Invariant natural killer T cells contribute to chronic-plus-binge ethanol-mediated liver injury by promoting hepatic neutrophil infiltration

Pathogenesis of Alcohol-Associated Liver Disease

The pathogenesis of alcohol-associated liver disease (ALD) is complex and multifactorial. Several intracellular, intrahepatic, and extrahepatic factors influence development of early fatty liver injury leading to inflammation and fibrosis. Alcohol metabolism, cellular stress, and gut-derived factors contribute to hepatocyte and immune cell injury leading to cytokine and chemokine production. The pathogenesis of alcohol-associated hepatitis (AH), an advanced form of acute-on-chronic liver failure due to excessive chronic intake in patients with underlying liver disease, is not well understood. While pathogenic mechanisms in early ALD are studied, the pathogenesis of AH requires further investigation to help design effective drugs for patients.

Tim-4 alleviates acute hepatic injury by modulating homeostasis and function of NKT cells

T-cell immunoglobulin and mucin domain-containing molecule 4 (Tim-4) is an immune checkpoint molecule, which involves in numerous inflammatory diseases. Tim-4 is mainly expressed on antigen-presenting cells. However, increasing evidence has shown that Tim-4 is also expressed on natural killer T (NKT) cells. The role of Tim-4 in maintaining NKT cell homeostasis and function remains unknown. In this study, we explored the effect of Tim-4 on NKT cells in acute liver injury. This study found that Tim-4 expression on hepatic NKT cells was elevated during acute liver injury. Tim-4 deficiency enhanced IFN-γ, TNF-α expression while impaired IL-4 production in NKT cells. Loss of Tim-4 drove NKT-cell effector lineages to be skewed to NKT1 subset. Furthermore, Tim-4 KO mice were more susceptible to α-Galactosylceramide (α-GalCer) challenge. In conclusion, our findings indicate that Tim-4 plays an important role in regulating homeostasis and function of NKT cells in acute liver injury. Therefore, Tim-4 might become a new regulator of NKT cells and a potential target for the therapy of acute hepatitis.

Role of Neutrophils in the Development of Steatotic Liver Disease

This review explores the biological aspects of neutrophils, their contributions to the development of steatotic liver disease, and their potential as therapeutic targets for the disease. Although alcohol-associated and metabolic dysfunction-associated liver diseases originate from distinct etiological factors, the two diseases frequently share excessive lipid accumulation as a common contributor to their pathogenesis, thereby classifying them as types of steatotic liver disease. Dysregulated lipid deposition in the liver induces hepatic injury, triggering the activation of the innate immunity, partially through neutrophil recruitment. Traditionally recognized for their role in microbial clearance, neutrophils have recently garnered attention for their involvement in sterile inflammation, a pivotal component of steatotic liver disease pathogenesis. In conclusion, technological innovations, including single-cell RNA sequencing, have gradually disclosed the existence of various neutrophil subsets; however, how the distinct subsets of neutrophil population contribute differentially to the development of steatotic liver disease remains unclear.

Inflammation in Alcohol-Associated Hepatitis: Pathogenesis and Therapeutic Targets

Alcohol-associated hepatitis (AH) is an acute-on-chronic liver injury that occurs in patients with chronic alcohol-associated liver disease (ALD). Patients with severe AH have high short-term mortality and lack effective pharmacologic therapies. Inflammation is believed to be one of the key factors promoting AH progression and has been actively investigated as therapeutic targets over the last several decades, but no effective inflammatory targets have been identified so far. In this review, we discuss how inflammatory cells and the inflammatory mediators produced by these cells contribute to the development and progression of AH, with focus on neutrophils and macrophages. The crosstalk between inflammatory cells and liver nonparenchymal cells in the pathogenesis of AH is elaborated. We also deliberate the application of recent cutting-edge technologies in characterizing liver inflammation in AH. Finally, the potential therapeutic targets of inflammatory mediators for AH are briefly summarized.

The Role of Cytokines in the Pathogenesis and Treatment of Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a major cause of chronic liver disease. This term covers a broad spectrum of liver lesions, from simple steatosis to alcoholic hepatitis and cirrhosis. The pathogenesis of ALD is multifactorial and not fully elucidated due to complex mechanisms related to direct ethanol toxicity with subsequent hepatic and systemic inflammation. The accumulation of pro-inflammatory cytokines and the reduction of anti-inflammatory cytokines promote the development and progression of ALD. To date, there are no targeted therapies to counter the progression of chronic alcohol-related liver disease and prevent acute liver failure. Corticosteroids reduce mortality by acting on the hepatic-systemic inflammation. On the other hand, several studies analyzed the effect of inhibiting pro-inflammatory cytokines and stimulating anti-inflammatory cytokines as potential therapeutic targets in ALD. This narrative review aims to clarify the role of the main cytokines involved in the pathogenesis and treatment of ALD.

Immune cell balance as potential biomarker of progressing non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a widespread chronic, slowly progressive metabolic multifactorial disease. It is represented by several clinical and morphological forms: steatosis, nonalcoholic steatohepatitis (NASH) (with or without fibrosis), and liver cirrhosis. The search for minimally invasive and cost-effective biomarkers of NAFLD is a key task in the diagnosis, staging of progression, and long-term monitoring of NAFLD. This article discusses the possibility of using immune cell balance as potential minimally invasive peripheral markers of NAFLD progression. In the progression of NASH from steatosis to fibrosis and cirrhosis, inflammation plays an important role because of the activation of Kupffer cells and increased migration of monocytes, dendritic cells, neutrophils, and activated T lymphocytes into the tissues. Macrophages originating from monocytes, with NASH progression, gradually begin to prevail over the pool of resident macrophages. The risk of NASH and fibrosis development in patients with NAFLD increases with the ratio of neutrophils/lymphocytes in the liver. An increase in the Th17 cell count and a decrease in T-regulatory cell count can contribute to increased hepatic steatosis and inflammation development in NAFLD and accelerate the transition from simple steatosis to steatohepatitis and fibrosis. Information on the participation of noncoding RNAs in the regulation of the balance of immune cells in NAFLD is presented, which also allows us to consider them as additional, along with cellular, markers of disease progression.

Ethanol changes Nestin-promoter induced neural stem cells to disturb newborn dendritic spine remodeling in the hippocampus of mice

Adolescent binge drinking leads to long-lasting disorders of the adult central nervous system, particularly aberrant hippocampal neurogenesis. In this study, we applied in vivo fluorescent tracing using NestinCreERT2::Rosa26-tdTomato mice and analyzed the endogenous neurogenesis lineage progression of neural stem cells (NSCs) and dendritic spine formation of newborn neurons in the subgranular zone of the dentate gyrus. We found abnormal orientation of tamoxifen-induced tdTomato+ (tdTom+) NSCs in adult mice 2 months after treatment with EtOH (5.0 g/kg, i.p.) for 7 consecutive days. EtOH markedly inhibited tdTom+ NSCs activation and hippocampal neurogenesis in mouse dentate gyrus from adolescence to adulthood. EtOH (100 mM) also significantly inhibited the proliferation to 39.2% and differentiation of primary NSCs in vitro. Adult mice exposed to EtOH also exhibited marked inhibitions in dendritic spine growth and newborn neuron maturation in the dentate gyrus, which was partially reversed by voluntary running or inhibition of the mammalian target of rapamycin-enhancer of zeste homolog 2 pathway. In vivo tracing revealed that EtOH induced abnormal orientation of tdTom+ NSCs and spatial misposition defects of newborn neurons, thus causing the disturbance of hippocampal neurogenesis and dendritic spine remodeling in mice.

Single-cell transcriptomics of peripheral blood mononuclear cells indicates impaired immune and inflammatory responses in alcohol-associated hepatitis

Alcohol-associated hepatitis (AH) is often diagnosed at advanced stages, and severe AH usually carries poor prognosis and high short-term mortality. In addition, it is challenging to understand the molecular mechanisms of immune dysregulation and inflammation in AH due to the cellular complexity and heterogeneity. Using single-cell RNA sequencing, previous studies found that AH causes dysfunctional innate immune response in monocytes, involving activation of pattern recognition receptors (PRRs) and cytokine signaling pathways. To better understand the coordinated systemic immune response in AH patients, we performed combined single-cell transcriptome, cell-surface protein, and lymphocyte antigen receptor analysis of peripheral blood mononuclear cell (PBMC) samples. Our results showed inflammatory cytokines and chemokines were highly expressed in AH, including IL-2, IL-32, CXC3R1 and CXCL16 in monocytes and NK cells, whereas HLA-DR genes were reduced in monocytes. In addition, we also found altered differentiation of T-helper cells (TH1 and TH17), which could further lead to neutrophil recruitment and macrophage activation. Lastly, our results also suggest impaired NK-cell activation and differentiation in AH with reduced gene expression of KLRC2 and increased gene expression of KLRG1. Our findings indicate different mechanisms may be involved in impaired immune and inflammatory responses for the cellular subtypes of the PBMCs in AH.

Therapeutic potential of stem cells in regeneration of liver in chronic liver diseases: Current perspectives and future challenges

The deposition of extracellular matrix and hyperplasia of connective tissue characterizes chronic liver disease called hepatic fibrosis. Progression of hepatic fibrosis may lead to hepatocellular carcinoma. At this stage, only liver transplantation is a viable option. However, the number of possible liver donors is less than the number of patients needing transplantation. Consequently, alternative cell therapies based on non-stem cells (e.g., fibroblasts, chondrocytes, keratinocytes, and hepatocytes) therapy may be able to postpone hepatic disease, but they are often ineffective. Thus, novel stem cell-based therapeutics might be potentially important cutting-edge approaches for treating liver diseases and reducing patient' suffering. Several signaling pathways provide targets for stem cell interventions. These include pathways such as TGF-β, STAT3/BCL-2, NADPH oxidase, Raf/MEK/ERK, Notch, and Wnt/β-catenin. Moreover, mesenchymal stem cells (MSCs) stimulate interleukin (IL)-10, which inhibits T-cells and converts M1 macrophages into M2 macrophages, producing an anti-inflammatory environment. Furthermore, it inhibits the action of CD4+ and CD8+ T cells and reduces the activity of TNF-α and interferon cytokines by enhancing IL-4 synthesis. Consequently, the immunomodulatory and anti-inflammatory capabilities of MSCs make them an attractive therapeutic approach. Importantly, MSCs can inhibit the activation of hepatic stellate cells, causing their apoptosis and subsequent promotion of hepatocyte proliferation, thereby replacing dead hepatocytes and reducing liver fibrosis. This review discusses the multidimensional therapeutic role of stem cells as cell-based therapeutics in liver fibrosis.

Sex-based differences in natural killer T cell-mediated protection against diet-induced steatohepatitis in Balb/c mice

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is prevalent in Western countries, evolving into metabolic dysfunction-associated steatohepatitis (MASH) with a sexual dimorphism. Fertile women exhibit lower MASLD risk than men, which diminishes post-menopause. While NKT-cell involvement in steatohepatitis is debated, discrepancies may stem from varied mouse strains used, predominantly C57BL6/J with Th1-dominant responses. Exploration of steatohepatitis, encompassing both genders, using Balb/c background, with Th2-dominant immune response, and CD1d-deficient mice in the Balb/c background (lacking Type I and Type II NKT cells) can clarify gender disparities and NKT-cell influence on MASH progression.

METHODS

A high fat and choline-deficient (HFCD) diet was used in male and female mice, Balb/c mice or CD1d-/- mice in the Balb/c background that exhibit a Th2-dominant immune response. Liver fibrosis and inflammatory gene expression were measured by qPCR, and histology assessment. NKT cells, T cells, macrophages and neutrophils were assessed by flow cytometry.

RESULTS

Female mice displayed milder steatohepatitis after 6 weeks of HFCD, showing reduced liver damage, inflammation, and fibrosis compared to males. Male Balb/c mice exhibited NKT-cell protection against steatohepatitis whereas CD1d-/- males on HFCD presented decreased hepatoprotection, increased liver fibrosis, inflammation, neutrophilic infiltration, and inflammatory macrophages. In contrast, the NKT-cell role was negligible in early steatohepatitis development in both female mice, as fibrosis and inflammation were similar despite augmented liver damage in CD1d-/- females. Relevant, hepatic type I NKT levels in female Balb/c mice were significantly lower than in male.

CONCLUSIONS

NKT cells exert a protective role against experimental steatohepatitis as HFCD-treated CD1d-/- males had more severe fibrosis and inflammation than male Balb/c mice. In females, the HFCD-induced hepatocellular damage and the immune response are less affected by NKT cells on early steatohepatitis progression, underscoring sex-specific NKT-cell influence in MASH development.

New insights into the molecular basis of alcohol abstinence and relapse in alcohol-associated liver disease

Alcohol use disorder remains a significant public health concern, affecting around 5% of adults worldwide. Novel pathways of damage have been described during the last years, providing insight into the mechanism of injury due to alcohol misuse beyond the direct effect of ethanol byproducts on the liver parenchyma and neurobehavioral mechanisms. Thus, the gut-liver-brain axis and immune system involvement could be therapeutic targets for alcohol use disorder. In particular, changes in gut microbiota composition and function, and bile acid homeostasis, have been shown with alcohol consumption and cessation. Alcohol can also directly disrupt intestinal and blood-brain barriers. Activation of the immune system can be triggered by intestinal barrier dysfunction and translocation of bacteria, pathogen-associated molecular patterns (such as lipopolysaccharide), cytokines, and damage-associated molecular patterns. These factors, in turn, promote liver and brain inflammation and the progression of liver fibrosis. Other involved mechanisms include oxidative stress, apoptosis, autophagy, and the release of extracellular vesicles and miRNA from hepatocytes. Potential therapeutic targets include gut microbiota (probiotics and fecal microbiota transplantation), neuroinflammatory pathways, as well as neuroendocrine pathways, for example, the ghrelin system (ghrelin receptor blockade), incretin mimetics (glucagon-like peptide-1 analogs), and the mineralocorticoid receptor system (spironolactone). In addition, support with psychological and behavioral treatments is essential to address the multiple dimensions of alcohol use disorder. In the future, a personalized approach considering these novel targets can contribute to significantly decreasing the alcohol-associated burden of disease.

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.

Interleukin-1 family cytokines in liver cell death: a new therapeutic target for liver diseases

INTRODUCTION

Liver cell death represents a basic biological process regulating the progression of liver diseases via distinct mechanisms. Accumulating evidence has uncovered participation of interleukin (IL)-1 family cytokines in liver cell death. Upon activation of cell death induced by hepatotoxic stimuli, IL1 family cytokines released by hepatic dead cells stimulate recruitment of immune cells, which in turn influence inflammation and subsequent liver injury, thus highlighting their potential as therapeutic targets in liver diseases. Enhancing our comprehension of mechanisms underlying IL1 family cytokine signaling in cell death responses could pave the way for novel therapeutic interventions aimed at addressing liver cell death-related liver pathologies.

AREAS COVERED

This review summarizes the recent findings reported in preclinical and clinical studies on mechanisms of liver cell death, alongside participation of IL1 family members consisting of IL1α, ILβ, IL18, and IL33 in liver cell death and their significant implications in liver diseases.

EXPERT OPINION

Discovery of new and innovative therapeutic approaches for liver diseases will need close cooperation between fundamental and clinical scientists to better understand the multi-step processes behind IL1 family cytokines' contributions to liver cell death.

Experimental models of fatty liver diseases: Status and appraisal

Fatty liver diseases, including alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease nonalcoholic fatty liver disease (NAFLD), affect a large number of people worldwide and become one of the major causes of end-stage liver disease, such as liver cirrhosis and hepatocellular carcinoma (HCC). Unfortunately, there are currently no approved pharmacological treatments for ALD or NAFLD. This situation highlights the urgent need to explore new intervention targets and discover effective therapeutics for ALD and NAFLD. The lack of properly validated preclinical disease models is a major obstacle to the development of clinical therapies. ALD and NAFLD models have been in the development for decades, but there are still no models that recapitulate the full spectrum of ALD and NAFLD. Throughout this review, we summarize the current in vitro and in vivo models used for research on fatty liver diseases and discuss the advantages and limitations of these models.

Altered Frequency, Activation, and Clinical Relevance of Circulating Innate and Innate-Like Lymphocytes in Patients With Alcoholic Liver Cirrhosis

Alcoholic liver cirrhosis (ALC) is caused by chronic alcohol overconsumption and might be linked to dysregulated immune responses in the gut-liver axis. However, there is a lack of comprehensive research on levels and functions of innate lymphocytes including mucosal-associated invariant T (MAIT) cells, NKT cells, and NK (NK) cells in ALC patients. Thus, the aim of this study was to examine the levels and function of these cells, evaluate their clinical relevance, and explore their immunologic roles in the pathogenesis of ALC. Peripheral blood samples from ALC patients (n = 31) and healthy controls (HCs, n = 31) were collected. MAIT cells, NKT cells, NK cells, cytokines, CD69, PD-1, and lymphocyte-activation gene 3 (LAG-3) levels were measured by flow cytometry. Percentages and numbers of circulating MAIT cells, NKT cells, and NK cells were significantly reduced in ALC patients than in HCs. MAIT cell exhibited increased production of IL-17 and expression levels of CD69, PD-1, and LAG-3. NKT cells displayed decreased production of IFN-γ and IL-4. NK cells showed elevated CD69 expression. Absolute MAIT cell levels were positively correlated with lymphocyte count but negatively correlated with C-reactive protein. In addition, NKT cell levels were negatively correlated with hemoglobin levels. Furthermore, log-transformed absolute MAIT cell levels were negatively correlated with the Age, Bilirubin, INR, and Creatinine score. This study demonstrates that circulating MAIT cells, NKT cells, and NK cells are numerically deficient in ALC patients, and the degree of cytokine production and activation status also changed. Besides, some of their deficiencies are related to several clinical parameters. These findings provide important information about immune responses of ALC patients.

New Insight into the Concanavalin A-Induced Apoptosis in Hepatocyte of an Animal Model: Possible Involvement of Caspase-Independent Pathway

Concanavalin A (Con A) is known to be a T-cell mitogen and has been shown to induce hepatitis in mice through the triggering of conventional T cells and NKT cells. However, it remains unknown whether Con A itself can directly induce rapid hepatocyte death in the absence of a functional immune system. Here, by using an immunodeficient mouse model, we found Con A rapidly induced liver injury in vivo despite a lack of immunocyte involvement. We further observed in vitro that hepatocytes underwent a dose-dependent but caspase-independent apoptosis in response to Con A stimulation in vitro. Moreover, transcriptome RNA-sequencing analysis revealed that apoptosis pathways were activated in both our in vivo and in vitro models. We conclude that Con A can directly induce rapid but non-classical apoptosis in hepatocytes without the participation of immunocytes. These findings provide new insights into the mechanism of Con A-induced hepatitis.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

Therapeutic Perspectives of IL1 Family Members in Liver Diseases: An Update

Interleukin (IL) 1 superfamily members are a cornerstone of a variety of inflammatory processes occurring in various organs including the liver. Progression of acute and chronic liver diseases regardless of etiology depends on the stage of hepatocyte damage, the release of inflammatory cytokines and disturbances in gut microbiota. IL1 cytokines and receptors can have pro- or anti-inflammatory roles, even dual functionalities conditioned by the microenvironment. Developing novel therapeutic strategies to block the IL1/IL1R signaling pathways seems like a reasonable option. This mode of action is now exploited by anakinra and canakinumab, which are used to treat different inflammatory illnesses, and studies in liver diseases are on the way. In this mini review, we have focused on the IL1 superfamily members, given their crucial role in liver inflammation diseases, specifically discussing their potential role in developing new treatment strategies.

The Tumor Microenvironment of Hepatocellular Carcinoma: Untying an Intricate Immunological Network

HCC, the most prevalent form of primary liver cancer, is prototypically an inflammation-driven cancer developing after years of inflammatory insults. Consequently, the hepatic microenvironment is a site of complex immunological activities. Moreover, the tolerogenic nature of the liver can act as a barrier to anti-tumor immunity, fostering cancer progression and resistance to immunotherapies based on immune checkpoint inhibitors (ICB). In addition to being a site of primary carcinogenesis, many cancer types have high tropism for the liver, and patients diagnosed with liver metastasis have a dismal prognosis. Therefore, understanding the immunological networks characterizing the tumor microenvironment (TME) of HCC will deepen our understanding of liver immunity, and it will underpin the dominant mechanisms controlling both spontaneous and therapy-induced anti-tumor immune responses. Herein, we discuss the contributions of the cellular and molecular components of the liver immune contexture during HCC onset and progression by underscoring how the balance between antagonistic immune responses can recast the properties of the TME and the response to ICB.

Mesenchymal stem cells-based therapy in liver diseases

Multiple immune cells and their products in the liver together form a complex and unique immune microenvironment, and preclinical models have demonstrated the importance of imbalances in the hepatic immune microenvironment in liver inflammatory diseases and immunocompromised liver diseases. Various immunotherapies have been attempted to modulate the hepatic immune microenvironment for the purpose of treating liver diseases. Mesenchymal stem cells (MSCs) have a comprehensive and plastic immunomodulatory capacity. On the one hand, they have been tried for the treatment of inflammatory liver diseases because of their excellent immunosuppressive capacity; On the other hand, MSCs have immune-enhancing properties in immunocompromised settings and can be modified into cellular carriers for targeted transport of immune enhancers by genetic modification, physical and chemical loading, and thus they are also used in the treatment of immunocompromised liver diseases such as chronic viral infections and hepatocellular carcinoma. In this review, we discuss the immunological basis and recent strategies of MSCs for the treatment of the aforementioned liver diseases. Specifically, we update the immune microenvironment of the liver and summarize the distinct mechanisms of immune microenvironment imbalance in inflammatory diseases and immunocompromised liver diseases, and how MSCs can fully exploit their immunotherapeutic role in liver diseases with both immune imbalance patterns.

New insights into iNKT cells and their roles in liver diseases

Natural killer T cells (NKTs) are an important part of the immune system. Since their discovery in the 1990s, researchers have gained deeper insights into the physiology and functions of these cells in many liver diseases. NKT cells are divided into two subsets, type I and type II. Type I NKT cells are also named iNKT cells as they express a semi-invariant T cell-receptor (TCR) α chain. As part of the innate immune system, hepatic iNKT cells interact with hepatocytes, macrophages (Kupffer cells), T cells, and dendritic cells through direct cell-to-cell contact and cytokine secretion, bridging the innate and adaptive immune systems. A better understanding of hepatic iNKT cells is necessary for finding new methods of treating liver disease including autoimmune liver diseases, alcoholic liver diseases (ALDs), non-alcoholic fatty liver diseases (NAFLDs), and liver tumors. Here we summarize how iNKT cells are activated, how they interact with other cells, and how they function in the presence of liver disease.

Advancements in the Alcohol-Associated Liver Disease Model

Alcohol-associated liver disease (ALD) is an intricate disease that results in a broad spectrum of liver damage. The presentation of ALD can include simple steatosis, steatohepatitis, liver fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). Effective prevention and treatment strategies are urgently required for ALD patients. In previous decades, numerous rodent models were established to investigate the mechanisms of alcohol-associated liver disease and explore therapeutic targets. This review provides a summary of the latest developments in rodent models, including those that involve EtOH administration, which will help us to understand the characteristics and causes of ALD at different stages. In addition, we discuss the pathogenesis of ALD and summarize the existing in vitro models. We analyse the pros and cons of these models and their translational relevance and summarize the insights that have been gained regarding the mechanisms of alcoholic liver injury.

Diallyl disulfide ameliorates ethanol-induced liver steatosis and inflammation by maintaining the fatty acid catabolism and regulating the gut-liver axis

Diallyl disulfide (DADS) has been suggested to possess hepatoprotection against alcoholic liver disease (ALD) by a couple of pilot studies, while the underlying mechanisms remain largely unknown. This study aimed to investigate the hepatoprotective effects of DADS against ethanol-induced liver steatosis and early inflammation by using the chronic-plus-binge mice model and cultured J774A.1 macrophages and AML12 hepatocytes. We found that DADS significantly attenuated ethanol-induced elevation of serum aminotransferase activities, accumulation of liver triglyceride, hepatocytes apoptosis, oxidative stress, infiltration of macrophages and neutrophils, and proinflammatory polarization of macrophages in mice livers. In addition, chronic-plus-binge drinking induced apparent intestinal mucosa damage and disturbance of gut microbiota, endotoxemia, and activation of hepatic NF-κB signaling and NLRP3 inflammasome, which was inhibited by DADS. In vitro studies using cocultured AML12/J774A.1 cells showed that DADS suppressed ethanol/LPS-induced cell injury and inflammatory activation of macrophages. Furthermore, DADS ameliorated ethanol-induced decline of peroxisome proliferator-activated receptor α (PPARα), carnitine palmitoyltransferase 1 (CPT1), and phosphorylated AMP-activated protein kinase (AMPK) protein levels in mice liver and AML12 cells. These results demonstrate that DADS could prevent ethanol-induced liver steatosis and early inflammation by regulating the gut-liver axis and maintaining fatty acid catabolism.

Molecular Mechanisms of Clonorchis sinensis-Host Interactions and Implications for Vaccine Development

Infections caused by Clonorchis sinensis remain a significant public health challenge for both humans and animals, causing pyogenic cholangitis, cholelithiasis, cholecystitis, biliary fibrosis, and even cholangiocarcinoma. However, the strategies used by the parasite and the immunological mechanisms used by the host have not yet been fully understood. With the advances in technologies and the accumulated knowledge of host-parasite interactions, many vaccine candidates against liver flukes have been investigated using different strategies. In this review, we explore and analyze in-depth the immunological mechanisms involved in the pathogenicity of C. sinensis. We highlight the different mechanisms by which the parasite interacts with its host to induce immune responses. All together, these data will allow us to have a better understanding of molecular mechansism of host-parasite interactions, which may shed lights on the development of an effective vaccine against C. sinensis.

Crosstalk between Oxidative Stress and Inflammatory Liver Injury in the Pathogenesis of Alcoholic Liver Disease

Alcoholic liver disease (ALD) is characterized by the injury, inflammation, and scarring in the liver owing to excessive alcohol consumption. Currently, ALD is a leading cause for liver transplantation. Therefore, extensive studies (in vitro, in experimental ALD models and in humans) are needed to elucidate pathological features and pathogenic mechanisms underlying ALD. Notably, oxidative changes in the liver have been recognized as a signature trait of ALD. Progression of ALD is linked to the generation of highly reactive free radicals by reactions involving ethanol and its metabolites. Furthermore, hepatic oxidative stress promotes tissue injury and, in turn, stimulates inflammatory responses in the liver, forming a pathological loop that promotes the progression of ALD. Accordingly, accumulating further knowledge on the relationship between oxidative stress and inflammation may help establish a viable therapeutic approach for treating ALD.

Pathogenesis of Concanavalin A induced autoimmune hepatitis in mice

Autoimmune hepatitis (AIH) is an autoimmune disease characterized by liver parenchymal destruction and chronic fibrosis. Its exact etiology and pathogenesis are not yet fully understood.(Please connect with the following, do not leave a line) Concanavalin A (Con A)-induced mice hepatitis model is a liver injury mediated by T cell and macrophage activation, and its pathogenesis and pathological changes are similar to human AIH. The establishment of this model has greatly promoted the research progress of AIH pathogenesis. However, the exact mechanism of Con A induced liver injury in mice, and its possible defects or deficiencies, has not yet been described in a clear and detailed manner. Therefore, the model has some limitations when applied to the study of the pathogenesis and treatment mechanism of AIH. This article reveals the pathogenesis of Con A induced liver injury in mice from the aspects of immune disorder and coagulation mechanism, expounds the significance of non-coding RNA in this model, summarizes the signal transduction pathways involved in this model, and summarizes the advantages and disadvantages of the model, which provides a theoretical basis and research target for the application of Con A induced liver injury model in AIH in the future.

Characterization of lymphocyte subsets in ascitic fluid and peripheral blood of decompensated cirrhotic patients with chronic hepatitis C and alcoholic liver disease: A pivotal study

Hepatitis C virus and alcoholic liver disease are major causes of chronic liver diseases worldwide. Little is known about differences between chronic hepatitis C and alcoholic liver disease in terms of lymphocytes’ sub-population. Aim of the present study was to compare the sub-populations of lymphocytes in both ascitic compartment and peripheral blood in patients with decompensated liver cirrhosis due to chronic hepatitis C and alcoholic liver disease. Patients with decompensated liver cirrhosis due to hepatitis C virus or alcoholic liver disease evaluated from April 2014 to October 2016 were enrolled. Whole blood and ascitic fluid samples were stained with monoclonal antibodies specific for human TCRɑβ, TCRɣδ, CD3, CD4, CD8, CD19, CCR6, CD16, CD56, CD25, HLA-DR, Vɑ24. Sixteen patients with decompensated liver cirrhosis were recruited (9 with hepatitis C virus and 7 with alcoholic liver disease). In ascitic fluid, the percentage of both CD3⁺CD56⁻ and CD3⁺CD56⁺iNKT cells resulted higher in hepatitis C virus patients than in alcoholic liver disease patients (1.82 ± 0.35% vs 0.70 ± 0.42% (p < 0.001) and 1.42 ± 0.35% vs 0.50 ± 0.30% (p < 0.001), respectively). Conversely, in peripheral blood samples, both CD3⁺CD56⁻ and CD3⁺CD56⁺iNKT cells resulted significantly higher in alcoholic liver disease than in hepatitis C virus patients (4.70 ± 2.69% vs 1.50 ± 1.21% (p < 0.01) and 3.10 ± 1.76% vs 1.00 ± 0.70% (p < 0.01), respectively). Both elevation of iNKT cells in ascitic fluid and reduction in peripheral blood registered in hepatitis C virus but not in alcoholic liver disease patients might be considered indirect signals of tissutal translocation. In conclusion, we described relevant differences between the two groups. Alcoholic liver disease patients displayed lower number of CD3⁺CD4⁺ cells and a higher percentage of CD3⁻CD16⁺, Vα24⁺CD3⁺CD56⁻ and Vα24⁺CD3⁺CD56⁺iNKT cells in ascitic fluid than hepatitis C virus positive subjects. Further studies might analyze the role of immune cells in the vulnerability toward infections and detect potential targets for new treatments especially for alcoholic liver disease patients.

Natural Killer T Cells in Various Mouse Models of Hepatitis

Natural killer T (NKT) cells are a key component of innate immunity. Importantly, a growing body of evidence indicates that NKT cells play an integral role in various acute and chronic liver injuries. NKT cells participate in the progression of an injury through the secretion of cytokines, which promote neutrophil infiltration and enhance Fas ligand (FasL) and granzyme-mediated NKT cytotoxic activity. Therefore, examining the role of NKT cells in hepatic disease is critical for a comprehensive understanding of disease pathogenesis and may provide insight into novel approaches for treatment. For more than a century, mouse models that imitate the physiopathological conditions of human disease have served as a critical tool in biological and medical basic research, including studies of liver disease. Here, we review the role of NKT cells in various mouse models of hepatitis.

Role of Neutrophils in the Pathogenesis of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) includes a spectrum of liver disorders, from fatty liver to nonalcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma. Compared with fatty liver, NASH is characterized by increased liver injury and inflammation, in which liver-infiltrating immune cells, with neutrophil infiltration as a hallmark of NASH, play a critical role in promoting the progression of fatty liver to NASH. Neutrophils are the first responders to injury and infection in various tissues, establishing the first line of defense through multiple mechanisms such as phagocytosis, cytokine secretion, reactive oxygen species production, and neutrophil extracellular trap formation; however, their roles in the pathogenesis of NASH remain obscure. The current review summarizes the roles of neutrophils that facilitate the progression of fatty liver to NASH and their involvement in inflammation resolution during NASH pathogenesis. The notion that neutrophils are potential therapeutic targets for the treatment of NASH is also discussed.

DX5+ NKT cells' increase was correlated with liver damage in FVB mice not in BALB/c mice infected by Clonorchis sinensis

AIMS

DX5⁺ NKT cells' distribution and population change in BALB/c and FVB mice infected by C sinensis and their function in liver damage were investigated.

METHODS AND RESULTS

Mice were infected by Clonorchis sinensis metacercariae, and lymphocytes were isolated from the livers, spleens and peripheral blood. NK, DX5⁺ NKT, INF-γ⁺ DX5⁺ NKT cells and liver fibrosis were analysed. The DX5⁺ NKT cells displayed the largest amount in normal BALB/c mice liver followed by peripheral blood and spleen. Although the hepatic DX5⁺ NKT cells of BALB/c mice were more than that of FVB mice, they did not show significant percentage change after C sinensis infection. The hepatic DX5⁺ NKT cells of FVB mice increased remarkably after infection accompanied with heavier liver injury and fibrosis than the BALB/c mice. And hydroxyproline content was also positively correlated with DX5⁺ NKT cells only in FVB mice. However, the increase of IFN-γ producing DX5⁺ NKT cells was lower in FVB mice than in BALB/c mice which showed sharp increase with mild liver damage after infection. The frequencies of anti-fibrotic NK cells were similar in both of the two mouse strains.

CONCLUSIONS

C sinensis could induce different DX5⁺ NKT cells responses in different mouse strains which may play roles in liver injury and fibrosis in FVB mice.

High Frequency of Gamma Interferon-Producing PLZFloRORγtlo Invariant Natural Killer 1 Cells Infiltrating Herpes Simplex Virus 1-Infected Corneas Is Associated with Asymptomatic Ocular Herpesvirus Infection

Invariant natural killer (iNKT) cells are among the first innate immune cells to elicit early protective immunity that controls invading viral pathogens. The role of the iNKT cell subsets iNKT1, iNKT2, and iNKT17 in herpesvirus immunity remains to be fully elucidated. In this study, we examined the protective role of cornea-resident iNKT cell subsets using the mouse model of ocular herpesvirus infection and disease. Wild-type (WT) C57BL/6 (B6) mice and CD1d knockout (KO) mice were infected ocularly with herpes simplex virus 1 (HSV-1) (strain McKrae). Cornea, spleen, and liver were harvested at 0, 2, 5, 8, and 14 days postinfection (p.i.), and the frequency and function of the three major iNKT cell subsets were analyzed and correlated with symptomatic and asymptomatic corneal herpesvirus infections. The profiles of 16 major pro- and anti-inflammatory cytokines were analyzed in corneal lysates using Western blot and Luminex assays. Early during ocular herpesvirus infection (i.e., day 2), the gamma interferon (IFN-γ)-producing PLZFloRORγtlo (promyelocytic leukemia zinc finger, retinoic acid-related orphan receptor gT) iNKT1 cell subset was the predominant iNKT cell subset in infected asymptomatic corneas. Moreover, compared to the asymptomatic corneas of HSV-1-infected WT mice, the symptomatic corneas CD1d KO mice, with iNKT cell deficiency, had increased levels of the inflammatory cytokine interleukin-6 (IL-6) and decreased levels of IL-12, IFN-γ, and the JAK1, STAT1, NF-κB, and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways. Our findings suggest that IFN-γ-producing PLZFloRORγtlo iNKT1 cells play a role in the protective innate immune response against symptomatic ocular herpes.IMPORTANCE We investigated the protective role of iNKT cell subsets in asymptomatic ocular herpesvirus infection. We found that early during ocular herpesvirus infection (i.e., on day 2 postinfection), IFN-γ-producing PLZFloRORγtlo iNKT1 cells were the predominant iNKT cell subset in infected corneas of asymptomatic B6 mice (with little to no corneal herpetic disease), compared to corneas of symptomatic mice (with severe corneal herpetic disease). Moreover, compared to asymptomatic corneas of wild-type (WT) B6 mice, the symptomatic corneas of CD1d KO mice, which lack iNKT cells, showed (i) decreases in the levels of IFN-γ and IL-12, (ii) an increase in the level of the inflammatory cytokine IL-6; and (iii) downregulation of the JAK1, STAT1, NF-κB, and ERK1/2 pathways. The findings suggest that early during ocular herpesvirus infection, cornea-resident IFN-γ-producing PLZFloRORγtlo iNKT1 cells provide protection from symptomatic ocular herpes.

Differential Activation of Unconventional T Cells, Including iNKT Cells, in Alcohol-Related Liver Disease

BACKGROUND

Liver is enriched in several innate-like unconventional T cells, but their role in alcohol-related liver disease (ALD) is not fully understood. Studies in several acute alcohol feeding models but not in chronic alcoholic steatohepatitis (ASH) model have shown that invariant natural killer T (iNKT) cells play a pathogenic role in ALD. Here, we investigated the activation of iNKT cells in an intragastric (iG) infusion model of chronic ASH as well as the frequency and cytokine phenotype of 3 different unconventional T cells: iNKT, mucosal-associated invariant T (MAIT), and CD8⁺ CD161^hi Vα7.2^- cells in peripheral blood of ALD patients.

METHODS

Hepatic iNKT cells were investigated using the iG model of chronic ASH that combines feeding of high-cholesterol/high-fat diet (HCFD) with intragastric feeding of ethanol diet (HCFD + iG Alc). Human iNKT, MAIT, and CD8⁺ CD161^hi Vα7.2^- cells were examined by flow cytometry in peripheral blood of patients with severe alcoholic hepatitis (SAH) and chronic alcoholics (ChA) and compared with healthy controls.

RESULTS

In the iG model of chronic ASH, IFNγ⁺ iNKT cells accumulate in their livers compared with pair-fed control mice and activated hepatic iNKT cells show high expression of Fas and FasL. Notably, IFNγ⁺ iNKT cells are also significantly increased in peripheral blood of ChA patients compared with SAH patients. MAIT cells are significantly reduced in all ALD patients, but CD8⁺ CD161^hi Vα7.2^- cells are increased in SAH patients. Although MAIT and CD8⁺ CD161^hi Vα7.2^- cells displayed a similar cytokine production profile, the production of IFNγ and TNFα is significantly increased in SAH patients, while significant IL-17A production is found in ChA patients.

CONCLUSIONS

We found that the 3 unconventional T cells are activated in ALD patients showing interesting differences in their frequency and cytokine production profile between SAH and ChA patients. In the iG murine model of chronic ASH, iNKT cells are also activated secreting proinflammatory cytokines suggesting their involvement in liver disease.

Mouse Model of Alcoholic Steatohepatitis

Alcoholic liver disease (ALD) is one of the most common causes of chronic liver disease in Western countries. The spectrum of ALD ranges from simple steatosis to steatohepatitis to cirrhosis and hepatocellular carcinoma. Over the past 50 years, several animal models of ALD have been developed. Although none of them faithfully recapitulates the human disease, they have proven to be invaluable tools to study the pathogenesis of ALD, to identify potential therapeutic targets and to test new drugs. Here, we describe the mouse model of chronic and binge ethanol feeding, also known as the NIAAA model or Gao binge model. This model combines chronic feeding of Lieber-DeCarli ethanol liquid diet with acute administration of high-dose ethanol by oral gavage to mimic the drinking patterns of many alcoholic patients who engage in episodes of binge drinking on top of chronic daily drinking. Short-term (10-day) chronic plus single binge ethanol feeding causes a substantial increase in serum transaminase levels, moderate steatosis and mild inflammation characterized by lobular neutrophil infiltration. Long-term (8-week) chronic plus single or multiple (twice a week) binge ethanol feeding induce more severe steatohepatitis and mild fibrosis. This clinically relevant, easy-to-perform model of ALD is currently used by many research laboratories to reproduce early stages of human alcoholic steatohepatitis.

Interleukin-1 Family Cytokines: Keystones in Liver Inflammatory Diseases

The pyrogenic property being the first activity described, members of the interleukin-1 superfamily (IL-1α, IL-1β, IL-18, and the newest members: IL-33, IL-36, IL-37, and IL-38) are now known to be involved in several inflammatory diseases such as obesity, atherosclerosis, cancer, viral and parasite infections, and auto-inflammatory syndromes as well as liver diseases. Inflammation processes are keystones of chronic liver diseases, of which the etiology may be viral or toxic, as in alcoholic or non-alcoholic liver diseases. Inflammation is also at stake in acute liver failure involving massive necrosis, and in ischemia-reperfusion injury in the setting of liver transplantation. The role of the IL-1 superfamily of cytokines and receptors in liver diseases can be either protective or pro-inflammatory, depending on timing and the environment. Our review provides an overview of current understanding of the IL-1 family members in liver inflammation, highlighting recent key investigations, and therapeutic perspectives. We have tried to apply the concept of trained immunity to liver diseases, based on the role of the members of the IL-1 superfamily, first of all IL-1β but also IL-18 and IL-33, in modulating innate lymphoid immunity carried by natural killer cells, innate lymphoid cells or innate T-αβ lymphocytes.

Recent Insights Into the Role of Immune Cells in Alcoholic Liver Disease

Accumulating clinical and experimental evidences have demonstrated that both innate and adaptive immunity are involved in the pathogenesis of alcoholic liver disease (ALD), in which the role of immunity is to fuel the inflammation and to drive the progression of ALD. Various immune cells are implicated in the pathogenesis of ALD. The activation of innate immune cells induced by alcohol and adaptive immune response triggered by oxidative modification of hepatic constituents facilitate the persistent hepatic inflammation. Meanwhile, the suppressed antigen-presenting capability of various innate immune cells and impaired function of T cells may consequently lead to an increased risk of infection in the patients with advanced ALD. In this review, we summarized the significant recent findings of immune cells participating in ALD. The pathways and molecules involved in the regulation of specific immune cells, and novel mediators protecting the liver from alcoholic injury via affecting these cells are particularly highlighted. This review aims to update the knowledge about immunity in the pathogenesis of ALD, which may facilitate to enhancement of currently available interventions for ALD treatment.

Hyperactivated peripheral invariant natural killer T cells correlate with the progression of HBV-relative liver cirrhosis

Invariant NKT (iNKT) cells express markers of both T and NK cells and may produce various cytokines to regulate liver immunity. However, the role of iNKT cells in the progression of HBV-relative liver cirrhosis (HBV-LC) is incompletely understood. Here, we investigated the impact of peripheral iNKT cells on a cohort of patients with HBV-LC. The frequency, number, activation status, apoptosis and proliferation ability of peripheral iNKT cells were detected with flow cytometry. The impact of peripheral iNKT cells on the proliferation of hepatocyte cell line (MIHA) and activation of hepatic stellate cell line (LX-2) was detected with flow cytometry and PCR. In HBV-LC patients, the frequency and absolute number of peripheral iNKT cells significantly reduced, but the expression levels of CD25, interleukin (IL)-4, IL-13 and interferon (IFN)-γ increased. No difference was observed in the proliferation and apoptosis of circulating iNKT cells between patients and healthy controls (HCs). CXCR6 (CD186), known to be closely associated with iNKT cells migration from the periphery to the liver, was highly expressed on peripheral iNKT cells in HBV-LC patients. Furthermore, peripheral iNKT cells had a profound impact on MIHA cell proliferation and LX-2 cell activation through IL-4 or IL-13. Our data suggest that in HBV-LC patients, highly activated peripheral iNKT cells may migrate to the liver and affect hepatocyte cell line (MIHA) proliferation and hepatic stellate cell line (LX-2) activation through the expression of type 2 cytokines, which may result in excessive healing and contributing to the progression of fibrosis toward cirrhosis in liver.

Inflammatory pathways in alcoholic steatohepatitis

Inflammatory processes are primary contributors to the development and progression of alcoholic steatohepatitis (ASH), with severe alcoholic hepatitis characterised by non-resolving inflammation. Inflammation in the progression of ASH is a complex response to microbial dysbiosis, loss of barrier integrity in the intestine, hepatocellular stress and death, as well as inter-organ crosstalk. Herein, we review the roles of multiple cell types that are involved in inflammation in ASH, including resident macrophages and infiltrating monocytes, as well as other cell types in the innate and adaptive immune system. In response to chronic, heavy alcohol exposure, hepatocytes themselves also contribute to the inflammatory process; hepatocytes express a large number of chemokines and inflammatory mediators and can also release damage-associated molecular patterns during injury and death. These cellular responses are mediated and accompanied by changes in the expression of pro- and anti-inflammatory cytokines and chemokines, as well as by signals which orchestrate the recruitment of immune cells and activation of the inflammatory process. Additional mechanisms for cell-cell and inter-organ communication in ASH are also reviewed, including the roles of extracellular vesicles and microRNAs, as well as inter-organ crosstalk. We highlight the concept that inflammation also plays an important role in promoting liver repair and controlling bacterial infection. Understanding the complex regulatory processes that are disrupted during the progression of ASH will likely lead to better targeted strategies for therapeutic interventions.

Cellular Abnormalities and Emerging Biomarkers in Alcohol-Associated Liver Disease

Alcohol-associated liver disease (AALD) is the third most common preventable cause for disease burden and mortality in the US. AALD, including alcoholic hepatitis (AH), contributes to half of admissions from decompensated liver disease and 20% of all liver transplants in the US. Peripheral blood cells contribute to systemic inflammation, oxidative stress, mitochondrial dysfunction, and fibrosis in AALD and AH. Alcohol dysregulates function of lymphocytes, neutrophils, monocytes, and tissue macrophages of the innate immune system. These alterations in turn can modulate adaptive immune responses. In this review, we describe these disruptive effects of alcohol on cells of the innate and adaptive immune system and focus on cellular-based emerging biomarkers on diagnosis and prognosis of patients with AALD and AH.

A Validated Score Predicts Acute Kidney Injury and Survival in Patients With Alcoholic Hepatitis

Identifying patients at high risk for acute kidney injury (AKI) during hospitalization among patients admitted with severe alcoholic hepatitis (AH) is an unmet clinical need. We performed a multicentric prospective cohort study using data from 4 different cohorts on well-characterized patients hospitalized with severe AH. Data collected on 773 AH patients from 4 cohorts across the globe were randomly split into test (n = 390) and validation (n = 383) cohorts. We found that 32% of the patients developed inpatient AKI in the test cohort. Approximately 60% of patients met criteria for systemic inflammatory response syndrome (SIRS) at admission. Hepatic encephalopathy, SIRS, and Model for End-Stage Liver Disease score at admission predicted inpatient AKI with odds ratios of 3.86, 2.24, and 1.14, respectively. The AKI risk score developed using these predictors stratified risk of inpatient AKI to low (score <3), moderate (3-4), and high (>4). These findings were replicated in the validation cohort. In the whole study cohort, patients with AKI had a lower 90-day survival (53% versus 77%; P < 0.001). Those with AKI risk score of >4 had significantly lower 90-day survival as compared with those with risk scores between 3 and 4 and <3 (47% versus 68% versus 88%; P < 0.001). In conclusion, AKI occurs frequently in AH patients and negatively impacts short-term mortality. The AKI risk score is useful in identifying patients at high risk for inpatient AKI and may be useful for developing new therapeutic strategies to prevent AKI in patients with AH.

Differential Activation of Hepatic Invariant NKT Cell Subsets Plays a Key Role in Progression of Nonalcoholic Steatohepatitis

Innate immune mechanisms play an important role in inflammatory chronic liver diseases. In this study, we investigated the role of type I or invariant NKT (iNKT) cell subsets in the progression of nonalcoholic steatohepatitis (NASH). We used α-galactosylceramide/CD1d tetramers and clonotypic mAb together with intracytoplasmic cytokine staining to analyze iNKT cells in choline-deficient l-amino acid-defined (CDAA)-induced murine NASH model and in human PBMCs, respectively. Cytokine secretion of hepatic iNKT cells in CDAA-fed C57BL/6 mice altered from predominantly IL-17+ to IFN-γ+ and IL-4+ during NASH progression along with the downmodulation of TCR and NK1.1 expression. Importantly, steatosis, steatohepatitis, and fibrosis were dependent upon the presence of iNKT cells. Hepatic stellate cell activation and infiltration of neutrophils, Kupffer cells, and CD8+ T cells as well as expression of key proinflammatory and fibrogenic genes were significantly blunted in Jα18-/- mice and in C57BL/6 mice treated with an iNKT-inhibitory RAR-γ agonist. Gut microbial diversity was significantly impacted in Jα18-/- and in CDAA diet-fed mice. An increased frequency of CXCR3+IFN-γ+T-bet+ and IL-17A+ iNKT cells was found in PBMC from NASH patients in comparison with nonalcoholic fatty liver patients or healthy controls. Consistent with their in vivo activation, iNKT cells from NASH patients remained hyporesponsive to ex-vivo stimulation with α-galactosylceramide. Accumulation of plasmacytoid dendritic cells in both mice and NASH patients suggest their role in activation of iNKT cells. In summary, our findings indicate that the differential activation of iNKT cells play a key role in mediating diet-induced hepatic steatosis and fibrosis in mice and its potential involvement in NASH progression in humans.

The Role of CD1d and MR1 Restricted T Cells in the Liver

The liver is one of the most important immunological organs that remains tolerogenic in homeostasis yet promotes rapid responses to pathogens in the presence of a systemic infection. The composition of leucocytes in the liver is highly distinct from that of the blood and other lymphoid organs, particularly with respect to enrichment of innate T cells, i.e., invariant NKT cells (iNKT cells) and Mucosal-Associated Invariant T cells (MAIT cells). In recent years, studies have revealed insights into their biology and potential roles in maintaining the immune-environment in the liver. As the primary liver-resident immune cells, they are emerging as significant players in the human immune system and are associated with an increasing number of clinical diseases. As such, innate T cells are promising targets for modifying host defense and inflammation of various liver diseases, including viral, autoimmune, and those of tumor origin. In this review, we emphasize and discuss some of the recent discoveries and advances in the biology of innate T cells, their recruitment and diversity in the liver, and their role in various liver diseases, postulating on their potential application in immunotherapy.

Astaxanthin alleviated ethanol-induced liver injury by inhibition of oxidative stress and inflammatory responses via blocking of STAT3 activity

Astaxanthin (AXT) is classified as a xanthophyll carotenoid compound which have broader functions including potent antioxidant, anti-inflammatory and neuroprotective properties. Considerable researches have demonstrated that AXT shows preventive and therapeutic properties against for Diabetes, Osteoarthritis and Rheumatoid Arthritis. However, the protective effect of AXT on liver disease has not yet been reported. In this study, we investigated effects of AXT on ethanol-induced liver injury in chronic plus binge alcohol feeding model. The hepatic steatosis and inflammation induced by ethanol administration were alleviated by AXT. Serum levels of aspartate transaminase and alanine transaminase were decreased in the livers of AXT administrated group. The ethanol-induced expression of cytochrome P450 2E1 (CYP2E1), pro-inflammatory proteins, cytokines, chemokines and reactive oxygen species (ROS) levels were also reduced in the livers of AXT administrated group. Moreover, ethanol-induced infiltration of neutrophils was decreased in the livers of AXT administrated group. Docking model and pull-down assay showed that AXT directly binds to the DNA binding site of STAT3. Moreover, AXT decreased STAT3 phosphorylation in the liver of AXT administration group. Therefore, these results suggest that AXT could prevent ethanol-induced hepatic injury via inhibition of oxidant and inflammatory responses via blocking of STAT3 activity.

Complex Network of NKT Cell Subsets Controls Immune Homeostasis in Liver and Gut

The liver-gut immune axis is enriched in several innate immune cells, including innate-like unconventional and adaptive T cells that are thought to be involved in the maintenance of tolerance to gut-derived antigens and, at the same time, enable effective immunity against microbes. Two subsets of lipid-reactive CD1d-restricted natural killer T (NKT) cells, invariant NKT (iNKT) and type II NKT cells present in both mice and humans. NKT cells play an important role in regulation of inflammation in the liver and gut due to their innate-like properties of rapid secretion of a myriad of pro-inflammatory and anti-inflammatory cytokines and their ability to influence other innate cells as well as adaptive T and B cells. Notably, a bi-directional interactive network between NKT cells and gut commensal microbiota plays a crucial role in this process. Here, we briefly review recent studies related to the cross-regulation of both NKT cell subsets and how their interactions with other immune cells and parenchymal cells, including hepatocytes and enterocytes, control inflammatory diseases in the liver, such as alcoholic and non-alcoholic steatohepatitis, as well as inflammation in the gut. Overwhelming experimental data suggest that while iNKT cells are pathogenic, type II NKT cells are protective in the liver. Since CD1d-dependent pathways are highly conserved from mice to humans, a detailed cellular and molecular understanding of these immune regulatory pathways will have major implications for the development of novel therapeutics against inflammatory diseases of liver and gut.

Spliceosome-Associated Protein 130 Exacerbates Alcohol-Induced Liver Injury by Inducing NLRP3 Inflammasome-Mediated IL-1β in Mice

Excessive alcohol consumption leads to chronic liver diseases. Macrophage-inducible C-type lectin (Mincle) is a C-type lectin receptor that recognizes spliceosome-associated protein 130 (SAP130) known as an endogenous ligand released from dying cells. The aim was to examine the role of Mincle-SAP130 in the pathogenesis of alcoholic liver disease. Alcohol-induced liver injury was induced in wild-type (WT) and Mincle knockout (KO) mice by using a chronic-binge ethanol-feeding model. Mincle KO mice showed significant lower hepatic steatosis, inflammation with neutrophil infiltration, and fibrosis compared with WT mice after alcohol feeding. In contrast, Mincle activation exacerbated alcohol-induced liver injury. Kupffer cells (KCs) are major sources of Mincle. IL-1β expression was significantly down-regulated in Mincle KO mice compared with that in WT mice after alcohol consumption. Interestingly, expression and production of IL-1β were significantly decreased in SAP130-treated KCs isolated from leucine-rich-containing family pyrin domain containing-3-deficient mice compared with those in WT KCs. Such results were also observed in cells treated with SAP130 plus Syk inhibitor. Furthermore, infiltration of invariant natural killer T cells was decreased in livers of Mincle KO mice. Finally, inhibition of Syk signaling ameliorated alcohol-induced liver injury. Collectively, these results demonstrated that interaction between Mincle and SAP130 may promote the progression of alcoholic liver disease by IL-1β production in KCs and consequently increase inflammatory immune cell infiltration.