Hepatic NKT Cells Research Articles

Heparin protects against septic mortality via ApoE-antagonism

Abstract Background Apolipoprotein E (apoE), a component of plasma lipoproteins, increases septic mortality in a rodent model of sepsis, presumably by enhancing lipid antigen presentation to antigen-presenting cells via the low-density lipoprotein receptor (LDLR). Downstream, this culminates in natural killer T (NKT) cell activation and cytokine secretion. To determine whether apoE antagonism would protect against septic mortality in mice, apoE-LDLR binding was antagonized using heparin, which can inhibit apoE's LDLR-binding site. Methods C57BL/6 mice underwent cecal ligation and puncture (CLP) and heparin infusion. Serum partial thromboplastin time and alanine aminotransferase were measured at 24 hours, and survival was monitored for 7 days after CLP. LDLR+/+ and LDLR−/− fibroblasts were incubated with apoE and heparin to measure apoE internalization. Hepatic NKT cells and cytokine levels were quantified via fluorescence-activated cell sorting. Results Heparin decreased CLP–induced mortality by 50% versus saline-treated controls, independent of anticoagulation. LDLR+/+ fibroblasts displayed decreased uptake of apoE when treated concurrently with heparin for 12 hours. In septic mice, hepatic alanine aminotransferase levels, hepatic NKT cells, and plasma cytokine levels decreased after heparin treatment. Conclusions This study demonstrates that heparin protects against septic mortality independent of its anticoagulant effect. This protective effect is associated with the inhibition of apoE-LDLR binding, diminished NKT proliferation and cytokine production, and hepatic dysfunction. These findings indicate a potential clinical role for apoE antagonism in the treatment of sepsis.

Dietary fatty acids modulate antigen presentation to hepatic NKT cells in nonalcoholic fatty liver disease

Dietary fatty acids are major contributors to the development and progression of insulin resistance and nonalcoholic fatty liver disease (NAFLD). Dietary fatty acids also alter hepatic NKT cells that are activated by antigens presented by CD1d. In the current study, we examine the mechanism of dietary fatty acid induced hepatic NKT cell deficiency and its causal relationship to insulin resistance and NAFLD. We discover that dietary saturated fatty acids (SFA) or monounsaturated fatty acids (MUFA), but not polyunsaturated fatty acids (PUFA), cause hepatic NKT cell depletion with increased apoptosis. Dietary SFA or MUFA also impair hepatocyte presentation of endogenous, but not exogenous, antigen to NKT cells, indicating alterations of the endogenous antigen processing or presenting pathway. In vitro treatment of normal hepatocytes with fatty acids also demonstrates impaired ability of CD1d to present endogenous antigen by dietary fatty acids. Furthermore, dietary SFA and MUFA activate the NFkappaB signaling pathway and lead to insulin resistance and hepatic steatosis. In conclusion, both dietary SFA and MUFA alter endogenous antigen presentation to hepatic NKT cells and contribute to NKT cell depletion, leading to further activation of inflammatory signaling, insulin resistance, and hepatic steatosis.

Prolonged Survival of Human Hepatocarcinoma Cells in the Liver of Newborn C57BL/6 Mice and Resulting Cellular Xenorejection, Especially the Activation of Hepatic Natural Killer T Cells

Objective: To investigate the fate of human hepatocellular carcinoma (HCC) in the livers of newborn mice and the resulting cellular rejection.Methods: Two HCC cell lines (HepG2 and HCCLM3) labeled with DMAHAS were orthotopically transplanted to newborn and adult mice with or without low-dose cyclosporin A (CsA) treatment (10 mg/kg). The fate of tumor xenografts was examined and the resulting cellular response was investigated. Results: Tumor xenografts survived in newborn mice for >4 weeks, with a delayed lymphocyte infiltration mediated by CD4+ T, CD8+ T and NK1.1+ cells. In contrast, the xenografts survived in adults <8–10 days with an acute cellular rejection by CD8+T cells, NK1.1+ cells, macrophages or neutrophils. Orthotopic transplantation of human HCC xenografts elicited a strong cytotoxic response in newborn mice (p < 0.05), and selective T/NK1.1+ cell deletion in vitro suggested that such effector cells were mainly CD8+ T cells. Moreover, tumor xenografts induced a rapid activation of hepatic natural killer T (NKT) cells in both newborn and adult mice with enhanced secretion of IL-4 and IFN-γ in serum and subsequent NKT-like cytotoxicity. The rapid activation of NKT cells could be efficiently suppressed by low-dose CsA treatment, possibly in a CD1d-independent manner. Conclusion:Our data suggest that the livers of newborn mice were more suitable for the survival of xenografts than those of adult mice. Cell-mediated tumor xenorejection in newborn mice was different from that in adults, and hepatic NKT cells may play an important role in early tumor xenorejection.

Activated NKT cells are depleted specifically in the liver and utilize different mechanisms for expansion that depend on TCR dependent vs independent mechanisms of activation (50.41)

Abstract Treatment of mice bearing implanted liver tumors with IL-18 plus IL-12 (IL-18+IL-12) elicited greater anti-tumor activity than IL-18 or IL-12 delivered as single agents. We found IL-18+IL-12-mediated anti-tumor activity was dependent on the reduction of hepatic NKT cells. Here we examine mechanisms regulating NKT cell modulation following TCR-dependent and independent activation using αGalCer or IL-18+IL-12 treatment of mice, respectively. We found acute treatment of mice with IL-18+IL-12 or αGalCer initially (24h) decreased NKT cells in the liver, but not in other lymphoid tissues. Specifically, treatment with αGalCer completely depleted the liver of NKT cells, while treatment with IL-18+IL-12 only depleted NK1.1(+) NKT cells. Following a loss of NKT cells at 24h with IL-18+IL-12 or αGalCer treatment, these cells reappear and expand by 72h. BrdU proliferation analysis revealed that IL-18+IL-12 and αGalCer expands the NK1.1(-) NKT cell subset in the liver. However, while NKT cell expansion induced with αGalCer requires an intact spleen and IFNγ, IL-18+IL-12-induced expansion does not. Finally, mice treated chronically with IL-18+IL-12 or αGalCer resulted in systemic NKT exhaustion which required an intact thymus for NKT cell repopulation of the liver. By characterizing the early response by NKT cells to various stimuli, these insights could better aid in understanding the role(s) NKT cells play in the control or treatment of infectious diseases, autoimmunity or cancer.

Reply†

We would like to thank Dr. Alisi and colleagues for their interest in our recent manuscript detailing the relationship between Kupffer cell-derived interleukin 12 (IL12) production and loss of hepatic natural killer T (NKT) cells in the steatotic liver.1 It is clear from our study and several others that NKT cells are highly sensitive to hepatic lipid accumulation, a process which we can link to IL12 production by Kupffer cells.1-4 In response to their first comment, we expected that if NKT cells were restored, hepatic lipid accumulation would also be reduced; we were very surprised to see otherwise. Indeed, these results in this model of nonalcoholic fatty liver suggest that NKT cell depletion is a consequence of lipid accumulation and Kupffer cell activation, which challenges the notion that they function to suppress hepatocellular lipid accumulation in nonalcoholic fatty liver disease. As for the mechanism(s) governing IL12 production by Kupffer cells in the nonalcoholic fatty liver, a number of potential possibilities exist with gut-liver interactions being a strong candidate. There is no doubt that gut-derived factors, including gut-derived lipopolysaccharide, contribute to Kupffer cell activation and IL12 production. Recent studies by Ma and colleagues have demonstrated the ability of probiotics, which likely alter gut microbial populations, to protect the hepatic NKT cells within the steatotic liver.5 In addition, it has been shown that Toll-like receptor-9 engagement can promote Kupffer cell-dependent and IL12-dependent NKT cell recruitment to the nonsteatotic liver and exacerbate concanavalin A-mediated hepatitis.6 This highlights the potential impact of gut-derived factors, including bacterial DNA, as key regulators of NKT cell function, although their direct influence on NKT cells within the steatotic liver remains to be determined. It is very likely that a combination of hepatocellular lipid accumulation and Kupffer cell activation promote this response. This complex association is evidenced by data from our study where isolated Kupffer cells from the steatotic liver do not produce more IL12 than those Kupffer cells isolated from a normal liver when activated in vitro, despite showing large and significant increases in its production when activated by lipopolysaccharide in vivo.1 Thus, multiple levels of regulation likely exist and gut-derived antigens no doubt contribute at least in part to this process. Current studies are directed at better understanding the mechanism(s) of Kupffer cell activation and IL12 production, as well as the potential contribution of gut-derived factors in this model of nonalcoholic fatty liver disease. Ian N. Hines Ph.D.*, * Department of Medicine, Division of Gastroenterology and Hepatology, University of North Carolina, Chapel Hill, NC.

The link between hepatosteatosis and cells of the immune system†

We read with great interest the article by Kremer et al., 1 on the role of interleukin-12 (IL-12) production by Kupffer cells in fatty liver, and its possible impact in the reduction of hepatic resident natural killer T (NKT) cells using an animal model of hepatosteatosis (mice fed choline-deficient diet for 0-20 weeks). As previously demonstrated, 2 in this study the authors found that hepatosteatosis in mice that were fed a chronic choline-deficient diet is characterized at the hepatic level by the induction of interferon-gamma and tumor necrosis factor-alpha, elevated content of IL-12, and by a remarkable reduction in the number and activity of NKT cells. Interestingly, all these effects are undetectable in IL-12–depleted mice fed a choline-deficient diet, even if fatty liver is equally present. Several studies 2- 4 conducted on different metabolic animal models of hepatic steatosis have reported the relationship between lipid accumulation, increased Th1 cytokine production (i.e., tumor necrosis factor, IL-12, and interferon-gamma), and hepatic NKT cell depletion. IL-12 is well known as a NKT cell inductor able to stimulate the production/release of large amounts of interferon-gamma and to activate specific transcription factors, including signal transducer and activator of transcription 4 (STAT4). 5 However, the IL-12 increase may not be the sole factor involved in death-dependent NKT cell depletion: others factors, such as dietary factors, might interfere, for example, with mechanisms that mediate the hepatic homing and apoptosis of NKT cells. 6 All these findings noticeably demonstrated that NKT cell reduction is an effect of a combination between intrahepatic fat accumulation and IL-12 increase rather than a cause of hepatosteatosis. However, the real unresolved question is the connection between intrahepatic fat accumulation and up-regulated hepatic IL-12 messenger RNA levels. Once again, as demonstrated by Kremer et al., 1 and as anticipated by other studies, 7 the activation of Kupffer cells by an endotoxin-mediated mechanism could be the link between fatty liver, inflammatory response, and a reduction of NKT cell population. Noteworthy, this phenomenon could be either an effect of fatty liver or an early signal for the development of fibrosis. 8 Therefore, it might be very interesting to investigate whether the number of NKT cells may be a predictive marker of liver fibrosis. Furthermore, research favors the hypothesis of the role of endotoxin and the toll like receptor-4 in diet-induced steatohepatitis. 9 Yet, we would emphasize how many points are still obscure on the molecular mechanisms regulating this intricate network of interactions between cells of the immune system and hepatocellular damage. Anna Alisi Ph.D.*, Nadia Panera*, Valerio Nobili M.D.*, * Liver Unit, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.

Transcriptional regulator Id2 controls survival of hepatic NKT cells

Natural killer T cells expressing an invariant T-cell receptor (iNKT) regulate activation of both innate and adaptive immunity in many contexts. iNKT cells accumulate in the liver and rapidly produce prodigious amounts of numerous cytokines upon activation, impacting the immune response to viral infection, immunosurveillance for malignant cells, and liver regeneration. However, little is known about the factors controlling iNKT homeostasis, survival and hepatic localization. Here, we report that the absence of the transcriptional regulator Id2 resulted in a severe, intrinsic defect in the accumulation of hepatic iNKT cells. Id2-deficient iNKT cells showed increased cell death in the liver, although migration and functional activity were not impaired in comparison to Id2-expressing iNKT cells. Id2-deficient iNKT cells exhibited diminished expression of CXCR6, a critical determinant of iNKT cell accumulation in the liver, and of the anti-apoptotic molecules bcl-2 and bcl-X(L), compared to Id2-sufficient iNKT cells. Furthermore, survival and accumulation of iNKT cells lacking Id2 expression was rescued by deficiency in bim, a key pro-apoptotic molecule. Thus, Id2 was necessary to establish a hepatic iNKT cell population, defining a role for Id2 and implicating the Id targets, E protein transcription factors, in the regulation of iNKT cell homeostasis.

Thioredoxin Binding Protein 2 Modulates Natural Killer T Cell-Dependent Innate Immunity in the Liver: Possible Link to Lipid Metabolism

Thioredoxin binding protein 2 (TBP2) plays a regulatory role in lipid metabolism and immune regulation. We previously reported the effect of TBP2 loss-of-function on lipid metabolism using TBP2 knockout (TBP2KO) mice. In this study, we employed TBP2 transgenic (TBP2TG) mice to analyze the in vivo effect of TBP2 gain-of-function. We revealed a decrease in the percentage of hepatic natural killer T (NKT) cells in TBP2KO mice and an increase in the percentage of hepatic NKT cells in TBP2TG mice. The TBP2KO mice were resistant to concanavalin A (ConA)-induced hepatitis, but they were highly susceptible to other types of hepatitis. TBP2 modulates lipid metabolism as well as NKT cell activity. Moreover, TBP2 expression was increased significantly in klotho-deficient mice, which exhibit a syndrome resembling aging human phenotypes. TBP2 may play multiple roles in lipid metabolism, innate immunity, and aging.

Kupffer Cell and Interleukin-12–Dependent Loss of Natural Killer T Cells in Hepatosteatosis

Hepatosteatosis is associated with increased expression of tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-12, major T helper (Th) 1 cytokines, and reduced hepatic natural killer T (NKT) cell numbers. The relationship between lipid accumulation, cytokine expression, and hepatic NKT cells is not known. This study was conducted to assess the role of IL-12 in the development of hepatic steatosis and its potential impact on liver NKT cells. Male C57Bl/6 wildtype (WT) and IL-12-deficient (IL-12(-/-)) mice were fed a choline-deficient diet (CDD) for 0, 10, or 20 weeks. CDD led to marked hepatosteatosis, reduced hepatic but not splenic NKT cell numbers and function, and increased hepatic expression of the T(h)1-type cytokines IL-12, interferon gamma (IFN-gamma), and TNF-alpha in WT mice. The absence of IL-12 resulted in similar CDD-induced hepatosteatosis, but preserved hepatic NKT cells and significantly reduced hepatic IFN-gamma and TNF-alpha expression. Treatment of CDD-fed mice with lipopolysaccharide led to a significant increase in hepatic IL-12 expression, and Kupffer cell (KC) depletion reduced liver IL-12 expression and restored NKT cells in CDD-induced fatty liver. Interestingly, KCs from CDD-fed mice failed to produce increased quantities of IL-12 upon activation in vitro when compared to similarly treated KCs from control fed mice, suggesting that secondary factors in vivo promote heightened IL-12 production. Finally, human livers with severe steatosis showed a substantial decrease in NKT cells. Hepatosteatosis reduces the numbers of hepatic NKT cells in a KC-and IL-12-dependent manner. Our results suggest a pivotal and multifunctional role of KC-derived IL-12 in the altered immune response in steatotic liver, a process that is likely active within human nonalcoholic fatty liver disease.

Application of tissue-specific NK and NKT cell activity for tumor immunotherapy

Natural killer (NK) and NKT cells are a first line of defense against pathogens and transformed cells. However, dysregulation of their function can lead to autoimmune disease. A better understanding of the mechanisms controlling NK and NKT effector function should lead to the development of improved strategies for the treatment of many diseases. The site in which NK and NKT cells reside should be taken into account, because accumulating evidence suggests that the tissue microenvironment strongly influences their function. In this regard, the liver represents a unique immunologic organ in which the balance between the need for tolerance and the ability to respond rapidly to pathogens and tissue injury is tightly regulated. NK cells in the liver have augmented cytolytic activity as compared to other organs, which is consistent with a role for liver-associated NK cells in being critical effector cells for inhibiting tumor metastasis in the liver. Several studies also suggest that hepatic NKT cells have different functions than those in other organs. Whereas splenic and thymic NKT cells have been shown to suppress diabetes development, facilitate the induction of systemic tolerance and are regulated by IL-4 and other Th2 cytokines, certain subsets of NKT cells in the liver are important sources of Th1 cytokines such as Interferon gamma, and are the primary mediators of anti-tumor responses. The unique properties and roles as critical effector cells make NK and NKT cells within the liver microenvironment attractive targets of immunotherapeutic approaches that have the goal of controlling tumor metastasis in the liver.

Prevention of Early Loss of Transplanted Islets in the Liver of Mice by Adenosine

The low efficiency of islet transplantation necessitating sequential transplantations with the use of 2 to 3 donors for a recipient has been a major obstacle facing clinical islet transplantation. We determined whether adenosine has any beneficial effects on preventing early loss of transplanted islets in the liver, thereby facilitating successful islet transplantation from one donor to one recipient in mice. Two hundred islets, the number of islets from a single mouse pancreas, were grafted into the liver of streptozotocin-induced diabetic C57BL/6 mice. Adenosine was administered once at the time of islet transplantation. Mononuclear cells in the liver of mice receiving islets were isolated and examined by flow cytometry. A single injection of adenosine at the time of transplantation ameliorated hyperglycemia of diabetic mice receiving 200 syngenic islets with suppression of interferon (IFN)-gamma production of hepatic NKT cells and neutrophils, while that of control did not. The IFN-gamma production of NKT cells and neutrophils in the liver of mice treated with alpha-galactosylceramide, a synthetic ligand of NKT cells was suppressed by adenosine. The beneficial effect of adenosine was also observed for BALB/c islet allografts when alloimmune rejection was prevented by anti-CD4 antibody. Adenosine suppresses the NKT cell-mediated IFN-gamma production of neutrophils in the liver of mice receiving islets, thus leading to prevention of early loss of transplanted syngenic and allogenic islets. The findings indicate that adenosine may improve efficiency of clinical islet transplantation.

Liver natural killer and natural killer T cells: immunobiology and emerging roles in liver diseases

Hepatic lymphocytes are enriched in NK and NKT cells that play important roles in antiviral and antitumor defenses and in the pathogenesis of chronic liver disease. In this review, we discuss the differential distribution of NK and NKT cells in mouse, rat, and human livers, the ultrastructural similarities and differences between liver NK and NKT cells, and the regulation of liver NK and NKT cells in a variety of murine liver injury models. We also summarize recent findings about the role of NK and NKT cells in liver injury, fibrosis, and repair. In general, NK and NKT cells accelerate liver injury by producing proinflammatory cytokines and killing hepatocytes. NK cells inhibit liver fibrosis via killing early-activated and senescent-activated stellate cells and producing IFN-gamma. In regulating liver fibrosis, NKT cells appear to be less important than NK cells as a result of hepatic NKT cell tolerance. NK cells inhibit liver regeneration by producing IFN-gamma and killing hepatocytes; however, the role of NK cells on the proliferation of liver progenitor cells and the role of NKT cells in liver regeneration have been controversial. The emerging roles of NK/NKT cells in chronic human liver disease will also be discussed.Understanding the role of NK and NKT cells in the pathogenesis of chronic liver disease may help us design better therapies to treat patients with this disease.

TLR-9 Activation Aggravates Concanavalin A-Induced Hepatitis via Promoting Accumulation and Activation of Liver CD4+ NKT Cells

Increasing evidence suggests that TLRs are involved in the pathogenesis of liver diseases; however, the underlying mechanisms remain obscure. In this study, we found that treatment with CpG-oligodeoxynucleotide (ODN) promoted the accumulation and activation of murine hepatic NKT cells. Additional experiments showed that CpG-ODN preferred to act on CD4(+) NKT cells, while having less effect on CD4(-) NKT cells. The effect of CpG-ODN on liver NKT cells depended on the presence of Kupffer cells and IL-12. Meanwhile, CpG-ODN pretreatment aggravated liver injury and promoted the production of inflammatory cytokines in a Con A-induced fulminant hepatitis model via TLR9 activation. Collectively, our data demonstrate that TLR9 stimulation prefers to promote the accumulation and activation of hepatic CD4(+) NKT cells and suggest that TLR9 signaling might be involved in the pathogenesis of human hepatitis.

The Role of Hepatic Invariant NKT Cells in Systemic/Local Inflammation and Mortality during Polymicrobial Septic Shock

NKT cells have been described as innate regulatory cells because of their rapid response to conserved glycolipids presented on CD1d via their invariant TCR. However, little is known about the contribution of the hepatic NKT cell to the development of a local and/or systemic immune response to acute septic challenge (cecal ligation and puncture (CLP)). We found not only that mice deficient in invariant NKT cells (Jalpha18(-/-)) had a marked attenuation in CLP-induced mortality, but also exhibited an oblation of the systemic inflammatory response (with little effect on splenic/peritoneal immune responsiveness). Flow cytometric data indicated that following CLP, there was a marked decline in the percentage of CD3(+)alpha-galactosylceramide CD1d tetramer(+) cells in the mouse C57BL/6J and BALB/c liver nonparenchymal cell population. This was associated with the marked activation of these cells (increased expression of CD69 and CD25) as well as a rise in the frequency of NKT cells positive for both Th1 and Th2 intracellular cytokines. In this respect, when mice were pretreated in vivo with anti-CD1d-blocking Ab, we observed not only that this inhibited the systemic rise of IL-6 and IL-10 levels in septic mice and improved overall septic survival, but that the CLP-induced changes in liver macrophage IL-6 and IL-10 expressions were inversely effected by this treatment. Together, these findings suggest that the activation of hepatic invariant NKT cells plays a critical role in regulating the innate immune/systemic inflammatory response and survival in a model of acute septic shock.

Natural killer T cells regulate the homing of chemokine CXC receptor 3-positive regulatory T cells to the liver in mice #

Natural killer T (NKT) cells and regulatory T cells (Tregs) are both found within the liver and are known to exhibit immune regulatory functions. Hepatic NKT cells are activated early during inflammatory responses and release cytokines, including interferon gamma (IFN-gamma), which we speculated could regulate Treg recruitment to the liver. To examine this, we treated C57BL/6 mice with a specific NKT cell activating ligand alpha galactosyl-C18-ceramide (alphaGal-C18-Cer) and examined the hepatic recruitment of Tregs. We found a time-dependant increase in the hepatic recruitment of Tregs after NKT cell activation, which was absent in NKT cell-deficient mice. Most recruited Tregs expressed interleukin (IL) 10, and to a lesser extent transforming growth factor beta (TGF-beta). Because IFN-gamma induces the production of chemokine (C-X-C motif) ligand 10 (CXCL10), and Tregs can express the cognate receptor for CXCL10 (that is, CXCR3), we considered that CXCL10 might mediate the hepatic recruitment of Tregs after NKT cell activation. Hepatic CXCL10 levels were markedly increased after alphaGal-C18-Cer administration in wild-type but not in NKT cell-deficient mice. Moreover, approximately 50% of Tregs recruited to the liver after alphaGal-C18-Cer administration expressed CXCR3 and CXCR3+ Treg recruitment into the liver was significantly inhibited in IFN-gamma KO mice, and after CXCL10 neutralization. In addition, prevention of CXCR3+ Treg recruitment into the liver enhanced inflammatory effector cell recruitment into the liver after alphaGal-C18-Cer treatment. These results show that activated NKT cells can induce the hepatic recruitment of Tregs through a cytokine-to-chemokine pathway, which could be relevant in the development of chemokine blocking or NKT cell activating strategies to treat liver diseases.

Apolipoprotein E-Mediated Immune Regulation in Sepsis

Lipids and lipoproteins have emerged as key constituents of the immune response to microbial infection. We, therefore, sought to understand the complex interaction between lipoprotein metabolism and sepsis. Apolipoprotein E (apoE), a component of plasma lipoproteins, has been suggested to bind and traffic Ags for NKT cell activation. However, apoE's role in sepsis has not been demonstrated. In this study, we examined the effect of exogenous apoE in a rat model of septic peritonitis, induced by cecal ligation and puncture. We demonstrate that 48 h after serial injections of apoE, septic mortality increased in a dose-dependent manner. While sepsis resulted in increased splenic and decreased hepatic and circulating NKT cell populations, serial injections of apoE for 24 h after cecal ligation and puncture increased the frequency, cell number, and BrdU uptake in splenic and hepatic NKT cell populations, while concomitantly depleting these populations in the circulation. These changes were correlated with elevated alanine amino transferase levels, an indicator of liver injury. Interestingly, while sepsis increased hepatic T cell apoptosis and necrosis, apoE reversed these changes. apoE also promoted increases in predominantly Th1 cytokine levels in sera and a decrease in IL-4, the main NKT cell-derived Th2 cytokine. Consequently, apoE treatment is associated with increased sepsis-induced mortality, and increased NKT cell frequency and proliferation in the liver and spleen, with concomitant decreases in these NKT cell parameters in the peripheral circulation. apoE treatment also promoted a Th1 cytokine response, increased the degree of liver injury, and decreased apoptosis in hepatic lymphocytes.

Probiotics improve high fat diet-induced hepatic steatosis and insulin resistance by increasing hepatic NKT cells

Dietary factors and intestinal bacteria play an important role in the rapidly increasing incidence of obesity and its associated conditions, such as steatosis and insulin resistance. In the current study, we evaluated the effect of probiotics, and their mechanisms on diet-induced obesity, steatosis and insulin resistance. Wild-type male C57BL6 mice were fed either normal or high fat diets. Some mice received VSL#3 probiotics. Animal weight, hepatic steatosis, insulin resistance, and their relationship to hepatic Natural Killer T cells (NKT) cell number and inflammatory signaling were evaluated. High fat diet induced a depletion of hepatic NKT cells thus leading to insulin resistance and steatosis. Oral probiotic treatment significantly improved the high fat diet-induced hepatic NKT cell depletion, insulin resistance and hepatic steatosis. This effect was NKT cell dependant, resulted from the attenuation of the tumor necrosis factor-alpha and IkappaB kinase inflammatory signaling, and led to an improved sensitivity in insulin signaling. Probiotics improve high fat diet-induced steatosis and insulin resistance. These effects of probiotics are likely due to increased hepatic NKT cell numbers and reduced inflammatory signaling.

Natural killer T cell dysfunction in CD39-null mice protects against concanavalin A–induced hepatitis

Concanavalin A (Con A)-induced injury is an established natural killer T (NKT) cell-mediated model of inflammation that has been used in studies of immune liver disease. Extracellular nucleotides, such as adenosine triphosphate, are released by Con A-stimulated cells and bind to specific purinergic type 2 receptors to modulate immune activation responses. Levels of extracellular nucleotides are in turn closely regulated by ectonucleotidases, such as CD39/NTPDase1. Effects of extracellular nucleotides and CD39 on NKT cell activation and upon hepatic inflammation have been largely unexplored to date. Here, we show that NKT cells express both CD39 and CD73/ecto-5'-nucleotidase and can therefore generate adenosine from extracellular nucleotides, whereas natural killer cells do not express CD73. In vivo, mice null for CD39 are protected from Con A-induced liver injury and show substantively lower serum levels of interleukin-4 and interferon-gamma when compared with matched wild-type mice. Numbers of hepatic NKT cells are significantly decreased in CD39 null mice after Con A administration. Hepatic NKT cells express most P2X and P2Y receptors; exceptions include P2X3 and P2Y11. Heightened levels of apoptosis of CD39 null NKT cells in vivo and in vitro appear to be driven by unimpeded activation of the P2X7 receptor. CD39 and CD73 are novel phenotypic markers of NKT cells. In turn, CD39 expression [corrected] modulates nucleotide-mediated cytokine production by, and limits apoptosis of, hepatic NKT cells. Deletion of CD39 is protective in [corrected] Con A-induced hepatitis. This study illustrates a [corrected] role for purinergic signaling in NKT-mediated mechanisms that result in liver immune injury.

Pathogenic role of natural killer T and natural killer cells in acetaminophen-induced liver injury in mice is dependent on the presence of dimethyl sulfoxide

Dimethyl sulfoxide (DMSO) is commonly used in biological studies to dissolve drugs and enzyme inhibitors with low solubility. Although DMSO is generally thought of as being relatively inert, it can induce biological effects that are often overlooked. An example that highlights this potential problem is found in a recent report demonstrating a pathogenic role for natural killer T (NKT) and natural killer (NK) cells in acetaminophen-induced liver injury (AILI) in C57Bl/6 mice in which DMSO was used to facilitate acetaminophen (APAP) dissolution. We report that NKT and NK cells do not play a pathologic role in AILI in C57Bl/6 mice in the absence of DMSO. Although AILI was significantly attenuated in mice depleted of NKT and NK cells prior to APAP treatment in the presence of DMSO, no such effect was observed when APAP was dissolved in saline. Because of this unexpected finding, the effects of DMSO on hepatic NKT and NK cells were subsequently investigated. When given alone, DMSO activated hepatic NKT and NK cells in vivo as evidenced by increased NKT cell numbers and higher intracellular levels of the cytotoxic effector molecules interferon-gamma (IFN-gamma) and granzyme B in both cell types. Similarly, when used as a solvent for APAP, DMSO again increased NKT cell numbers and induced IFN-gamma and granzyme B expression in both cell types. These data demonstrate a previously unappreciated effect of DMSO on hepatic NKT and NK cells, suggesting that DMSO should be used cautiously in experiments involving these cells.

Hepatic NKT cells: friend or foe?

The innate immune system represents a critical first line of host response to infectious, injurious and inflammatory insults. NKT cells (natural killer T-cells) are an important, but relatively poorly understood, component of the innate immune response. Moreover, NKT cells are enriched within the liver, suggesting that within the hepatic compartment NKT cells probably fulfil important roles in the modulation of the immune response to infection or injury. NKT cells are characterized by their rapid activation and secretion of large amounts of numerous types of cytokines, including those within the Th1-type, Th2-type and Th17-type groups, which in turn can interact with a multitude of other cell types within the liver. In addition, NKT cells are capable of participating in a wide array of effector functions with regards to other cell types via NKT cell-surface-molecule expression [e.g. FASL (FAS ligand) and CD40L (CD40 ligand)] and the release of mediators (e.g. perforin and granzyme) contained in cellular granules, which in turn can activate or destroy other cells (i.e. immune or parenchymal cells) within the liver. Given the huge scope of potential actions that can be mediated by NKT cells, it has become increasingly apparent that NKT cells may fulfil both beneficial (e.g. clearance of virally infected cells) and harmful (e.g. induction of autoimmunity) roles in the setting of liver disease. This review will outline the possible roles which may be played by NKT cells in the setting of specific liver diseases or conditions, and will discuss the NKT cell in the context of its role as either a 'friend' or a 'foe' with respect to the outcome of these liver disorders.