Role of Valpha 14 NKT cells in the development of impaired liver regeneration in vivo

Invariant natural killer T cells in autoimmune cholangiopathies: Mechanistic insights and therapeutic implications

Invariant natural killer T cells (iNKT cells) constitute a specialized subset of lymphocytes that bridges innate and adaptive immunity through a combination of traits characteristic of both conventional T cells and innate immune cells. iNKT cells are characterized by their invariant T cell receptors and discerning recognition of lipid antigens, which are presented by the non-classical MHC molecule, CD1d. Within the hepatic milieu, iNKT cells hold heightened prominence, contributing significantly to the orchestration of organ homeostasis. Their unique positioning to interact with diverse cellular entities, ranging from epithelial constituents like hepatocytes and cholangiocytes to immunocytes including Kupffer cells, B cells, T cells, and dendritic cells, imparts them with potent immunoregulatory abilities. Emergering knowledge of liver iNKT cells subsets enable to explore their therapeutic potential in autoimmne liver diseases. This comprehensive review navigates the landscape of iNKT cell investigations in immune-mediated cholangiopathies, with a particular focus on primary biliary cholangitis and primary sclerosing cholangitis, across murine models and human subjects to unravel the intricate involvements of iNKT cells in liver autoimmunity. Additionally, we also highlight the prospectives of iNKT cells as therapeutic targets in cholangiopathies. Modulation of the equilibrium between regulatory and proinflammatory iNKT subsets can be defining determinant in the dynamics of hepatic autoimmunity. This discernment not only enriches our foundational comprehension but also lays the groundwork for pioneering strategies to navigate the multifaceted landscape of liver autoimmunity.

Absence of indoleamine 2,3‑dioxygenase 2 promotes liver regeneration after partial hepatectomy in mice

The partial loss of liver due to liver transplantation or acute liver failure induces rapid liver regeneration. Recently, we reported that the selective inhibition of indoleamine 2,3‑dioxygenase (Ido) 1 promotes early liver regeneration. However, the role of Ido2 in liver regeneration remains unclear. Wild‑type (WT) and Ido2‑deficient (Ido2‑KO) mice were subjected to 70% partial hepatectomy (PHx). Hepatocyte growth was measured using immunostaining. The mRNA expression of inflammatory cytokines and production of kynurenine in intrahepatic mononuclear cells (MNCs) were analyzed using reverse transcription‑quantitative PCR and high‑performance liquid chromatography. The activation of NF‑κB was determined by both immunocytochemistry and western blotting analysis. The ratio of liver to body weight and the frequency of proliferation cells after PHx were significantly higher in Ido2‑KO mice compared with in WT mice. The expression of IL‑6 and TNF‑α in MNCs were transiently increased in Ido2‑KO mice. The nuclear transport of NF‑κB was significantly higher in peritoneal macrophages of Ido2‑KO mice compared with WT mice. These results suggested that Ido2 deficiency resulted in transiently increased production of inflammatory cytokines through the activation of NF‑kB, thereby promoting liver regeneration. Therefore, the regulation of Ido2 expression in MNCs may play a therapeutic role in liver regeneration under injury and disease conditions.

Tissue-specific functions of invariant natural killer T cells

Invariant natural killer T cells (iNKT cells) are an innate-like T cell subset that expresses an invariant T cell receptor (TCR) α-chain and recognizes lipids presented on CD1d. They secrete diverse cytokines and can influence many types of immune responses. Despite having highly similar TCR specificities, iNKT cells differentiate in the thymus into distinct subsets that are analogous to T helper 1 (T_H1), T_H2 and T_H17 cell subsets. Additional iNKT cell subsets that may require peripheral activation have also been described, including one that produces IL-10. In general, iNKT cells are non-circulating, tissue-resident lymphocytes, but the prevalence of different iNKT cell subsets differs markedly between tissues. Here, we summarize the functions of iNKT cells in four tissues in which they are prevalent, namely, the liver, the lungs, adipose tissue and the intestine. Importantly, we explain how local iNKT cell responses at each site contribute to tissue homeostasis and protection from infection but can also contribute to tissue inflammation and damage.

Induction of humoral and cellular immune response to HBV vaccine can be up-regulated by STING ligand

A persistent hepatitis B virus (HBV) infection is characterized by a lack of or a weak immune response to HBV. Efficient induction of the HBV-specific immune response leads to the clearance of HBV. Stimulator of interferon (IFN) genes (STING) is a cytoplasmic sensor of intracellular DNA from microbes and host cells. In the present study, we examined the efficacy of cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) that is a ligand of the STING pathway as an HBV vaccine adjuvant. Wild-type (WT) mice and HBV-transgenic (HBV-Tg) mice were immunized with hepatitis B surface antigen (HBsAg) and cGAMP. The vaccination with HBsAg and cGAMP significantly enhanced the humoral and cellular immune response to HBsAg in WT and HBV-Tg mice. Cytokine production related to Th1 and Th2 responses and the activation of antigen-presenting cells in lymphoid tissues were induced by cGAMP. Vaccination using cGAMP may overcome tolerance in patients with chronic HBV infection.

HBV induces different responses of the hepatocytes and oval cells during HBV-related hepatic cirrhosis

Although hepatitis B virus (HBV)-related cirrhosis and hepatocellular carcinoma (HCC) cause a sever health problem worldwide, the underlying mechanisms are still elusive. This study aimed to investigate the responses of different cell types isolated from HBV transgenic mice. A cross-sectional set of hepatocytes and oval cells were obtained from HBV transgenic and control mice. Flow cytometry, immunohistochemistry and microarray were applied to investigate the cell biology of the hepatocytes and oval cells. Our results showed that HBV induced the proliferation of both cell oval cells and hepatocytes, and induced cell death of HBV hepatocytes while had minimal effects on oval cells. Further molecular and pathways analysis identified some genes and signaling pathways may be responsible for the different responses between oval cells and hepatocytes. In addition, analyses of selectively ten genes by IHC staining in human samples were consistent with microarray data. In summary, HBV transgenic mice is a useful model for studying the biological behaviors of oval cells affected by HBV and HBV-cirrhosis. Also, our results help better understand the mechanisms of HBV induced cirrhosis, and provide novel progenitor markers or prognostic/therapeutic markers.

The Inhibition of Indoleamine 2,3-Dioxygenase Accelerates Early Liver Regeneration in Mice After Partial Hepatectomy

BACKGROUND AND AIM

The inflammatory response accelerates early liver regeneration after liver injury and resection. Recent studies have demonstrated that indoleamine 2,3-dioxygenase-1 (IDO1) suppresses the activation of inflammatory cells and induces immune tolerance. In this study, we examined the role of IDO1 in liver regeneration after partial hepatectomy (PHx).

METHODS

WT or IDO1-knockout (IDO1-KO) mice received 70% PHx. The liver-body weight ratio after PHx was measured and hepatocyte growth was assessed by immunostaining. The expression of cell cycle genes and pro-inflammatory cytokines in the liver was analyzed by quantitative RT-PCR. In addition, 1-methyl-DL-tryptophan (1-MT), which is an IDO1 inhibitory agent, was given to WT mice and the liver-body weight ratio was measured after PHx.

RESULTS

The liver-body weight ratio was significantly increased in IDO1-KO mice compared with that in WT mice after PHx. More Ki-67-positive cells were present in IDO1-KO mice than in WT mice after PHx. The expression of cell cycle genes (cyclin D1, cyclin E) and pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) was up-regulated in the remnant liver of IDO1-KO mice compared with WT mice. Moreover, treatment with 1-MT promoted liver regeneration.

CONCLUSION

IDO1 deficiency promoted early liver regeneration after PHx, indicating that IDO1 suppresses the production of inflammatory cytokines and subsequently inhibits hepatocyte proliferation during liver regeneration.

The inhibition of NLRP3 signaling attenuates liver injury in an α-galactosylceramide-induced hepatitis model

Inflammasomes are involved in innate immune responses. Several NOD-Like receptors (NLRs) participate in the formation of inflammasomes. NACHT, LRR and PYD domains-containing protein 3 (NALP3) belongs to the NLR family and recognizes adenosine triphosphate (ATP), crystals, and Reactive Oxygen Species (ROS). This study examined the effect of inflammasomes on alpha-galactosylceramide (GalCer)-induced liver injury using NALP3-knockout (KO) mice. GalCer administration induced inflammasome activation and IL-1β-maturation. In NALP3-KO mice treated with GalCer, serum ALT levels were significantly reduced compared with those in GalCer-treated WT mice. Histological examination revealed decreased necrosis in NALP3-KO mice compared with WT mice, consistent with ALT levels. Expression of proinflammatory cytokines (such as IL-6, and TNF-α) and chemokines was also significantly suppressed in NALP3-KO mice. Moreover, flow cytometry analysis revealed fewer infiltrating immune cells in the livers of GalCer-treated NALP3-KO mice. Inportantly, the frequency of MDSCs (CD11b⁺Gr-1^int cells), which suppress the immune response, was significantly increased in GalCer-treated NALP3-KO mice. In conclusion, NALP3 inhibition attenuated liver injury in GalCer-induced hepatitis. The inhibition of NALP3 signaling coused be a therapeutic target in immune-mediated liver injury.

Induction of humoral and cellular immune response to hepatitis B virus (HBV) vaccine can be upregulated by CpG oligonucleotides complexed with Dectin-1 ligand

A persistent hepatitis B virus (HBV) infection is characterized by a lack of or a weak immune response to HBV, which may be reflective of tolerance to HBV. Efficient induction of HBV-specific immune response leads to the clearance of HBV in patients with a chronic HBV infection. CpG oligodeoxynucleotides (ODN) has a powerful adjuvant effect in HBV vaccination. A recent report demonstrated that the immunization by B/K CpG ODN (K3) wrapped by the nonagonistic Dectin-1 ligand, schizophyllan (SPG), namely K3-SPG, was more effective in the induction of antigen-specific immune response than that by K3. In this study, we examined the efficacy of K3-SPG as a HBV vaccine adjuvant. Wild-type (WT) mice and HBV transgenic (HBV-Tg) mice were subcutaneously immunized with hepatitis B surface antigen (HBsAg) alone, HBsAg and K3, or HBsAg and K3-SPG. The vaccination with HBsAg and K3-SPG significantly enhanced humoral and cellular immune response to HBV antigen compared to the other vaccinations in WT and HBV-Tg mice. K3-SPG induced the accumulation of dendritic cells (DCs) into draining lymph node and the activation of DCs. The expression of cytokines and chemokines related to Th1 and Th2 responses was upregulated after the vaccination including with K3-SPG. In conclusion, these results indicated that the vaccination using K3-SPG may overcome tolerance even in patients with chronic HBV infection.

Impact of NKT Cells and LFA-1 on Liver Regeneration under Subseptic Conditions

Background

Activation of the immune system in terms of subseptic conditions during liver regeneration is of paramount clinical importance. However, little is known about molecular mechanisms and their mediators that control hepatocyte proliferation. We sought to determine the functional role of immune cells, especially NKT cells, in response to partial hepatectomy (PH), and to uncover the impact of the integrin lymphocyte function-associated antigen-1 (LFA-1) on liver regeneration in a subseptic setting.

Methods

Wild-type (WT) and LFA-1^-/- mice underwent a 2/3 PH and low-dose lipopolysaccharid (LPS) application. Hepatocyte proliferation, immune cell infiltration, and cytokine profile in the liver parenchyma were determined.

Results

Low-dose LPS application after PH results in a significant delay of liver regeneration between 48h and 72h, which is associated with a reduced number of CD3⁺ cells within the regenerating liver. In absence of LFA-1, an impaired regenerative capacity was observed under low-dose LPS application. Analysis of different leukocyte subpopulations showed less CD3⁺NK1.1⁺ NKT cells in the liver parenchyma of LFA-1^-/- mice after PH and LPS application compared to WT controls, while CD3^-NK1.1⁺ NK cells markedly increased. Concordantly with this observation, lower levels of NKT cell related cytokines IL-12 and IL-23 were expressed in the regenerating liver of LFA-1^-/- mice, while the expression of NK cell-associated CCL5 and IL-10 was increased compared to WT mice.

Conclusion

A subseptic situation negatively alters hepatocyte proliferation. Within this scenario, we suggest an important impact of NKT cells and postulate a critical function for LFA-1 during processes of liver regeneration.

Inhibition of iNOS activity enhances the anti-tumor effects of alpha-galactosylceramide in established murine cancer model

Alpha-garactosylceramide (GalCer) has been shown to have anti-tumor effect in the basic research and clinical studies. However, anti-tumor effect of GalCer is limited. The administration of GalCer increases the production of IFN-γ which is involved in the suppression of tumor growth. On the other hand, the enhancement of IFN-γ production increases immunosuppressive factors such as nitric oxide. This suppressive action might impair the anti-tumor effect of GalCer. In the present study, we evaluated the anti-tumor effect of GalCer in the absence of inducible nitric oxide synthase (iNOS). In lung metastatic model, the number of tumor nodules in the lung of iNOS-KO mice treated with GalCer was significantly reduced compared with that of WT mice treated with GalCer. Moreover, L-NAME, which is the inhibitor for iNOS, enhanced the anti-tumor effect of GalCer in lung metastatic model. The frequency of CD8+ cells in bronchoalveolar lavage fluid increased in iNOS-KO mice treated with GalCer. The administration of GalCer increased the frequency of myeloid-derived suppressor cells (MDSCs) in the lung from tumor-bearing WT mice, but the increase of MDSCs in the lung was not induced in iNOS-KO mice. The subcutaneous tumor experiments revealed that the administration of GalCer in the absence of iNOS expression significantly enhanced the induction of tumor antigen-specific response. Finally, our results indicated that the inhibition of iNOS expression could enhance the therapeutic efficacy of GalCer via the increase of tumor antigen-specific immune response and the suppression of MDSCs.

Role of invariant NKT cells in lipopolysaccharide-induced lethal shock during encephalomyocarditis virus infection

Viral infections can give rise to secondary bacterial infections. In the present study, we examined the role of invariant natural killer T (iNKT) cells in lipopolysaccharide (LPS)-induced lethal shock during encephalomyocarditis virus (EMCV) infection. Wild-type (WT) mice and Jα18 gene knockout (Jα18 KO) mice were inoculated with EMCV, 5days prior to challenging with LPS. The survival rate of Jα18 KO mice subjected to EMCV and LPS was significantly higher than that of WT mice. TNF-α and nitric oxide (NO) production were increased in WT mice, than that in Jα18 KO mice, after the administration of EMCV and LPS. EMCV infection increased the number of iNKT cells and IFN-γ production by iNKT cells in WT mice. Moreover, EMCV infection enhanced the expression of Toll-like receptor 4 (TLR4) in the lung and spleen. IFN-γ also increased the expression of TLR4 in splenocytes. These findings indicated that EMCV infection activated iNKT cells, and IFN-γ secreted from the iNKT cells up-regulated the expression of TLR4 in various tissues. As a result, EMCV-infected mice were susceptible to LPS and easily developed the lethal shock. In conclusion, iNKT cells were involved in the development of LPS-induced lethal shock during EMCV infection.

Role of NK, NKT cells and macrophages in liver transplantation

Liver transplantation has become the treatment of choice for acute or chronic liver disease. Because the liver acts as an innate immunity-dominant organ, there are immunological differences between the liver and other organs. The specific features of hepatic natural killer (NK), NKT and Kupffer cells and their role in the mechanism of liver transplant rejection, tolerance and hepatic ischemia-reperfusion injury are discussed in this review.

Pre-stimulated Mice with Carbon Tetrachloride Accelerate Early Liver Regeneration After Partial Hepatectomy

BACKGROUND AND AIM

The liver has a high capacity of its regeneration. Most hepatic cells are quiescent unless otherwise stimulated such as their injury or ablation. A previous study suggest that pre-activated hepatic cells have a positive effect on their regeneration. In this study, we examined whether the pre-activated hepatic cells for regeneration accelerate the subsequent liver regeneration.

METHODS

We administered a single injection of carbon tetrachloride (CCl4) to mice 7 days before partial hepatectomy (PHx). Liver weight/body weight ratio and several parameters for cell proliferation such as mitotic index and the number of Ki67 positive cells in the liver were examined after PHx as indexes of liver regeneration.

RESULTS

Compared to control mice, those pre-stimulated with CCl4 showed earlier liver regeneration 48 h after PHx. Regardless of their accelerated regeneration, pre-stimulated mice showed less cell proliferation than did control mice during liver regeneration. Hepatic fibrosis was not observed in both control and CCl4-pretreated mice after PHx. Mice pre-treated with CCl4 showed the higher matrix metalloproteinase 9 (MMP9) expression than those pre-treated with olive oil. When matrix metalloproteinase 9 (MMP9) activity was inhibited, the pre-stimulated mice did not demonstrate accelerated liver regeneration and they returned to the original state for cell proliferations after PHx.

CONCLUSIONS

Pre-activated liver by CCl4 promoted its subsequent regeneration after PHx. This was not a cause of fibrosis and partly dependent on MMP9 pre-activity rather than cell proliferation in liver. Our findings would not only provide a novel strategy for liver regeneration without cell proliferation as much as possible and also propose a new method for liver transplantation.

Safety and immunogenicity of therapeutic DNA vaccine with antiviral drug in chronic HBV patients and its immunogenicity in mice

BACKGROUND & AIMS

Here, we evaluated the safety and immunogenicity of hepatitis B virus (HBV) DNA vaccine, HB-110, in mice and Korean patients with chronic hepatitis B (CHB) undergoing adefovir dipivoxil (ADV) treatment.

METHODS

For animal study, mice (BALB/c or HBV transgenic) were immunized with mHB-110, and T-cell and antibody responses were evaluated. For clinical study, 27 patients randomly received either ADV alone or ADV in combination with HB-110. Liver function tests, serum HBV DNA levels and the presence of HBeAg/anti-HBe were analysed. T-cell responses were estimated by ELISPOT and FACS analysis.

RESULTS

mHB-110 induced higher T-cell and antibody responses than mHB-100 in mice. No adverse effects were observed by HB-110 cotreated with ADV. HBV-specific T-cell responses were induced in a portion of patients in medium to high dose of HB-110. Interestingly, HB-110 exhibited positive effects on ALT normalization and maintenance of HBeAg seroconversion. One patient, who received high dose of HB-110 exhibited HBeAg seroconversion during vaccination, which correlated with vaccine-induced T-cell responses without ALT elevation.

CONCLUSIONS

HB-110 was safe and tolerable in CHB patients. In contrast to results in animal models, HB-110 in Korean patients exhibited weaker capability of inducing HBV-specific T-cell responses and HBeAg seroconversion than HB-100 in Caucasian patients. As Asian patients, who are generally infected via vertical transmission, appeared to have higher level of immune tolerance than Caucasian, novel approaches for breaking immune tolerance rather than enhancing immunogenicity may be more urgently demanded to develop effective therapeutic HBV DNA vaccines.

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

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

CONCLUSIONS

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

Activation of invariant natural killer T cells impedes liver regeneration by way of both IFN-γ- and IL-4-dependent mechanisms

Invariant natural killer T (iNKT) cells are a major subset of lymphocytes found in the liver. These cells mediate various functions, including hepatic injury, fibrogenesis, and carcinogenesis. However, the function of iNKT cells in liver regeneration remains unclear. In the present study, partial hepatectomy (PHx) was used to study liver regeneration. α-Galactosylceramide (α-GalCer), a specific ligand for iNKT cells, was used to induce iNKT cell activation. After PHx, two strains of iNKT cell-deficient mice, CD1d(-/-) and Jα281(-/-) mice, showed normal liver regeneration. Injection of α-GalCer before or after PHx, which rapidly stimulated interferon-gamma (IFN-γ) and interleukin (IL)-4 production by iNKT cells, markedly inhibited liver regeneration. In vitro treatment with IFN-γ inhibited hepatocyte proliferation. In agreement with this in vitro finding, genetic disruption of IFN-γ or its downstream signaling molecule signal transducer and activator of transcription (STAT)1 significantly abolished the α-GalCer-mediated inhibition of liver regeneration. In vitro exposure to IL-4 did not affect hepatocyte proliferation, but surprisingly, genetic ablation of IL-4 or its downstream signaling molecule STAT6 partially eliminated the inhibitory effect of α-GalCer on liver regeneration. Further studies revealed that IL-4 contributed to α-GalCer-induced iNKT cell expansion and IFN-γ production, thereby inhibiting liver regeneration.

CONCLUSION

iNKT cells play a minor role in controlling liver regeneration after PHx under healthy conditions. Activation of iNKT cells by α-GalCer induces the production of IFN-γ, which directly inhibits liver regeneration, and IL-4, which indirectly attenuates liver regeneration by stimulating iNKT cell expansion and IFN-γ production.

Prometheus unbound: NKT cells inhibit hepatic regeneration

Although natural killer T (NKT) cells were discovered over 20 years ago, our understanding of their immunobiology continues to evolve and surprise. NKT cells are T lymphocytes: they arise in the bone marrow, are selected in the thymus, and express a T cell receptor. Unlike classic T cells, however, they are not strictly “adaptive” immune cells: in particular, as a population they express a very narrow range of T cell receptors. The vast majority of mouse NKT cells, for example, express the Vα14-J281 chain and only a finite number of Vβ chains (1). In addition, they express NK cell surface markers, such as NK 1.1. Moreover, unlike classical T cells, they are not restricted by MHC Class I or Class II, but by an MHC-like molecule, CD1d (2). Furthermore, NKT cells do not recognize peptides in the context of CD1d, but rather specialized lipids (3). Functionally NKT cells also reflect major differences from conventional T cells: they are able to produce both classic Th1 (IFN-γ) and Th2 (IL-4) cytokines without prior peripheral stimulation, but when stimulated by their glycolipid antigens downregulate TCR, expand, and divert to a Th1 phenotype (4). Like classical T cells, they are selected in the thymus by a self-molecule: however, it is not a protein, but a trihexosylceramide, iGb3, bound to CD1d (5). Mice deficient in iGb3 demonstrated a severe deficiency of NKT cells, illustrating its critical role in NKT cells selection and survival (5). These features of NKT cells place them into the expanding category of “innate-like” lymphocytes (6). “Innate” immunity has classically been defined by “stereotypical” responses mediated by invariant receptors to defined ligands: for example, the signaling and functional responses of TLR4 when bound to its ligand, LPS. Since the overall TCR repertoire of NKT cells is so limited, the population as a whole responds “innately” to just a few lipid antigens, rather than retaining a population-capability to respond to the full universe of T cell antigens. Finally, and of great interest to the field of hepatic immunity, NKT cells do not circulate freely, but tend to home to and reside for life in specific tissues such as the liver, where they compose ~30% of the intrahepatic lymphoid pool (7).

Induction of hepatitis B virus surface antigen-specific cytotoxic T lymphocytes can be up-regulated by the inhibition of indoleamine 2, 3-dioxygenase activity

Cytotoxic T lymphocytes (CTLs) are thought to be major effectors involved in viral clearance during acute infections, including hepatitis B virus (HBV) infection. A persistent HBV infection is characterized by a lack of or a weak CTL response to HBV, which may be reflective of tolerance to HBV. Efficient induction of HBV-specific CTLs leads to the clearance of HBV in patients with a chronic HBV infection. Previously, we reported that α-galactosylceramide (α-GalCer), a specific natural killer T (NKT) cell agonist, enhanced the induction of HBV surface antigen (HBsAg)-specific CTLs. In the present study, we found that inhibition of indoleamine 2,3-dioxygenase (IDO) activity enhanced the induction of HBsAg-specific CTLs after immunization with HBsAg and α-GalCer. The administration of HBsAg and α-GalCer increased the production of interleukin-2 and interleukin-12b, which are crucial for the induction of HBsAg-specific CTLs. The production of these cytokines was more strongly enhanced in IDO knockout mice compared with wild-type mice. In addition, α-GalCer induced the production of IDO in CD11b(+) cells, and these cells inhibited proliferation of HBsAg-specific CTLs. Our results lead to strategies for improving the induction of HBsAg-specific CTLs.

Type I NKT-cell-mediated TNF-α is a positive regulator of NLRP3 inflammasome priming

The NLRP3 inflammasome plays a crucial role in the innate immune response to pathogens and exogenous or endogenous danger signals. Its activity must be precisely and tightly regulated to generate tailored immune responses. However, the immune cell subsets and cytokines controlling NLRP3 inflammasome activity are still poorly understood. Here, we have shown a link between NKT-cell-mediated TNF-α and NLRP3 inflammasome activity. The NLRP3 inflammasome in APCs was critical to potentiate NKT-cell-mediated immune responses, since C57BL/6 NLRP3 inflammasome-deficient mice exhibited reduced responsiveness to α-galactosylceramide. Importantly, NKT cells were found to act as regulators of NLRP3 inflammasome signaling, as NKT-cell-derived TNF-α was required for optimal IL-1β and IL-18 production by myeloid cells in response to α-galactosylceramide, by acting on the NLRP3 inflammasome priming step. Thus, NKT cells play a role in the positive regulation of NLRP3 inflammasome priming by mediating the production of TNF-α, thus demonstrating another means by which NKT cells control early inflammation.

Effects of indoleamine 2,3-dioxygenases in carbon tetrachloride-induced hepatitis model of rats

Indoleamine 2,3-dioxygenase (IDO) converts tryptophan to l-kynurenine, and it is noted as a relevant molecule in promoting tolerance and suppressing adaptive immunity. In this study, to investigate the effects of IDO in carbon tetrachloride (CCl(4) )-induced hepatitis model, the levels of IDO enzymic activities in the mock group, the control group and the 1-methyl-D-tryptophan (1-MT)-treated group were confirmed by determination of l-kynurenine concentrations. Serum alanine aminotransferase levels in 1-MT-treated rats after CCl(4) injection significantly increased compared with those in mock and control groups. In CCl(4)-induced hepatitis models, tumour necrosis factor-α (TNF-α) is critical in the development of liver injury. The mRNA expression and secretion levels of TNF-α in the liver from 1-MT-treated rats were more enhanced compared with those in the mock and the control groups. Moreover, the levels of cytokine and chemokine from mock, control group and 1-MT-treated rats after treated with CCl(4) were analyzed by ELISA, and the level of interleukin-6 was found to increase in 1-MT-treated rats. It was concluded that the deficiency of IDO exacerbated liver injury in CCl(4)-induced hepatitis and its effect may be connected with TNF-α and interleukin-6.

A complement-IL-4 regulatory circuit controls liver regeneration

The involvement of IL-4 in liver regeneration has not yet been recognized. In this article, we show that IL-4, produced by NKT cells that accumulate in regenerating livers after partial hepatectomy, contributes to this process by regulating the activation of complement after liver resection in mice. The mechanism of this regulation was associated with the maintenance of an appropriate level of IgM in mouse blood, because IgM deposited in liver parenchyma most likely initiated complement activation during liver regeneration. By controlling complement activation, IL-4 regulated the induction of IL-6, thereby influencing a key pathway involved in regenerating liver cell proliferation and survival. Furthermore, the secretion of IL-4 was controlled by complement through the recruitment of NKT cells to regenerating livers. Our study thus reveals the existence of a regulatory feedback mechanism involving complement and IL-4 that controls liver regeneration.

Activated lymphocytes and high liver expression of IFN-γ are associated with fulminant hepatic failure in patients

BACKGROUND & AIMS

To study immunological mechanisms of fulminant hepatic failure (FHF) derived from extensive liver lesions, 14 patients with FHF induced by different aetiologies were investigated by observance of both lymphocyte phenotyping and cytokine levels.

METHODS

Five patients bearing benign acute hepatitis B (AHB) and seven healthy liver donors (HC) were used as controls. Samples of liver and blood from both FHF patients and HC were obtained during transplantation procedures. Plasma levels of IL-1β, IL-4, IL-6, IL-8, IL-10, IFN-γ, TNF-α, MCP-1, RANTES and MIP-1α were quantified using a multiplex immunoassay. Cell characterization was carried out by flow cytometry. IFN-γ staining was performed on liver sections using immunofluorescence methods.

RESULTS

An increase of peripheral frequency of natural killer (NK) cells expressing early activation markers (CD69, HLA-DR and CD38) and adhesion molecule CD44 was observed in FHF patients. Elevated frequency of T lymphocytes CD4(+) and CD8(+) expressing CD38 and adhesion molecules CD29 and CD44 was also observed in FHF. Additionally, an increase of natural killer T cells (NKT) was detected in FHF patients. High plasma cytokine levels were not statistically different between FHF and AHB patients. In comparison to HC, a strong liver expression of IFN-γ was detected in FHF patients. The increased frequency of CD4(+) CD44(+) and IL-8 cytokine was found in patients with poor prognosis.

CONCLUSIONS

These findings indicate the involvement of NK and NKT cells as well as T lymphocytes CD4(+) and CD8(+) in the inflammatory process inducing FHF, confirmed by the high hepatic expression of IFN-γ.

Abnormal changes in NKT cells, the IGF-1 axis, and liver pathology in an animal model of ALS

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing fatal neurodegenerative disorder characterized by the selective death of motor neurons (MN) in the spinal cord, and is associated with local neuroinflammation. Circulating CD4⁺ T cells are required for controlling the local detrimental inflammation in neurodegenerative diseases, and for supporting neuronal survival, including that of MN. T-cell deficiency increases neuronal loss, while boosting T cell levels reduces it. Here, we show that in the mutant superoxide dismutase 1 G93A (mSOD1) mouse model of ALS, the levels of natural killer T (NKT) cells increased dramatically, and T-cell distribution was altered both in lymphoid organs and in the spinal cord relative to wild-type mice. The most significant elevation of NKT cells was observed in the liver, concomitant with organ atrophy. Hepatic expression levels of insulin-like growth factor (IGF)-1 decreased, while the expression of IGF binding protein (IGFBP)-1 was augmented by more than 20-fold in mSOD1 mice relative to wild-type animals. Moreover, hepatic lymphocytes of pre-symptomatic mSOD1 mice were found to secrete significantly higher levels of cytokines when stimulated with an NKT ligand, ex-vivo. Immunomodulation of NKT cells using an analogue of α-galactosyl ceramide (α-GalCer), in a specific regimen, diminished the number of these cells in the periphery, and induced recruitment of T cells into the affected spinal cord, leading to a modest but significant prolongation of life span of mSOD1 mice. These results identify NKT cells as potential players in ALS, and the liver as an additional site of major pathology in this disease, thereby emphasizing that ALS is not only a non-cell autonomous, but a non-tissue autonomous disease, as well. Moreover, the results suggest potential new therapeutic targets such as the liver for immunomodulatory intervention for modifying the disease, in addition to MN-based neuroprotection and systemic treatments aimed at reducing oxidative stress.

Elevated interferon gamma signaling contributes to impaired regeneration in the aged liver

Our previous study on immune-related changes in the aged liver described immune cell infiltration and elevation of inflammation with age. Levels of interferon (IFN)-γ, a known cell cycle inhibitor, were elevated in the aging liver. Here, we determine the role played by IFN-γ in the delayed regenerative response observed in the aged livers. We observed elevated IFN signaling in both aged hepatocytes and regenerating livers post-partial hepatectomy. In vivo deletion of the major IFN-γ producers-the macrophages and the natural killer cells, leads to a reduction in the IFN-γ levels accompanied with the restoration of the DNA synthesis kinetics in the aged livers. Eighteen-month-old IFN-γ-/- mice livers, upon resection, exhibited an earlier entry into the cell cycle compared with age-matched controls. Thus, our study strongly suggests that an age-related elevation in inflammatory conditions in the liver often dubbed as "inflammaging" has a detrimental effect on the regenerative response.

Targeting the diverse immunological functions expressed by hepatic NKT cells

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Ability of IDO to attenuate liver injury in alpha-galactosylceramide-induced hepatitis model

IDO converts tryptophan to l-kynurenine, and it is noted as a relevant molecule in promoting tolerance and suppressing adaptive immunity. In this study, we examined the effect of IDO in α-galactosylceramide (α-GalCer)-induced hepatitis. The increase in IDO expression in the liver of wild-type (WT) mice administered α-GalCer was confirmed by real-time PCR, Western blotting, and IDO immunohistochemical analysis. The serum alanine aminotransferase levels in IDO-knockout (KO) mice after α-GalCer injection significantly increased compared with those in WT mice. 1-Methyl-D-tryptophan also exacerbated liver injury in this murine hepatitis model. In α-GalCer-induced hepatitis models, TNF-α is critical in the development of liver injury. The mRNA expression and protein level of TNF-α in the liver from IDO-KO mice were more enhanced compared with those in WT mice. The phenotypes of intrahepatic lymphocytes from WT mice and IDO-KO mice treated with α-GalCer were analyzed by flow cytometry, and the numbers of CD49b(+) and CD11b(+) cells were found to have increased in IDO-KO mice. Moreover, as a result of the increase in the number of NK cells and macrophages in the liver of IDO-KO mice injected with α-GalCer, TNF-α secretion in these mice was greater than that in WT mice. Deficiency of IDO exacerbated liver injury in α-GalCer-induced hepatitis. IDO induced by proinflammatory cytokines may decrease the number of TNF-α-producing immune cells in the liver. Thus, IDO may suppress overactive immune response in the α-GalCer-induced hepatitis model.

Regulation of the induction and function of cytotoxic T lymphocytes by natural killer T cell

Cytotoxic T lymphocytes (CTLs) play a crucial role in the infections and the antitumor immunity. Induction and activation of antigen-specific CTLs is an important strategy in immunotherapy for various diseases, and several researchers have focused on the modulation of CTL induction and function. Natural killer T (NKT) cells are an important focus area of researchers studying immunomodulatory responses to tumors and infectious diseases. CD1d-restricted NKT cells consist of type I NKT cells and type II NKT cells. α-galactosylceramide (α-GalCer)-activated type I NKT cells secrete both Th1 (e.g., IFN-γ) and Th2 cytokines, affect the expression of costimulatory molecules in immune cells, and regulate the host immune system. Type II NKT cells, however, are stimulated by sulfatide, a self-glycolipid derived from myelin, and play an immunosuppressive role in animal model of autoimmune diseases. CTL generation, activation, and suppression are strongly affected by activated type I and type II NKT cells. Thus, the regulation of these NKT cells leads to the modification of CTL function. CTLs contribute to antimicrobial responses, antitumor immune and autoimmune responses. Understanding the role of NKT cells in the regulation of CTL generation, activation, and suppression enable the development of novel treatment strategies for these diseases.

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.

CONCLUSION

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.

Signal molecule-mediated hepatic cell communication during liver regeneration

Liver regeneration is a complex and well-orchestrated process, during which hepatic cells are activated to produce large signal molecules in response to liver injury or mass reduction. These signal molecules, in turn, set up the connections and cross-talk among liver cells to promote hepatic recovery. In this review, we endeavor to summarize the network of signal molecules that mediates hepatic cell communication in the regulation of liver regeneration.

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.

Focal liver necrosis appears early after partial hepatectomy and is dependent on T cells and antigen delivery from the gut

INTRODUCTION

Progressive liver failure may develop following removal of a large part of the liver or transplantation of a small for size liver graft. The pathophysiology of this clinical syndrome is only partially understood.

METHODS

We assessed liver damage and hepatocyte 5-bromo-2'-deoxyuridine (BrdU) incorporation following partial hepatectomy (PH) in C57BL/6, BALB/C and immune-deficient mice. Hepatic lymphocyte subpopulations were characterized. Lipopolysaccharide (LPS) treatment and bowel decontamination determined the role of gut antigens.

RESULTS

Discrete, round necrotic lesions were observed as early as 2 h following 70%, but not 30% PH. In immune competent mice the extent of hepatocyte necrosis inversely correlated with BrdU incorporation. T, natural killer and natural killer T cells were recruited to the liver early after PH; however, only T-cell depletion abrogated hepatic necrosis. Hepatic injury was significantly reduced in non-obese diabetic/severe combined immunodeficient mice undergoing PH, while BrdU incorporation was not affected. Liver injury was augmented by LPS injection and reduced by gut decontamination.

CONCLUSIONS

A distinct pattern of early focal hepatic necrosis is observed following extensive PH in mice. T cells infiltrating the liver immediately after PH and gut-derived antigens are indispensable for the observed liver necrosis and may thus provide therapeutic targets to ameliorate liver damage following PH.

Both tacrolimus and sirolimus decrease Th1/Th2 ratio, and increase regulatory T lymphocytes in the liver after ischemia/reperfusion

The protective effects of immunosuppressants against ischemia/reperfusion (I/R) injury have been attributed to their non-specific anti-inflammatory effect. However, these effects may also depend on their effect on T lymphocytes, which are increasingly considered to be key players in I/R. Here, we studied the effects of tacrolimus and sirolimus on lymphocyte subpopulations in an I/R rat model. The animals were treated with tacrolimus, sirolimus or vehicle, before undergoing a 60-min ischemia event of the right hepatic lobe, followed by excision of the remaining liver. After 2 h, I/R rats showed increased mortality, plasma lactate dehydrogenase (LDH) levels, hepatocyte apoptosis, liver histological injury and parenchymal infiltration by neutrophils, macrophages, NK cells and T lymphocytes. Most of the changes were antagonized by both immunosuppressants. Tacrolimus augmented the proportion of cycling cells in I/R rats, whereas sirolimus showed the opposite effect. The increased Th1/Th2 ratio found in I/R livers after 2 h was reverted by immunosuppressants, which also amplified the proportion of CD4(+)CD25(+)Foxp3(+) regulatory T lymphocytes at 24 h. The protective effects of both tacrolimus and sirolimus correlated well with a decreased ratio of proinflammatory to anti-inflammatory T lymphocytes, and with an increase in the Treg proportion. This suggests a new mechanism to explain the known beneficial effect shown by immunosuppressants early after I/R.

Upregulation of indoleamine 2,3-dioxygenase in hepatocyte during acute hepatitis caused by hepatitis B virus-specific cytotoxic T lymphocytes in vivo

BACKGROUND/AIMS

Indoleamine-2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme inducing suppression of T-cell function and immune tolerance. In hepatitis B virus (HBV) transgenic (Tg) mice, the adoptive transfer of HBV-specific cytotoxic T lymphocytes (CTL) causes a necroinflammatory liver disease that is histologically similar to acute viral hepatitis in man. The present study aimed to determine IDO expression in the liver and hepatocytes during an acute hepatitis model.

METHODS

Serum l-kynurenine (l-Kyn) concentration in HBV Tg mice administered with HBV-specific CTL was measured over time, together with serum levels of alanine aminotransferase (ALT). Furthermore, we examined the expression of IDO in the total liver and isolated hepatocytes of HBV Tg mice after CTL injection using immunohistochemical analysis and reverse-transcription polymerase chain reaction (PCR).

RESULTS

In HBV Tg mice, HBV-specific CTL induced, over the course of several days, a chronic increase in serum l-Kyn levels, which was associated with a sustained enhancement of liver IDO activity. In particular, IDO expression was enhanced in the liver parenchymal cells (hepatocytes) after HBV-specific CTL injection both in immunohistochemical analysis and in reverse-transcription PCR. Moreover, murine recombinant interferon-gamma (IFN-gamma) directly increased the IDO expression in primary hepatocytes in vitro.

CONCLUSIONS

Cytotoxic T lymphocytes transduction results in the upregulation of IDO, which might downregulate T-cell responsiveness. Our findings provide evidence that hepatocyte itself expresses IDO and increases levels of l-Kyn in the blood in acute lethal hepatitis of mice. These data indicate that HBV infection facilitates the induction of IDO in response to proinflammatory cytokines, particularly IFN-gamma.

T cell-derived lymphotoxin regulates liver regeneration

BACKGROUND & AIMS

The ability of the liver to regenerate hepatic mass is essential to withstanding liver injury. The process of liver regeneration is tightly regulated by distinct signaling cascades involving components of the innate immune system, cytokines, and growth factors. However, the role of the adaptive immune system in regulation of liver regeneration is not well-defined. The role of adaptive immune system in liver regeneration was investigated in lymphocyte-deficient mice and in conditional lymphotoxin-deficient mice.

METHODS

A model of liver regeneration after 70% partial hepatectomy was used, followed by examination of liver pathology, survival, DNA synthesis, and cytokine expression.

RESULTS

We found that mice deficient in T cells show a reduced capacity for liver regeneration following partial hepatectomy. Furthermore, surface lymphotoxin, provided by T cells, is critical for liver regeneration. Mice specifically deficient in T-cell lymphotoxin had increased liver damage and a reduced capacity to initiate DNA synthesis after partial hepatectomy. Transfer of splenocytes from wild-type but not lymphotoxin-deficient mice improved liver regeneration in T cell-deficient mice. We found that an agonistic antibody against the lymphotoxin beta receptor was able to facilitate liver regeneration by reducing liver injury, increasing interleukin-6 production, hepatocyte DNA synthesis, and survival of lymphocyte-deficient (Rag) mice after partial hepatectomy.

CONCLUSIONS

The adaptive immune system directly regulates liver regeneration via a T cell-derived lymphotoxin axis, and pharmacological stimulation of lymphotoxin beta receptor might represent a novel therapeutic approach to improve liver regeneration.

Zinc finger protein A20 promotes regeneration of small-for-size liver allograft and suppresses rejection and results in a longer survival in recipient rats

BACKGROUND

Small-for-size liver allografts without immunosuppression have decreased survival compared with full-for-size grafts for the concomitant regeneration-induced accelerated rejection. This study was designed to examine the effect of zinc finger protein A20 on liver allograft regeneration and acute rejection using a high responder rat model (DA-->Lewis) of 30% partial liver transplantation.

MATERIALS AND METHODS

Adenovirus carrying the full length of A20 was introduced into liver grafts by ex vivo perfusion via the portal vein during preservation, physiological saline (PS), and empty Ad vector rAdEasy served as controls; then small-sized liver transplants were performed. Liver graft regeneration was assessed, as well as graft rejection, hepatocyte apoptosis, nuclear factor kappa B activation, and intercellular adhesion molecule-1 mRNA expression in liver graft sinusoidal endothelial cells (LSECs), infiltration of liver graft infiltrating mononuclear cells (LIMCs), and the subproportion of NK and NKT cells, activity of liver graft NK-like cells, interferon gamma (IFN-gamma) production, and animal survival.

RESULTS

Ex vivo transfer of the A20 gene resulted in overexpression of A20 protein in LSECs and hepatocytes 24 h after partial liver transplantation. Regeneration of the small-sized liver allograft was augmented by A20 overexpression, the DNA synthesis of hepatocytes on d 4 post-transplant was increased in A20 group compared with PS and rAdEasy groups (P < 0.01). Hepatocyte apoptosis was inhibited by A20 (P < 0.001). On d 4 after transplantation, histological examination revealed a more exiguous cellular infiltration and mild rejection in A20 group but a more vigorous cellular infiltration in the sinusoidal area and more severe rejection in PS and rAdEasy group. Nuclear factor kappa B activation and intercellular adhesion molecule-1 mRNA expression in LSECs were suppressed by A20 overexpression. Flow cytometry analysis showed a marked down-regulation of LIMCs number by A20, including more prominent decrease in the subproportion of NK and NKT cells. Activity of liver graft NK-like cells, IFN-gamma mRNA expression in LIMCs, and serum IFN-gamma protein level were also suppressed by A20 overexpression (P < 0.05), respectively. Survival days of A20 rats were longer than those of PS rats and rAdEasy rats (P < 0.01), whereas survival days of rAdEasy rats were shorter than those of PS rats (P < 0.01).

CONCLUSIONS

These data suggest that A20 overexpression could effectively promote small-sized liver allograft regeneration, suppress rejection, and prolong survival of recipient rat. These effects of A20 could be related to an inhibition of LSECs activation, suppression of infiltration of LIMCs, and the subpopulations such as NK and NKT cells into liver graft, and inhibition of hepatocyte apoptosis.

Role of Valpha14+ NKT cells in the development of Hepatitis B virus-specific CTL: activation of Valpha14+ NKT cells promotes the breakage of CTL tolerance

CTLs are thought to be major effectors for clearing viruses in acute infections including hepatitis B virus (HBV). Persistent HBV infection is characterized by a lack of or a weak CTL response to HBV, which is thought to reflect tolerance to HBV antigens. In the present study, we found that alpha-galactosylceramide (alpha-GalCer), a ligand for Valpha14-positive NKT cells, strongly enhanced the induction and proliferation of HBV-specific CTLs by HBsAg. In HBsAg transgenic mice, which are thought to be tolerant to HBV-encoded antigens, administration of HBsAg or alpha-GalCer alone failed to induce HBsAg-specific CTLs, but they were induced by co-administration of both compounds. Furthermore, by limiting dilution analysis, we confirmed the existence of HBsAg-specific CTL precursors in the HBsAg transgenic mice immunized with HBsAg and alpha-GalCer. A blocking experiment using antibodies to cytokines and CD40 ligand showed that IL-2 and CD40-CD40L interaction mediate the enhancement of CTL induction caused by alpha-GalCer through NKT cell activation. Our results may open up a new method for clearing the virus from patients with persistent HBV infection.

Expression of tumor necrosis factor-alpha converting enzyme in liver regeneration after partial hepatectomy

AIM: To study the expression of tumor necrosis factor-alpha converting enzyme (TACE) and evaluate its significance in liver regeneration after partial hepatectomy in vivo.

METHODS: Male SD rats underwent 70% partial hepatectomy. The remaining liver and spleen tissue samples were collected at indicated time points after hepatectomy. TACE expression was investigated by Western blotting, immunohistochemistry, and serial section immunostaining.

RESULTS: Expression of TACE in liver and spleen tissues after partial hepatectomy was a time-dependent alteration, reaching a maximal level between 24 and 48 h and remaining elevated for more than 168 h. TACE protein was localized to mononuclear cells (MNC), which infiltrated the liver from the spleen after hepatectomy. The kinetics of TACE expression was in accordance with the number of TACE-staining MNCs and synchronized with those of transforming growth factor-α (TGFα). In addition, TACE-staining MNC partially overlapped with CD3⁺ T lymphocytes.

CONCLUSION: TACE may be involved in liver regeneration by pathway mediated with TGFα-EGFR in the cell-cycle progressive phase in vivo. TACE production and effect by paracrine may be a pathway of involvement in liver regeneration for the activated CD3⁺ T lymphocytes.

Innate immunity and alcoholic liver fibrosis

The hepatic innate immune system consists of predominant innate immunity, which plays an important role in innate defense against infection and tumor transformation. Emerging evidence suggests that innate immunity also contributes to liver injury, repair, and fibrosis. The present review summarizes the recent findings on the role of innate immunity in liver fibrosis. In general, Kupffer cells stimulate liver fibrosis via production of reactive oxygen species and pro-inflammatory cytokines, whereas natural killer (NK) cells inhibit liver fibrosis by directly killing activated hepatic stellate cells and production of gamma-interferon (IFN-gamma). Complement components, interferons, and Toll-like receptors have also been shown to regulate liver fibrosis. Recent evidence also suggests that modulation of innate immunity by alcohol plays an important role in the pathogenesis of alcoholic liver fibrosis. These include alcohol amplification of the profibrotic effects of Kupffer cells and suppression of the antifibrotic effects of NK/IFN-gamma.

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.

Impaired liver regeneration and increased oval cell numbers following T cell-mediated hepatitis

The regeneration of liver tissue following transplantation is often complicated by inflammation and tissue damage induced by a number of factors, including ischemia and reperfusion injury and immune reactions to the donor tissue. The purpose of the current study is to characterize the effects of T cell-mediated hepatitis induced by concanavalin A (ConA) on the regenerative response in vivo. Liver regeneration following a partial (70%) hepatectomy (pHx) was associated with elevations in serum enzymes and the induction of key cell cycle proteins (cyclin D, cyclin E, and Stat3) and hepatocyte proliferation. The induction of T cell-mediated hepatitis 4 days before pHx increased serum enzymes 48 hours after pHx, reduced early cyclin D expression and Stat3 activation, and suppressed hepatocyte proliferation. This inhibition of proliferation was also associated with increased expression of p21, the activation of Smad2, the induction of transforming growth factor beta and interferon gamma expression, and reduced hepatic interleukin 6 production. Moreover, the ConA pretreatment increased the numbers of separate oval cell-like CD117(+) cells and hematopoietic-like Sca-1(+) cell populations 48 hours following pHx. The depletion of natural killer (NK) cells, an important component of the innate immune response, did not affect liver injury or ConA-induced impairment of hepatocyte proliferation but did increase the numbers of both CD117-positive and Sca-1-positive cell populations. Finally, splenocytes isolated from ConA-pretreated mice exerted cytotoxicity toward autologous bone marrow cells in an NK cell-dependent manner.

CONCLUSION

T cell-mediated hepatitis alters early cytokine responses, reduces hepatocellular regeneration, and induces NK cell-sensitive oval cell and hematopoietic-like cell expansion following pHx.

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.

Activation of mouse natural killer T cells accelerates liver regeneration after partial hepatectomy

BACKGROUND & AIMS

Activation of natural killer T cells with the synthetic ligand alpha-galactosylceramide (alpha-GalCer) induced hepatotoxicity through the tumor necrosis factor (TNF) and Fas-ligand-mediated pathway in aged mice. The aim of this study was to elucidate how alpha-GalCer-activated natural killer T cells function in hepatocyte proliferation and liver regeneration in partially hepatectomized (PHx) mice.

METHODS

Mice were injected with alpha-GalCer at 36 hours after 70% PHx. Hepatocyte mitosis was evaluated by either mitotic figures or proliferating cell nuclear antigen staining. The role of TNF and Fas-ligand in hepatocyte mitosis also was assessed.

RESULTS

In PHx mice injected with alpha-GalCer, hepatocyte mitosis was greatly enhanced at 44 hours after surgery and the increase was more obvious in aged mice than in young mice. The expression of both TNF receptor 1 and Fas-ligand in liver natural killer T cells tended to increase after alpha-GalCer injection in PHx mice. Treatment of mice with anti-NK1.1 Ab 3 days before and just after hepatectomy greatly inhibited the effect of alpha-GalCer on hepatocyte mitosis and liver regeneration. Furthermore, pretreatment of PHx mice with either anti-TNF Ab or anti-FasL Ab 1 hour before alpha-GalCer injection mostly abrogated the increase in hepatocyte proliferation. alpha-GalCer injection did not accelerate hepatocyte proliferation in Fas-mutated lpr mice after PHx. CD1d-/- mice without alpha-GalCer injection showed decreased hepatocyte mitosis after PHx.

CONCLUSIONS

Activated natural killer T cells help hepatocyte proliferation and liver regeneration after PHx via the TNF and Fas/Fas-ligand-mediated pathway.

Implication of B lymphocytes in endotoxin-induced hepatic injury after partial hepatectomy in rats

BACKGROUND

Lymphocyte population constitutes major defense mechanism against endotoxemia, but the role of B lymphocytes in endotoxin-induced hepatic injury after hepatectomy is not clear.

METHODS

We used lymphopenic (L(-)) rats by single administration of anti-rat lymphocyte serum, nu/nu athymic (T(-)) rats, B cell-ablated (B(-))rats by intermittent injection of anti-immunoglobulin (Ig) micro-chain from birth, and their vehicle controls. These animals were subjected to two-thirds hepatectomy with subsequent intravenous lipopolysaccharides (LPS, 1.5 mg/kg) administration. The survival rate, plasma alanine transaminase (ALT), tumor necrosis factor-alpha (TNF-alpha) and IgM levels, and total hemolytic activity (CH50) were determined. Hepatic tissue deposition of IgM or C3 was assessed with immunohistochemistry.

RESULTS

The 24-h survival rate in control animals was 20%, whereas those in L(-), T(-), and B (-) animals were 80, 0, and 100%, respectively. Lymphocyte-sufficient control (L(+)) and B cell-sufficient control (B(+)) animals showed a rapid elevation of plasma TNF-alpha levels 1 h after the challenge, followed by an increase in plasma ALT levels. In B(+) group, plasma IgM levels were increased and CH50 activities were decreased 4 h after LPS injection with significant difference compared to those at time 0. Liver histology showed massive hepatic necrosis with a dense accumulation of IgM and C3 deposits 4 h after LPS administration. B cell ablation significantly ameliorated plasma ALT, IgM, and CH50 levels, showing less histological liver damage.

CONCLUSION

B lymphocytes susceptible to LPS might be implicated in the development of endotoxin-induced hepatic injury after partial hepatectomy.