Involvement of natural killer cells in PolyI:C-induced liver injury

Toll-like receptor 3 in liver diseases

Toll-like receptor 3 (TLR3) is a member of the TLR family that can recognize double-stranded RNA (dsRNA), playing an important role in antiviral immunity. Recent studies have shown that TLR3 is also expressed on parenchymal and nonparenchymal cells in the liver as well as on several types of immune cells. In this review, we summarize the role of TLR3 in liver injury, inflammation, regeneration, and liver fibrosis, and discuss the implication of TLR3 in the pathogenesis of human liver diseases including viral hepatitis and autoimmune liver disease.

Activation of natural killer cells inhibits liver regeneration in toxin-induced liver injury model in mice via a tumor necrosis factor-alpha-dependent mechanism

Liver lymphocytes are enriched in natural killer (NK) cells, and activation of NK cells by injection of polyinosinic-polycytidylic acid (poly I:C) inhibits liver regeneration in the partial hepatectomy model via production of IFN-gamma. However, the role of NK cells in liver regeneration in a model of carbon tetrachloride (CCl(4))-induced liver injury remains unknown. In this study, we investigated the effect of activation of NK cells induced by poly I:C on liver regeneration in the CCl(4) model. Administration of poly I:C suppressed liver regeneration in CCl(4)-treated mice. Depletion of NK cells but not Kupffer cells or T cells restored liver regeneration in poly I:C/CCl(4)-treated mice. Poly I:C and CCl(4) cotreatment synergistically induced accumulation of NK cells in the liver and NK cell production of IFN-gamma and tumor necrosis factor (TNF)-alpha. Serum levels of these two cytokines were also synergistically induced after poly I:C and CCl(4) treatment. Finally, blockage of TNF-alpha but not IFN-gamma restored liver regeneration in poly I:C/CCl(4)-treated mice. Taken together, these findings suggest that poly I:C treatment inhibits liver regeneration in the CCl(4)-induced liver injury model via induction of NK cell production of TNF-alpha.

Toll-like receptor 3 ligand dampens liver inflammation by stimulating Valpha 14 invariant natural killer T cells to negatively regulate gammadeltaT cells

Valpha14 invariant natural killer T (Valpha14iNKT) cells are at the interface between the innate and adaptive immune responses and are thus critical for providing full engagement of host defense. We investigated the role of polyriboinosinic:polycytidylic acid (poly I:C), a replication-competent viral double-stranded RNA mimic and a specific agonist that recognizes the cellular sensor Toll-like receptor 3 (TLR3), in regulating Valpha14iNKT cell activation. We established for the first time that hepatic Valpha14iNKT cells up-regulate TLR3 extracellularly after poly I:C treatment. Notably, activation of TLR3-expressing hepatic Valpha14iNKT cells by a TLR3 ligand was suppressed by TLR3 deficiency. Our studies also revealed that Valpha14iNKT cell activation in response to poly I:C administration uniquely suppressed the accumulation and activation of intrahepatic gammadeltaT cells (but not natural killer cells) by inducing apoptosis. Furthermore, we established that activated hepatic Valpha14iNKT cells (via cytokines and possibly reactive oxygen species) influenced the frequency and absolute number of intrahepatic gammadeltaT cells, as evidenced by increased hepatic gammadeltaT cell accumulation in Valpha14iNKT cell-deficient mice after poly I:C treatment relative to wild-type mice. Thus, hepatic Valpha14iNKT cells and intrahepatic gammadeltaT cells are functionally linked on application of TLR3 agonist. Overall, our results demonstrate a novel and previously unrecognized anti-inflammatory role for activated hepatic Valpha14iNKT cells in negatively regulating intrahepatic gammadeltaT cell accumulation (probably through TLR3 signaling) and thereby preventing potentially harmful activation of intrahepatic gammadeltaT cells.

The beta2 integrin CD11b attenuates polyinosinic:polycytidylic acid-induced hepatitis by negatively regulating natural killer cell functions

The beta2 integrins play a key role in inflammation and immune responses. The beta2 integrin CD11b has been shown recently to be important in the maintenance of tolerance; however, the underlying mechanisms remain to be fully understood. Natural killer (NK) cells are an important effector of innate immunity but are also a regulator of adaptive immune response. How the activating and inhibitory signals are balanced to determine NK cell function needs to be further identified. CD11b expression was dramatically up-regulated on NK cells once they matured and became activated; therefore, we investigated the role of inducible CD11b in the regulation of NK cells. Neutralizing anti-CD11b antibody enhanced cytotoxicity, interferon-gamma (IFN-gamma) and granzyme B production of Toll-like receptor 3 (TLR3)-triggered NK cells. CD11b-deficient NK cells stimulated with or without the TLR3 ligand polyinosinic:polycytidylic acid [poly(I:C)] exhibited more potent cytotoxicity, and higher production of IFN-gamma and granzyme B. Through in vivo depletion of NK cells and adoptive transfer of CD11b-deficient NK cells, we demonstrated that CD11b-mediated suppression of NK cell function was responsible for attenuation of poly(I:C)-induced acute hepatitis by CD11b.

CONCLUSION

Our findings demonstrate that CD11b negatively regulates NK cell activation and thus attenuates poly(I:C)-induced acute hepatitis. Our study provides a new mechanistic explanation for maintenance of tolerance and control of inflammation by CD11b.

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.

NKG2D-retinoic acid early inducible-1 recognition between natural killer cells and Kupffer cells in a novel murine natural killer cell-dependent fulminant hepatitis

Increasing evidence suggests the contribution of natural killer (NK) cells to pathogenesis of human hepatitis, but the detailed mechanisms have yet to be clearly elucidated. In this study, injection of polyinosinic:polycytidylic acid (poly I:C) and D-galactosamine (D-GalN) was used to establish a novel murine fulminant hepatitis model: results showed that predepletion of either NK cells or Kupffer cells could completely abolish the liver injury. Injection of poly I:C/D-GalN into mice could promote tumor necrosis factor-alpha production and surface retinoic acid early inducible-1 (Rae1) protein expression by Kupffer cells, which then activated NK cells to produce interferon-gamma via NKG2D-Rae1 recognition. NK cell-derived interferon-gamma and Kupffer cell-derived tumor necrosis factor-alpha synergistically mediated the severe liver injury. Moreover, Kupffer cell-derived interleukin-12 and interleukin-18 were also found to improve cross talk between NK cells and Kupffer cells.

CONCLUSION

These results provide the first in vivo evidence that NKG2D/ligand interaction is involved in the synergic effects of NK cells and Kupffer cells on acute liver injury.

Effect of polyI:C cotreatment on halothane-induced liver injury in mice

Drug-induced liver injury (DILI) is a challenging problem in drug development and clinical practice. Patient susceptibility to DILI is multifactorial, making these reactions difficult to predict and prevent. Clinical observations have suggested that concurrent bacterial and viral infections represent an important risk factor in determining patient susceptibility to developing adverse drug reactions, although the underlying mechanism is not clear. In the present study, we employed the viral RNA mimetic (polyinosinic-polycytidylic acid [polyI:C]) to emulate viral infection and examined its effect on halothane-induced liver injury. Although pretreatment of mice with polyI:C attenuated halothane hepatotoxicity due to its inhibitory effect on halothane metabolism, posttreatment significantly exacerbated liver injury with hepatocellular apoptosis being significantly higher than that in mice treated with polyI:C alone or halothane alone. The pan-caspase inhibitor z-VAD-fmk suppressed liver injury induced by polyI:C/posthalothane cotreatment, suggesting that the increased hepatocyte apoptosis contributes to the exacerbation of liver injury. Posttreatment with polyI:C also caused activation of hepatic Kupffer cells (KCs) and natural killer (NK) cells and upregulated multiple proapoptotic factors, including tumor necrosis factor-alpha (TNF-alpha), NK receptor group 2, member D (NKG2D), and Fas ligand (FasL). These factors may play important roles in mediating polyI:C-induced hepatocyte apoptosis.

CONCLUSION

This is the first study to provide evidence that concurrent viral infection can inhibit cytochrome (CYP)450 activities and activate the hepatic innate immune system to proapoptotic factors. DILI may be attenuated or exacerbated by pathogens depending on the time of infection.

CD4+ CD25+ Foxp3+ regulatory T cells protect against T cell-mediated fulminant hepatitis in a TGF-beta-dependent manner in mice

Regulatory T cells (Tregs), which are characterized by expression of CD4, CD25, and Foxp3, play a crucial role in the control of immune responses to both self and non-self Ags. To date, there are only limited data on their role in physiological and pathological hepatic immune responses. In this study, we examined the role of hepatic Tregs in immune-mediated liver injury by using the murine Con A-induced hepatitis model. Con A treatment was associated with an increased number of Foxp3(+) Tregs in liver but not in spleen. Moreover, the expression levels of Foxp3, CTLA-4, glucocorticoid-induced TNF receptor, as well as the frequency of CD103 of Tregs were increased after Con A injection, being significantly higher in liver than in spleen. Depleting CD25(+) cells aggravated liver injury, whereas adoptively transferring CD25(+) cells or Tregs reduced liver injury in Con A-treated recipients. Con A treatment induced elevated serum levels and hepatic mononuclear mRNA expressions of TGF-beta, which were reduced by Tregs depletion. In addition, anti-TGF-beta mAbs blocked the suppressive function of Tregs from Con A-treated mice in vitro. Finally, TGF-beta receptor II dominant-negative mice, whose T cells express a dominant negative form of TGFbetaRII and therefore cannot respond to TGF-beta, had a higher mortality rate and severer liver injury than normal mice injected with the same dose of Con A. These results indicate that CD4(+)CD25(+) Tregs play an important role in limiting the liver injury in Con A-induced hepatitis via a TGF-beta-dependent mechanism.

Characterization of the role of TCR gammadelta in NK cell accumulation during viral liver inflammation

Polyinosinic-polyctidylic acid (Poly I:C) is a viral RNA mimic that can induce immune responses similar to that seen during viral infection. Although poly I:C administration into mice is associated increased NK cell infiltrates in the liver, the mechanisms underlying increased hepatic NK cell accumulation in response to poly I:C administration are incompletely defined. In the current study, we have identified a novel and important role for gammadelta T cells in driving the accumulation and activation of NK cells in the liver during poly I:C-mediated viral liver infection. Specifically, NK cell accumulation but not activation in gammadelta T cell deficient mice following poly I:C administration was significantly attenuated in comparison to that seen in poly I:C-treated wildtype mice. The ability of gammadelta T cells to promote NK cell accumulation and activation in the liver may be virus-specific since NK cell accumulation in the liver was not altered by TCR gammadelta deficiency following adenovirus administration.

The importance of immune dysfunction in determining outcome in acute liver failure

Acute liver failure (ALF) shares striking similarities with septic shock with regard to the features of systemic inflammation, progression to multiple organ dysfunction and functional immunoparesis. While the existence of opposing systemic pro- and anti-inflammatory profiles resulting in organ failure and immune dysfunction are well recognised in septic shock, characterization of these processes in ALF has only recently been described. This review explores the evolution of the systemic inflammation in acute liver failure, its relation to disease progression, exacerbation of liver injury and development of innate immune dysfunction and extra-hepatic organ failure as sequelae. Defects in innate immunity are described in hepatic and extra-hepatic compartments. Clinical studies measuring levels of pro- and anti-inflammatory cytokines and expression of the antigen presentation molecule HLA-DR on monocytes, in combination with ex-vivo experiments, demonstrate that the persistence of a compensatory anti-inflammatory response syndrome, leading to functional monocyte deactivation, is a central event in the evolution of systemic immune dysfunction. Accurate immune profiling in ALF may permit the development of immunomodulatory strategies in order to improve outcome in this condition.

NK and NKT cells in liver injury and fibrosis

The innate immune mechanisms of the liver represent an important first line of defense against bacterial products, toxins, and food antigens coming from the intestine. Natural Killer (NK) and Natural Killer T cells (NKT) are components of the innate immune system with increased presence in the liver compared to other organs and have been reported to participate in the inflammatory processes during hepatic diseases. However significant confusion has been noted in this field mainly due to changes in the characterization of these cells as new knowledge accumulates and due to differences in the approaches used for their study. Both cell types can mediate hepatic injury in several models but studies in human liver diseases have not managed to fully explain their functions. However accumulating evidence supports an antifibrotic role of NK cells mainly via an inhibitory effect on hepatic stellate cells by inducing apoptosis and via production of interferon-gamma. Therefore, downregulation of NK cells during most types of liver injury may facilitate liver fibrosis. Data about the role of NKT cells in liver fibrosis are limited. This review will summarize the studies about the role of NK and NKT cells in liver diseases with a special interest in hepatic injury and liver fibrosis.

Relationship between Kupffer cells and the liver injury induced by chronic HBV infection

The infection of hepatitis B virus (HBV) is the most common cause of many kinds of chronic liver diseases such as liver cirrhosis and liver cancer. Kupffer cells are the first cells to be exposed to the materials absorbed from gastrointestinal tract, and play a key role in innate immune responses and host defence. Activated Kupffer cells can express TLRs, FasL, PD-L1 and secret lots of inflammatory mediators, reactive oxygen species, nitric oxide (NO) and so on, which can take effect on HBV-infected hepatocytes, and play critical roles in the progress of immunotolerance of chronic HBV infection and subsequent liver injury.

Activation of innate immunity (NK/IFN-gamma) in rat allogeneic liver transplantation: contribution to liver injury and suppression of hepatocyte proliferation

Liver transplantation is presently the only curative treatment for patients with end-stage liver disease. However, the mechanisms underlying liver injury and hepatocyte proliferation posttransplantation remain obscure. In this investigation, liver injury and hepatocyte proliferation in syngeneic and allogeneic animal models were compared. Male Lewis and Dark Agouti (DA) rats were subjected to orthotopic liver transplantation (OLT). Rat OLT was performed in syngeneic (Lewis-Lewis) and allogeneic (Lewis-DA or DA-Lewis) animal models. Allogeneic liver grafts exhibited greater injury and cellular apoptosis than syngeneic grafts but less hepatocyte proliferation after OLT. Expression of IFN-gamma mRNA and activation of the downstream signal transducer and activator of transcription 1 (STAT1) and genes (interferon regulatory factor-1 and cyclin-dependent kinase inhibitor p21(CDKN1A)) were also greater in the allogeneic grafts compared with the syngeneic grafts. In contrast, STAT3 activation was lower in the allogeneic grafts. Furthermore, in the allogeneic grafts, depletion of natural killer (NK) cells decreased IFN-gamma/STAT1 activation but enhanced hepatocyte proliferation. These findings suggest that, compared with syngeneic transplantation, innate immunity (NK/IFN-gamma) is activated after allogeneic transplantation, which likely contributes to liver injury and inhibits hepatocyte proliferation.

Activation of natural killer cells inhibits liver fibrosis: a novel strategy to treat liver fibrosis

Liver lymphocytes are enriched in natural killer (NK) cells, which are involved in innate immune defenses against viral infection and tumor transformation in the liver. Recent evidence indicates that NK cell activation by IFN-alpha, IFN-gamma or dsRNA attenuates liver fibrosis through the direct killing of activated hepatic stellate cells (HSCs). Interestingly, NK cells do not kill quiescent or fully activated HSCs, but only early-activated HSCs, as only these cells express elevated levels of the NK cell-activating ligand retinoic acid-induced early transcript (RAE)-1 and TNF-related apoptosis-inducing ligand receptors, in addition to downregulated levels of the NK-cell inhibitory ligand, MHC-I. Inhibition of liver fibrosis by NK cells can also be achieved through production of IFN-gamma, which induces HSC cell cycle arrest and apoptosis in a STAT1-dependent manner. Clinically, it has also been observed that NK cell activity is negatively correlated with liver fibrosis in patients with chronic hepatitis C infection. Therefore, since NK cells inhibit liver fibrosis, stimulating NK activity could potentially be a novel strategy to treat liver fibrosis. Clinical studies will be required to confirm whether stimulating NK cell activity is effective and safe in treating human liver fibrosis.

Liver-specific HBsAg transgenic mice are over-sensitive to Poly(I:C)-induced liver injury in NK cell- and IFN-gamma-dependent manner

BACKGROUND/AIMS

The role of natural killer (NK) cells in the development of hepatitis B virus (HBV)-associated liver injury remains obscure. In this study, we elucidated the role of NK cells in liver injury of HBsAg transgenic mice (HBs-B6), a mimic of human healthy chronic HBsAg carriers, triggered by polyinosinic:polycytidylic acid [Poly(I:C)].

METHODS

HBs-B6 or wild B6 mice were intraperitoneally injected with Poly(I:C) at different doses. Liver injury was evaluated by serum transaminase activity and histopathologic changes.

RESULTS

HBs-B6 mice were over-sensitive to Poly(I:C)-induced liver injury, which was absolutely dependent on the presence of NK cells and IFN-gamma produced by intrahepatic NK cells. Much stronger IFN-gamma receptor expression was observed on hepatocytes of HBs-B6 mice, which was significantly enhanced by Poly(I:C) injection. Treatment with IFN-gammain vitro triggered much higher activation of downstream signals (pSTAT1-IRF-1) in hepatocytes of HBs-B6 mice. Depletion of Kupffer cells and neutralization of endogenous IL-12 did not affect Poly(I:C)-induced over-sensitive liver injury in HBs-B6 mice.

CONCLUSIONS

NK cells played a critical role in an IFN-gamma dependent, Kupffer cell- and IL-12-independent manner in over-sensitive liver injury triggered by Poly(I:C) in murine chronic HBsAg carriers.

CCR5 deficiency drives enhanced natural killer cell trafficking to and activation within the liver in murine T cell-mediated hepatitis

Natural killer (NK) cells are innate immune cells that are enriched in the liver, but the processes underlying NK cell trafficking to the liver and cellular activation within the liver of patients with T cell-mediated liver diseases remain poorly defined. Concanavalin A (Con A) hepatitis is a murine model mimicking many aspects of human T cell-mediated liver diseases. Here we demonstrate that severe hepatitis in CCR5-deficient (KO) mice is associated with increased hepatic NK cell recruitment driven by enhanced hepatic production of CCL5 acting via CCR1 and by enhanced hepatic NK cell activation relative to that observed in wild-type mice after Con A administration. Furthermore, NK cell depletion ameliorated severe hepatitis in CCR5 KO mice but did not alter hepatitis in wild-type mice after Con A treatment. We propose that in the setting of CCR5 deficiency NK cells assume a profound effector role in Con A hepatitis via enhanced CCL5-CCR1 driven hepatic recruitment in addition to augmented cytokine-driven NK cell activation to produce interferon-gamma. These results highlight the potential profound impact of altered chemokine receptor expression on the innate immune response in the setting of T cell-mediated hepatitis.

Impairment of liver regeneration correlates with activated hepatic NKT cells in HBV transgenic mice

A fraction of HBV carriers have a risk to develop liver cancer. Because liver possesses a strong regeneration capability, surgical resection of cancerous liver or transplantation with healthy liver is an alternate choice for HBV-caused hepatocarcinoma therapy. How HBV infection affects the regeneration of hepatectomized or transplanted liver remains elusive. We report that partial hepatectomy (PHx)-induced liver regeneration was reduced in HBV transgenic (HBV-tg) mice, a model of human HBV infection. PHx markedly triggered natural killer T (NKT) cell accumulation in the hepatectomized livers of HBV-tg mice, simultaneously with enhanced interferon gamma (IFN-gamma) production and CD69 expression on hepatic NKT cells at the early stage of liver regeneration. The impairment of liver regeneration in HBV-tg mice was largely ameliorated by NKT cell depletion, but not by natural killer (NK) cell depletion. Blockage of CD1d-NKT cell interaction considerably alleviated NKT cell activation and their inhibitory effect on regenerating hepatocytes. Neutralization of IFN-gamma enhanced bromodeoxyuridine incorporation in HBV-tg mice after PHx, and IFN-gamma mainly induced hepatocyte cell cycle arrest. Adoptive transfer of NKT cells from regenerating HBV-tg liver, but not from normal mice, could inhibit liver regeneration in recipient mice.

CONCLUSION

Activated NKT cells negatively regulate liver regeneration of HBV-tg mice in the PHx model.

Chronic ethanol consumption inhibits hepatic natural killer cell activity and accelerates murine cytomegalovirus-induced hepatitis

BACKGROUND

Chronic alcohol drinking accelerates the progression of liver disease in patients with hepatitis viral infection; however, the underlying mechanisms are not fully understood.

METHODS

Here, we examined the effects of chronic ethanol feeding on hepatic natural killer (NK) cells and liver injury in 2 murine models of liver injury: injection of synthetic double-stranded RNA polyinosinic-polycytidylic acid (poly I:C), which mimics viral infection, and infection with murine cytomegalovirus (MCMV). Mice were fed the Lieber-DeCarli liquid diet containing 5% (vol/vol) ethanol for 8 weeks, resulting in a significant decrease in the percentage and total number of NK cells in the liver.

RESULTS

In control, pair-fed mice, poly I:C injection induced NK cell accumulation in the liver and activated hepatic NK cell cytotoxicity, whereas such induction and activation were diminished in ethanol-fed mice. Treatment with poly I:C also induced expression of NKG2D, granzyme B, perforin, Fas L, TRAIL, and IFN-gamma on liver lymphocytes, which were delayed or reduced in ethanol-treated mice compared with pair-fed mice. In contrast, chronic ethanol feeding did not affect poly I:C-induced mild liver injury. Furthermore, MCMV infection activated hepatic NK cells and induced hepatic inflammation and injury. Chronic ethanol consumption inhibited hepatic NK cell activation during MCMV infection, but enhanced MCMV-induced liver injury, viral titer, and inflammation in the liver.

CONCLUSIONS

Taken together, these findings suggest that chronic ethanol consumption decreases hepatic NK activity, thereby accelerating MCMV-induced hepatitis and liver injury.

The adjuvant effects of the toll-like receptor 3 ligand polyinosinic-cytidylic acid poly (I:C) on antigen-specific CD8+ T cell responses are partially dependent on NK cells with the induction of a beneficial cytokine milieu

Poly (I:C), a TLR3 ligand, has shown promise as a vaccine adjuvant to CD8(+) T cell responses. The underlying mechanisms involved in creating this adjuvant response in vivo, however, have not been well defined. In this study, we explored the contribution of NK cells and inflammatory cytokines in mediation the poly (I:C) adjuvant effects. Enhanced antigen-specific CD8(+) T cell responses were observed only when poly (I:C) was administered within 4h of peptide vaccination. Poly (I:C) treatment was associated with a rapid induction of inflammatory cytokines in the serum, including IL-6, IL-10, MCP-1, TNF-alpha, IFN-alpha, and IFN-gamma, and selective increases in the numbers of NK (NK1.1(+)CD11b(+)) cells and Mvarphi (NK1.1(-)CD11b(+)), but not NK T (CD3(+)NK1.1(+)) cells. NK cells were required for the adjuvant effects of poly (I:C). Poly (I:C) treatment in TNF-alpha, type I IFNR, IFN-gamma, IL-6, IL-12Rbeta2, or IL-15 gene-deficient mice revealed a reciprocal interaction and interdependence in the induction of these cytokines, where the absence of one cytokine impacted on the production of others. Further, the adjuvant effects of poly (I:C) were dependent on the endogenous levels of type I IFNs, TNF-alpha, IFN-gamma, IL-12, and IL-15. IFN-alpha and IFN-beta, but not TNF-alpha or IL-6, were able to mimic the adjuvant effects of poly (I:C). We conclude that the adjuvant effects of poly (I:C) on antigen-specific CD8(+) T cells appeared to be exquisitely dependent on the rapid induction of certain beneficial cytokines produced in part by NK cells.

Increased killing activity and decreased cytokine production in NK cells in patients with primary biliary cirrhosis

Although the pathogenesis of primary biliary cirrhosis (PBC) remains enigmatic, the immune system plays a key role in the initiation and subsequent development of pathology. Previous studies have indicated a critical role of the innate immune system. Importantly, natural killer (NK) cells are abundant in liver where they serve as sentinels of the immune system. In addition, NK cells have significant biologic activity based on their production of immunoregulatory cytokines. To address this issue, we have investigated several qualitative and quantitative activities of NK cells in patients with PBC as well as normal and liver diseased controls. We report herein a marked increase in the frequency and absolute number of blood and liver NK cells in PBC patients. Moreover, the cytotoxic activity and perforin expression by isolated NK cells were significantly increased in PBC patients associated with increased levels of plasma IL-8 and the expression of CD128a (IL-8 receptor) on NK cells. In contrast, the levels of IFN-gamma, IL-6 and IL-8 synthesized by NK cells were significantly decreased in PBC patients as compared to controls. In conclusion, data from this study provide compelling evidence supporting a biologic role of NK cells in the immunopathogenesis of PBC.

Impaired NK cell cytotoxicity by high level of interferon-gamma in concanavalin A-induced hepatitis

Unlike T cells, the role of natural killer (NK) cells is not well documented in the concanavalin (ConA)- induced hepatitis model. This study aimed to investigate the regulatory effect of high levels of interferon-gamma (IFN-gamma) on NK cells in ConA-induced hepatitis. The cytotoxicities of NK cells from ConA-injected mice or NK cell lines (NK92 and NKL) were detected by the 4-h 51Cr release assay. Depletion of NK cells with AsGM1 antibody was used to assess the NK cell role in ConA-induced hepatitis. Expression of NK cell receptors and cytotoxic molecules was measured by reverse transcription-polymerase chain reaction. Twelve hours after ConA injection, serum IFN-gamma was significantly increased in wild mice, but not in severe combined immunodeficiency mice, and hepatic NK cells exerted impaired cytotoxicity against YAC-l cells in wild mice. Eight hours after NK cells were incubated in serum from ConA-treated mice, NK cell cytotoxicity was down-modulated and the effect was abolished by pretreatment with neutralizing serum IFN-gamma with specific antibody in vitro. A high concentration of IFN-gamma (> 1000 U/mL) inhibited the cytotoxicities of 2 NK cell lines in vitro, accompanied with down-regulation of NKG2D transcripts and up-regulation of NKG2A/B and KIR2DL transcripts. The inhibitive role of IFN-gamma was not seen in NKG2D ligand negative cells. These results suggest that NK cell cytotoxicity was inhibited by high levels of IFN-gamma in ConA-induced hepatitis, which may relate to the dispensable role of NK cells.

Differential liver sensitization to toll-like receptor pathways in mice with alcoholic fatty liver

Gut-derived, endotoxin-mediated hepatocellular damage has been postulated to play a crucial role in the pathogenesis of alcohol-induced liver injury in rodents. Endotoxins induce production of tumor necrosis factor alpha (TNF-alpha) by Kupffer cells via Toll-like receptor (TLR) 4 and contribute to liver injury. This study addressed the contribution of other TLRs and ligands to alcoholic fatty liver. C57Bl6/J mice were fed a modified Lieber-DeCarli diet. Serum aminotransferase measurements, histological analysis, and quantification of liver TNF-alpha and TLR1-9 messenger RNA (mRNA) were performed. The effect of TLR ligands on liver injury was assessed in vivo. Neomycin and metronidazole or diphenyleneiodonium sulfate (DPI) were administered to evaluate the role of gut bacteria and NADPH oxidase activity, respectively, in hepatic TLR expression. Enteral ethanol (EtOH) exposure induced steatosis and increased liver weight, aminotransferase levels, and expression of TLR1, 2, 4, 6, 7, 8, and 9 liver mRNA. Injection of lipoteichoic acid, peptidoglycan (PGN), lipopolysaccharide (LPS), loxoribine, and oligonudeotide containing CpG (ISS-ODN) increased TNF-alpha mRNA expression more in the livers of EtOH-fed mice than in control mice. PGN, LPS, flagellin, and ISS-ODN induced liver inflammatory infiltrate in EtOH-fed mice but not control mice. Addition of antibiotics reduced the severity of alcoholic fatty liver without affecting TLR expression, whereas daily DPI injections reduced the EtOH-mediated upregulation of TLR2, 4, 6, and 9 mRNA. In conclusion, EtOH-fed mice exhibited an oxidative stress dependent on upregulation of multiple TLRs in the liver and are sensitive to liver inflammation induced by multiple bacterial products recognized by TLRs.

Poly I:C prevents T cell-mediated hepatitis via an NK-dependent mechanism

BACKGROUND/AIMS

T cell immune responses play key roles in the pathogenesis of viral hepatitis, and innate immunity is known to be also activated during this process, however, the effects of innate immunity activation on T cell-mediated hepatitis remain obscure. Here we examined the effect of the activation of NK cells induced by toll-like receptor 3 (TLR3) ligand, polyinosinic-polycytidylic acid (poly I:C), on concanavalin A (Con A)-induced T cell-mediated liver injury.

METHODS

Mice received nontoxic intraperitoneal poly I:C injection before Con A intravenous administration. The liver injury was examined by measuring serum transaminase and pathology, and the function of hepatic lymphocytes was detected by FACS analysis.

RESULTS

Poly I:C pretreatment protected against T cell-mediated hepatitis, as evidenced by decreased mortality, hepatic necrosis, serum transaminase levels and inflammatory cytokines (IL-4, IFN-gamma). The protective effect of poly I:C was diminished in NK-depleted mice, which could be partially restored by adoptive transfer of NK cells. Administration of poly I:C caused NKT and T cell apoptosis via enhancing expression of Fas protein on these cells and expression of Fas ligand on NK cells.

CONCLUSIONS

These findings suggest that activation of NK cells by poly I:C prevents Con A-induced T cell-hepatitis via downregulation of T/NKT cells and subsequent reduction of inflammatory cytokines.

Natural killer cells ameliorate liver fibrosis by killing activated stellate cells in NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent manners

BACKGROUND & AIMS

Viral hepatitis infection, which is a major cause of liver fibrosis, is associated with activation of innate immunity. However, the role of innate immunity in liver fibrosis remains obscure.

METHODS

Liver fibrosis was induced either by feeding mice with the 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet or by injecting them with carbon tetrachloride. The Toll-like receptor 3 ligand, polyinosinic-polycytidylic acid, was used to activate innate immunity cells and mediators, including natural killer cells and interferon gamma.

RESULTS

In the mouse model of DDC-induced liver fibrosis, natural killer cell activation by polyinosinic-polycytidylic acid induced cell death to activated hepatic stellate cells and attenuated the severity of liver fibrosis. Polyinosinic-polycytidylic acid treatment also ameliorated liver fibrosis induced by carbon tetrachloride. The observed protective effect of polyinosinic-polycytidylic acid on liver fibrosis was diminished through either depletion of natural killer cells or by disruption of the interferon gamma gene. Expression of retinoic acid early inducible 1, the NKG2D ligand, was undetectable on quiescent hepatic stellate cells, whereas high levels were found on activated hepatic stellate cells, which correlated with the resistance and susceptibility of quiescent hepatic stellate cells and activated hepatic stellate cells to natural killer cell lysis, respectively. Moreover, treatment with polyinosinic-polycytidylic acid or interferon gamma enhanced the cytotoxicity of natural killer cells against activated hepatic stellate cells and increased the expression of NKG2D and tumor necrosis factor-related apoptosis-inducing ligand on liver natural killer cells. Blocking NKG2D or tumor necrosis factor-related apoptosis-inducing ligand with neutralizing antibodies markedly diminished the cytotoxicity of polyinosinic-polycytidylic acid-activated natural killer cells against activated hepatic stellate cells.

CONCLUSIONS

Our findings suggest that natural killer cells kill activated hepatic stellate cells via retinoic acid early inducible 1/NKG2D-dependent and tumor necrosis factor-related apoptosis-inducing ligand-dependent mechanisms, thereby ameliorating liver fibrosis.

Pre-activation of T lymphocytes by low dose of concanavalin A aggravates toll-like receptor-3 ligand-induced NK cell-mediated liver injury

Concanavalin A (Con A), a widely used murine T cell stimulator, could induce T cell-mediated hepatitis when used in an abundant dosage. However, the immune-modulating role of non-hepatotoxic dosage of Con A in hepatic immune responses remains obscure. In order to evaluate the effect of non-hepatotoxic Con A on hepatic NK cells, pretreatment of mice with low dose of Con A was performed on polyinosinic-polycytidylic acid (poly I:C) [toll-like receptor-3 (TLR-3) ligand]-induced NK cell-mediated hepatitis. The role of the Con A-pre-activated T cells in NK cell function was then determined. The results demonstrated that Con A pretreatment aggravated poly I:C-induced liver injury with elevation of serum transaminases, hepatic necrosis and serum IFN-gamma level. In parallel to the enhanced accumulation of activated NK cells into liver, the natural cytotoxicity and IFN-gamma production by hepatic NK cells were significantly augmented. Moreover, depletion of T cells suppressed the aggravating effect of Con A pretreatment. Collectively, the aggravation of poly I:C-induced hepatitis by Con A pretreatment may be due to the generation of more vigorous NK cells which is dependent on the presence of T cells. This investigation will help to explain the synergistic effects of NK and T cells in liver inflammatory injury.

Impaired function of hepatic natural killer cells from murine chronic HBsAg carriers

In the present study, we demonstrated hepatic NK cells in murine chronic HBsAg carriers for the first time. It was found that the number of hepatic NK cells was decreased; natural activation of hepatic NK cells was declined; and cytotoxicity of hepatic NK cells was attenuated, which might relate to the down-regulated expression of TRAIL on hepatic NK cells. Additionally, the response of hepatic NK cells to the specific stimulation of Poly (I:C) in murine chronic HBsAg carriers was changed. The increase in anti-tumor cytotoxic activity of intrahepatic activated NK cells was markedly impaired in the transgenic mice. The transgenic mice used here had high incidence of hepatocellular carcinoma, which might result from the relative weak reactivity and impaired anti-tumor activity of NK cells in the liver. Furthermore, remarkable liver injury was observed after stimulation of Poly (I:C), demonstrating the hypersensitivity to Poly (I:C) of murine chronic HBsAg carriers which might be related to the accumulated NK cells in the liver. Why the murine chronic HBsAg carriers are characterized with impaired hepatic NK cells and the implication of the impaired hepatic NK cells in pathogenesis of HBV-related diseases, such as hepatocellular carcinoma and recrudescent hepatitis, is worth of further investigating. These results of the functions of hepatic NK cells in murine chronic HBsAg carriers would contribute to interpreting the immune responses of NK cells in the liver and the immunological mechanisms of liver diseases in human chronic HBsAg carriers.

Toll-like receptor 3 ligand attenuates LPS-induced liver injury by down-regulation of toll-like receptor 4 expression on macrophages

This study demonstrates that pretreatment with polyinosinic-polycytidylic acid (poly I:C) significantly decreased the mortality and liver injury caused by injection of lipopolysaccharide (LPS) in the presence of d-galactosamine (d-GalN) in C57BL/6 mice. Depletion of natural killer, natural killer T, and T cells did not change the protective effect of poly I:C on LPS/d-GalN-induced liver injury in vivo. However, depletion of macrophages abolished LPS/d-GalN-induced fulminant hepatitis, which could be restored by adoptive transfer of macrophages but not by transfer of poly I:C-treated macrophages. Treatment with poly I:C down-regulated the expression of the toll-like receptor 4 (TLR4) on macrophages and reduced the sensitivity of macrophages (Kupffer cells and peritoneal macrophages from C57BL/6 mice, or RAW264.7 cells) to LPS stimulation. Poly I:C pretreatment also impaired the signaling of mitogen-activated protein kinases and NF-kappaB induced by LPS in RAW264.7 cells. Blockade of TLR3 with a TLR3 antibody abolished poly I:C down-regulation of TLR4 expression and LPS stimulation of TNF-alpha production in RAW264.7 cells. Taken together, our findings suggest that activation of TLR3 by its ligand, poly I:C, induced LPS tolerance by down-regulation of TLR4 expression on macrophages.

He Jie Tang in the treatment of chronic hepatitis B patients

AIM: To explore the effect of He Jie Tang (decoction for medication) on serum levels of T lymphocyte subsets, NK cell activity and cytokines in chronic hepatitis B patients.

METHODS: Eighty-five patients with chronic hepatitis B were divided randomly into two groups. Fifty patients in group I were treated with He Jie Tang (HJT) and 35 patients in group II were treated with combined medication. The levels of T-lymphocyte subsets (CD₃⁺, CD₄⁺, CD₈⁺), NK cell activity, cytokines (TNF-α, IL-8, sIL-2R) were observed before and after the treatment. Another 20 normal persons served as group 3.

RESULTS: The level of CD₄⁺ cells and NK cell activity were lower, whereas the level of CD₈⁺ cells in patients was higher than that in normal persons (t = 2.685, 3.172, and 2.754 respectively; P<0.01). The levels of TNF-α, IL-8, and sIL-2R in chronic hepatitis B patients were higher than those in normal persons (t = 3.526, 3.170, and 2.876 respectively; P<0.01). After 6 months of treatment, ALT, AST, and TB levels in the two groups were obviously decreased (t = 3.421, 3.106, and 2.857 respectively; P<0.01). The level of CD₄⁺ cells and NK cell activity were increased whereas the level of CD₈⁺ cells decreased (t = 2.179, 2.423, and 2.677 respectively; P<0.05) in group I. The levels of TNF-α, IL-8, and sIL-2R in group I were decreased significantly after the treatment (t = 2.611, 2.275, and 2.480 respectively; P<0.05) but had no significant difference in group II after the treatment (t = 1.906, 1.833, and 2.029 respectively; P>0.05). The total effective rate had no significant difference between the two groups (X² = 2.882, P>0.05) but the markedly effective rate was significantly different between the two groups (X² = 5.340, P<0.05).

CONCLUSION: HJT is effective in treating chronic hepatitis B. HJT seems to exert its effect by improving the cellular immune function and decreasing inflammatory cytokines in chronic hepatitis B patients. The function of HJT in protecting liver function in the process of eliminating virus needs to be further studied.