Protective role of interleukin-17 in murine NKT cell-driven acute experimental hepatitis

Role of the type 3 cytokines IL-17 and IL-22 in modulating metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) comprises a spectrum of liver diseases that span simple steatosis, metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis and may progress to cirrhosis and cancer. The pathogenesis of MASLD is multifactorial and is driven by environmental, genetic, metabolic and immune factors. This review will focus on the role of the type 3 cytokines IL-17 and IL-22 in MASLD pathogenesis and progression. IL-17 and IL-22 are produced by similar adaptive and innate immune cells such as Th17 and innate lymphoid cells, respectively. IL-17-related signaling is upregulated during MASLD resulting in increased chemokines and proinflammatory cytokines in the liver microenvironment, enhanced recruitment of myeloid cells and T cells leading to exacerbation of inflammation and liver disease progression. IL-17 may also act directly by activating hepatic stellate cells resulting in increased fibrosis. In contrast, IL-22 is a pleiotropic cytokine with a dominantly protective signature in MASLD and is currently being tested as a therapeutic strategy. IL-22 also exhibits beneficial metabolic effects and abrogates MASH-related inflammation and fibrosis development via inducing the production of anti-oxidants and anti-apoptotic factors. A sex-dependent effect has been attributed to both cytokines, most importantly to IL-22 in MASLD or related conditions. Altogether, IL-17 and IL-22 are key effectors in MASLD pathogenesis and progression. We will review the role of these two cytokines and cells that produce them in the development of MASLD, their interaction with host factors driving MASLD including sexual dimorphism, and their potential therapeutic benefits.

Natural Killer T (NKT) Cells in Autoimmune Hepatitis: Current Evidence from Basic and Clinical Research

Natural killer T (NKT) cells are unconventional T cells that are activated by glycolipid antigens. They can produce a variety of inflammatory and regulatory cytokines and, therefore, modulate multiple aspects of the immune response in different pathological settings, including autoimmunity. NKT cells have also been implicated in the immunopathogenesis of autoimmune hepatitis, and in this review we summarize and analyze the main studies investigating the involvement and/or homeostasis of NKT cells in this disease. In detail, the evidence from both basic and clinical research has been specifically analyzed. Even though the experimental murine models supported a relevant role of NKT cells in immune-mediated hepatic injury, very few studies specifically investigated NKT cell homeostasis in patients with autoimmune hepatitis; however, these initial studies reported some alterations of NKT cells in these patients, which may also correlate with the disease activity to some extent. Further clinical studies are needed to investigate the potential role and use of NKT cell analysis as a disease marker of clinical relevance, and to better understand the precise cellular and molecular mechanisms by which NKT cells contribute to the pathogenesis of autoimmune hepatitis.

Targeting adrenergic receptors to mitigate invariant natural killer T cells-induced acute liver injury

Invariant Natural Killer T (iNKT) cell activation by α-galactosylceramide (αGC) potentiates cytotoxic immune responses against tumors. However, αGC-induced liver injury is a limiting factor for iNKT-based immunotherapy. Although adrenergic receptor stimulation is an important immunosuppressive signal that curbs tissue damage induced by inflammation, its effect on the antitumor activity of invariant Natural Killer T (iNKT) cells remains unclear. We use mouse models and pharmacological tools to show that the stimulation of the sympathetic nervous system (SNS) inhibits αGC-induced liver injury without impairing iNKT cells' antitumoral functions. Mechanistically, SNS stimulation prevents the collateral effect of TNF-α production by iNKT cells and neutrophil accumulation in hepatic parenchyma. Our results suggest that the modulation of the adrenergic signaling can be a complementary approach to αGC-based immunotherapy to mitigate iNKT-induced liver injury without compromising its antitumoral activity.

Activation of cDCs and iNKT cells contributes to triptolide-induced hepatotoxicity via STING signaling pathway and endoplasmic reticulum stress

Triptolide (TP) exhibits therapeutic potential against multiple diseases. However, its application in clinics is limited by TP-induced hepatoxicity. TP can activate invariant natural killer T (iNKT) cells in the liver, shifting Th1 cytokine bias to Th2 cytokine bias. The damaging role of iNKT cells in TP-induced hepatoxicity has been established, and iNKT cell deficiency can mitigate hepatotoxicity. However, the activation of iNKT cells in vitro by TP requires the presence of antigen-presenting cells. Therefore, we hypothesized that TP could induce dendritic cells (DCs) to activate iNKT cells, thereby leading to hepatotoxicity. The hepatic conventional DCs (cDCs) exhibited immunogenic activities after TP administration, upregulating the expression of CD1d, co-stimulatory molecules, and IL-12. Neutralization with IL-12p40 antibody extenuated TP-induced hepatotoxicity and reduced iNKT cell activation, suggesting that IL-12 could cause liver injury by activating iNKT cells. TP triggered the activation and upregulation of STING signaling pathway and increased endoplasmic reticulum (ER) stress. Downregulation of STING reduced cDC immunogenicity, inhibiting the activation of iNKT cells and hepatic damage. These indicated the regulatory effects of STING pathway on cDCs and iNKT cells, and the important roles it plays in hepatoxicity. ER stress inhibitor, 4-phenylbutyrate (4-PBA), also suppressed iNKT cell activation and liver injury, which might be regulated by the STING signaling pathway. Our results demonstrated the possible mechanisms underlying TP-induced hepatoxicity, where the activation of cDCs and iNKT cells was stimulated by upregulated STING signaling and increased ER stress as a result of TP administration.

IL-17A in Human Liver: Significant Source of Inflammation and Trigger of Liver Fibrosis Initiation

IL-17A is considered to guide liver inflammation and fibrosis. From twenty-two human liver samples of different fibrosis stages (F0 to F4), IL-17A, IL-22, and TGFβ1 protein expression in liver tissue lysates were analyzed. Ten paired samples of liver tissue (F0–F1 stage) and blood from the same patient were used to analyze intrahepatic and blood T-lymphoid IL-17A⁺ cells by flow cytometry. The analyses have been performed regardless of pathology, considering the stage of fibrosis. Human liver tissue was used for the primary human liver slice cultures, followed by subsequent cytokine stimulation and fibrotic markers’ analysis by ELISA. IL-17A production in human liver tissue was significantly higher in the early fibrotic stage compared with the advanced stage. Th17 T cells and, to a lesser extent, MAIT cells were the main sources of IL-17A in both compartments, the liver and the blood. Moreover, the presence of liver Th17IL-17A⁺INFγ⁺ cells was detected in the liver. IL-17A stimulation of human liver slice culture increased the expression of profibrotic and pro-inflammatory markers. IL-17A, secreted by Th17 and MAIT cells in the liver, triggered fibrosis by inducing the expression of IL-6 and profibrotic markers and could be a target for antifibrotic treatment. Further amplitude studies are needed to confirm the current results.

The role of the immune system in the pathogenesis of NAFLD and potential therapeutic impacts of mesenchymal stem cell-derived extracellular vesicles

Non-Alcoholic Fatty Liver Disease (NAFLD) is characterized by intra-hepatocyte triglyceride accumulation and concomitant involvement of the immune system with subsequent histological changes, tissue damage, and clinical findings. There are various molecular pathways involved in the progression of NAFLD including lipotoxicity, endoplasmic reticulum stress, and the immune response. Both innate and adaptive immune systems are involved in the NAFLD pathogenesis, and crosstalk between the immune cells and liver cells participates in its initiation and progression. Among the various treatments for this disease, new cell based therapies have been proposed. Extracellular vesicles (EVs) derived from mesenchymal stem cells (MSC) (MSC-EVs) are new cell-free vehicles with low immunogenicity, which can suppress detrimental immune responses in inflamed tissues. This review aimed to express the immune system's molecular pathways associated with the initiation and progression of NAFLD. Then, the possible role of MSC-EVs in the treatment of this entity through immune response modulation was discussed. Finally, engineered EVs enhanced by specific therapeutic miRNA were suggested for alleviating the pathological cellular events in liver disease.

ADAM Metalloproteinase Domain 17 Regulates Cholestasis-Associated Liver Injury and Sickness Behavior Development in Mice

Disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) is a ubiquitously expressed membrane-bound enzyme that mediates shedding of a wide variety of important regulators in inflammation including cytokines and adhesion molecules. Hepatic expression of numerous cytokines and adhesion molecules are increased in cholestatic liver diseases including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), however, the pathophysiological role of ADAM17 in regulating these conditions remains unknown. Therefore, we evaluated the role of ADAM17 in a mouse model of cholestatic liver injury due to bile duct ligation (BDL). We found that BDL enhanced hepatic ADAM17 protein expression, paralleled by increased ADAM17 bioactivity. Moreover, inhibition of ADAM17 bioactivity with the specific inhibitor DPC 333 significantly improved both biochemical and histological evidence of liver damage in BDL mice. Patients with cholestatic liver disease commonly experience adverse behavioral symptoms, termed sickness behaviors. Similarly, BDL in mice induces reproducible sickness behavior development, driven by the upregulated expression of cytokines and adhesion molecules that are in turn regulated by ADAM17 activity. Indeed, inhibition of ADAM17 activity significantly ameliorated BDL-associated sickness behavior development. In translational studies, we evaluated changes in ADAM17 protein expression in liver biopsies obtained from patients with PBC and PSC, compared to normal control livers. PSC and PBC patients demonstrated increased hepatic ADAM17 expression in hepatocytes, cholangiocytes and in association with liver-infiltrating immune cells compared to normal controls. In summary, cholestatic liver injury in mice and humans is associated with increased hepatic ADAM17 expression. Furthermore, inhibition of ADAM17 activity improves both cholestatic liver injury and associated sickness behavior development, suggesting that ADAM17 inhibition may represent a novel therapeutic approach for treating patients with PBC/PSC.

Th17 cells in the liver: balancing autoimmunity and pathogen defense

In addition to carcinogenesis, T helper 17 (Th17) cells (a subtype of CD4 + T lymphocytes) are involved in the acute, chronic, and cirrhotic phases of liver diseases; however, their role in the development and progression of liver diseases remains unclear. It is difficult to elucidate the role of Th17 cells in liver diseases due to their dichotomous nature, i.e., plasticity in terms of pathogenic or host protective function depending on environmental and time phase factors. Moreover, insufficient depletion of Th17 cells by inhibiting the cytokines and transcription factors involved in their production causes difficulties in analyzing their specific role in vitro and in vivo murine models, partially due to complex interaction. This review summarizes the recent progress in understanding the plasticity and function of hepatic Th17 cells and type 3 cytokines.

Retinoic Acid: A New Old Friend of IL-17A in the Immune Pathogeny of Liver Fibrosis

Despite all the medical advances mortality due to cirrhosis and hepatocellular carcinoma, the end stages of fibrosis, continuously increases. Recent data suggest that liver fibrosis is guided by type 3 inflammation with IL-17A at the top of the line. The storage of vitamin A and its active metabolites, as well as genetics, can influence the development and progression of liver fibrosis and inflammation. Retinoic acid (active metabolite of vitamin A) is able to regulate the differentiation of IL-17A⁺/IL-22–producing cells as well as the expression of profibrotic markers. IL-17A and its pro-fibrotic role in the liver is the most studied, while the interaction and communication between IL-17A, IL-22, and vitamin A–active metabolites has not been investigated. We aim to update what is known about IL-17A, IL-22, and retinoic acid in the pathobiology of liver diseases.

Lipid antigens in bile from patients with chronic liver diseases activate natural killer T cells

Natural killer T (NKT) cells are an abundant subset of liver lymphocytes activated by lipid antigens presented on CD1d molecules that are expressed by cholangiocytes. We aimed to determine if bile from patients with chronic liver diseases contains antigenic lipids that can activate NKT cells. Using murine invariant (24.7, 24.8 and DN32.D3) and non-invariant (14S.6, 14S.7 and 14S.10) NKT hybridomas we investigated the presence of lipid antigens in bile collected from the gallbladder of patients undergoing liver transplantation due to end-stage liver disease. Biliary microbiota profiles were generated using 16S rRNA amplicon sequencing. We found that the patient bile samples contain antigens that activate both invariant and non-invariant NKT hybridomas (24.7, 24.8, DN32.D3, 14S.6, 14S.7 and 14S.10), as demonstrated by activation of at least one hybridoma by eight of 10 bile samples. Activation at high dilutions suggests that some antigens are highly potent. We used the non-invariant NKT hybridoma 14S.6 to screen 21 additional patient bile samples for NKT-reactivity and demonstrated that 12 of 21 bile samples resulted in activation, three of which gave a strong activation. Four of 12 activating bile samples contained microbial DNA. Our results reveal an immunological pathway that could be of critical importance in biliary immunology.

Antigen presentation, autoantibody production, and therapeutic targets in autoimmune liver disease

The liver is an important immunological organ that controls systemic tolerance. The liver harbors professional and unconventional antigen-presenting cells that are crucial for tolerance induction and maintenance. Orchestrating the immune response in homeostasis depends on a healthy and well-toned immunological liver microenvironment, which is maintained by the crosstalk of liver-resident antigen-presenting cells and intrahepatic and liver-infiltrating leukocytes. In response to pathogens or autoantigens, tolerance is disrupted by unknown mechanisms. Intrahepatic parenchymal and nonparenchymal cells exhibit unique antigen-presenting properties. The presentation of microbial and endogenous lipid-, metabolite- and peptide-derived antigens from the gut via conventional and nonconventional mechanisms can educate intrahepatic immune cells and elicit effector responses or tolerance. Perturbation of this balance results in autoimmune liver diseases, such as autoimmune hepatitis, primary biliary cholangitis, and primary sclerosing cholangitis. Although the exact etiologies of these autoimmune liver diseases are unknown, it is thought that the disruption of tolerance towards self-antigens and microbial metabolites and lipids, as well as alterations in bile acid composition, may result in changes in effector cell activation and polarization and may reduce or impair protective anti-inflammatory regulatory T and B cell responses. Additionally, the canonical and noncanonical transmission of antigens and antigen:MHC complexes via trogocytosis or extracellular vesicles between different (non) immune cells in the liver may play a role in the induction of hepatic inflammation and tolerance. Here, we summarize emerging aspects of antigen presentation, autoantibody production, and the application of novel therapeutic approaches in the characterization and treatment of autoimmune liver diseases.

Animal Models of Autoimmune Liver Diseases: a Comprehensive Review

Autoimmune liver diseases (AILDs) are potentially life-threatening chronic liver diseases which include autoimmune hepatitis, primary biliary cholangitis, primary sclerosing cholangitis, and recently characterized IgG4-related sclerosing cholangitis. They are caused by immune attack on hepatocytes or bile ducts, with different mechanisms and clinical manifestations. The etiologies of AILDs include a susceptible genetic background, environment insults, infections, and changes of commensal microbiota, but remain complicated. Understanding of the underlying mechanisms of AILDs is mandatory for early diagnosis and intervention, which is of great importance for better prognosis. Thus, animal models are developed to mimic the pathogenesis, find biomarkers for early diagnosis, and for therapeutic attempts of AILDs. However, no animal models can fully recapitulate features of certain AILD, especially the late stages of diseases. Certain limitations include different living condition, cell composition, and time frame of disease development and resolution. Moreover, there is no IgG4 in rodents which exists in human. Nevertheless, the understanding and therapy of AILDs have been greatly advanced by the development and mechanistic investigation of animal models. This review will provide a comprehensive overview of traditional and new animal models that recapitulate different features and etiologies of distinct AILDs.

Role of Interleukin-33 in Staphylococcus epidermidis-Induced Septicemia

Interleukin (IL)-33 is a member of the IL-1 family, which plays an important role in inflammatory response. In this study, we evaluated the effect of IL-33 on septicemia and the underlying mechanisms by establishing a Staphylococcus epidermidis (S. epidermidis)-induced septicemic mouse model. The expression of IL-33, IL-1α, IL-1β, IL-6, IL-17A, IL-22, and PGE2 were measured by double antibody sandwich enzyme-linked immunosorbent assay, and bacterial colony formation in peripheral blood and kidneys were counted postinfection. The percentages of neutrophils, eosinophils, and inflammatory monocytes were evaluated by flow cytometry, and tissue damage was assessed by hematoxylin and eosin (H&E) staining. The survival of septicemic mice was monitored daily. IL-33 expression was significantly augmented following S. epidermidis infection. High IL-33 expression significantly decreased the survival of model mice, and aggravated the damage of lung, liver, and kidney tissues. However, administration of ST2 (receptor for IL-33) to the S. epidermidis-infected mice blocked the IL-33 signaling pathway, which elevated PGE2, IL-17A, and IL-22, and promoted healing of organ damage. In addition, ST2 suppressed the mobilization of inflammatory monocytes, but promoted the accumulation of neutrophils and eosinophils in S. epidermidis-infected mice. Inhibition of PGE2, IL-17A, and IL-22 facilitated the development of septicemia and organ damage in S. epidermidis-infected mice, as well as reducing their survival. Our findings reveal that IL-33 aggravates organ damage in septicemic mice by inhibiting PGE2, IL-17A, and IL-22 production.

Type 3 cytokines in liver fibrosis and liver cancer

The type 3 cytokines IL-17 and IL-22 play a crucial, well synchronized physiological role in wound healing and repairing tissue damage due to infections or injury at barrier surfaces. These cytokines act on epithelial cells to induce secretion of early immune mediators, recruitment of inflammatory cells to the site of injury, and to trigger tissue repair mechanisms. However, if the damage persists or if these cytokines are dysregulated, then they contribute to a number of inflammatory pathologies, autoimmune conditions and cancer. The liver is a multifunctional organ that plays an essential role in metabolism, detoxification, and immune surveillance. It is also exposed to a variety of pathogens, toxins and injuries. Over the past decade, IL-17 and IL-22 have been implicated in various aspects of liver inflammation. IL-17 is upregulated in chronic liver injury and associated with liver disease progression. In contrast, IL-22 was shown to be hepatoprotective during acute liver injury but exhibited inflammatory effects in other models. Furthermore, IL-22 and IL-17 are both associated with poor prognosis in liver cancer. Finally, the regulatory mechanisms governing the physiological versus the pathological role of these two cytokines during acute and chronic liver injury remain poorly understood. In this review, we will summarize the current state of knowledge about IL-17 and IL-22 in wound healing during acute and chronic liver injury, their contribution to pathogenesis, their regulation, and their role in the transition from advanced liver disease to liver cancer.

The zinc-finger transcription factor MAZR regulates iNKT cell subset differentiation

Invariant natural killer T (iNKT) cells represent a subgroup of innate-like T cells and play an important role in immune responses against certain pathogens. In addition, they have been linked to autoimmunity and antitumor immunity. iNKT cells consist of several subsets with distinct functions; however, the transcriptional networks controlling iNKT subset differentiation are still not fully characterized. Myc-associated zinc-finger-related factor (MAZR, also known as PATZ1) is an essential transcription factor for CD8⁺ lineage differentiation of conventional T cells. Here, we show that MAZR plays an important role in iNKT cells. T-cell lineage-specific deletion of MAZR resulted in an iNKT cell-intrinsic defect that led to an increase in iNKT2 cell numbers, concurrent with a reduction in iNKT1 and iNKT17 cells. Consistent with the alteration in the subset distribution, deletion of MAZR also resulted in an increase in the percentage of IL-4-producing cells. Moreover, MAZR-deficient iNKT cells displayed an enhanced expression of Erg2 and ThPOK, key factors for iNKT cell generation and subset differentiation, indicating that MAZR controls iNKT cell development through fine-tuning of their expression levels. Taken together, our study identified MAZR as an essential transcription factor regulating iNKT cell subset differentiation and effector function.

Natural killer T cells mediate inflammation in the bile ducts

Cholangiocytes function as antigen-presenting cells with CD1d-dependent activation of natural killer T (NKT) cells in vitro. NKT cells may act both pro- and anti-inflammatory in liver immunopathology. We explored this immune pathway and the antigen-presenting potential of NKT cells in the bile ducts by challenging wild-type and Cd1d^-/- mice with intrabiliary injection of the NKT cell activating agent oxazolone. Pharmacological blocking of CD1d-mediated activation was performed with a monoclonal antibody. Intrabiliary oxazolone injection in wild-type mice caused acute cholangitis with significant weight loss, elevated serum levels of alanine transaminase, aspartate transaminase, alkaline phosphatase and bilirubin, increased histologic grade of cholangitis and number of T cells, macrophages, neutrophils and myofibroblasts per portal tract after 7 days. NKT cells were activated after intrabiliary injection of oxazolone with upregulation of activation markers. Cd1d^-/- and wild-type mice pretreated with antibody blocking of CD1d were protected from disease. These findings implicate that cells in the bile ducts function as antigen-presenting cells in vivo and activate NKT cells in a CD1d-restricted manner. The elucidation of this biliary immune pathway opens up for potentially new therapeutic approaches for cholangiopathies.

IL-17 and IL-17-producing cells and liver diseases, with focus on autoimmune liver diseases

The pro-inflammatory cytokine interleukin(IL)-17 and IL-17-producing cells are important players in the pathogenesis of many autoimmune / inflammatory diseases. More recently, they have been associated with liver diseases. This review first describes the general knowledge on IL-17 and IL-17 producing cells. The second part describes the in vitro and in vivo effects of IL-17 on liver cells and the contribution of IL-17 producing cells to liver diseases. IL-17 induces immune cell infiltration and liver damage driving to hepatic inflammation and fibrosis and contributes to autoimmune liver diseases. The circulating levels of IL-17 and the frequency of IL-17-producing cells are elevated in a variety of acute and chronic liver diseases. The last part focuses on the effects of IL-17 deletion or neutralization in various murine models. Some of these observed beneficial effects suggest that targeting the IL-17 axis could be a new therapeutic strategy to prevent chronicity and progression of various liver diseases.

Differentiation of IL-17-Producing Invariant Natural Killer T Cells Requires Expression of the Transcription Factor c-Maf

c-Maf belongs to the large Maf family of transcription factors and plays a key role in the regulation of cytokine production and differentiation of T_H2, T_H17, T_FH, and Tr1 cells. Invariant natural killer T (iNKT) cells can rapidly produce large quantity of T_H-related cytokines such as IFN-γ, IL-4, and IL-17A upon stimulation by glycolipid antigens, such as α-galactosylceramide (α-GalCer). However, the role of c-Maf in iNKT cells and iNKT cells-mediated diseases remains poorly understood. In this study, we demonstrate that α-GalCer-stimulated iNKT cells express c-Maf transcript and protein. By using c-Maf-deficient fetal liver cell-reconstituted mice, we further show that c-Maf-deficient iNKT cells produce less IL-17A than their wild-type counterparts after α-GalCer stimulation. While c-Maf deficiency does not affect the development and activation of iNKT cells, c-Maf is essential for the induction of IL-17-producing iNKT (iNKT17) cells by IL-6, TGF-β, and IL-1β, and the optimal expression of RORγt. Accordingly, c-Maf-deficient iNKT17 cells lose the ability to recruit neutrophils into the lungs. Taken together, c-Maf is a positive regulator for the expression of IL-17A and RORγt in iNKT17 cells. It is a potential therapeutic target in iNKT17 cell-mediated inflammatory disease.

Mesenchymal stem cells attenuate acute liver injury by altering ratio between interleukin 17 producing and regulatory natural killer T cells

Mesenchymal stem cells (MSCs) are, due to immunomodulatory characteristics, considered as novel agents in the treatment of immune-mediated acute liver failure. Although it is known that MSCs can regulate activation of T lymphocytes, their capacity to modulate function of neutrophils and natural killer T (NKT) cells, major interleukin (IL) 17-producing cells in acute liver injury, is still unknown. By using 2 well-established murine models of neutrophil and NKT cell-mediated acute liver failure (induced by carbon tetrachloride and α-galactoceramide), we investigated molecular and cellular mechanisms involved in MSC-mediated modulation of IL17 signaling during acute liver injury. Single intravenous injection of MSCs attenuate acute hepatitis and hepatotoxicity of NKT cells in a paracrine, indoleamine 2,3-dioxygenase (IDO)-dependent manner. Decreased levels of inflammatory IL17 and increased levels of immunosuppressive IL10 in serum, reduced number of interleukin 17-producing natural killer T (NKT17) cells, and increased presence of forkhead box P3 + IL10-producing natural killer T regulatory cells (NKTregs) were noticed in the injured livers of MSC-treated mice. MSCs did not significantly alter the total number of IL17-producing neutrophils, CD4+, and CD8 + T lymphocytes in the injured livers. Injection of mesenchymal stem cell-conditioned medium (MSC-CM) resulted with an increased NKTreg/NKT17 ratio in the liver and attenuated hepatitis in vivo and significantly reduced hepatotoxicity of NKT cells in vitro. This phenomenon was completely abrogated in the presence of IDO inhibitor, 1-methyltryptophan. In conclusion, the capacity of MSCs to alter NKT17/NKTreg ratio and suppress hepatotoxicity of NKT cells in an IDO-dependent manner may be used as a new therapeutic approach in IL17-driven liver inflammation. Liver Transplantation 23 1040-1050 2017 AASLD.

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.

γδ T cells are indispensable for interleukin-23-mediated protection against Concanavalin A-induced hepatitis in hepatitis B virus transgenic mice

Hepatitis B virus surface antigen (HBsAg) carriers are highly susceptible to liver injury triggered by environmental biochemical stimulation. Previously, we have reported an inverse correlation between γδ T cells and liver damage in patients with hepatitis B virus (HBV). However, whether γδ T cells play a role in regulating the hypersensitivity of HBsAg carriers to biochemical stimulation-induced hepatitis is unknown. In this study, using HBV transgenic (HBs-Tg) and HBs-Tg T-cell receptor-δ-deficient (TCR-δ^-/- ) mice, we found that mice genetically deficient in γδ T cells exhibited more severe liver damage upon Concanavalin A (Con A) treatment, as indicated by substantially higher serum alanine aminotransferase levels, further elevated interferon-γ (IFN-γ) levels and more extensive necrosis. γδ T-cell deficiency resulted in elevated IFN-γ in CD4⁺ T cells but not in natural killer or natural killer T cells. The depletion of CD4⁺ T cells and neutralization of IFN-γ reduced liver damage in HBs-Tg and HBs-Tg-TCR-δ^-/- mice to a similar extent. Further investigation revealed that HBs-Tg mice showed an enhanced interleukin-17 (IL-17) signature. The administration of exogenous IL-23 enhanced IL-17A production from Vγ4 γδ T cells and ameliorated liver damage in HBs-Tg mice, but not in HBs-Tg-TCR-δ^-/- mice. In summary, our results demonstrated that γδ T cells played a protective role in restraining Con A-induced hepatitis by inhibiting IFN-γ production from CD4⁺ T cells and are indispensable for IL-23-mediated protection against Con A-induced hepatitis in HBs-Tg mice. These results provided a potential therapeutic approach for treating the hypersensitivity of HBV carriers to biochemical stimulation-induced liver damage.

TNFα Augments Cytokine-Induced NK Cell IFNγ Production through TNFR2

NK cells play a central role in innate immunity, acting directly through cell-mediated cytotoxicity and by secreting cytokines. TNFα activation of TNFR2 enhances NK cell cytotoxicity, but its effects on the other essential function of NK cells - cytokine production, for which IFNγ is paramount - are poorly defined. We identify the expression of both TNFα receptors on human peripheral blood NK cells (TNFR2 > TNFR1) and show that TNFα significantly augments IFNγ production from IL-2-/IL-12-treated NK cells in vitro, an effect mimicked by a TNFR2 agonistic antibody. TNFα also enhanced murine NK cell IFNγ production via TNFR2 in vitro. In a mouse model characterized by the hepatic recruitment and activation of NK cells, TNFR2 also regulated NK cell IFNγ production in vivo. Specifically, in this model, after activation of an innate immune response, hepatic numbers of TNFR2-expressing and IFNγ-producing NK cells were both significantly increased; however, the frequency of IFNγ-producing hepatic NK cells was significantly reduced in TNFR2-deficient mice. We delineate an important role for TNFα, acting through TNFR2, in augmenting cytokine-induced NK cell IFNγ production in vivo and in vitro, an effect with significant potential implications for the regulation of innate and adaptive immune responses.

Modulation of liver tolerance by conventional and nonconventional antigen-presenting cells and regulatory immune cells

The liver is a tolerogenic organ with exquisite mechanisms of immune regulation that ensure upkeep of local and systemic immune tolerance to self and foreign antigens, but that is also able to mount effective immune responses against pathogens. The immune privilege of liver allografts was recognized first in pigs in spite of major histo-compatibility complex mismatch, and termed the "liver tolerance effect". Furthermore, liver transplants are spontaneously accepted with only low-dose immunosuppression, and induce tolerance for non-hepatic co-transplanted allografts of the same donor. Although this immunotolerogenic environment is favorable in the setting of organ transplantation, it is detrimental in chronic infectious liver diseases like hepatitis B or C, malaria, schistosomiasis or tumorigenesis, leading to pathogen persistence and weak anti-tumor effects. The liver is a primary site of T-cell activation, but it elicits poor or incomplete activation of T cells, leading to their abortive activation, exhaustion, suppression of their effector function and early death. This is exploited by pathogens and can impair pathogen control and clearance or allow tumor growth. Hepatic priming of T cells is mediated by a number of local conventional and nonconventional antigen-presenting cells (APCs), which promote tolerance by immune deviation, induction of T-cell anergy or apoptosis, and generating and expanding regulatory T cells. This review will focus on the communication between classical and nonclassical APCs and lymphocytes in the liver in tolerance induction and will discuss recent insights into the role of innate lymphocytes in this process.

Natural killer T cells in liver injury, inflammation and cancer

The liver is an organ that has the largest amount of natural killer T(NKT) cells, which play critical roles in the pathogenesis of liver diseases. In this article, the authors summarize recent findings about the roles of NKT cells in liver injury, inflammation, fibrosis, regeneration and cancer. In brief, NKT cells accelerate liver injury by producing pro-inflammatory cytokines and directly killing hepatocytes. NKT cells are involved in complex roles in liver fibrogenesis. For instance, NKT cells inhibit liver fibrosis via suppressing hepatic stellate cell activation and can also promote liver fibrosis via enhancing liver inflammation and injury. Inactivated or weakly activated NKT cells play a minimal role in controlling liver regeneration, whilst activated NKT cells have an inhibitory effect on liver regeneration. In liver cancer, NKT cells play both pro-tumor and anti-tumor roles in controlling tumor progress.

Immunology in the liver--from homeostasis to disease

The liver is a central immunological organ with a high exposure to circulating antigens and endotoxins from the gut microbiota, particularly enriched for innate immune cells (macrophages, innate lymphoid cells, mucosal-associated invariant T (MAIT) cells). In homeostasis, many mechanisms ensure suppression of immune responses, resulting in tolerance. Tolerance is also relevant for chronic persistence of hepatotropic viruses or allograft acceptance after liver transplantation. The liver can rapidly activate immunity in response to infections or tissue damage. Depending on the underlying liver disease, such as viral hepatitis, cholestasis or NASH, different triggers mediate immune-cell activation. Conserved mechanisms such as molecular danger patterns (alarmins), Toll-like receptor signalling or inflammasome activation initiate inflammatory responses in the liver. The inflammatory activation of hepatic stellate and Kupffer cells results in the chemokine-mediated infiltration of neutrophils, monocytes, natural killer (NK) and natural killer T (NKT) cells. The ultimate outcome of the intrahepatic immune response (for example, fibrosis or resolution) depends on the functional diversity of macrophages and dendritic cells, but also on the balance between pro-inflammatory and anti-inflammatory T-cell populations. As reviewed here, tremendous progress has helped to understand the fine-tuning of immune responses in the liver from homeostasis to disease, indicating promising targets for future therapies in acute and chronic liver diseases.

Transgenic animal models of type 2 autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic liver disease putatively caused by loss of tolerance to hepatocyte specific autoantigens. It is currently divided into types 1 and 2, based on the expression of autoantibodies. Autoantigenic epitopes have been identified only for the less frequent type 2 AIH. Many type 2 AIH mouse models have been well developed in recent years. This review focuses on some kinds of well-established type 2 AIH mouse models.

Rapid activation and hepatic recruitment of innate-like regulatory B cells after invariant NKT cell stimulation in mice

BACKGROUND & AIMS

Invariant natural killer T (iNKT) cells are present within the liver and have been implicated in the development of many liver diseases. Upon activation by glycolipid ligands (including α-galactosylceramide; αGalCer), hepatic iNKT cells produce numerous cytokines and recruit both pro-inflammatory and regulatory immune cells. However, the involvement of B cells in this process is poorly defined.

METHODS

Wild-type (male, C57BL/6), B cell deficient, or B cell depleted mice were injected with αGalCer or vehicle, hepatic B cell phenotype and liver injury was subsequently determined.

RESULTS

iNKT cell activation resulted in liver injury and the rapid activation and hepatic recruitment of B cells (mainly innate-like B1 and MZ-like B cells) from the spleen and peritoneal cavity. B cells recruited to the liver produce IL-10 and TGFβ, and express cell surface CD73 (ectoenzyme which generates adenosine). B cell deficient mice developed augmented αGalCer-induced hepatitis, enhanced neutrophil recruitment and striking alterations in the hepatic cytokine milieu. αGalCer-induced hepatitis was unaltered in IL-10(-/-) mice, or after TGFβ neutralization, but was significantly worsened in mice treated with a CD73 inhibitor.

CONCLUSIONS

iNKT cell stimulation recruits innate-like regulatory B cells to the liver which suppress hepatic inflammation through IL-10 and TGFβ1 independent mechanisms, but involve CD73 activity. These findings highlight an important inflammation suppressing role for B cells at early time points during the development of an innate immune response within the liver, and represent a potential therapeutic target for the treatment of liver disease.

Immunity, tolerance and autoimmunity in the liver: A comprehensive review

The hepatic immune system is constantly exposed to a massive load of harmless dietary and commensal antigens, to which it must remain tolerant. Immune tolerance in the liver is mediated by a number of specialized antigen-presenting cells, including dendritic cells, Kupffer cells, liver sinusoidal endothelial cells and hepatic stellate cells. These cells are capable of presenting antigens to T cells leading to T cell apoptosis, anergy, or differentiation into regulatory T cells. However, the hepatic immune system must also be able to respond to pathogens and tumours and therefore must be equipped with mechanisms to override immune tolerance. The liver is a site of accumulation of a number of innate lymphocyte populations, including natural killer cells, CD56(+) T cells, natural killer T cells, γδ T cells, and mucosal-associated invariant T cells. Innate lymphocytes recognize conserved metabolites derived from microorganisms and host cells and respond by killing target cells or promoting the differentiation and/or activation of other cells of the immune system. Innate lymphocytes can promote the maturation of antigen-presenting cells from their precursors and thereby contribute to the generation of immunogenic T cell responses. These cells may be responsible for overriding hepatic immune tolerance to autoantigens, resulting in the induction and maintenance of autoreactive T cells that mediate liver injury causing autoimmune liver disease. Some innate lymphocyte populations can also directly mediate liver injury by killing hepatocytes or bile duct cells in murine models of hepatitis, whilst other populations may protect against liver disease. It is likely that innate lymphocyte populations can promote or protect against autoimmune liver disease in humans and that these cells can be targeted therapeutically. Here I review the cellular mechanisms by which hepatic antigen-presenting cells and innate lymphocytes control the balance between immunity, tolerance and autoimmunity in the liver.

IL-30 (IL27p28) attenuates liver fibrosis through inducing NKG2D-rae1 interaction between NKT and activated hepatic stellate cells in mice

Chronic hepatic diseases, such as cirrhosis, hepatocellular carcinoma, and virus-mediated immunopathogenic infections, affect billions of people worldwide. These diseases commonly initiate with fibrosis. Owing to the various side effects of antifibrotic therapy and the difficulty of diagnosing asymptomatic patients, suitable medication remains a major concern. To overcome this drawback, the use of cytokine-based sustained therapy might be a suitable alternative with minimal side effects. Here, we studied the therapeutic efficacy and potential mechanisms of interleukin (IL)-30 as antifibrosis therapy in murine liver fibrosis models. CCl4 or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) 0.1% (wt/wt) Purina 5015 Chow (LabDiet, St. Louis, MO) was fed for 3 weeks to induce liver fibrosis. Either control vector (pCtr) or pIL30 was injected hydrodynamically once per week. A significant decrease in collagen deposition and reduced expression of alpha-smooth muscle actin (α-SMA) protein indicated that IL-30-based gene therapy dramatically reduced bridging fibrosis that was induced by CCl4 or DDC. Immunophenotyping and knockout studies showed that IL-30 recruits natural-killer-like T (NKT) cells to the liver to remove activated hepatic stellate cells (HSCs) significantly and ameliorate liver fibrosis. Both flow cytometric and antibody-mediated neutralization studies showed that liver NKT cells up-regulate the natural killer group 2, member D (NKG2D) ligand and bind with the NKG2D ligand, retinoic acid early inducible 1 (Rae1), and positively activated HSCs to ameliorate liver fibrosis. Furthermore, adoptive transfer of liver NKT cells in T-cell-deficient mice showed reduction of fibrosis upon IL-30 administration.

CONCLUSIONS

Highly target-specific liver NKT cells selectively remove activated HSCs through an NKG2D-Rae1 interaction to ameliorate liver fibrosis after IL-30 treatment.

Defective IL-17- and IL-22-dependent mucosal host response to Candida albicans determines susceptibility to oral candidiasis in mice expressing the HIV-1 transgene

BACKGROUND

The tissue-signaling cytokines IL-17 and IL-22 are critical to host defense against oral Candida albicans infection, by their induction of oral antimicrobial peptide expression and recruitment of neutrophils. Mucosal Th17 cells which produce these cytokines are preferentially depleted in HIV-infected patients. Here, we tested the hypothesis that defective IL-17- and IL-22-dependent host responses to C. albicans determine the phenotype of susceptibility to oropharyngeal candidiasis (OPC) in transgenic (Tg) mice expressing HIV-1.

RESULTS

Naïve CD4+ T-cells and the differentiated Th1, Th2, Th17, Th1Th17 and Treg lineages were all profoundly depleted in cervical lymph nodes (CLNs) of these Tg mice. However, naive CD4+ cells from Tg mice maintained the capacity to differentiate into these lineages in response to polarizing cytokines in vitro. Expression of Il17, Il22, S100a8 and Ccl20 was enhanced in oral mucosal tissue of non-Tg, but not of Tg mice, after oral infection with C. albicans. Treatment of infected Tg mice with the combination of IL-17 and IL-22, but not IL-17 or Il-22 alone, significantly reduced oral burdens of C. albicans and abundance of Candida hyphae in the epithelium of tongues of infected Tg mice, and restored the ability of the Tg mice to up-regulate expression of S100a8 and Ccl20 in response to C. albicans infection.

CONCLUSIONS

These findings demonstrate that defective IL-17- and IL-22-dependent induction of innate mucosal immunity to C. albicans is central to the phenotype of susceptibility to OPC in these HIV transgenic mice.

Hepatitis mouse models: from acute-to-chronic autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease associated with interface hepatitis, raised plasma liver enzymes, the presence of autoantibodies and regulatory T-cell (Tregs) dysfunction. The clinical course is heterogeneous, manifested by a fulminant or indolent course. Although genetic predisposition is well accepted, the combination with currently undefined environmental factors is crucial for the development of the disease. Progress in the development of reliable animal models provides added understanding of the pathophysiology of AIH, and these will be very useful in evaluating potential therapeutics. It appears that artificially breaking tolerance in the liver is easy. However, maintaining this state of tolerance breakdown, to get chronic hepatitis, is difficult because liver immune homeostasis is strongly regulated by several immune response inhibitory mechanisms. For example, Tregs are crucial regulators in acute and chronic hepatitis, and C57BL/6 mice are most prone to experimental AIH. Immunization of C57BL/6 mice with liver (AIH) autoantigens (CYP2D6/FTCD or IL-4R) and the disturbance of liver regulatory mechanism(s), leading to experimental AIH, are likely to be most representative of human AIH pathology.

Intrahepatic innate lymphoid cells secrete IL-17A and IL-17F that are crucial for T cell priming in viral infection

Intrahepatic cell-derived, early IL-17 is important for activating APCs in viral infection; however, the source and regulation of this IL-17 surge in the liver microenvironment are not well defined. In this article, we present evidence for a significant expansion of IL-17A/F-producing cells in mouse liver within 24 h of adenovirus infection. In addition to γδ T cells, a subset of IL-17A/F(+) cells expressed no myeloid or lymphoid lineage markers. Instead, they expressed high levels of stem cell markers, IL-7R and RORγt, consistent with the newly described innate lymphoid cells (ILCs). Based on their unique surface markers and cytokine profiles, these cells were confirmed as group 3 ILCs. In addition to adenovirus infection, group 3 ILCs were also found in mouse liver within 24 h of lymphocytic choriomeningitis virus infection. They contributed significantly to the establishment of the early cytokine milieu in virus-infected liver. Functional studies with mice deficient of IL-17R, IL-17A, and IL-17F further revealed that IL-17 signaling was critical for priming T cell responses in viral hepatitis. IL-17A repressed IL-17F secretion in vitro and in vivo; IL-17F(+) intrahepatic cells expanded more vigorously in IL-17A knockout animals, permitting efficient Ag presentation and T cell function. However, IL-17F neither inhibited IL-17A in vitro nor regulated its secretion in vivo. Together, this study has demonstrated the importance of a unique intrahepatic subpopulation and subsequent IL-17A/F regulation at initial stages of viral infection in the liver. These results have important implications for anticytokine biologic therapy and vaccine development.

Dengue virus infection: current concepts in immune mechanisms and lessons from murine models

Dengue viruses (DENV), a group of four serologically distinct but related flaviviruses, are responsible for one of the most important emerging viral diseases. This mosquito-borne disease has a great impact in tropical and subtropical areas of the world in terms of illness, mortality and economic costs, mainly due to the lack of approved vaccine or antiviral drugs. Infections with one of the four serotypes of DENV (DENV-1-4) result in symptoms ranging from an acute, self-limiting febrile illness, dengue fever, to severe dengue haemorrhagic fever or dengue shock syndrome. We reviewed the existing mouse models of infection, including the DENV-2-adapted strain P23085. The role of CC chemokines, interleukin-17 (IL-17), IL-22 and invariant natural killer T cells in mediating the exacerbation of disease in immune-competent mice is highlighted. Investigations in both immune-deficient and immune-competent mouse models of DENV infection may help to identify key host–pathogen factors and devise novel therapies to restrain the systemic and local inflammatory responses associated with severe DENV infection.

Invariant NKT cell activation induces neutrophil accumulation and hepatitis: opposite regulation by IL-4 and IFN-γ

Alpha-Galactosylceramide (α-Galcer), a specific agonist for invariant natural killer T (iNKT) cells, is being evaluated in clinical trials for the treatment of viral hepatitis and liver cancer. However, the results from α-Galcer treatment are mixed, partially because of the variety of cytokines produced by activated iNKT cells that have an unknown synergistic effect on the progression of liver disease. It is well documented that injection of α-Galcer induces mild hepatitis with a rapid elevation in the levels of interleukin (IL)-4 and a delayed elevation in the levels of interferon-gamma (IFN-γ), and both of these cytokines are thought to mediate many functions of iNKT cells. Surprisingly, genetic deletion of both IL-4 and IFN-γ aggravated, rather than abolished, α-Galcer-induced iNKT hepatitis. Moreover, genetic ablation of IL-4, the IL-4 receptor, or its downstream signaling molecule signal transducer and activator of transcription (STAT)6 ameliorated α-Galcer-induced neutrophil infiltration, liver injury, and hepatitis. In contrast, genetic deletion of IFN-γ, the IFN-γ receptor, or its downstream signaling molecule STAT1 enhanced liver neutrophil accumulation, thereby exacerbating liver injury and hepatitis. Moreover, depletion of neutrophils eradicated α-Galcer-induced liver injury in wild-type, STAT1 knockout, and IFN-γ knockout mice.

CONCLUSION

Our results propose a model in which activated iNKT cells rapidly release IL-4, which promotes neutrophil survival and hepatitis but also sequentially produce IFN-γ, which acts in a negative feedback loop to ameliorate iNKT hepatitis by inducing neutrophil apoptosis. Thus, modification of iNKT production of IL-4 and IFN-γ may have the potential to improve the efficacy of α-Galcer in the treatment of liver disease.

Diacylglycerol kinase zeta positively controls the development of iNKT-17 cells

Invariant natural killer T (iNKT) cells play important roles in bridging innate and adaptive immunity via rapidly producing a variety of cytokines. A small subset of iNKT cells produces IL-17 and is generated in the thymus during iNKT-cell ontogeny. The mechanisms that control the development of these IL-17-producing iNKT-17 cells (iNKT-17) are still not well defined. Diacylglycerol kinase ζ (DGKζ) belongs to a family of enzymes that catalyze the phosphorylation and conversion of diacylglycerol to phosphatidic acid, two important second messengers involved in signaling from numerous receptors. We report here that DGKζ plays an important role in iNKT-17 development. A deficiency of DGKζ in mice causes a significant reduction of iNKT-17 cells, which is correlated with decreased RORγt and IL-23 receptor expression. Interestingly, iNKT-17 defects caused by DGKζ deficiency can be corrected in chimeric mice reconstituted with mixed wild-type and DGKζ-deficient bone marrow cells. Taken together, our data identify DGKζ as an important regulator of iNKT-17 development through iNKT-cell extrinsic mechanisms.

The liver works as a school to educate regulatory immune cells

Because of its unique blood supply, the liver maintains a special local immune tolerogenic microenvironment. Moreover, the liver can impart this immune tolerogenic effect on other organs, thus inducing systemic immune tolerance. The network of hepatic regulatory cells is an important mechanism underlying liver tolerance. Many types of liver-resident antigen-presenting cells (APCs) have immune regulatory function, and more importantly, they can also induce the differentiation of circulating immune cells into regulatory cells to further extend systemic tolerance. Thus, the liver can be seen as a type of 'school', where liver APCs function as 'teachers' and circulating immune cells function as 'students.'

HMGB1 promotes the differentiation of Th17 via up-regulating TLR2 and IL-23 of CD14+ monocytes from patients with rheumatoid arthritis

High-mobility group box 1 (HMGB1) is a non-histone nuclear protein that is released extracellulary and has been implicated in autoimmune disease. Toll-like receptor 2 (TLR2) signalling is thought to be essential for the inflammatory response and for immune disorders. In recent studies, enhanced HMGB1 and TLR2 expressions have been found in rheumatoid arthritis (RA), respectively. The aim of this study is to explore whether HMGB1 stimulation can up-regulate the expression of TLR2 on CD14(+) monocytes from patients with RA and to clarify the subsequent events involving Th17 cells and Th17 cell-associated cytokine changes. Our results showed that the frequency of CD14(+) cells in peripheral blood mononuclear cell (PBMC) was obviously increased, and enhanced expression of TLR2 on CD14(+) monocytes was also found in patients with RA, compared with healthy controls with statistical significance (P < 0.001). In addition, the levels of IL-17, IL-23 and IL-6 in supernatants from cultured monocytes from patients and in patient's plasma were increased, and NF-κB, the downstream target of TLR2, also showed a marked elevation after monocytes were stimulated by HMGB1. This implies that the enhanced TLR2 pathway and Th17 cell polarization may be due to HMGB1 stimulation in rheumatoid arthritis.

IL-33/ST2 axis in inflammation and immunopathology

Interleukin-33 (IL-33), a member of the IL-1 family of cytokines, binds to its plasma membrane receptor, heterodimeric complex consisted of membrane-bound ST2L and IL-1R accessory protein, inducing NFkB and MAPK activation. IL-33 exists as a nuclear precursor and may act as an alarmin, when it is released after cell damage or as negative regulator of NFκB gene transcription, when acts in an intracrine manner. ST2L is expressed on several immune cells: Th2 lymphocytes, NK, NKT and mast cells and on cells of myeloid lineage: monocytes, dendritic cells and granulocytes. IL-33/ST2 axis can promote both Th1 and Th2 immune responses depending on the type of activated cell and microenvironment and cytokine network in damaged tissue. We previously described and discuss here the important role of IL-33/ST2 axis in experimental models of type 1 diabetes, experimental autoimmune encephalomyelitis, fulminant hepatitis and breast cancer. We found that ST2 deletion enhance the development of T cell-mediated autoimmune disorders, EAE and diabetes mellitus type I. Disease development was accompanied by dominantly Th1/Th17 immune response but also higher IL-33 production, which suggest that IL-33 in receptor independent manner could promote the development of inflammatory autoreactive T cells. IL-33/ST2 axis has protective role in Con A hepatitis. ST2-deficient mice had more severe hepatitis with higher influx of inflammatory cells in liver and dominant Th1/Th17 systemic response. Pretreatment of mice with IL-33 prevented Con A-induced liver damage through prevention of apoptosis of hepatocytes and Th2 amplification. Deletion of IL-33/ST2 axis enhances cytotoxicity of NK cells, production of IFN-γ in these cells and systemic production of IFN-γ, IL-17 and TNF-α, which leads to attenuated tumor growth. IL-33 treatment of tumor-bearing mice suppresses activity of NK cells, dendritic cell maturation and enhances alternative activation of macrophages. In conclusion, we observed that IL-33 has attenuated anti-inflammatory effects in T cell-mediated responses and that both IL-33 and ST2 could be further explored as potential therapeutic targets in treatment of immune-mediated diseases.

Liver TCRγδ(+) CD3(+) CD4(-) CD8(-) T cells contribute to murine hepatitis virus strain 3-induced hepatic injury through a TNF-α-dependent pathway

The mechanisms of each subset of immune cells contributing to the pathogenesis of viral hepatitis remain incompletely understood. In this study, we examined the role of liver CD4(-) CD8(-) (double negative, DN) T cells during murine hepatitis virus strain 3 (MHV-3)-induced hepatitis in C3H/HeJ mice. We demonstrate that predominant population of DN T cells in the liver of healthy or MHV-3-infected mice express TCRγδ(+). The proportion of TCRγδ(+) DN T cells in liver CD3(+) T cells was markedly increased after MHV-3 infection. Adoptive transfer of TCRγδ(+) DN T cells led to dramatically decreased survival in MHV-3-infected mice, accompanied by deteriorated histopathology and elevated ALT and AST levels. It was found that these cells were hyperactivated after MHV-3 infection with a production of TNF-α, IFN-γ, IL-2 and IL-17A. Highly activated liver TCRγδ(+) DN T cells were cytotoxic to MHV-3-infected hepatocytes in vitro and this effect did not require cell-cell contact. Moreover, the cytotoxic effect of liver TCRγδ(+) DN T cells against hepatocytes involves TNF-α pathway, but not IL-17A or IFN-γ. These results indicate that liver TCRγδ(+) DN T cells play a critical role in the liver injury in MHV-3-induced hepatitis, via a TNF-α dependent pathway.

Role of γδ T cells in α-galactosylceramide-mediated immunity

Attempts to harness mouse type I NKT cells in different therapeutic settings including cancer, infection, and autoimmunity have proven fruitful using the CD1d-binding glycolipid α-galactosylceramide (α-GalCer). In these different models, the effects of α-GalCer mainly relied on the establishment of a type I NKT cell-dependent immune cascade involving dendritic cell, NK cell, B cell, or conventional CD4(+) and CD8(+) T cell activation/regulation as well as immunomodulatory cytokine production. In this study, we showed that γδ T cells, another population of innate-like T lymphocytes, displayed a phenotype of activated cells (cytokine production and cytotoxic properties) and were required to achieve an optimal α-GalCer-induced immune response. Using gene-targeted mice and recombinant cytokines, a critical need for IL-12 and IL-18 has been shown in the α-GalCer-induced IFN-γ production by γδ T cells. Moreover, this cytokine production occurred downstream of type I NKT cell response, suggesting their bystander effect on γδ T cells. In line with this, γδ T cells failed to directly recognize the CD1d/α-GalCer complex. We also provided evidence that γδ T cells increase their cytotoxic properties after α-GalCer injection, resulting in an increase in killing of tumor cell targets. Moreover, using cancer models, we demonstrated that γδ T cells were required for an optimal α-GalCer-mediated anti-tumor activity. Finally, we reported that immunization of wild-type mice with α-GalCer enhanced the adaptive immune response elicited by OVA, and this effect was strongly mediated by γδ T cells. We conclude that γδ T cells amplify the innate and acquired response to α-GalCer, with possibly important outcomes for the therapeutic effects of this compound.

Protective role of IL-33/ST2 axis in Con A-induced hepatitis

BACKGROUND & AIMS

We used Concanavalin A-induced liver injury to study the role of Interleukin 33 and its receptor ST2 in the induction of inflammatory pathology and hepatocellular damage.

METHODS

We tested susceptibility to Concanavalin A induced hepatitis in ST2 deficient and wild type BALB/c mice and analyzed the effects of single injection of Interleukin 33 as evaluated by liver enzyme test, quantitative histology, mononuclear cell infiltration, cytokine production, intracellular staining of immune cells, and markers of apoptosis in the liver.

RESULTS

ST2 deficient mice developed significantly more severe hepatitis and had significantly higher number of mononuclear cells in the liver, CD4+ and CD8+ T cells, NKp46+ and CD3+NKp46+ cells, and F4/80+ macrophages. The level of pro-inflammatory cytokines in the sera and number of TNF alpha, IFN gamma, and IL-17 producing cells was higher in ST2 deficient mice. In contrast, number of CD4+Foxp3+ cells was statistically higher in wild type mice. Additionally, treatment of wild type mice with single (1 μg) injection of Interleukin 33 led to attenuation of the liver injury and milder infiltration of mononuclear cells, increase in total number of liver CD4+Foxp3+ cells and IL-4 producing CD4+ T cells. Interleukin 33 also suppressed the activation of caspase 3, prevented the expression of BAX, and enhanced the expression of antiapoptotic Bcl-2 in the liver.

CONCLUSIONS

We concluded that Interleukin 33/ST2 axis downregulated Concanavalin A-induced liver injury and should be evaluated as potential target in fulminant hepatitis in humans.

Interleukin-23 promotes natural killer T-cell production of IL-17 during rat liver transplantation

INTRODUCTION

Cytokine interleukin-17 (IL-17) is a key proinflammatory mediator promoting allograft cytokine and chemokine production. In addition to Th17 cells, natural killer T (NKT) cells have also been shown to be capable of rapidly producing IL-17 after activation.

METHODS

The levels of IL-17 and IL-23 of liver allografts were determined using enzyme-linked immunosorbent assay (ELISA). IL-17-positive cells in CD1d CD4+ cells of grafts were detected using flow cytometry.

RESULTS

High expression of IL-17 and IL-23 was observed in liver allografts. The ratios of NKT cells were dramatically increased in the allograft group compared with that in the control group (P < .01). In vitro, blockage of IL-23 using anti-IL-23 antibody can inhibit increasing expression of IL-17 (P < .01).

CONCLUSION

NKT cells contribute to production of IL-17 mediated by IL-23 on a rat acute allograft rejection model of orthotopic liver transplantation (OLT).

Vγ4 γδ T cell-derived IL-17A negatively regulates NKT cell function in Con A-induced fulminant hepatitis

Con A-induced fulminant hepatitis is a well-known animal model for acute liver failure. However, the role of γδ T cells in this model is undefined. In this report, using TCR δ(-/-) mice, we demonstrated a protective role of γδ T cells in Con A-induced hepatitis model. TCR δ(-/-) mice showed significantly decreased levels of IL-17A and IL-17F in the Con A-treated liver tissue, and reconstitution of TCR δ(-/-) mice with wild-type (Wt), but not IL-17A(-/-), γδ T cells significantly reduced hepatitis, strongly suggesting a critical role of IL-17A in mediating the protective effect of γδ T cells. Interestingly, only Vγ4, but not Vγ1, γδ T cells exerted such a protective effect. Furthermore, depletion of NKT cells in TCR δ(-/-) mice completely abolished hepatitis, and NKT cells from Con A-challenged liver tissues of TCR δ(-/-) mice expressed significantly higher amounts of proinflammatory cytokine IFN-γ than those from Wt mice, indicating that γδ T cells protected hepatitis through targeting NKT cells. Finally, abnormal capacity of IFN-γ production by NKT cells of TCR δ(-/-) mice could only be downregulated by transferring Wt, but not IL-17(-/-), Vγ4 γδ T cells, confirming an essential role of Vγ4-derived IL-17A in regulating the function of NKT cells. In summary, our report thus demonstrated a novel function of Vγ4 γδ T cells in mediating a protective effect against Con A-induced fulminant hepatitis through negatively regulating function of NKT cells in an IL-17A-dependent manner, and transferring Vγ4 γδ T cells may provide a novel therapeutic approach for this devastating liver disease.

Role of NKT cells in autoimmune liver disease

The three main broad categories of autoimmune liver disease are autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC). The etiologies of these diseases are still incompletely understood, but seem to involve a combination of immune, genetic and environmental factors. Although each of these diseases has relatively distinct clinical, serologic and histological profiles, all of them share common pathways of immune-mediated liver injury. The development of autoimmune liver diseases is thought to be due to an imbalance of proinflammatory and anti-inflammatory immune responses within the liver, with proinflammatory immune responses being upregulated and anti-inflammatory ones downregulated. The available evidence, suggest that during autoimmune responses within the liver, "self" antigens are presented by antigen presenting cells (APCs) which then activate, directly and/or indirectly, NKT cells and other innate immune cells within the liver. Importantly, the hepatic innate immune system plays an increasingly recognized role in the development and propagation of autoimmune liver injury. NKT cells predominantly reside in the liver sinusoids, and through their ability to rapidly produce a wide variety of cytokines (e.g. Th1, TH2, Th17 cytokine patterns), are a critical checkpoint that bridges innate and adaptive immune responses. Specifically, activated NKT cells are capable of transactivating other innate and adaptive immune cells within the liver to amplify and regulate subsequent immune responses within the liver. It has been hypothesized that NKT cells in the setting of autoimmune liver disease can play diverse roles, including driving both anti-inflammatory and proinflammatory responses, as well as regulating the hepatic recruitment of other types of immunoregulatory cells, including regulatory T cells.

Targeting the diverse immunological functions expressed by hepatic NKT cells

INTRODUCTION

NKT cells comprise approximately 30% of the hepatic lymphoid population in mice (∼ 50% in humans). Most mouse hepatic NKT cells [invariant (i)NKT cells] express T cell receptors, composed of invariant Vα14Jα18 chains. Unlike conventional T cells, iNKT cells recognize glycolipids presented in association with MHC class Ib (CD1d) molecules. Purportedly, iNKT cells serve key functions in several immunological events; the nature of these is often unclear. The consequences of hepatic iNKT cell activation can be beneficial or detrimental. α-Galactosylceramide stimulates the production of IFN-γ and IL-4. The reciprocal suppression exhibited by these cytokines limits the potential therapeutic value of α-galactosylceramide. Efforts are ongoing to develop α-galactosylceramide analogs that modulate iNKT cell activity and selectively promote IFN-γ or IL-4.

AREAS COVERED

An overview of hepatic iNKT cells and their purported role in liver disease. Efforts to develop therapeutic agents that promote their beneficial contributions.

EXPERT OPINION

While a growing body of literature documents the differential effects of α-GalCer analogs on IFN-γ and IL-4 production, the effects of these analogs on other iNKT cell activities remain to be determined. An exhaustive examination of the effects of these analogs on inflammation and liver injury in animal models remains prior to considering their utility in clinical trials.

Kupffer cells contribute to concanavalin A-induced hepatic injury through a Th1 but not Th17 type response-dependent pathway in mice

BACKGROUND

Increasing evidence suggests that a close interaction of Kupffer cells with T cells plays a central role in concanavalin A-induced hepatic injury in mice, but the underlying mechanisms remain obscure. The present study aimed to determine the relative roles of Th1 and Th17 type responses in concanavalin A-induced hepatic injury in mice, and to investigate whether or not Kupffer cells contribute to hepatic injury via a Th1 or Th17 type response-dependent pathway.

METHODS

Immune-mediated hepatic injury was induced in C57BL/6 mice by intravenous injection of concanavalin A. Kupffer cells were inactivated by pretreatment with gadolinium chloride 24 hours before the concanavalin A injection. The interferon-gamma (IFN-gamma) and interleukin-17 (IL-17) pathways were blocked by specific neutralizing antibodies. Hepatic injury was assessed using serum transferase activity and pathological analysis. Expression of inflammatory cytokines within the liver was detected by real-time polymerase chain reaction and immunohistochemistry.

RESULTS

Neutralization of IFN-gamma significantly attenuated concanavalin A-induced hepatic injury. However, neutralization of IL-17 failed to suppress the injury. Inactivation of Kupffer cells by gadolinium chloride pretreatment protected against concanavalin A-induced injury and significantly reduced hepatic cytokine levels including TNF-alpha, IL-6 and IFN-gamma but not IL-17.

CONCLUSION

Our findings suggest that Kupffer cells contribute to concanavalin A-induced hepatic injury via a Th1 type response-dependent pathway and production of inflammatory cytokines including TNF-alpha, IL-6 and IFN-gamma.