Natural killer group 2 member D, its ligands, and liver disease: good or bad?

Group 1 innate lymphoid cell activation via recognition of NKG2D and liver resident macrophage MULT-1: Collaborated roles in triptolide induced hepatic immunotoxicity in mice

Triptolide (TP) is the major bioactive component of traditional Chinese medicine Tripterygium wilfordii Hook. F., a traditional Chinese medicinal plant categorized within the Tripterygium genus of the Celastraceae family. It is recognized for its therapeutic potential in addressing a multitude of diseases. Nonetheless, TP is known to exhibit multi-organ toxicity, notably hepatotoxicity, which poses a significant concern for the well-being of patients undergoing treatment. The precise mechanisms responsible for TP-induced hepatotoxicity remain unresolved. In our previous investigation, it was determined that TP induces heightened hepatic responsiveness to exogenous lipopolysaccharide (LPS). Additionally, natural killer (NK) cells were identified as a crucial effector responsible for mediating hepatocellular damage in this context. However, associated activating receptors and the underlying mechanisms governing NK cell represented innate lymphoid cell (ILC) activation remained subjects of inquiry and were not yet investigated. Herein, activating receptor Killer cell lectin like receptor K1 (NKG2D) of group 1 ILCs was specifically upregulated in TP- and LPS-induced acute liver failure (ALF), and in vivo blockade of NKG2D significantly reduced group 1 ILC mediated cytotoxicity and mitigated TP- and LPS-induced ALF. NKG2D ligand UL16-binding protein-like transcript 1 (MULT-1) was found upregulated in liver resident macrophages (LRMs) after TP administration, and LRMs did exhibit NK cell activating effect. Furthermore, M1 polarization of LRMs cells was observed, along with an elevation in intracellular tumor necrosis factor (TNF)-α levels. In vivo neutralization of TNF-α significantly alleviated TP- and LPS-induced ALF. In conclusion, the collaborative role of group 1 ILCs and LRMs in mediating hepatotoxicity was confirmed in TP- and LPS-induced ALF. TP-induced MULT-1 expression in LRMs was the crucial mechanism in the activation of group 1 ILCs via MULT-1-NKG2D signal upon LPS stimulation, emphasizing the importance of infection control after TP administration.

Immune dysregulation and pathophysiology of alcohol consumption and alcoholic liver disease

Alcoholic liver disease (ALD) is a clinical-pathologic entity caused by the chronic excessive consumption of alcohol. The disease includes a broad spectrum of anomalies at the cellular and tissual level that can cause acute-on-chronic (alcoholic hepatitis) or chronic (fibrosis, cirrhosis, hepatocellular cancer) injury, having a great impact on morbidity and mortality worldwide. Alcohol is metabolized mainly in the liver. During alcohol metabolism, toxic metabolites, such as acetaldehyde and oxygen reactive species, are produced. At the intestinal level, alcohol consumption can cause dysbiosis and alter intestinal permeability, promoting the translocation of bacterial products and causing the production of inflammatory cytokines in the liver, perpetuating local inflammation during the progression of ALD. Different study groups have reported systemic inflammatory response disturbances, but reports containing a compendium of the cytokines and cells involved in the pathophysiology of the disease, from the early stages, are difficult to find. In the present review article, the role of the inflammatory mediators involved in ALD progression are described, from risky patterns of alcohol consumption to advanced stages of the disease, with the aim of understanding the involvement of immune dysregulation in the pathophysiology of ALD.

NK cell immunometabolism as target for liver cancer therapy

Natural killer (NK) cells are being used effectively as a potential candidate in tumor immunotherapy. However, the migration and transport of NK cells to solid tumors is inadequate. NK cell dysfunction, tumor invasiveness, and metastasis are associated with altered metabolism of NK cells in the liver cancer microenvironment. However, in liver cancers, metabolic impairment of NK cells is still not understood fully. Evidence from various sources has shown that the interaction of NK cell's immune checkpoints with its metabolic checkpoints is responsible for the regulation of the development and function of these cells. How immune checkpoints contribute to metabolic programming is still not fully understood, and how this can be beneficial needs a better understanding, but they are emerging to be incredibly compelling to rebuilding the function of NK cells in the tumor. It is expected to represent a potential aim that focuses on improving the efficacy of therapies based on NK cells for treating liver cancer. Here, the recent advancements made to understand the NK cell's metabolic reprogramming in liver cancer have been summarized, along with the possible interplay between the immune and the metabolic checkpoints in NK cell function. Finally, an overview of some potential metabolic-related targets that can be used for liver cancer therapy treatment has been presented.

Natural Killer Group 2D Receptor and B1a Cells Crosstalk in Post-Hepatitis C Virus Infection Hepatocellular Carcinoma and Cirrhosis

Background

Natural killer (NK) and B1a cells are implicated in innate immune surveillance against chronic hepatitis C virus (CHCV). NK group 2D (NKG2D) receptor is important for B cell differentiation. This study was designed to assess whether B1a cells and NK Cells expressing NKG2D are implicated in post-hepatitis C infection hepatocellular carcinoma (post-HCV HCC) and cirrhosis using flow cytometry and investigate the association between NK-expressing NKG2D and B1a in complications of CHCV infection.

Methods

In this cross-sectional study, 111 participants were included and divided into the post-HCV HCC (n = 50), post-HCV liver cirrhosis (n = 31), and CHCV (n = 30) groups.

Results

The percentage of B1a cells (B1a%) and the mean fluorescence intensity (MFI) of NKG2D (NKG2D MFI) showed a significant increase in the CHCV group compared with those in the post-HCV liver cirrhosis and post-HCV HCC groups (P < 0.05). A positive correlation was observed between NKG2D MFI and B1a% (r = 0.6, P < 0.001). The receiver operating characteristic (ROC) curve revealed that NKG2D MFI and B1a% differentiated between patients with CHCV infection and those with HCC with a sensitivity of 92% and 98%, respectively, and differentiated between patients with CHCV infection and those with liver cirrhosis with a sensitivity of 94% and 90%, respectively.

Conclusion

Downregulation of B1a frequency and NKG2D intensity is implicated in the progression of CHCV infection to cirrhosis and HCC. NKG2D receptor is associated with the frequency of circulating B1a cells. NKG2D intensity and B1a% can be used as indicators of CHCV progression.

Drug-Induced Vanishing Bile Duct Syndrome: From Pathogenesis to Diagnosis and Therapeutics

The most concerned issue in the context of drug/herb-induced chronic cholestasis is vanishing bile duct syndrome. The progressive destruction of intrahepatic bile ducts leading to ductopenia is usually not dose dependent, and has a delayed onset that should be suspected when abnormal serum cholestasis enzyme levels persist despite drug withdrawal. Immune-mediated cholangiocyte injury, direct cholangiocyte damage by drugs or their metabolites once in bile, and sustained exposure to toxic bile salts when biliary epithelium protective defenses are impaired are the main mechanisms of cholangiolar damage. Current therapeutic alternatives are scarce and have not shown consistent beneficial effects so far. This review will summarize the current literature on the main diagnostic tools of ductopenia and its histological features, and the differential diagnostic with other ductopenic diseases. In addition, pathomechanisms will be addressed, as well as the connection between them and the supportive and curative strategies for ductopenia management.

The Emergence of Immune-checkpoint Inhibitors in Colorectal Cancer Therapy

Immunotherapy has revolutionized the treatment landscape in a number of solid tumors. In colorectal cancer, evidence suggests that microsatellite high (MSI-H) tumors are the most responsive to immune checkpoint blockade due to increased neo-antigen load and a favorable tumor microenvironment. Indeed, Pembrolizumab now represents a first-line option in such patients. However, MSI-H tumors represent the minority and a proportion of patients' progress despite initially responding. Trials are investigating different immunotherapy combinatorial strategies to enhance immune response in less immunogenic colorectal tumors. Such strategies include dual immune checkpoint blockade, combining immune checkpoint inhibitors with other treatment modalities such as radiotherapy, chemotherapy or other biological or targeted agents. Moreover, there is an increasing drive to identify biomarkers to better select patients most likely to respond to immunotherapy and understand intrinsic and acquired resistance mechanisms. Apart from MSI-H tumors, there is a strong rationale to suggest that tumors with alterations in DNA polymerase epsilon and DNA polymerase delta are also likely to respond to immunotherapy and trials in this subpopulation are underway. Other strategies such as priming O6-methylguanineDNA methyltransferase silenced tumors with alkylating agents to make them receptive to immune checkpoint blockade are also being investigated. Here we discuss different colorectal subpopulations together with their likelihood of response to immune checkpoint blockade and strategies to overcome barriers to a successful clinical outcome. We summarize evidence from published clinical trials and provide an overview of trials in progress whilst discussing newer immunotherapy strategies such as adoptive cell therapies and cancer vaccines.

Revisiting the Role of Natural Killer Cells in Non-Alcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) is the most common form of chronic liver disease. The histological spectrum of NAFLD ranges from simple steatosis to chronic inflammation and liver fibrosis during Non-Alcoholic Steatohepatitis (NASH). The current view is that innate immune mechanisms represent a key element in supporting hepatic inflammation in NASH. Natural Killer (NK) cells are lymphoid cells and a component of the innate immune system known to be involved in NASH progression. Increasing evidence has shed light on the differential function of circulating and tissue-resident NK cells, as well as on the relevance of metabolism and the microenvironment in regulating their activity. Here, we revisit the complex role of NK cells as regulators of NASH progression as well as potential therapeutic approaches based on their modulation.

Role of altered immune cells in liver diseases: a review

Immune cells play an important role in controlling liver tumorigenesis, viral hepatitis, liver fibrosis and contribute to pathogenesis of liver inflammation and injury. Accumulating evidence suggests the effectiveness of natural killer (NK) cells and Kupffer cells (KCs) against viral hepatitis, hepatocellular damage, liver fibrosis, and carcinogenesis. Activation of natural killer cells provides a novel therapeutic strategy to cure liver related diseases. This review discusses the emerging roles of immune cells in liver disorders and it will provide baseline data to scientists to design better therapies for treatment.

Opposite cross-talk by oleate and palmitate on insulin signaling in hepatocytes through macrophage activation

Chronic low grade inflammation in adipose tissue during obesity is associated with an impairment of the insulin signaling cascade. In this study, we have evaluated the impact of palmitate or oleate overload of macrophage/Kupffer cells in triggering stress-mediated signaling pathways, in lipoapoptosis, and in the cross-talk with insulin signaling in hepatocytes. RAW 264.7 macrophages or Kupffer cells were stimulated with oleate or palmitate, and levels of M1/M2 polarization markers and the lipidomic profile of eicosanoids were analyzed. Whereas proinflammatory cytokines and total eicosanoids were elevated in macrophages/Kupffer cells stimulated with palmitate, enhanced arginase 1 and lower leukotriene B4 (LTB4) levels were detected in macrophages stimulated with oleate. When hepatocytes were pretreated with conditioned medium (CM) from RAW 264.7 or Kupffer cells loaded with palmitate (CM-P), phosphorylation of stress kinases and endoplasmic reticulum stress signaling was increased, insulin signaling was impaired, and lipoapoptosis was detected. Conversely, enhanced insulin receptor-mediated signaling and reduced levels of the phosphatases protein tyrosine phosphatase 1B (PTP1B) and phosphatase and tensin homolog (PTEN) were found in hepatocytes treated with CM from macrophages stimulated with oleate (CM-O). Supplementation of CM-O with LTB4 suppressed insulin sensitization and increased PTP1B and PTEN. Furthermore, LTB4 decreased insulin receptor tyrosine phosphorylation in hepatocytes, activated the NFκB pathway, and up-regulated PTP1B and PTEN, these effects being mediated by LTB4 receptor BTL1. In conclusion, oleate and palmitate elicit an opposite cross-talk between macrophages/Kupffer cells and hepatocytes. Whereas CM-P interferes at the early steps of insulin signaling, CM-O increases insulin sensitization, possibly by reducing LTB4.

MICA SNPs and the NKG2D system in virus-induced HCC

Hepatocellular carcinoma (HCC) is one of the most frequent causes of cancer-related death globally. Above well-known risk factors for HCC development ranging from various toxins to diseases such as diabetes mellitus, chronic infection with hepatitis B virus and hepatitis C virus (HCV) poses the most serious threat, constituting the cause in more than 80 % of cases. In addition to the viral genes intensively investigated, the pathophysiological importance of host genetic factors has also been greatly and increasingly appreciated. Genome-wide association studies (GWAS) comprehensively search the host genome at the single-nucleotide level, and have successfully identified the genomic region associated with a whole variety of diseases. With respect to HCC, there have been reports from several groups on single nucleotide polymorphisms (SNPs) associated with hepatocarcinogenesis, among which was our GWAS discovering MHC class I polypeptide-related sequence A (MICA) as a susceptibility gene for HCV-induced HCC. MICA is a natural killer (NK) group 2D (NKG2D) ligand, whose interaction with NKG2D triggers NK cell-mediated cytotoxicity toward the target cells, and is a key molecule in tumor immune surveillance as its expression is induced on stressed cells such as transformed tumor cells for the detection by NK cells. In this review, the latest understanding of the MICA-NKG2D system in viral HCC, particularly focused on its antitumor properties and the involvement of MICA SNPs, is summarized, followed by a discussion of targets for state-of-the-art cancer immunotherapy with personalized medicine in view.

Phenotypic features of innate and adaptive immunity in patients with chronic hepatitis C and end-stage renal disease

BACKGROUND

The knowledge of the immunological profile of patients with chronic hepatitis C (CHC) and end-stage renal disease (ESRD) on haemodialysis (HD) is still limited.

AIMS

This study investigated the immune response profile in HCV patients with concomitant ESRD focusing on the influence of the renal disease on the phenotypic profile of peripheral blood lymphocytes.

METHODS

Immunophenotypic features of peripheral blood leucocytes were assessed by flow cytometry in two distinct groups: HCV patients with ESRD (CHC+ESRD, n = 16) and HCV patients with normal renal function (CHC, n = 20). Two control groups that were included were as follows: HCV negative blood donors (BD, n = 15) and HCV negative patients with ESRD (ESRD, n = 19).

RESULTS

Higher frequency of macrophage-like and pro-inflammatory monocytes along with enhanced frequency of CD3(-) CD16(-) CD56(+) , mainly CD56(dim) NK-cells, were the hallmark of CHC+ESRD patients. Lower frequency of B cells with significant decreased of B1 and CD23(+) B-cells were associated with ESRD, regardless the HCV infection. Although higher rates of activated CD4(+) and CD8(+) T cells were observed in the CHC and CHC+ESRD groups, the chemotaxis of T-cell subsets, based on their chemokine receptor expression, was affected by ESRD.

CONCLUSIONS

Chronic hepatitis C patients with ESRD on HD exhibit distinctive phenotypic profile of circulating leucocytes. It may be implicated in the natural history of HCV infection in this particular group of patients and warrants further investigation.

KLRG1 negatively regulates natural killer cell functions through the Akt pathway in individuals with chronic hepatitis C virus infection

In this study, we demonstrate that killer cell lectin-like receptor subfamily G member 1 (KLRG1), a transmembrane protein preferentially expressed on T cells, is highly expressed on CD56(+) NK cells, which are significantly reduced in their numbers and functions in the peripheral blood of patients with chronic hepatitis C virus (HCV) infection compared to subjects without infection. KLRG1 expression is also upregulated on healthy NK cells exposed to Huh-7 hepatocytes infected with HCV in vitro. Importantly, the expression levels of KLRG1 are inversely associated with the capacity of NK cells to proliferate and to produce gamma interferon (IFN-γ) but positively associated with apoptosis of NK cells in response to inflammatory cytokine stimulation. KLRG1(+) NK cells, including CD56(bright) and CD56(dim) subsets, exhibit impaired cell activation and IFN-γ production but increased apoptosis compared to KLRG1(-) NK cells, particularly in HCV-infected individuals. Importantly, blockade of KLRG1 signaling significantly recovered the impaired IFN-γ production by NK cells from HCV-infected subjects. Blockade of KLRG1 also enhanced the impaired phosphorylation of Akt (Ser473) in NK cells from HCV-infected subjects. Taken together, these results indicate that KLRG1 negatively regulates NK cell numbers and functions via the Akt pathway, thus providing a novel marker and therapeutic target for HCV infection.

Natural killer cells in liver disease

Natural killer (NK) cells are enriched in lymphocytes within the liver and have unique phenotypic features and functional properties, including tumor necrosis factor-related apoptosis-inducing ligand-dependent cytotoxicity and specific cytokine profiles. As a key component of innate immunity in the liver, NK cells perform critical roles in host defense against pathogens and tumors through their natural cytotoxicity and cytokine production, and they also act as regulatory cells by engaging in reciprocal interactions with other types of liver cells through cell-to-cell contact and the production of cytokines. Accumulating evidence from the last decade suggests that NK cells play an important role in controlling viral hepatitis, liver fibrosis, and liver tumorigenesis, but also contribute to the pathogenesis of liver injury and inflammation. The characterization of intrahepatic NK cell functions has not only helped us to better understand the pathogenesis of liver disease, but has also revealed new therapeutic targets for managing this disease.

Innate immune cells in liver inflammation

Innate immune system is the first line of defence against invading pathogens that is critical for the overall survival of the host. Human liver is characterised by a dual blood supply, with 80% of blood entering through the portal vein carrying nutrients and bacterial endotoxin from the gastrointestinal tract. The liver is thus constantly exposed to antigenic loads. Therefore, pathogenic microorganism must be efficiently eliminated whilst harmless antigens derived from the gastrointestinal tract need to be tolerized in the liver. In order to achieve this, the liver innate immune system is equipped with multiple cellular components; monocytes, macrophages, granulocytes, natural killer cells, and dendritic cells which coordinate to exert tolerogenic environment at the same time detect, respond, and eliminate invading pathogens, infected or transformed self to mount immunity. This paper will discuss the innate immune cells that take part in human liver inflammation, and their roles in both resolution of inflammation and tissue repair.

Inhibition of natural killer cells protects the liver against acute injury in the absence of glycine N-methyltransferase

Glycine N-methyltransferase (GNMT) catabolizes S-adenosylmethionine (SAMe), the main methyl donor of the body. Patients with cirrhosis show attenuated GNMT expression, which is absent in hepatocellular carcinoma (HCC) samples. GNMT(-/-) mice develop spontaneous steatosis that progresses to steatohepatitis, cirrhosis, and HCC. The liver is highly enriched with innate immune cells and plays a key role in the body's host defense and in the regulation of inflammation. Chronic inflammation is the major hallmark of nonalcoholic steatohepatitis (NASH) progression. The aim of our study was to uncover the molecular mechanisms leading to liver chronic inflammation in the absence of GNMT, focusing on the implication of natural killer (NK) / natural killer T (NKT) cells. We found increased expression of T helper (Th)1- over Th2-related cytokines, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-R2/DR5, and several ligands of NK cells in GNMT(-/-) livers. Interestingly, NK cells from GNMT(-/-) mice were spontaneously activated, expressed more TRAIL, and had strong cytotoxic activity, suggesting their contribution to the proinflammatory environment in the liver. Accordingly, NK cells mediated hypersensitivity to concanavalin A (ConA)-mediated hepatitis in GNMT(-/-) mice. Moreover, GNMT(-/-) mice were hypersensitive to endotoxin-mediated liver injury. NK cell depletion and adoptive transfer of TRAIL(-/-) liver-NK cells protected the liver against lipopolysaccharide (LPS) liver damage.

CONCLUSION

Our data allow us to conclude that TRAIL-producing NK cells actively contribute to promote a proinflammatory environment at early stages of fatty liver disease, suggesting that this cell compartment may contribute to the progression of NASH.

Role of stress-induced NKG2D ligands in liver diseases

Cell death by apoptosis is a prominent feature in a variety of liver diseases. It is likely that apoptosis is the initial cellular response to hepatocyte and biliary injury, which then leads to the initiation of cellular and cytokine cascades culminating in hepatocyte death with subsequent fibrosis and cirrhosis. This sequence of events is of paramount clinical importance. Recently, soluble forms of the major histocompatibility complex class I-related chains A and closely related B (MIC A and B) were reported to be increased in patients with a variety of liver diseases. MIC A and B are cell surface glycoproteins that function as indicators for cellular stress and thus activate circulating cytotoxic natural killer (NK) cells. The interaction between MIC A and B with their cognate receptor natural killer group 2 member D (NKG2D) culminates in enhanced liver cell death, which is mediated in part by apoptotic mechanisms. The present overview focuses on the role of the stress-induced NKG2D ligands MIC A and B in diverse liver diseases. Critical insights into these complex relations may help to promote rationally based therapies in liver diseases. Importantly, we hope that this overview will help to stimulate further studies into mechanisms by which stress ligands mediate cell death and its sequale.

Interaction between Toll-like receptors and natural killer cells in the destruction of bile ducts in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by chronic nonsuppurative destructive cholangitis (CNSDC) associated with destruction of small bile ducts. Although there have been significant advances in the dissection of the adaptive immune response against the mitochondrial autoantigens, there are increasing data that suggest a contribution of innate immune mechanisms in inducing chronic biliary pathology. We have taken advantage of our ability to isolate subpopulations of liver mononuclear cells (LMC) and examined herein the role of Toll-like receptors (TLRs), their ligands, and natural killer (NK) cells in modulating cytotoxic activity against biliary epithelial cells (BECs). In particular, we demonstrate that Toll-like receptor 4 ligand (TLR4-L)-stimulated NK cells destroy autologous BECs in the presence of interferon alpha (IFN-α) synthesized by TLR 3 ligand (TLR3-L)-stimulated monocytes (Mo). Indeed, IFN-α production by hepatic Mo is significantly increased in patients with PBC compared to disease controls. There were also marked increases in the cytotoxic activity of hepatic NK cells from PBC patients compared to NK cells from controls but only when the NK cells were prepared following ligation of both TLR3-L- and TLR4-L-stimulated LMC. These functional data are supported by the immunohistochemical observation of an increased presence of CD56-positive NK cells scattered around destroyed small bile ducts more frequently in liver tissues from PBC patients than controls.

CONCLUSION

These data highlight critical differences in the varied roles of Mo and NK cells following TLR3-L and TLR4-L stimulation.

Molecular mechanisms of alcoholic liver disease: innate immunity and cytokines

Alcohol consumption is a predominant etiological factor in the pathogenesis of chronic liver diseases worldwide, causing fatty liver, alcoholic hepatitis, fibrosis/cirrhosis, and hepatocellular carcinoma. In the past few decades, significant progress has been made in our understanding of the molecular mechanisms underlying alcoholic liver injury. Activation of innate immunity components such as Kupffer cells, LPS/TLR4, and complements in response to alcohol exposure plays a key role in the development and progression of alcoholic liver disease (ALD). LPS activation of Kupffer cells also produces IL-6 and IL-10 that may play a protective role in ameliorating ALD. IL-6 activates signal transducer and activator of transcription 3 (STAT3) in hepatocytes and sinusoidal endothelial cells, while IL-10 activates STAT3 in Kupffer cells/macrophages, subsequently protecting against ALD. In addition, alcohol consumption also inhibits some components of innate immunity such as natural killer (NK) cells, a type of cells that play key roles in anti-viral, anti-tumor, and anti-fibrotic defenses in the liver. Ethanol inhibition of NK cells likely contributes significantly to the pathogenesis of ALD. Understanding the roles of innate immunity and cytokines in alcoholic liver injury may provide insight into novel therapeutic targets in the treatment of alcoholic liver disease.

Roles of liver innate immune cells in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most common liver disease in the United States and other developed countries and is expected to increase in the next few years. Emerging data suggest that some patients with NAFLD may progress to nonalcoholic steatohepatitis (NASH), cirrhosis and even hepatocellular carcinoma. NAFLD can also promote the development and progression of disease in other organ systems, such as the cardiovascular and endocrine (i.e. diabetes) systems. Thus, understanding the pathogenesis of NAFLD is of great clinical importance and is critical for the prevention and treatment of the disease. Although the “two-hit hypothesis” is generally accepted, the exact pathogenesis of NAFLD has not been clearly established. The liver is an important innate immune organ with large numbers of innate immune cells, including Kupffer cells (KCs), natural killer T (NKT) cells and natural killer (NK) cells. Recent data show that an imbalance in liver cytokines may be implicated in the development of fatty liver disease. For example, Th1 cytokine excess may be a common pathogenic mechanism for hepatic insulin resistance and NASH. Innate immune cells in the liver play important roles in the excessive production of hepatic Th1 cytokines in NAFLD. In addition, liver innate immune cells participate in the pathogenesis of NAFLD in other ways. For example, activated KCs can generate reactive oxygen species, which induce liver injury. This review will focus primarily on the possible effect and mechanism of KCs, NKT cells and NK cells in the development of NAFLD.