ST2(+) Treg cells and control of NK cells.

TLR4-Dependent Secretion by Hepatic Stellate Cells of the Neutrophil-Chemoattractant CXCL1 Mediates Liver Response to Gut Microbiota

Background & Aims

The gut microbiota significantly influences hepatic immunity. Little is known on the precise mechanism by which liver cells mediate recognition of gut microbes at steady state. Here we tested the hypothesis that a specific liver cell population was the sensor and we aimed at deciphering the mechanism by which the activation of TLR4 pathway would mediate liver response to gut microbiota.

Methods

Using microarrays, we compared total liver gene expression in WT versus TLR4 deficient mice. We performed in situ localization of the major candidate protein, CXCL1. With an innovative technique based on cell sorting, we harvested enriched fractions of KCs, LSECs and HSCs from the same liver. The cytokine secretion profile was quantified in response to low levels of LPS (1ng/mL). Chemotactic activity of stellate cell-derived CXCL1 was assayed in vitro on neutrophils upon TLR4 activation.

Results

TLR4 deficient liver had reduced levels of one unique chemokine, CXCL1 and subsequent decreased of neutrophil counts. Depletion of gut microbiota mimicked TLR4 deficient phenotype, i.e., decreased neutrophils counts in the liver. All liver cells were responsive to low levels of LPS, but hepatic stellate cells were the major source of chemotactic levels of CXCL1. Neutrophil migration towards secretory hepatic stellate cells required the TLR4 dependent secretion of CXCL1.

Conclusions

Showing the specific activation of TLR4 and the secretion of one major functional chemokine—CXCL1, the homolog of human IL-8-, we elucidate a new mechanism in which Hepatic Stellate Cells play a central role in the recognition of gut microbes by the liver at steady state.

Oncostatin M induces IL-33 expression in liver endothelial cells in mice and expands ST2+CD4+ lymphocytes

Interleukin (IL)-33 is crucially involved in liver pathology and drives hepatoprotective functions. However, the regulation of IL-33 by cytokines of the IL-6 family, including oncostatin M (OSM) and IL-6, is not well studied. The aim of the present study was to determine whether OSM mediates regulation of IL-33 expression in liver cells. Intramuscular administration in mice of an adenovirus encoding OSM (AdOSM) leads to increase in expression of OSM in muscles, liver, and serum of AdOSM-infected mice compared with control mice. The increase of circulating OSM markedly regulated mRNA of genes associated with blood vessel biology, chemotaxis, cellular death, induction of cell adhesion molecules, and the alarmin cytokine IL-33 in liver. Steady-state IL-33 mRNA was upregulated by OSM at an early phase (8 h) following AdOSM infection. At the protein level, the expression of IL-33 was significantly induced in liver endothelial cells [liver sinusoidal endothelial cells (LSEC) and vascular endothelial cells] with a peak at 8 days post-AdOSM infection in mice. In addition, we found OSM-stimulated human microvascular endothelial HMEC-1 cells and human LSEC/TRP3 cells showed a significant increase in expression of IL-33 mRNA in a dose-dependent manner in cell culture. The OSM-mediated overexpression of IL-33 was associated with the activation/enrichment of CD4(+)ST2(+) cells in liver of AdOSM-infected mice compared with adenovirus encoding green fluorescent protein-treated control mice. In summary, these data suggest that the cytokine OSM regulates the IL-33 expression in liver endothelial cells in vivo and in HMEC-1/TRP3 cells in vitro and may specifically expand the target CD4(+)ST2(+) cells in liver.

Inhibition of type I natural killer T cells by retinoids or following sulfatide-mediated activation of type II natural killer T cells attenuates alcoholic liver disease in mice

Innate immune mechanisms leading to liver injury subsequent to chronic alcohol ingestion are poorly understood. Natural killer T (NKT) cells, enriched in the liver and comprised of at least two distinct subsets, type I and II, recognize different lipid antigens presented by CD1d molecules. We have investigated whether differential activation of NKT cell subsets orchestrates inflammatory events leading to alcoholic liver disease (ALD). We found that after chronic plus binge feeding of Lieber-DeCarli liquid diet in male C57BL/6 mice, type I, but not type II, NKT cells are activated, leading to recruitment of inflammatory Gr-1(high) CD11b(+) cells into the liver. A central finding is that liver injury after alcohol feeding is dependent upon type I NKT cells. Thus, liver injury is significantly inhibited in Jα18(-/-) mice deficient in type I NKT cells as well as after their inactivation by sulfatide-mediated activation of type II NKT cells. Furthermore, we have identified a novel pathway involving all-trans retinoic acid (ATRA) and its receptor (RARγ) signaling that inhibits type I NKT cells and, consequently, ALD. A semiquantitative polymerase chain reaction analysis of hepatic gene expression of some of the key proinflammatory molecules shared in human disease indicated that their up-regulation in ALD is dependent upon type I NKT cells.

CONCLUSIONS

Type I, but not type II, NKT cells become activated after alcohol feeding. Type I NKT cell-induced inflammation and neutrophil recruitment results in liver tissue damage whereas type II NKT cells protect from injury in ALD. Inhibition of type I NKT cells by retinoids or by sulfatide prevents ALD. Given that the CD1d pathway is highly conserved between mice and humans, NKT cell subsets might be targeted for potential therapeutic intervention in ALD.

The chemical inhibitors of cellular death, PJ34 and Necrostatin-1, down-regulate IL-33 expression in liver

Interleukin-33 (IL-33), a cytokine belonging to the IL-1 family, is crucially involved in inflammatory pathologies including liver injury and linked to various modes of cell death. However, a link between IL-33 and necroptosis or programmed necrosis in liver pathology remains elusive. We aimed to investigate the regulation of IL-33 during necroptosis-associated liver injury. The possible regulation of IL-33 during liver injury by receptor-interacting protein kinase 1 (RIPK1) and poly(ADP-ribose) polymerase 1 (PARP-1) was investigated in mice in vivo and in hepatic stellate cells in vitro. The liver immunohistopathology, flow cytometry, serum transaminase measurement, ELISA, and qPCR-based cytokine measurement were carried out. By using a chemical approach, we showed that pretreatment of mice with Necrostatin-1 (Nec-1) (inhibitor of RIPK1) and/or PJ34 (inhibitor of PARP-1) significantly protected mice against concanavalin A (ConA) liver injury (aspartate amino-transferase (AST)/alanine amino-transferase (ALT)) associated with down-regulated hepatocyte-specific IL-33 expression. In contrast, the expression level of most systemic cytokines (except for IL-6) or activation of liver immune cells was not altered by chemical inhibitors rather an increased infiltration of neutrophils in the liver. During polyinosine-polycytidylic acid (Poly(I:C))-induced acute hepatitis, liver injury and hepatocyte-specific IL-33 expression was also inhibited by PJ34 without any protective effect of PJ34 in CCl4-induced liver injury. Moreover, PJ34 down-regulated the protein expression of IL-33 in activated hepatic stellate cells by cocktail of cytokines or staurosporine in vitro. In conclusion, we evidenced that the Nec-1/PJ34 is a potent inhibitor of liver injury and Nec-1/PJ34 down-regulated hepatocyte-specific IL-33 expression in the liver in vivo or in hepatic stellate cells in vitro, suggesting IL-33 as a possible readout of necroptosis-involved liver pathologies.

KEY MESSAGE

Necroptosis inhibitors can protect mice against liver injury induced by ConA or Poly(I:C). IL-33 expression in liver injury in vivo is inhibited by PJ34. IL-33 expression in hepatic stellate cells in vitro is inhibited by PJ34. Hepatocyte-specific IL-33 expression is down-regulated by Nec-1/PJ34 during hepatitis. IL-33 is a new marker of necroptosis-associated liver injuries.

Cross-activating invariant NKT cells and kupffer cells suppress cholestatic liver injury in a mouse model of biliary obstruction

Both Kupffer cells and invariant natural killer T (iNKT) cells suppress neutrophil-dependent liver injury in a mouse model of biliary obstruction. We hypothesize that these roles are interdependent and require iNKT cell-Kupffer cell cross-activation. Female, wild-type and iNKT cell-deficient C57Bl/6 mice were injected with magnetic beads 3 days prior to bile duct ligation (BDL) in order to facilitate subsequent Kupffer cell isolation. On day three post-BDL, the animals were euthanized and the livers dissected. Necrosis was scored; Kupffer cells were isolated and cell surface marker expression (flow cytometry), mRNA expression (qtPCR), nitric oxide (NO^.) production (Griess reaction), and protein secretion (cytometric bead-array or ELISAs) were determined. To address the potential role of NO^. in suppressing neutrophil accumulation, a group of WT mice received 1400W, a specific inducible nitric oxide synthase (iNOS) inhibitor, prior to BDL. To clarify the mechanisms underlying Kupffer cell-iNKT cell cross-activation, WT animals were administered anti-IFN-γ or anti-lymphocyte function-associated antigen (LFA)-1 antibody prior to BDL. Compared to their WT counterparts, Kupffer cells obtained from BDL iNKT cell-deficient mice expressed lower iNOS mRNA levels, produced less NO^., and secreted more neutrophil chemoattractants. Both iNOS inhibition and IFN-γ neutralization increased neutrophil accumulation in the livers of BDL WT mice. Anti-LFA-1 pre-treatment reduced iNKT cell accumulation in these same animals. These data indicate that the LFA-1-dependent cross-activation of iNKT cells and Kupffer cells inhibits neutrophil accumulation and cholestatic liver injury.

Pathogenic mouse hepatitis virus or poly(I:C) induce IL-33 in hepatocytes in murine models of hepatitis

The IL-33/ST2 axis is known to be involved in liver pathologies. Although, the IL-33 levels increased in sera of viral hepatitis patients in human, the cellular sources of IL-33 in viral hepatitis remained obscure. Therefore, we aimed to investigate the expression of IL-33 in murine fulminant hepatitis induced by a Toll like receptor (TLR3) viral mimetic, poly(I:C) or by pathogenic mouse hepatitis virus (L2-MHV3). The administration of poly(I:C) plus D-galactosamine (D-GalN) in mice led to acute liver injury associated with the induction of IL-33 expression in liver sinusoidal endothelial cells (LSEC) and vascular endothelial cells (VEC), while the administration of poly(I:C) alone led to hepatocyte specific IL-33 expression in addition to vascular IL-33 expression. The hepatocyte-specific IL-33 expression was down-regulated in NK-depleted poly(I:C) treated mice suggesting a partial regulation of IL-33 by NK cells. The CD1d KO (NKT deficient) mice showed hepatoprotection against poly(I:C)-induced hepatitis in association with increased number of IL-33 expressing hepatocytes in CD1d KO mice than WT controls. These results suggest that hepatocyte-specific IL-33 expression in poly(I:C) induced liver injury was partially dependent of NK cells and with limited role of NKT cells. In parallel, the L2-MHV3 infection in mice induced fulminant hepatitis associated with up-regulated IL-33 expression as well as pro-inflammatory cytokine microenvironment in liver. The LSEC and VEC expressed inducible expression of IL-33 following L2-MHV3 infection but the hepatocyte-specific IL-33 expression was only evident between 24 to 32h of post infection. In conclusion, the alarmin cytokine IL-33 was over-expressed during fulminant hepatitis in mice with LSEC, VEC and hepatocytes as potential sources of IL-33.

IL-17A plays a critical role in the pathogenesis of liver fibrosis through hepatic stellate cell activation

Liver fibrosis is a severe, life-threatening clinical condition resulting from nonresolving hepatitis of different origins. IL-17A is critical in inflammation, but its relation to liver fibrosis remains elusive. We find increased IL-17A expression in fibrotic livers from HBV-infected patients undergoing partial hepatectomy because of cirrhosis-related early-stage hepatocellular carcinoma in comparison with control nonfibrotic livers from uninfected patients with hepatic hemangioma. In fibrotic livers, IL-17A immunoreactivity localizes to the inflammatory infiltrate. In experimental carbon tetrachloride-induced liver fibrosis of IL-17RA-deficient mice, we observe reduced neutrophil influx, proinflammatory cytokines, hepatocellular necrosis, inflammation, and fibrosis as compared with control C57BL/6 mice. IL-17A is produced by neutrophils and T lymphocytes expressing the Th17 lineage-specific transcription factor Retinoic acid receptor-related orphan receptor γt. Furthermore, hepatic stellate cells (HSCs) isolated from naive C57BL/6 mice respond to IL-17A with increased IL-6, α-smooth muscle actin, collagen, and TGF-β mRNA expression, suggesting an IL-17A-driven fibrotic process. Pharmacologic ERK1/2 or p38 inhibition significantly attenuated IL-17A-induced HSC activation and collagen expression. In conclusion, IL-17A(+) Retinoic acid receptor-related orphan receptor γt(+) neutrophils and T cells are recruited into the injured liver driving a chronic, fibrotic hepatitis. IL-17A-dependent HSC activation may be critical for liver fibrosis. Thus, blockade of IL-17A could potentially benefit patients with chronic hepatitis and liver fibrosis.

TGF-β-responsive myeloid cells suppress type 2 immunity and emphysematous pathology after hookworm infection

Transforming growth factor β (TGF-β) regulates inflammation, immunosuppression, and wound-healing cascades, but it remains unclear whether any of these functions involve regulation of myeloid cell function. The present study demonstrates that selective deletion of TGF-βRII expression in myeloid phagocytes i) impairs macrophage-mediated suppressor activity, ii) increases baseline mRNA expression of proinflammatory chemokines/cytokines in the lung, and iii) enhances type 2 immunity against the hookworm parasite Nippostrongylus brasiliensis. Strikingly, TGF-β-responsive myeloid cells promote repair of hookworm-damaged lung tissue, because LysM(Cre)TGF-βRII(flox/flox) mice develop emphysema more rapidly than wild-type littermate controls. Emphysematous pathology in LysM(Cre)TGF-βRII(flox/flox) mice is characterized by excessive matrix metalloprotease (MMP) activity, reduced lung elasticity, increased total lung capacity, and dysregulated respiration. Thus, TGF-β effects on myeloid cells suppress helminth immunity as a consequence of restoring lung function after infection.

The chemokine receptor CXCR3 limits injury after acute toxic liver damage

Although acute liver failure is a rare disease, its presence is associated with high morbidity and mortality in affected patients. While a contribution of the immune system to the outcome of toxic liver failure is anticipated, functionally relevant immune cell receptors for liver cell damage need to be better defined. We here investigate the relevance of the chemokine receptor CXCR3, which is important for hepatic immune cell infiltration, in a model of experimental acute liver failure. Liver injury was induced by a single intraperitoneal injection of carbon tetrachloride (CCl(4)) in CXCR3(-/-), CCR1(-/-), CCR5(-/-) and wild-type mice. In this model, CXCR3(-/-) mice displayed augmented liver damage compared with all other mouse strains as assessed by liver histology and serum transaminases 24 and 72 h after injury. Phenotypically, CXCR3(-/-) mice had significantly reduced intrahepatic NK and NKT cells after injury at all investigated time points (all P<0.05), but strongly elevated expression levels of IL1-β, TNF-α and IFN-γ. In line with a functional role of innate immune cells, wild-type mice depleted for NK cells with an anti-ASIALO GM1 antibody before liver injury also displayed increased liver injury after CCl(4) challenge. CXCR3(-/-) and NK cell-depleted mice show reduced apoptotic liver cells (TUNEL assay), but more necrotic hepatocytes. Functionally, the augmented liver cell necrosis in CXCR3(-/-) and NK cell-depleted mice was associated with increased expression of high mobility group 1 (HMGB1) protein and a consecutive enhanced infiltration of neutrophils into the liver. In conclusion, the results demonstrate a primarily unexpected beneficial role of CXCR3 in acute toxic liver injury. These findings should be taken into account when planning trials with CXCR3 antagonists.

Invariant NKT cells drive hepatic cytokinic microenvironment favoring efficient granuloma formation and early control of Leishmania donovani infection

The development of inflammatory granulomas around infected Kupffer cells is necessary for hepatic parasite clearance during visceral leishmaniasis. Invariant NKT (iNKT) cells are predominant T cells in the mouse liver and can synthesize large quantities of IL-4 and IFN-γ, two cytokines involved in granuloma formation. This study analyzed the role of iNKT cells in the hepatic immune response during Leishmania donovani infection, using a murine model of wild-type (WT) and iNKT cell-deficient (Jα18^-/-) C57BL/6 mice sacrificed 15, 30 or 60 days post-infection. We recorded hepatic parasite loads, cytokine expression, and analyzed granulomatous response by immunohistochemistry and hepatic immune cell infiltration by flow cytometry. Whereas WT animals rapidly controlled the infection and developed an inflammatory response associated with a massive influx of iNKT cells observed by flow cytometry, Jα18^-/- mice had significantly higher parasitic loads on all time points. This lack of control of parasite burden was associated with a delay in granuloma maturation (28.1% of large granulomas at day 60 versus 50.7% in WT). Cytokine transcriptome analysis showed that mRNA of 90/101 genes encoding chemokines, cytokines and their receptors, was underexpressed in Jα18^-/- mice. Detection of IL-4 and TNF-α by ELISA in liver extracts was also significantly lower in Jα18^-/- mice. Consistent with flow cytometry analysis, cytokinome profile in WT mice showed a bias of expression towards T cell-chemoattractant chemokines on D15, and displayed a switch towards expression of granulocytes and/or monocytes -chemoattractant chemokines on D60. In Jα18^-/- mice, the significantly lower expression of CXCL5, MIP-2 and CCL2 mRNA was correlated with a defect in myeloperoxidase positive-cell attraction observed by immunohistochemistry and with a lower granulocyte and monocyte infiltration in the liver, as shown by flow cytometry. These data indicate that iNKT cells play a role in early and sustained pro-inflammatory cytokine response warranting efficient organization of hepatic granulomas and parasite clearance.

NKT cells are required to induce high IL-33 expression in hepatocytes during ConA-induced acute hepatitis

Interleukin-33 (IL-33) is thought to be released during cellular death as an alarming cytokine during the acute phase of disease, but its regulation in vivo is poorly understood. We investigated the expression of IL-33 in two mouse models of acute hepatitis by administering either carbon tetrachloride (CCl(4) ) or concanavalin A (ConA). IL-33 was overexpressed in both models but with a stronger induction in ConA-induced hepatitis. IL-33 was weakly expressed in vascular and sinusoidal endothelial cells from normal liver and was clearly induced in CCl(4) -treated mice. Surprisingly, we found that hepatocytes strongly expressed IL-33 exclusively in the ConA model. CD1d knock-out mice, which are deficient in NKT cells and resistant to ConA-induced hepatitis, no longer expressed IL-33 in hepatocytes following ConA administration. Interestingly, invariant NKT (iNKT) cells adoptively transferred into ConA-treated CD1d KO mouse restored IL-33 expression in hepatocytes. This strongly suggests that NKT cells are responsible for the induction of IL-33 in hepatocytes.