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

Anti-Tumour Immunity Relies on Targeting Tissue Homeostasis Through Monocyte-Driven Responses Rather Than Direct Tumour Cytotoxicity

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) can progress to hepatocellular carcinoma (HCC), yet the immune mechanisms driving this transition remain unclear.

METHODS

In a chronic Western diet (WD) mouse model, we performed single-nuclei RNA sequencing to track MAFLD progression into HCC and subsequent tumour inhibition upon dietary correction.

RESULTS

Carcinogenesis begins during MAFLD, with tumour cells entering dormancy when HCC is mitigated. Rather than purely tolerogenic, the liver actively engages immune responses targeting myofibroblasts, fibroblasts and hepatocytes to maintain tissue homeostasis. Cytotoxic cells contribute to the turnover of liver cells but do not primarily target the tumour. NKT cells predominate under chronic WD, while monocytes join them in HCC progression on a WD. Upon dietary correction, monocyte-driven immunity confers protection against HCC through targeting tissue homeostatic pathways and antioxidant mechanisms. Crucially, liver tissue response-not merely immune activation-dictates whether tumours grow or regress, emphasising the importance of restoring liver tissue integrity. Also, protection against HCC is linked to a distinct immunological pattern, differing from healthy controls, underscoring the need for immune reprogramming.

CONCLUSION

These findings reveal the dual roles of similar pathways, where immune patterns targeting different cells shape distinct outcomes. Restoring tissue homeostasis and regeneration creates a tumour-hostile microenvironment, whereas tumour-directed approaches fail to remodel the TME. This underscores the need for tissue remodelling strategies in cancer prevention and treatment.

Anti-tumor immunity relies on targeting tissue homeostasis through monocyte-driven responses rather than direct tumor cytotoxicity

Background

Metabolic dysfunction-associated fatty liver disease (MAFLD) can progress to hepatocellular carcinoma (HCC), yet the immune mechanisms driving this transition remain unclear.

Methods

In a chronic Western diet (WD) mouse model, we performed single-nuclei RNA sequencing to track MAFLD progression into HCC and subsequent tumor inhibition upon dietary correction.

Results

Carcinogenesis begins during MAFLD, with tumor cells entering dormancy when HCC is mitigated. Rather than purely tolerogenic, the liver actively engages immune responses targeting myofibroblasts, fibroblasts and hepatocytes to maintain tissue homeostasis. Cytotoxic cells contribute to turnover of liver cells but do not primarily target the tumor. NKT cells predominate under chronic WD, while monocytes join them in HCC progression on a WD. Upon dietary correction, monocyte-driven immunity confers protection against HCC through targeting tissue homeostatic pathways and antioxidant mechanisms. Crucially, liver tissue response-not merely immune activation-dictates whether tumors grow or regress, emphasizing the importance of restoring liver tissue integrity. Also, protection against HCC is linked to a distinct immunological pattern, differing from healthy controls, underscoring the need for immune reprogramming.

Conclusion

These findings reveal the dual roles of similar pathways, where immune patterns targeting different cells shape distinct outcomes. Restoring tissue homeostasis and regeneration creates a tumor-hostile microenvironment, whereas tumor-directed approaches fail to remodel the TME. This underscores the need for tissue remodeling strategies in cancer prevention and treatment.

Molecular mechanisms in liver repair and regeneration: from physiology to therapeutics

Liver repair and regeneration are crucial physiological responses to hepatic injury and are orchestrated through intricate cellular and molecular networks. This review systematically delineates advancements in the field, emphasizing the essential roles played by diverse liver cell types. Their coordinated actions, supported by complex crosstalk within the liver microenvironment, are pivotal to enhancing regenerative outcomes. Recent molecular investigations have elucidated key signaling pathways involved in liver injury and regeneration. Viewed through the lens of metabolic reprogramming, these pathways highlight how shifts in glucose, lipid, and amino acid metabolism support the cellular functions essential for liver repair and regeneration. An analysis of regenerative variability across pathological states reveals how disease conditions influence these dynamics, guiding the development of novel therapeutic strategies and advanced techniques to enhance liver repair and regeneration. Bridging laboratory findings with practical applications, recent clinical trials highlight the potential of optimizing liver regeneration strategies. These trials offer valuable insights into the effectiveness of novel therapies and underscore significant progress in translational research. In conclusion, this review intricately links molecular insights to therapeutic frontiers, systematically charting the trajectory from fundamental physiological mechanisms to innovative clinical applications in liver repair and regeneration.

MicroRNA-183 accelerates the proliferation of hepatocyte during liver regeneration through targeting programmed cell death protein 6

BACKGROUND

Liver regeneration is a highly orchestrated process concerning the modulation of various microRNAs (miRs). miR-183 was recently found to be involved in the process of liver regeneration, that miR-183 was remarkably up-regulated at 2-6 h after partial hepatectomy.

OBJECTIVE

This study was aimed to explore the mechanism of miR-183 in on liver regeneration.

METHODS

After partial hepatectomy (PH) or transfection, we measured the changes of miR-183 and programmed cell death protein 6 (PDCD6) levels in rats and the hepatocytes. The histopathology was observed with hematoxylin-eosin staining. The miR-183 mimic and inhibitor plasmids were intravenously injected into rats, and the liver weight/body weight ratio was calculated. The prediction of TargetScan and the validation of luciferase activity assay were employed to confirm the targeting relationship between miR-183 and PDCD6. The viability, apoptosis and cell cycle of transfected rat hepatocyte BRL-3A were determined via MTT and flow cytometry assays.

RESULTS

MiR-183 expression showed a contrary tendency with that of PDCD6 during liver regeneration. Enhanced miR-183 in rats could notably increase liver/body weight ratio, while its inhibition did conversely. Overexpressed PDCD6, a target of miR-183, repressed the viability and cell cycle in hepatocytes, whereas its silence led to contrary results. Overexpressed miR-183 in BRL-3A cells enhanced cell viability and promoted the cell cycle yet suppressed apoptosis, whereas its inhibition showed contrary results, which were offset by PDCD6.

CONCLUSIONS

Collectively, miR-183 promoted liver regeneration via targeting PDCD6.

Infections, Reactions of Natural Killer T Cells and Natural Killer Cells, and Kidney Injury

Natural killer T (NKT) cells and NK cells are representative innate immune cells that perform antitumor and antimicrobial functions. The involvement of these cells in various renal diseases, including acute kidney injury (AKI), has recently become evident. Murine NKT cells are activated and cause AKI in response to various stimuli, such as their specific ligand, cytokines, and bacterial components. Both renal vascular endothelial cell injury (via the perforin-mediated pathway) and tubular epithelial cell injury (via the tumor necrosis factor-alpha/Fas ligand pathway) are independently involved in the pathogenesis of AKI. NK cells complement the functions of NKT cells, thereby contributing to the development of infection-associated AKI. Human CD56⁺ T cells, which are a functional counterpart of murine NKT cells, as well as a subpopulation of CD56⁺ NK cells, strongly damage intrinsic renal cells in vitro upon their activation, possibly through mechanisms similar to those in mice. These cells are also thought to be involved in the acute exacerbation of pre-existing glomerulonephritis triggered by infection in humans, and their roles in sepsis-associated AKI are currently under investigation. In this review, we will provide an overview of the recent advances in the understanding of the association among infections, NKT and NK cells, and kidney injury, which is much more profound than previously considered. The important role of liver macrophages in the activation of NKT cells will also be introduced.

Liver X receptors regulate natural killer T cell population and antitumor activity in the liver of mice

The nuclear receptors liver X receptor α (LXRα) and LXRβ are lipid sensors that regulate lipid metabolism and immunity. Natural killer T (NKT) cells, a T cell subset expressing surface markers of both natural killer cells and T lymphocytes and involved in antitumor immunity, are another abundant immune cell type in the liver. The potential function of the metabolic regulators LXRα/β in hepatic NKT cells remains unknown. In this study, we examined the role of LXRα and LXRβ in NKT cells using mice deficient for LXRα and/or LXRβ, and found that hepatic invariant NKT (iNKT) cells are drastically decreased in LXRα/β-KO mice. Cytokine production stimulated by the iNKT cell activator α-galactosylceramide was impaired in LXRα/β-KO hepatic mononuclear cells and in LXRα/β-KO mice. iNKT cell-mediated antitumor effect was also disturbed in LXRα/β-KO mice. LXRα/β-KO mice transplanted with wild-type bone marrow showed decreased iNKT cells in the liver and spleen. The thymus of LXRα/β-KO mice showed a decreased population of iNKT cells. In conclusion, LXRα and LXRβ are essential for NKT cell-mediated immunity, such as cytokine production and hepatic antitumor activity, and are involved in NKT cell development in immune tissues, such as the thymus.

Liver X Receptors Regulate Cholesterol Metabolism and Immunity in Hepatic Nonparenchymal Cells

Excess dietary cholesterol intake and the dysregulation of cholesterol metabolism are associated with the pathogenesis and progression of nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, and fibrosis. Hepatic accumulation of free cholesterol induces activation of nonparenchymal cells, including Kupffer cells, macrophages, and hepatic stellate cells, which leads to persistent inflammation and fibrosis. The nuclear receptors liver X receptor α (LXRα) and LXRβ act as negative regulators of cholesterol metabolism through the induction of hepatocyte cholesterol catabolism, excretion, and the reverse cholesterol transport pathway. Additionally, LXRs exert an anti-inflammatory effect in immune cell types, such as macrophages. LXR activation suppresses acute hepatic inflammation that is mediated by Kupffer cells/macrophages. Acute liver injury, diet-induced steatohepatitis, and fibrosis are exacerbated by significant hepatic cholesterol accumulation and inflammation in LXR-deficient mice. Therefore, LXRs regulate hepatic lipid metabolism and immunity and they are potential therapeutic targets in the treatment of hepatic inflammation that is associated with cholesterol accumulation.

Combination of pentoxifylline and α-galactosylceramide with radiotherapy promotes necro-apoptosis and leukocyte infiltration and reduces the mitosis rate in murine melanoma

Despite the success for the treatment of melanoma such as targeted molecular therapy, the use of such treatments are expensive For this reason, this study was carried out to explore the anti-cancer properties of available drugs that are able to modify the melanoma prognosis. The study was conducted in two phases: Evaluation of pharmacological effects of pentoxifylline (PTX) administered above (60 mg/kg) which is the therapeutic dose that is aimed at reducing the side-effect of radiotherapy, and of α- galactosylceramide (GalCer) administered at 100 μg/kg, as well as their combination using a murine model (BDF1 mice) of melanoma cell line (B16-F1, ATCC). For the radiotherapy phase, 9 Gy was applied in the tumor area, before (3 days), during (30 min) and after (3 days) the PTX + GalCer treatment. In both study phases, the mitosis rate, leukocyte infiltration and necro-apoptosis were assessed using histological and immunohistochemical approach and tumor volume evaluation as biomarkers. All treatments showed good prognosis results estimated as reduction of mitosis rate (PTX + GalCer after radiotherapy and GalCer), increased leukocyte infiltrate (PTX + GalCer after radiotherapy and GalCer) and necro-apoptosis augmentation (PTX + GalCer after radiotherapy and radiotherapy control). Nevertheless, a lower development of tumor volume was found in GalCer treatment. In this way, it is possible to suggest that the integrated treatment with immuno-stimulators such as GalCer, plus drug used for peripheral vascular disease (PTX) after radiotherapy is probably an alternative for controlling aggressive melanoma in murine model.

Roles of Natural Killer T Cells and Natural Killer Cells in Kidney Injury

Mouse natural killer T (NKT) cells and natural killer (NK) cells are innate immune cells that are highly abundant in the liver. In addition to their already-known antitumor and antimicrobial functions, their pathophysiological roles in the kidney have recently become evident. Under normal circumstances, the proportion of activated NKT cells in the kidney increases with age. Administration of a synthetic sphingoglycolipid ligand (alpha-galactosylceramide) further activates NKT cells, resulting in injury to renal vascular endothelial cells via the perforin-mediated pathway and tubular epithelial cells via the TNF-α/Fas ligand pathway, causing acute kidney injury (AKI) with hematuria. Activation of NKT cells by common bacterial DNA (CpG-ODN) also causes AKI. In addition, NKT cells together with B cells play significant roles in experimental lupus nephritis in NZB/NZW F1 mice through their Th2 immune responses. Mouse NK cells are also assumed to be involved in various renal diseases, and there may be complementary roles shared between NKT and NK cells. Human CD56⁺ T cells, a functional counterpart of mouse NKT cells, also damage renal cells through a mechanism similar to that of mice. A subpopulation of human CD56⁺ NK cells also exert strong cytotoxicity against renal cells and contribute to the progression of renal fibrosis.

Activated natural killer T cells in mice induce acute kidney injury with hematuria through possibly common mechanisms shared by human CD56+ T cells

Although activation of mouse natural killer T (NKT) cells by α-galactosylceramide (α-GalCer) causes failure of multiple organs, including the kidneys, the precise mechanisms underlying kidney injury remain unclear. Here, we showed that α-GalCer-activated mouse NKT cells injured both kidney vascular endothelial cells and tubular epithelial cells in vitro, causing acute kidney injury (AKI) with hematuria in middle-aged mice. The perforin-mediated pathway was mainly involved in glomerular endothelial cell injury, whereas the TNF-α/Fas ligand pathway played an important role in the injury of tubular epithelial cells. Kidney injury in young mice was mild but could be significantly exacerbated if NKT cells were strongly activated by NK cell depletion alone or in combination with IL-12 pretreatment. When stimulated by a combination of IL-2 and IL-12, human CD56⁺ T cells, a functional counterpart of mouse NKT cells, also damaged both glomerular endothelial cells and tubular epithelial cells, with the former being affected in a perforin-dependent manner. These data suggest that both mouse NKT cells and human CD56⁺ T cells are integral to the processes that mediate AKI. Targeting CD56⁺ T cells may, therefore, be a promising approach to treat AKI.

Update on the Mechanisms of Liver Regeneration

Liver possesses many critical functions such as synthesis, detoxification, and metabolism. It continually receives nutrient-rich blood from gut, which incidentally is also toxin-rich. That may be why liver is uniquely bestowed with a capacity to regenerate. A commonly studied procedure to understand the cellular and molecular basis of liver regeneration is that of surgical resection. Removal of two-thirds of the liver in rodents or patients instigates alterations in hepatic homeostasis, which are sensed by the deficient organ to drive the restoration process. Although the exact mechanisms that initiate regeneration are unknown, alterations in hemodynamics and metabolism have been suspected as important effectors. Key signaling pathways are activated that drive cell proliferation in various hepatic cell types through autocrine and paracrine mechanisms. Once the prehepatectomy mass is regained, the process of regeneration is adequately terminated. This review highlights recent discoveries in the cellular and molecular basis of liver regeneration.

Impaired liver regeneration is associated with reduced cyclin B1 in natural killer T cell-deficient mice

Background

It has been shown that the proportion of natural killer T cells is markedly elevated during liver regeneration and their activation under different conditions can modulate this process. As natural killer T cells and liver injury are central in liver regeneration, elucidating their role is important.

Methods

The aim of the current study is to explore the role of natural killer T cells in impaired liver regeneration. Concanvalin A was injected 4 days before partial hepatectomy to natural killer T cells- deficient mice or to anti CD1d1-treated mice. Ki-67 and proliferating cell nuclear antigen were used to measure hepatocytes proliferation. Expression of hepatic cyclin B1 and proliferating cell nuclear antigen were evaluated by Western Blot and liver injury was assessed by ALT and histology.

Results

Natural killer T cells- deficient or mice injected with anti CD1d antibodies exhibited reduced liver regeneration. These mice were considerably resistant to ConA-induced liver injury. In the absence of NKT cells hepatic proliferating cell nuclear antigen and cyclin B1 decreased in mice injected with Concanvalin A before partial hepatectomy. This was accompanied with reduced serum interleukin-6 levels.

Conclusions

Natural killer T cells play an important role in liver regeneration, which is associated with cyclin B1 and interleukin-6.

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.

Natural killer T cells in liver injury, inflammation and cancer

The liver is an organ that has the largest amount of natural killer T(NKT) cells, which play critical roles in the pathogenesis of liver diseases. In this article, the authors summarize recent findings about the roles of NKT cells in liver injury, inflammation, fibrosis, regeneration and cancer. In brief, NKT cells accelerate liver injury by producing pro-inflammatory cytokines and directly killing hepatocytes. NKT cells are involved in complex roles in liver fibrogenesis. For instance, NKT cells inhibit liver fibrosis via suppressing hepatic stellate cell activation and can also promote liver fibrosis via enhancing liver inflammation and injury. Inactivated or weakly activated NKT cells play a minimal role in controlling liver regeneration, whilst activated NKT cells have an inhibitory effect on liver regeneration. In liver cancer, NKT cells play both pro-tumor and anti-tumor roles in controlling tumor progress.

Mouse CD11b+Kupffer Cells Recruited from Bone Marrow Accelerate Liver Regeneration after Partial Hepatectomy

TNF and Fas/FasL are vital components, not only in hepatocyte injury, but are also required for hepatocyte regeneration. Liver F4/80⁺Kupffer cells are classified into two subsets; resident radio-resistant CD68⁺cells with phagocytic and bactericidal activity, and recruited radio-sensitive CD11b⁺cells with cytokine-producing capacity. The aim of this study was to investigate the role of these Kupffer cells in the liver regeneration after partial hepatectomy (PHx) in mice. The proportion of Kupffer cell subsets in the remnant liver was examined in C57BL/6 mice by flow cytometry after PHx. To examine the role of CD11b⁺Kupffer cells/Mφ, mice were depleted of these cells before PHx by non-lethal 5 Gy irradiation with or without bone marrow transplantation (BMT) or the injection of a CCR2 (MCP-1 receptor) antagonist, and liver regeneration was evaluated. Although the proportion of CD68⁺Kupffer cells did not significantly change after PHx, the proportion of CD11b⁺Kupffer cells/Mφ and their FasL expression was greatly increased at three days after PHx, when the hepatocytes vigorously proliferate. Serum TNF and MCP-1 levels peaked one day after PHx. Irradiation eliminated the CD11b⁺Kupffer cells/Mφ for approximately two weeks in the liver, while CD68⁺Kupffer cells, NK cells and NKT cells remained, and hepatocyte regeneration was retarded. However, BMT partially restored CD11b⁺Kupffer cells/Mφ and recovered the liver regeneration. Furthermore, CCR2 antagonist treatment decreased the CD11b⁺Kupffer cells/Mφ and significantly inhibited liver regeneration. The CD11b⁺Kupffer cells/Mφ recruited from bone marrow by the MCP-1 produced by CD68⁺Kupffer cells play a pivotal role in liver regeneration via the TNF/FasL/Fas pathway after PHx.

Oral ampicillin inhibits liver regeneration by breaking hepatic innate immune tolerance normally maintained by gut commensal bacteria

Commensal bacteria have been proposed to play a role in liver repair after partial (67%) hepatectomy. However, the underlying immune mechanisms remain elusive. Here, we show that liver regeneration was impaired in antibiotic (Atb) water-treated mice and this impairment strongly correlated with commensal bacterial load. Among the various Atbs used in our cocktail, ampicillin-sensitive commensal bacterial was associated with normal liver regeneration. The number of CD1d-dependent natural killer T (NKT) cells in Atb-treated hepatectomized mice was markedly increased, and these NKT cells were functionally overactivated to produce higher interferon-γ. Deficiency of NKT cells or antibody blockade of the CD1d-NKT interaction increased hepatocyte proliferation, which improved liver regeneration. Importantly, an increased number of Kupffer cells were observed in Atb-treated mice, and these Kupffer cells produced higher interleukin-12, which then functioned to activate hepatic NKT cells. Interleukin-12p40 deficiency or treatment with an anti-interleukin-12 antibody significantly inhibited NKT cell overactivation and recovered liver regeneration in Atb-treated mice.

CONCLUSION

Commensal bacteria play a critical role in maintaining Kupffer cells in a tolerant state, preventing subsequent NKT cell overactivation during liver regeneration. Moreover, our data suggest that long-term Atb use, which can impair the gut microbiota, may influence liver function by retarding liver regeneration.

TIGIT safeguards liver regeneration through regulating natural killer cell-hepatocyte crosstalk

Overactivation of innate immunity, particularly natural killer (NK) cells, is harmful to liver regeneration; however, the molecular mechanisms that limit NK cell overactivation during liver regeneration are still elusive. Here we show that a coinhibitory receptor, T cell Ig and ITIM domain (TIGIT), was selectively up-regulated on NK cells, along with high expression of its ligand, poliovirus receptor (PVR/CD155), on hepatocytes during liver regeneration. The absence of TIGIT impaired liver regeneration in vivo, along with overactivation of NK cells and higher NK-derived interferon-gamma (IFN-γ) production. We also show that both depletion of NK cells and deficiency of IFN-γ, but not deficiency of RAG1, rescued impaired liver regeneration caused by the absence of TIGIT. Adoptive transfer of Tigit(-/-) NK cells into NK-deficient Nfil3(-/-) mice sufficiently led to impairment of liver regeneration. On the other hand, silencing PVR in hepatocytes rescued impaired liver regeneration caused by TIGIT deficiency in vivo, while blockade of TIGIT in NK-hepatocyte coculture increased IFN-γ production by NK cells in vitro.

CONCLUSION

TIGIT is a safeguard molecule to improve liver regeneration through negatively regulating NK-hepatocyte crosstalk. This finding suggests a novel mechanism of NK cell self-tolerance towards regenerative hyperplasia of the host.

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).

Innate immune responses involving natural killer and natural killer T cells promote liver regeneration after partial hepatectomy in mice

To clarify the roles of innate immune cells in liver regeneration, here, we investigated the alteration in regenerative responses after partial hepatectomy (PH) under selective depletion of natural killer (NK) and/or NKT cells. Male, wild-type (WT; C57Bl/6), and CD1d-knockout (KO) mice were injected with anti-NK1.1 or anti-asialo ganglio-N-tetraosylceramide (GM1) antibody and then underwent the 70% PH. Regenerative responses after PH were evaluated, and hepatic expression levels of cytokines and growth factors were measured by real-time RT-PCR and ELISA. Phosphorylation of STAT3 was detected by Western blotting. Depletion of both NK and NKT cells with an anti-NK1.1 antibody in WT mice caused drastic decreases in bromodeoxyuridine uptake, expression of proliferating cell nuclear antigen, and cyclin D1, 48 h after PH. In mice given NK1.1 antibody, increases in hepatic TNF-α, IL-6/phospho-STAT3, and hepatocyte growth factor (HGF) levels following PH were also blunted significantly, whereas IFN-γ mRNA levels were not different. CD1d-KO mice per se showed normal liver regeneration; however, pretreatment with an antiasialo GM1 antibody to CD1d-KO mice, resulting in depletion of both NK and NKT cells, also blunted regenerative responses. Collectively, these observations clearly indicated that depletion of both NK and NKT cells by two different ways results in impaired liver regeneration. NK and NKT cells most likely upregulate TNF-α, IL-6/STAT3, and HGF in a coordinate fashion, thus promoting normal regenerative responses in the liver.

Activation of CD11b+ Kupffer cells/macrophages as a common cause for exacerbation of TNF/Fas-ligand-dependent hepatitis in hypercholesterolemic mice

We have reported that the mouse hepatic injury induced by either α-galactosylceramide (α-GalCer) or bacterial DNA motifs (CpG-ODN) is mediated by the TNF/NKT cell/Fas-ligand (FasL) pathway. In addition, F4/80(+) Kupffer cells can be subclassified into CD68(+) subset with a phagocytosing capacity and CD11b(+) subset with a TNF-producing capacity. CD11b(+) subset increase if mice are fed high-fat and cholesterol diet (HFCD). The present study examined how a HFCD affects the function of NKT cells and F4/80(+) CD11b(+) subset and these hepatitis models. After the C57BL/6 mice received a HFCD, high-cholesterol diet (HCD), high-fat diet (HFD) and control diet (CD) for four weeks, the HFCD mice increased surface CD1d and intracellular TLR-9 expression by the CD11b(+) population compared to CD mice. Hepatic injury induced either by α-GalCer or CpG-ODN was more severe in HCD and HFCD mice compared to CD mice, which was in proportion to the serum TNF levels. In addition, liver cholesterol levels but not serum cholesterol levels nor liver triglyceride levels were involved in the aggravation of hepatitis. The FasL expression of NKT cells induced by both reagents was upregulated in HFCD mice. Furthermore, the liver mononuclear cells and purified F4/80(+) CD11b(+) subset from HFCD mice stimulated with either reagent in vitro produced a larger amount of TNF than did those from CD mice. Intracellular TNF production in F4/80(+) CD11b(+) cells was confirmed. The increased number of F4/80(+) CD11b(+) Kupffer cells/macrophages by HFCD and their enhanced TNF production thus play a pivotal role in TNF/NKT cell/FasL dependent hepatic injury.

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.

Antitumor immunity produced by the liver Kupffer cells, NK cells, NKT cells, and CD8 CD122 T cells

Mouse and human livers contain innate immune leukocytes, NK cells, NKT cells, and macrophage-lineage Kupffer cells. Various bacterial components, including Toll-like receptor (TLR) ligands and an NKT cell ligand (α-galactocylceramide), activate liver Kupffer cells, which produce IL-1, IL-6, IL-12, and TNF. IL-12 activates hepatic NK cells and NKT cells to produce IFN-γ, which further activates hepatic T cells, in turn activating phagocytosis and cytokine production by Kupffer cells in a positive feedback loop. These immunological events are essentially evoked to protect the host from bacterial and viral infections; however, these events also contribute to antitumor and antimetastatic immunity in the liver by activated liver NK cells and NKT cells. Bystander CD8⁺CD122⁺ T cells, and tumor-specific memory CD8⁺T cells, are also induced in the liver by α-galactocylceramide. Furthermore, adoptive transfer experiments have revealed that activated liver lymphocytes may migrate to other organs to inhibit tumor growth, such as the lungs and kidneys. The immunological mechanism underlying the development of hepatocellular carcinoma in cirrhotic livers in hepatitis C patients and liver innate immunity as a double-edged sword (hepatocyte injury/regeneration, septic shock, autoimmune disease, etc.) are also discussed.

New insights into liver regeneration

Even if the Greeks probably anticipated rather than discovered the extraordinary regenerative capacity of the liver with the Prometheus myth, this phenomenon still fascinates scientists nowadays with the same enthusiasm. There are good reasons to decipher this process other than to find an answer to our fantasy of immortality: it could indeed help patients needing large liver resections or living-donor liver transplantation, it could increase our understanding of liver pathology and finally it could enable novel cell-therapy approaches. For decades, most of our knowledge about the mechanisms involved in liver regeneration came from the classic two-thirds partial hepatectomy (PH) model. In this scenario, hepatocytes play the leading role, which raises the question of the simple existence of a stem cell population. Recently however, hepatic progenitor cells come again under the limelight, seeming to play a role in liver physiology and in various liver diseases such as steatosis or cirrhosis. Excellent reviews have recently addressed liver regeneration. Our goal is therefore to focus on recent improvements in the field, highlighting data mostly published in the last two years in order to draw a putative picture of what the future research axes on liver regeneration might look like.

Hepatic stellate cells and innate immunity in alcoholic liver disease

Constant alcohol consumption is a major cause of chronic liver disease, and there has been a growing concern regarding the increased mortality rates worldwide. Alcoholic liver diseases (ALDs) range from mild to more severe conditions, such as steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. The liver is enriched with innate immune cells (e.g. natural killer cells and Kupffer cells) and hepatic stellate cells (HSCs), and interestingly, emerging evidence suggests that innate immunity contributes to the development of ALDs (e.g. steatohepatitis and liver fibrosis). Indeed, HSCs play a crucial role in alcoholic steatosis via production of endocannabinoid and retinol metabolites. This review describes the roles of the innate immunity and HSCs in the pathogenesis of ALDs, and suggests therapeutic targets and strategies to assist in the reduction of ALD.

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.

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.

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.

Novel mechanism of C-reactive protein for enhancing mouse liver innate immunity

Although C-reactive protein (CRP) is a representative acute-phase protein produced by hepatocytes, the role of CRP in liver innate immunity remains unclear. Using C57BL/6 mice, the present study investigated how CRP affects the functions of liver macrophages, Kupffer cells, and natural killer / natural killer T (NK/NKT) cells under various conditions, including Escherichia coli infection, septic shock, and multiorgan dysfunction induced by interleukin (IL)-12/lipopolysaccharide (LPS) (generalized Shwartzman reaction [GSR]), and LPS-induced lethal hepatitis in Propionibacterium acnes-primed mice. When mice were challenged with a lethal dose of E. coli, synthetic CRP peptide decreased the mortality without decreasing serum tumor necrosis factor (TNF), presumably by enhancing the phagocytic activity of Kupffer cells. Synthetic CRP greatly decreased the production of TNF and reactive oxygen species from Kupffer cells and thereby rescued mice after lethal LPS challenge. CRP also decreased the mortality from GSR and lethal hepatitis by inhibiting TNF production from Kupffer cells, especially phagocytosing Kupffer cells. However, interferon-gamma production from NK/NKT cells was generally not so affected. CRP reportedly binds to FcgammaRI and FcgammaRII, and the injection of anti-FcgammaRII/III Ab into mice abrogated TNF production from, but increased the phagocytic activity of, Kupffer cells. Furthermore, CRP pretreatment restored the decreased phagocytic activity of Kupffer cells in burn-injured mice and decreased TNF production by Kupffer cells and thereby inhibited mortality after sublethal E. coli infection. If CRP was injected into mice at 1 hour after lethal E. coli challenge, it slightly but significantly increased the survival rate.

CONCLUSION

CRP thus enhances the phagocytosis of Kupffer cells but decreases their TNF production in a complex manner in which the pathway by way of FcgammaRII may be involved.

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.

Superoxide produced by Kupffer cells is an essential effector in concanavalin A-induced hepatitis in mice

Although concanavalin A (Con-A)-induced experimental hepatitis is thought to be induced by activated T cells, natural killer T (NKT) cells, and cytokines, precise mechanisms are still unknown. In the current study, we investigated the roles of Kupffer cells, NKT cells, FasL, tumor necrosis factor (TNF), and superoxide in Con-A hepatitis in C57BL/6 mice. Removal of Kupffer cells using gadolinium chloride (GdCl(3)) from the liver completely inhibited Con-A hepatitis, whereas increased serum TNF and IFN-gamma levels were not inhibited at all. Unexpectedly, anti-FasL antibody pretreatment did not inhibit Con-A hepatitis, whereas it inhibited hepatic injury induced by a synthetic ligand of NKT cells, alpha-galactosylceramide. Furthermore, GdCl(3) pretreatment changed neither the activation-induced down-regulation of NK1.1 antigens as well as T cell receptors of NKT cells nor the increased expression of the CD69 activation antigen of hepatic T cells. CD68(+) Kupffer cells greatly increased in proportion in the early phase after Con-A injection; this increase was abrogated by GdCl(3) pretreatment. Anti-TNF antibody (Ab) pretreatment did not inhibit the increase of Kupffer cells, but it effectively suppressed superoxide/reactive oxygen production from Kupffer cells and the resulting hepatic injury. Conversely, depletion of NKT cells in mice by NK1.1 Ab pretreatment did suppress both the increase of CD68(+) Kupffer cells and Con-A hepatitis. Consistently, the diminution of oxygen radicals produced by Kupffer cells by use of free radical scavengers greatly inhibited Con-A hepatitis without suppressing cytokine production. However, adoptive transfer experiments also indicate that a close interaction/cooperation of Kupffer cells with NKT cells is essential for Con-A hepatitis.

CONCLUSION

Superoxide produced by Kupffer cells may be the essential effector in Con-A hepatitis, and TNF and NKT cells support their activation and superoxide production.

Functional alterations of liver innate immunity of mice with aging in response to CpG-oligodeoxynucleotide

Immune functions of liver natural killer T (NKT) cells induced by the synthetic ligand alpha-galactosylceramide enhanced age-dependently; hepatic injury and multiorgan dysfunction syndrome (MODS) induced by ligand-activated NKT cells were also enhanced. This study investigated how aging affects liver innate immunity after common bacteria DNA stimulation. Young (6 weeks) and old (50-60 weeks) C57BL/6 mice were injected with CpG oligodeoxynucleotides (CpG-ODN), and the functions of liver leukocytes were assessed. A CpG-ODN injection into the old mice remarkably increased tumor necrosis factor (TNF) production in Kupffer cells, and MODS and lethal shock were induced, both of which are rarely seen in young mice. Old Kupffer cells showed increased Toll-like receptor-9 expression, and CpG-ODN challenge augmented TNF receptor and Fas-L expression in liver NKT cells. Experiments using mice depleted of natural killer (NK) cells by anti-asialoGM1 antibody (Ab), perforin knockout mice, and mice pretreated with neutralizing interferon (IFN)-gamma Ab demonstrated the important role of liver NK cells in antitumor immunity. The production capacities of old mice for IFN-gamma, IFN-alpha, and perforin were much lower than those of young mice, and the CpG-induced antitumor cytotoxicity of liver NK cells lessened. Lethal shock and MODS greatly decreased in old mice depleted/deficient in TNF, FasL, or NKT cells. However, depletion of NK cells also decreased serum TNF levels and FasL expression of NKT cells, which resulted in improved hepatic injury and survival, suggesting that NK cells are indirectly involved in MODS/lethal shock induced by NKT cells. Neutralization of TNF did not reduce the CpG-induced antitumor effect in the liver.

CONCLUSION

Hepatic injury and MODS mediated by NKT cells via the TNF and FasL-mediated pathway after CpG injection increased, but the antitumor activity of liver NK cells decreased with aging.

Role of natural killer T cells in liver diseases

Natural killer T (NKT) cells are a unique subset of lymphocytes, which express both T and NK cell surface markers as well as functional characteristics. They connect innate and acquired immunity, and restrictedly recognize glycolipid antigens presented by CD1d molecule. NKT cells secrete a great quantity of cytokines rapidly which regulate human immune response after being activated. For there are abundant NKT cells in human liver, researchers have a great interest in their roles.

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.

Pretransplantation CD56(+) innate lymphocyte populations associated with severity of hepatitis C virus recurrence

Cluster of differentiation (CD)56(+) lymphocytes are believed to play important roles in the innate immune response to viral infections by production of interferon (IFN)-gamma and/or the recognition of virally infected cells, but their role in liver transplantation (LT) has not been characterized. Here, for the first time, we examine the phenotypic and functional features of these cells in patients undergoing LT for hepatitis C virus (HCV)-related liver failure. The study was comprised of four patient groups: patients with mild HCV recurrence (n = 9), severe HCV recurrence (n = 10), patients with non-HCV-related liver failure (n =10), and normal healthy subjects (n = 10). Pre-LT, the frequency of circulating CD56(+) lymphocytes was significantly lower in patients who subsequently developed severe HCV recurrence, relative to those patients who developed mild histologic recurrence, as well as non-HCV controls. HCV was associated with impaired lymphokine-activated killing and natural cytotoxicity. We found that natural T (NT) cells that coexpressed CD4/CD8 or expressed CD8 alone were more frequent in patients who subsequently developed severe recurrence. In contrast, NT cells that expressed only CD4 appeared to be depleted in HCV infection relative to controls. A significantly higher percentage of NTs in both HCV groups expressed the inhibitory receptor NKG2A relative to HCV-negative controls with liver disease. In conclusion, these results demonstrate a previously unappreciated association between pretransplantation CD56(+) lymphocytes and outcome of HCV recurrence and provide novel mechanistic insights into the immunopathogenesis of HCV recurrence, as well as potential targets for therapeutic manipulation.

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.