Details of an isolation method for hepatic lymphocytes in mice

Recovered Hepatocytes Promote Macrophage Apoptosis through CXCR4 after Acetaminophen-Induced Liver Injury in Mice

Acetaminophen (APAP) overdose is the main cause of acute liver failure in Western countries. The mechanism of APAP hepatotoxicity is associated with centrilobular necrosis which initiates infiltration of neutrophils, monocytes, and other leukocytes to the area of necrosis. While it has been recognized that this infiltration of immune cells plays a critical role in promoting liver repair, mechanism of immune cell clearance that is important for resolution of inflammation and the return to normal homeostasis are not well characterized. CXCR4 is a chemokine receptor expressed on hepatocytes as well as neutrophils, monocytes, and hematopoietic stem cells. CXCR4 function is dependent on its selective expression on different cell types and thus can vary depending on the pathophysiology. This study aimed to investigate the crosstalk between hepatocytes and macrophages through CXCR4 to promote macrophage apoptosis after APAP overdose. C57BL/6J mice were subjected to APAP overdose (300 mg/kg). Flow cytometry and immunohistochemistry were used to determine the mode of cell death of macrophages and expression pattern of CXCR4 during the resolution phase of APAP hepatotoxicity. The impact of CXCR4 in regulation of macrophage apoptosis and liver recovery was assessed after administration of a monoclonal antibody against CXCR4. RNAseq analysis was performed on flow cytometry sorted CXCR4+ macrophages at 72 h to confirm the apoptotic cell death of macrophages. Our data indicate that the inflammatory response is resolved by recovering hepatocytes through induction of CXCR4 on macrophages, which triggers their cell death by apoptosis at the end of the recovery phase.

Activation of the adenosine A2B receptor even beyond the therapeutic window of N-acetylcysteine accelerates liver recovery after an acetaminophen overdose

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in the USA. The short therapeutic window of the current antidote, N-acetylcysteine (NAC) highlights the need for novel late acting therapeutics. The neuronal guidance cue netrin-1 provides delayed protection against APAP hepatotoxicity through the adenosine A2B receptor (A2BAR). The clinical relevance of this mechanism was investigated here by administration of the A2BAR agonist BAY 60-6583, after an APAP overdose (300 or 600 mg/kg) in fasted male and female C57BL/6J mice with assessment of liver injury 6 or 24 h after APAP in comparison to NAC. BAY 60-6583 treatment 1.5 h after APAP overdose (600 mg/kg) protected against liver injury at 6 h by preserving mitochondrial function despite JNK activation and its mitochondrial translocation. Gender independent protection was sustained when BAY 60-6583 was given 6 h after APAP overdose (300 mg/kg), when NAC administration did not show benefit. This protection was accompanied by enhanced infiltration of macrophages with the reparative anti-inflammatory phenotype by 24 h, accompanied by a decrease in neutrophil infiltration. Thus, our data emphasize the remarkable therapeutic utility of using an A2BAR agonist, which provides delayed protection long after the standard of care NAC ceased to be effective.

Kupffer cells regulate liver recovery through induction of chemokine receptor CXCR2 on hepatocytes after acetaminophen overdose in mice

Acetaminophen (APAP) is a widely used analgesic, but also a main cause of acute liver injury in the United States and many western countries. APAP hepatotoxicity is associated with a sterile inflammatory response as shown by the infiltration of neutrophils and monocytes. While the contribution of the immune cells to promote liver repair have been demonstrated, the direct interactions between macrophages or neutrophils with hepatocytes to help facilitate hepatocyte proliferation and tissue repair remain unclear. The purpose of this study was to investigate the relationship between resident macrophages (Kupffer cells) and hepatocytes with a focus on the chemokine receptor CXCR2. C57BL/6J mice were subjected to an APAP overdose (300 mg/kg) and the role of CXCR2 on hepatocytes was investigated using a selective antagonist, SB225002. In addition, clodronate liposomes were used to deplete Kupffer cells to assess changes in CXCR2 expression. Our data showed that CXCR2 was mainly expressed on hepatocytes and it was induced specifically in hepatocytes around the necrotic area 24 h after APAP treatment. Targeting this receptor using an inhibitor caused a delayed liver recovery. Depletion of Kupffer cells significantly prevented CXCR2 induction on hepatocytes. In vitro and in vivo experiments also demonstrated that Kupffer cells regulate CXCR2 expression and pro-regenerative gene expression in surviving hepatocytes through production of IL-10. Thus, Kupffer cells support the transition of hepatocytes around the area of necrosis to a proliferative state through CXCR2 expression.

Protective Role of microRNA-31 in Acetaminophen-Induced Liver Injury: A Negative Regulator of c-Jun N-Terminal Kinase (JNK) Signaling Pathway

BACKGROUND & AIMS

Sustained c-Jun N-terminal kinase (JNK) activation plays a major role in drug-induced liver injury (DILI). Stress-responsive microRNA-31 (miR-31) has been implicated in regulating different cellular damage, and JNK activation could induce miR-31 expression. However, the regulatory role of miR-31 in DILI has not been studied previously. We aimed to investigate whether miR-31 could ameliorate DILI and ascertain potential molecular mechanism.

METHODS

miR-31 gene knockout (31-KO) and wild-type C57BL/6J mice were used to construct an acetaminophen (APAP)-induced DILI model. Primary mouse hepatocytes, as well as alpha mouse liver 12 (AML-12) cell lines, were used for in vitro experiments. Argonaute 2-associated RNA immunoprecipitation combined with high-throughput sequencing were performed to identify specific targets of miR-31.

RESULTS

31-KO mice showed a higher mortality rate, liver transaminase levels, and hepatic necrosis compared with those in wild-type mice after APAP-induced hepatotoxicity. The protective role of miR-31 on hepatocytes has been analyzed via constructing bone marrow chimeric mice. Mechanistically, we found that hepatic JNK phosphorylation increased significantly in 31-KO mice. This caused mitochondrial phosphorylated Src (p-Src) inactivation and more reactive oxygen species production, which directly amplifies hepatocyte necrotic cell death, while administration of JNK-specific inhibitor SP600125 could abrogate the differences. Moreover, bioinformatics analysis of RNA immunoprecipitation combined with high-throughput sequencing identified that guanosine triphosphatase, cell division cycle protein 42 (Cdc42), the upstream molecule of JNK signaling, was the specific target of miR-31 and could form a miR-31/Cdc42/phosphorylated mixed-lineage kinase 3 (p-MLK3) negative feedback loop to restrict JNK overactivation. Clinically, both miR-31 and phosphorylated JNK (p-JNK) were highly increased in liver tissues of DILI patients with different etiologies.

CONCLUSIONS

miR-31 can down-regulate Cdc42 to restrict overactivation of reactive oxygen species/JNK/mitochondria necrotic death loop in hepatocytes of APAP-induced DILI, which might provide a new therapeutic target for alleviating JNK overactivation-based liver injury.

The SGLT2 inhibitor empagliflozin negatively regulates IL-17/IL-23 axis-mediated inflammatory responses in T2DM with NAFLD via the AMPK/mTOR/autophagy pathway

Empagliflozin is a SGLT2 inhibitor that reduces the concentration of blood glucose by inhibiting glucose reabsorption and promoting glucose excretion. Interestingly, empagliflozin also has some additional benefits, including cardiovascular protection, decreasing uric acid levels and improving NAFLD-related liver injury. However, the specific mechanism by which empagliflozin ameliorates NAFLD-related liver injury, especially how empagliflozin regulates hepatic immune inflammatory responses, is still unknown. In this study, male C57BL/6J mice were fed a high-fat diet and injected with streptozotocin to establish an animal model of T2DM with NAFLD. Then, diabetic mice with NAFLD were administered empagliflozin by gavage. We found that empagliflozin ameliorated liver injury and lipid metabolism disorder in T2DM mice with NAFLD. Empagliflozin significantly enhanced autophagy in hepatic macrophages via the AMPK/mTOR signalling pathway. After blocking autophagy and AMPK activity, empagliflozin could not prevent NAFLD-related liver injury. Furthermore, the expression levels of IL-17/IL-23 axis-related molecules were inhibited by empagliflozin through enhancing macrophage autophagy. Inhibition of IL-17/IL-23 axis activity attenuated liver injury in T2DM mice with NAFLD. In summary, these results suggested that empagliflozin could significantly ameliorate NAFLD-related liver injury, through enhancing hepatic macrophage autophagy via the AMPK/mTOR signalling pathway and further inhibiting IL-17/IL-23 axis-mediated inflammatory responses. This study provides a theoretical basis for the rational application of empagliflozin to treat T2DM with NAFLD and improve the quality of life of T2DM patients with NAFLD, which will have social benefits.

Therapeutic Role of Inducible Nitric Oxide Synthase Expressing Myeloid-Derived Suppressor Cells in Acetaminophen-Induced Murine Liver Failure

Background

Acetaminophen (APAP) overdose is one of the major etiologies of liver failure. Hepatocyte necrosis induced by toxic metabolites of APAP can activate proinflammatory responses, including elastase-expressing neutrophils, to exacerbate liver injury. Myeloid-derived suppressor cells (MDSCs) increased in inflammation can inhibit proinflammatory responses. Our aim is to investigate the role of MDSC in APAP-induced liver failure and the possible therapeutic application.

Methods

BLAB/c mice were injected with a sublethal/lethal dose of APAP as the murine model of liver failure. MDSCs were defined as CD11b⁺Gr-1⁺ cells with the ability of T-cell suppression.

Results

A sublethal challenge of APAP could increase the intrahepatic MDSC and protect mice against subsequent lethal challenge of APAP, lipopolysaccharide (LPS)/D-galatosamine or concanavalin A. This protection was lost if MDSCs were depleted and inducible nitric oxide synthase (iNOS) was the key molecule in this MDSC-mediated protection. Taking advantage of these observations, different bone marrow-derived MDSCs (BM-MDSCs) were generated. Among different cytokine-treated BM-MDSCs, tumor necrosis factor alpha/LPS-primed MDSCs (TNF-α/LPS MDSCs) had the strongest liver-protection ability after adoptive transfer. Further mechanistic explorations showed, iNOS-expressing TNF-α/LPS MDSCs induced the apoptosis of activated neutrophil and decreased the intrahepatic infiltration of elastase-expressing neutrophil. Moreover, we generated MDSCs from human peripheral blood mononuclear cells (PBMCs) with similar phenotype.

Conclusion

We demonstrated the protective role of MDSCs and therapeutic effect of TNF-α/LPS MDSCs in APAP-induced liver failure. MDSC might protect against the APAP-induced liver failure by reducing the intrahepatic infiltration of activated neutrophil to limit inflammation. Therefore, a therapeutic role of MDSCs for APAP-induced liver failure was proposed.

Long non-coding RNAs play regulatory roles in acetaminophen-induced liver injury

OBJECTIVE

To explore the expression profile and role of hepatic long non-coding RNA (lncRNA) in acetaminophen-induced liver injury mouse model by analyzing lncRNA-mRNA co-expression.

METHODS

Serum aminotransferase, liver pathology and inflammatory cells were analyzed in mice model at different time points after treated with acetaminophen 300 mg/kg. High-throughput RNA sequencing was performed to investigate hepatic expression profiles of messenger RNA (mRNA) and lncRNA. The relationship between the lncRNA and mRNA was delineated by the co-expression network using Cytoscape software. Differential mRNAs co-expressed with lncRNAs were analyzed using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes enrichment. Differential mRNAs and lncRNAs were selected for quantitative reverse transcription polymerase chain reaction validation, and the conservation of lncRNA between human and mouse was analyzed.

RESULTS

Liver injury was more severe at 24 hours than at 6 hours. There was a substantial infiltration of monocytes instead of neutrophil and Kupffer cells at 24 hours compared with 6 hours. The mRNAs co-expressed with the differential lncRNAs at 24 vs 6 hours were mainly enriched in protein processing in endoplasmic reticulum, MAPK and PPAR signaling pathways. The co-expression network delineated with four lncRNAs and 94 mRNAs presented the core position of lncRNA in the network. A conservation analysis indicated that four differential mouse lncRNAs (NONMMUT023651.2, NONMMUT029382.2, NONMMUT029383.2 and NONMMUT102053.1) could all be mapped to the relevant human lncRNAs.

CONCLUSION

Four lncRNAs may play regulatory roles through metabolic and apoptosis-related pathways during hepatic homeostasis maintenance and repair progress.

NKG2A is a NK cell exhaustion checkpoint for HCV persistence

Exhaustion of cytotoxic effector natural killer (NK) and CD8⁺ T cells have important functions in the establishment of persistent viral infections, but how exhaustion is induced during chronic hepatitis C virus (HCV) infection remains poorly defined. Here we show, using the humanized C/O^Tg mice permissive for persistent HCV infection, that NK and CD8⁺ T cells become sequentially exhausted shortly after their transient hepatic infiltration and activation in acute HCV infection. HCV infection upregulates Qa-1 expression in hepatocytes, which ligates NKG2A to induce NK cell exhaustion. Antibodies targeting NKG2A or Qa-1 prevents NK exhaustion and promotes NK-dependent HCV clearance. Moreover, reactivated NK cells provide sufficient IFN-γ that helps rejuvenate polyclonal HCV CD8⁺ T cell response and clearance of HCV. Our data thus show that NKG2A serves as a critical checkpoint for HCV-induced NK exhaustion, and that NKG2A blockade sequentially boosts interdependent NK and CD8⁺ T cell functions to prevent persistent HCV infection.

Immune cells may become less responsive, or ‘exhausted’, upon chronic viral infection, but the underlying mechanism and crosstalk are still unclear. Here the authors show that, upon chronic hepatitis C virus (HCV) infection, natural killer cell exhaustion is induced by NKG2A signalling to instruct downstream exhaustion of CD8⁺ T cells and HCV persistence.

Immunization With a Subunit Hepatitis C Virus Vaccine Elicits Pan-Genotypic Neutralizing Antibodies and Intrahepatic T-Cell Responses in Nonhuman Primates

Background

The global control of hepatitis C virus (HCV) infection remains a great burden, owing to the high prices and potential drug resistance of the new direct-acting antivirals (DAAs), as well as the risk of reinfection in DAA-cured patients. Thus, a prophylactic vaccine for HCV is of great importance. We previously reported that a single recombinant soluble E2 (sE2) vaccine produced in insect cells was able to induce broadly neutralizing antibodies (NAbs) and prevent HCV infection in mice. Here the sE2 vaccine was evaluated in non-human primates.

Methods

Rhesus macaques were immunized with sE2 vaccine in combination with different adjuvants. Vaccine-induced NAbs in antisera were tested for neutralization activities against a panel of cell culture-derived HCV (HCVcc), while T-cell responses were evaluated in splenocytes, peripheral blood mononuclear cells, and hepatic lymphocytes.

Results

sE2 is able to elicit NAbs against HCVcc harboring structural proteins from multiple HCV genotypes in rhesus macaques. Moreover, sE2-immunized macaques developed systemic and intrahepatic memory T cells specific for E2. A significant correlation between the sE2-specific immunoglobulin G titers and neutralization spectrum was observed, highlighting the essential role of sE2 immunogenicity on achieving broad NAbs.

Conclusions

sE2 is a promising HCV vaccine candidate that warrants further preclinical and clinical development.

Macrophage-derived IL-1α promotes sterile inflammation in a mouse model of acetaminophen hepatotoxicity

The metabolic intermediate of acetaminophen (APAP) can cause severe hepatocyte necrosis, which triggers aberrant immune activation of liver non-parenchymal cells (NPC). Overzealous hepatic inflammation determines the morbidity and mortality of APAP-induced liver injury (AILI). Interleukin-1 receptor (IL-1R) signaling has been shown to play a critical role in various inflammatory conditions, but its precise role and underlying mechanism in AILI remain debatable. Herein, we show that NLRP3 inflammasome activation of IL-1β is dispensable to AILI, whereas IL-1α, the other ligand of IL-1R1, accounts for hepatic injury by a lethal dose of APAP. Furthermore, Kupffer cells function as a major source of activated IL-1α in the liver, which is activated by damaged hepatocytes through TLR4/MyD88 signaling. Finally, IL-1α is able to chemoattract and activate CD11b⁺Gr-1⁺ myeloid cells, mostly neutrophils and inflammatory monocytes, to amplify deteriorated inflammation in the lesion. Therefore, this work identifies that MyD88-dependent activation of IL-1α in Kupffer cells plays a central role in the immunopathogenesis of AILI and implicates that IL-1α is a promising therapeutic target for AILI treatment.

γδ T cells are indispensable for interleukin-23-mediated protection against Concanavalin A-induced hepatitis in hepatitis B virus transgenic mice

Hepatitis B virus surface antigen (HBsAg) carriers are highly susceptible to liver injury triggered by environmental biochemical stimulation. Previously, we have reported an inverse correlation between γδ T cells and liver damage in patients with hepatitis B virus (HBV). However, whether γδ T cells play a role in regulating the hypersensitivity of HBsAg carriers to biochemical stimulation-induced hepatitis is unknown. In this study, using HBV transgenic (HBs-Tg) and HBs-Tg T-cell receptor-δ-deficient (TCR-δ^-/- ) mice, we found that mice genetically deficient in γδ T cells exhibited more severe liver damage upon Concanavalin A (Con A) treatment, as indicated by substantially higher serum alanine aminotransferase levels, further elevated interferon-γ (IFN-γ) levels and more extensive necrosis. γδ T-cell deficiency resulted in elevated IFN-γ in CD4⁺ T cells but not in natural killer or natural killer T cells. The depletion of CD4⁺ T cells and neutralization of IFN-γ reduced liver damage in HBs-Tg and HBs-Tg-TCR-δ^-/- mice to a similar extent. Further investigation revealed that HBs-Tg mice showed an enhanced interleukin-17 (IL-17) signature. The administration of exogenous IL-23 enhanced IL-17A production from Vγ4 γδ T cells and ameliorated liver damage in HBs-Tg mice, but not in HBs-Tg-TCR-δ^-/- mice. In summary, our results demonstrated that γδ T cells played a protective role in restraining Con A-induced hepatitis by inhibiting IFN-γ production from CD4⁺ T cells and are indispensable for IL-23-mediated protection against Con A-induced hepatitis in HBs-Tg mice. These results provided a potential therapeutic approach for treating the hypersensitivity of HBV carriers to biochemical stimulation-induced liver damage.

BLT1 signalling protects the liver against acetaminophen hepatotoxicity by preventing excessive accumulation of hepatic neutrophils

Leukotriene B₄ (LTB₄) is a potent chemoattractant for neutrophils. Signalling of LTB₄ receptor type 1 (BLT₁) has pro-inflammatory functions through neutrophil recruitment. In this study, we investigated whether BLT₁ signalling plays a role in acetaminophen (APAP)-induced liver injury by affecting inflammatory responses including the accumulation of hepatic neutrophils. BLT₁-knockout (BLT₁^−/−) mice and their wild-type (WT) counterparts were subjected to a single APAP overdose (300 mg/kg), and various parameters compared within 24 h after treatment. Compared with WT mice, BLT₁^−/− mice exhibited exacerbation of APAP-induced liver injury as evidenced by enhancement of alanine aminotransferase level, necrotic area, hepatic neutrophil accumulation, and expression of cytokines and chemokines. WT mice co-treated with APAP and ONO-0457, a specific antagonist for BLT₁, displayed amplification of the injury, and similar results to those observed in BLT₁^−/− mice. Hepatic neutrophils in BLT₁^−/− mice during APAP hepatotoxicity showed increases in the production of reactive oxygen species and matrix metalloproteinase-9. Administration of isolated BLT₁-deficient neutrophils into WT mice aggravated the liver injury elicited by APAP. These results demonstrate that BLT₁ signalling dampens the progression of APAP hepatotoxicity through inhibiting an excessive accumulation of activated neutrophils. The development of a specific agonist for BLT₁ could be useful for the prevention of APAP hepatotoxicity.

Persistent hepatitis C virus infections and hepatopathological manifestations in immune-competent humanized mice

The majority of hepatitis C virus (HCV) infection develops chronic infection, which causes steatosis, cirrhosis and hepatocellular carcinoma. However, understanding HCV chronicity and pathogenesis is hampered by its narrow host range, mostly restricted to human and chimpanzee. Recent endeavour to infect a variety of humanized mice has not been able to achieve persistent HCV infection unless the essential innate immune responsive genes are knocked out. Nevertheless, such immune-compromised humanized mice still lacked HCV infection-induced hepatopathogenesis. Here we report that transgenic mice in ICR background harboring both human CD81 and occludin genes (C/O^Tg) are permissive to HCV infection at a chronicity rate comparable to humans. In this mouse model, HCV accomplishes its replication cycle, leading to sustained viremia and infectivity for more than 12 months post infection with expected fibrotic and cirrhotic progression. Host factors favorable for HCV replication, and inadequate innate immune-response may contribute to the persistence. Lastly, NS3/4 protease inhibitor telaprevir can effectively inhibit de novo RNA synthesis and acute HCV infection of C/O^Tg mice. Thus, chronic HCV infection with complete replication cycle and hepatopathologic manifestations is recapitulated, for the first time, in immune-competent mice. This model will open a new venue to study the mechanisms of chronic hepatitis C and develop better treatments.

Neutrophil activation during acetaminophen hepatotoxicity and repair in mice and humans

Following acetaminophen (APAP) overdose there is an inflammatory response triggered by the release of cellular contents from necrotic hepatocytes into the systemic circulation which initiates the recruitment of neutrophils into the liver. It has been demonstrated that neutrophils do not contribute to APAP-induced liver injury, but their role and the role of NADPH oxidase in injury resolution are controversial. C57BL/6 mice were subjected to APAP overdose and neutrophil activation status was determined during liver injury and liver regeneration. Additionally, human APAP overdose patients (ALT: >800 U/L) had serial blood draws during the injury and recovery phases for the determination of neutrophil activation. Neutrophils in the peripheral blood of mice showed an increasing activation status (CD11b expression and ROS priming) during and after the peak of injury but returned to baseline levels prior to complete injury resolution. Hepatic sequestered neutrophils showed an increased and sustained CD11b expression, but no ROS priming was observed. Confirming that NADPH oxidase is not critical to injury resolution, gp91(phox)⁻/⁻ mice following APAP overdose displayed no alteration in injury resolution. Peripheral blood from APAP overdose patients also showed increased neutrophil activation status after the peak of liver injury and remained elevated until discharge from the hospital. In mice and humans, markers of activation, like ROS priming, were increased and sustained well after active liver injury had subsided. The similar findings between surviving patients and mice indicate that neutrophil activation may be a critical event for host defense or injury resolution following APAP overdose, but not a contributing factor to APAP-induced injury.

Rapid and non-enzymatic in vitro retrieval of tumour cells from surgical specimens

The study of tumourigenesis commonly involves the use of established cell lines or single cell suspensions of primary tumours. Standard methods for the generation of short-term tumour cell cultures include the disintegration of tissue based on enzymatic and mechanical stress. Here, we describe a simple and rapid method for the preparation of single cells from primary carcinomas, which is independent of enzymatic treatment and feeder cells. Tumour biopsies are processed to 1 mm(3) cubes termed explants, which are cultured 1-3 days on agarose-coated well plates in specified medium. Through incisions generated in the explants, single cells are retrieved and collected from the culture supernatant and can be used for further analysis including in vitro and in vivo studies. Collected cells retain tumour-forming capacity in xenotransplantation assays, mimic the phenotype of the primary tumour, and facilitate the generation of cell lines.

Role of hepatocyte-derived IL-7 in maintenance of intrahepatic NKT cells and T cells and development of B cells in fetal liver

The liver contains a variety of resident immune cells, such as NK cells, NKT cells, T cells, macrophages, and dendritic cells. However, little is known about how IL-7, which is produced by hepatocytes, functions locally in development and maintenance of liver immune cells. To address this question, we established IL-7-floxed mice and crossed them with albumin promoter-driven Cre (Alb-Cre) transgenic mice to establish conditional knockout of IL-7 in hepatocytes. The levels of IL-7 transcripts were reduced 10-fold in hepatocyte fraction. We found that the absolute numbers of NKT and T cells were significantly decreased in adult liver of IL-7(f/f) Alb-Cre mice compared with IL-7(f/f) control mice. In contrast, NK cells, dendritic cells, and B cells were unchanged in the IL-7(f/f) Alb-Cre liver. The number of Vα14(+) invariant NKT cells was significantly reduced in liver, but not in thymus and spleen, of IL-7(f/f) Alb-Cre mice. Furthermore, B cell development was impaired in perinatal liver of IL-7(f/f) Alb-Cre mice. This study demonstrates that hepatocyte-derived IL-7 plays an indispensable role in maintenance of NKT and T cells in adult liver and development of B cells in fetal liver, and suggests that hepatocytes provide a unique IL-7 niche for intrahepatic lymphocytes.

Natural killer T cells are required for lipopolysaccharide-mediated enhancement of atherosclerosis in apolipoprotein E-deficient mice

Lipopolysaccharide (LPS) has been shown to accelerate atherosclerosis and to increase the prevalence of IL-4-producing natural killer T (NKT) cells in various tissues. However, the role of NKT cells in the development of LPS-induced atherosclerotic lesions has not been fully tested in NKT cell-deficient mice. Here, we examined the lesion development in apolipoprotein E knockout (apoE-KO) mice and apoE-KO mice on an NKT cell-deficient, CD1d knockout (CD1d-KO) background (apoE-CD1d double knockout; DKO). LPS (0.5 μg/g body weight/wk) or phosphate-buffered saline (PBS) was intraperitoneally administered to apoE-KO and DKO mice (8-wk old) for 5 wk and atherosclerotic lesion areas were quantified thereafter. Consistent with prior reports, NKT cell-deficient DKO mice showed milder atherosclerotic lesions than apoE-KO mice. Notably, LPS administration significantly increased the lesion size in apoE-KO, but not in DKO mice, compared to PBS controls. Our findings suggest that LPS, and possibly LPS-producing bacteria, aggravate the development of atherosclerosis primarily through NKT cell activation and subsequent collaboration with NK cells.

Type II NKT cells stimulate diet-induced obesity by mediating adipose tissue inflammation, steatohepatitis and insulin resistance

The progression of obesity is accompanied by a chronic inflammatory process that involves both innate and acquired immunity. Natural killer T (NKT) cells recognize lipid antigens and are also distributed in adipose tissue. To examine the involvement of NKT cells in the development of obesity, C57BL/6 mice (wild type; WT), and two NKT-cell-deficient strains, Jα18(-/-) mice that lack the type I subset and CD1d(-/-) mice that lack both the type I and II subsets, were fed a high fat diet (HFD). CD1d(-/-) mice gained the least body weight with the least weight in perigonadal and brown adipose tissue as well as in the liver, compared to WT or Jα18(-/-) mice fed an HFD. Histologically, CD1d(-/-) mice had significantly smaller adipocytes and developed significantly milder hepatosteatosis than WT or Jα18(-/-) mice. The number of NK1.1(+)TCRβ(+) cells in adipose tissue increased when WT mice were fed an HFD and were mostly invariant Vα14Jα18-negative. CD11b(+) macrophages (Mφ) were another major subset of cells in adipose tissue infiltrates, and they were divided into F4/80(high) and F4/80(low) cells. The F4/80(low)-Mφ subset in adipose tissue was increased in CD1d(-/-) mice, and this population likely played an anti-inflammatory role. Glucose intolerance and insulin resistance in CD1d(-/-) mice were not aggravated as in WT or Jα18(-/-) mice fed an HFD, likely due to a lower grade of inflammation and adiposity. Collectively, our findings provide evidence that type II NKT cells initiate inflammation in the liver and adipose tissue and exacerbate the course of obesity that leads to insulin resistance.

Apolipoprotein A-II suppressed concanavalin A-induced hepatitis via the inhibition of CD4 T cell function

Con A-induced hepatitis has been used as a model of human autoimmune or viral hepatitis. During the process of identifying immunologically bioactive proteins in human plasma, we found that apolipoprotein A-II (ApoA-II), the second major apolipoprotein of high-density lipoprotein, inhibited the production of IFN-γ by Con A-stimulated mouse and human CD4 T cells. Con A-induced hepatitis was attenuated by the administration of ApoA-II. The beneficial effect of ApoA-II was associated with reduced leukocyte infiltration and decreased production of T cell-related cytokines and chemokines in the liver. ApoA-II inhibited the Con A-induced activation of ERK-MAPK and nuclear translocation of NFAT in CD4 T cells. Interestingly, exacerbated hepatitis was observed in ApoA-II-deficient mice, indicating that ApoA-II plays a suppressive role in Con A-induced hepatitis under physiological conditions. Moreover, the administration of ApoA-II after the onset of Con A-induced hepatitis was sufficient to suppress disease. Thus, the therapeutic effect of ApoA-II could be useful for patients with CD4 T cell-related autoimmune and viral hepatitis.

Interferon-gamma negatively regulates Th17-mediated immunopathology during mouse hepatitis virus infection

Fulminant hepatitis can cause acute liver failure and death in both humans and mice. However, the cellular and molecular mechanisms underlying the acute disease are still not well understood. Here, we examine the role of Th17 response in the development of the acute hepatitis following infection with mouse hepatitis virus (MHV). We show that IL-17 levels in serum are rapidly elevated and positively correlated to liver damage and death of the mice. In IFN-γR^−/− mice, Th17 response is enhanced and the elevated IL-17 production contributes to severe liver damage as well as detrimental inflammation because neutralization of IL-17 effectively suppresses inflammation and protects mice from liver injury. We further show that IFN-γ facilitates antigen-induced apoptosis of Th17 cells and adoptive transferred IFN-γR^−/−, but not IFN-γR^+/+; CD4⁺ T cells promotes an enhanced liver damage in wild-type mice. The results demonstrate an essential role of Th17 cells in MHV-induced immunopathology and the importance of IFN-γ in maintaining immune balance between Th1 and Th17 responses during acute viral infection.

Tumor necrosis factor is critical for cytolytic T cell activity against allospecific hepatocytes and splenic targets in major histocompatibility complex class I disparate graft versus host disease

The present studies determined the role of tumor necrosis factor (TNF)/tumor necrosis factor receptor (TNFR) interactions on cytolytic (CTL) activity of splenic and intrahepatic lymphocytes (IHL) isolated from mice undergoing graft versus host disease, induced by transfer of B6 T cells to major histocompatibility complex (MHC) class I disparate bm1 × B6 F1 mice. Allospecific killing of anti-H-2(bm1) splenic and hepatocyte targets was assessed by 4-h (51)Cr release and 16-h DNA lysis assays, respectively, utilizing spleen cells (SpC) and IHL isolated (1) from sublethally irradiated bm1 × B6 F1 who had received B6 spleen and bone marrow cells, and a control adenovirus (Adv-βgal) or a TNF inhibitor expressing adenovirus (Adv-TNFi), or (2) from bm1 × B6 F1 recipients of B6, B6.129-Tnfrsf1a(tm1Mak)/J (TNFR1(-/-)), B6.129S2-Tnfrsf1b(tm1Mwm)/J (TNFR2(-/-)), or B6.129S-Tnfrsf1a(tm1Imx) Tnfrsf1b(tm1Imx)/J (TNFR(-/-)) SpC and bone marrow cells, or (3) from in vitro-activated SpC. Splenic and IHL from bone marrow transplant recipients who had received Adv-TNFi at the time of transplant displayed lower allospecific CTL activity than controls. Addition of TNFR-Ig or a TNF antibody before the CTL activity assay further reduced allospecific killing against bm1 SpC blast targets. Both TNF/TNFR1 and TNF/TNFR2 interactions were critical for the development of optimal CTL activity against allospecific hepatocyte targets. Further, TNFR1- and TNFR2-deficient SpC from MHC class I disparate mixed lymphocyte cultures displayed lower CTL activity and expression of effector molecules than control B6 SpC. TNF/TNFR interactions were critical for the development of optimal CTL activity of IHL and splenic cytotoxic T cells against MHC class I disparate SpC blast and hepatocyte targets in MHC class I disparate graft versus host disease.

Acetaminophen-induced hepatic neutrophil accumulation and inflammatory liver injury in CD18-deficient mice

BACKGROUND

Acetaminophen (APAP) hepatotoxicity is currently the most frequent cause of acute liver failure in the US and many European countries. Although intracellular signalling mechanisms are critical for hepatocellular injury, a contribution of inflammatory cells, especially neutrophils, has been suggested. However, conflicting results were obtained when using immunological intervention strategies.

AIMS

The role of neutrophils was investigated using a CD18-deficient mouse model.

RESULTS

Treatment of C57Bl/6 wild type mice with 300 mg/kg APAP resulted in severe liver cell necrosis at 12 and 24 h. This injury was accompanied by formation of cytokines and chemokines and accumulation of neutrophils in the liver. However, there was no difference in the inflammatory response or liver injury in CD18-deficient mice compared with wild-type animals. In contrast to treatment with endotoxin, no upregulation of CD11b or priming for reactive oxygen was observed on neutrophils isolated from the peripheral blood or the liver after APAP administration. Furthermore, animals treated with endotoxin 3 h after APAP experienced an exaggerated inflammatory response as indicated by substantially higher cytokine and chemokine formation and twice the number of neutrophils in the liver. However, liver injury in the two-hit model was the same as with APAP alone.

CONCLUSIONS

Our data do not support the hypothesis that neutrophils contribute to APAP hepatotoxicity or that a neutrophil-mediated injury phase could be provoked by a second, pro-inflammatory hit. Thus, APAP-induced liver injury in mice is dominated by intracellular mechanisms of cell death rather than by neutrophilic inflammation.

Quality of the transgene-specific CD8+ T cell response induced by adenoviral vector immunization is critically influenced by virus dose and route of vaccination

Adenoviral vectors have been widely used for experimental gene therapy and vaccination, yet there is a surprising lack of knowledge connecting the route and dose of adenovirus administration to the induced transgene-specific immune response. We have recently demonstrated polyfunctional CD8(+) T cells and protective memory responses using adenoviral vectors, which seem to contrast with recent reports suggesting that an exhausted CD8(+) T cell phenotype is induced by inoculation with adenoviral vectors. Accordingly, we investigated the route and dose interrelationship for transgene-specific CD8(+) T cells using adenoviral vectors encoding beta-galactosidase applied either s.c. or i.v. Irrespective of the route of inoculation, most of the adenoviral inoculum was found to disseminate systemically as the dose was raised beyond 10(9) particles. The number of transgene-specific CD8(+) T cells correlated positively with dissemination, whereas the functional capacity of the generated T cells correlated inversely with vector dissemination. A comparison of the immune response to s.c. or i.v. administration at moderate doses revealed that inoculation by both routes induced a transient peak of IFN-gamma-producing CD8(+) T cells 2 to 3 wk postinfection, but following i.v. administration, these cells were only detected in the liver. Two to four months after systemic, but not peripheral, immunization, dysfunctional transgene-specific CD8(+) T cells impaired in both cytokine production and important in vivo effector functions, accumulated in the spleen. These findings indicate that the localization of the adenoviral inoculum and not the total Ag load determines the quality of the CD8(+) T cell response induced with adenoviral vaccines.

Thioredoxin binding protein 2 modulates natural killer T cell-dependent innate immunity in the liver: possible link to lipid metabolism

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

Macrophage interleukin-6 and tumour necrosis factor-alpha are induced by coronavirus fixation to Toll-like receptor 2/heparan sulphate receptors but not carcinoembryonic cell adhesion antigen 1a

A rapid antiviral immune response may be related to viral interaction with the host cell leading to activation of macrophages via pattern recognition receptors (PPRs) or specific viral receptors. Carcinoembryonic cell adhesion antigen 1a (CEACAM1a) is the specific receptor for the mouse hepatitis virus (MHV), a coronavirus known to induce acute viral hepatitis in mice. The objective of this study was to understand the mechanisms responsible for the secretion of high-pathogenic MHV3-induced inflammatory cytokines. We report that the induction of the pro-inflammatory cytokines interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in peritoneal macrophages does not depend on CEACAM1a, as demonstrated in cells isolated from Ceacam1a(-/-) mice. The induction of IL-6 and TNF-alpha production was related rather to the fixation of the spike (S) protein of MHV3 on Toll-like receptor 2 (TLR2) in regions enriched in heparan sulphate and did not rely on viral replication, as demonstrated with denatured S protein and UV-inactivated virus. High levels of IL-6 and TNF-alpha were produced in livers from infected C57BL/6 mice but not in livers from Tlr2(-/-) mice. The histopathological observations were correlated with the levels of those inflammatory cytokines. Depending on mouse strain, the viral fixation to heparan sulfate/TLR2 stimulated differently the p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-kappaB in the induction of IL-6 and TNF-alpha. These results suggest that TLR2 and heparan sulphate receptors can act as new viral PPRs involved in inflammatory responses.

An early burst of IFN-gamma induced by the pre-erythrocytic stage favours Plasmodium yoelii parasitaemia in B6 mice

BACKGROUND

In murine models of malaria, an early proinflammatory response has been associated with the resolution of blood-stage infection. To dissect the protective immune mechanism that allow the control of parasitaemia, the early immune response of C57BL/6 mice induced during a non-lethal plasmodial infection was analysed.

METHODS

Mice were infected with Plasmodium yoelii 265BY sporozoites, the natural invasive form of the parasite, in order to complete its full life cycle. The concentrations of three proinflammatory cytokines in the sera of mice were determined by ELISA at different time points of infection. The contribution of the liver and the spleen to this cytokinic response was evaluated and the cytokine-producing lymphocytes were identified by flow cytometry. The physiological relevance of these results was tested by monitoring parasitaemia in genetically deficient C57BL/6 mice or wild-type mice treated with anti-cytokine neutralizing antibody. Finally, the cytokinic response in sera of mice infected with parasitized-RBCs was analysed.

RESULTS

The early immune response of C57BL/6 mice to sporozoite-induced malaria is characterized by a peak of IFN-gamma in the serum at day 5 of infection and splenic CD4 T lymphocytes are the major producer of this cytokine at this time point. Somewhat unexpected, the parasitaemia is significantly lower in P. yoelii-infected mice in the absence of IFN-gamma. More precisely, at early time points of infection, IFN-gamma favours parasitaemia, whereas helping to clear efficiently the blood-stage parasites at later time points. Interestingly, the early IFN-gamma burst is induced by the pre-erythrocytic stage.

CONCLUSION

These results challenge the current view regarding the role of IFN-gamma on the control of parasite growth since they show that IFN-gamma is not an essential mediator of protection in P. yoelii-infected C57BL/6 mice. Moreover, the mice parasitaemia is more efficiently controlled in the absence of an early IFN-gamma production, suggesting that this cytokine promotes parasite's growth. Finally, this early burst of IFN-gamma is induced by the pre-erythrocytic stage, showing the impact of this stage on the immune response taking place during the subsequent erythrocytic stage.

A synergistic interferon-gamma production is induced by mouse hepatitis virus in interleukin-12 (IL-12)/IL-18-activated natural killer cells and modulated by carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1a receptor

The production of interferon-gamma (IFN-gamma) by infiltrating natural killer (NK) cells in liver is involved in the control of mouse hepatitis virus (MHV) infection. The objectives of this study were to identify the mechanisms used by MHV type 3 to modulate the production of IFN-gamma by NK cells during the acute hepatitis in susceptible C57BL/6 mice. Ex vivo and in vitro experiments revealed that NK cells, expressing carcinoembryonic antigen-related cell adhesion molecules (CEACAM) 1a (the MHV receptor), can produce a higher level of IFN-gamma in the presence of both L2-MHV3 and interleukin-12 (IL-12)/IL-18. The synergistic production of IFN-gamma by NK cells depends on viral replication rather than viral fixation only, because it is inhibited or not induced in cells infected with ultraviolet-inactivated viruses and in cells from Ceacam1a(-/-) mice infected with virulent viruses. The synergistic IFN-gamma production involves the p38 mitogen-activated protein kinase (MAPK) rather than the extracellular signal-regulated kinase-1/2 MAPK signalling pathway. However, the signal triggered through the engagement of CEACAM1a decreases the production of IFN-gamma, when these molecules are cross-linked using specific monoclonal antibodies. These results suggest that control of acute hepatitis by IFN-gamma-producing NK cells may depend on both production of IL-12 and IL-18 in the liver environment and viral infection of NK cells.

New insights into mechanisms of spontaneous liver transplant tolerance: the role of Foxp3-expressing CD25+CD4+ regulatory T cells

Liver allografts in mice are accepted across MHC barriers without requirement for immunosuppressive therapy. The mechanisms underlying this phenomenon remain largely undefined. In this study, we investigated the role of Foxp3-expressing CD25(+)CD4(+) regulatory T cells (Treg) in the induction of murine liver transplant tolerance. Foxp3(+)CD25(+)CD4(+) T cells were increased in liver grafts and recipient spleens from day 5 to day 100 posttransplantation, associated with enhanced CTLA4 and TGF-beta expression and IL-4 production. Depletion of recipient CD25(+)CD4(+) T cells using anti-CD25 mAb (250 microg/day) induced acute liver allograft rejection. This was associated with a decreased ratio of Foxp3(+) Treg: T effector cells, decreased IL-4 and elevated IL-10 and IL-2 production by graft-infiltrating T cells, and reduced apoptotic activity of graft-infiltrating CD4(+) and CD8(+) T cells in anti-CD25-mAb-treated recipients. Thus, the data suggest that Foxp3(+)CD25(+)CD4(+)Treg are involved in spontaneous acceptance of liver allografts in mice. The ratio of Treg to T effector cells appears to determine liver transplant outcome. CTLA4, IL-4, TGF-beta and apoptosis of graft-infiltrating T cells are also associated with liver transplant tolerance and may contribute, at least in part, to the mechanisms of Treg-mediated immune regulation in this model.

Periplocoside A, a pregnane glycoside from Periploca sepium Bge, prevents concanavalin A-induced mice hepatitis through inhibiting NKT-derived inflammatory cytokine productions

Periploca sepium Bge, a traditional Chinese herb medicine, is widely used for treating rheumatoid arthritis in china. Periplocoside A (PSA), a pregnane glycoside, is a new nature product compound isolated from P. sepium Bge. We examined the protective effects of PSA, on concanavaline A (ConA)-induced hepatitis. Pretreatment with PSA dramatically ameliorated ConA-induced liver injury, which was characterized by reducing serum alanine transaminase (ALT), pathogenic cytokines of interleukin (IL)-4 and interferon (IFN)-gamma levels, impeding the liver necrosis, and thus elevating the survival rate. In vitro, PSA inhibited IL-4 and IFN-gamma productions of alpha-galactosylceramide (alpha-GalCer) or anti-CD3-activated Natural killer T (NKT) cells. Enzyme Linked Immunosorbent Assay (ELISA) and Reverse Transcription Polymerase Chain Reaction (RT-PCR) assays revealed PSA suppressed IL-4 transcription and IFN-gamma translation. In conclusion, PSA had significantly preventative effect on ConA-induced hepatitis, which was closely associated with inhibition of NKT-derived inflammatory cytokine productions. These findings suggested that PSA has the therapeutic potential for treatment of human autoimmune-related hepatitis.

Assessment of natural killer (NK) and NKT cells in murine spleens and livers

Natural killer (NK) cells part of innate immunity. NK cells have been assigned numerous functions, including the ability to serve as a bridge between innate and adaptive immunity. In evaluating NK cell function, two pathways need to be examined: their ability to kill certain tumors spontaneously and their ability to secrete cytokines, interferon-gamma (IFN-gamma), in particular. Although NK cells are distinct from T lymphocytes, a new lymphocyte subset, termed NKT cell, has been described. NKT cells express surface markers that are unique to NK cells (e.g., NK1.1) as well as markers that are unique to T cells (e.g., CD3). Most NKT cells recognize glycolipids and are thought to play an important immunoregulatory role. This chapter will detail the methodology needed for examination of NK and NKT cells in mice.

Complementation in trans of altered thymocyte development in mice expressing mutant forms of the adaptor molecule SLP76

The adaptor protein SLP76 directs signaling downstream of the T cell receptor (TCR) and is essential for thymocyte development. SLP76 contains three N-terminal tyrosines that are critical for its function. To define the role of these residues in thymocyte development, we generated two lines of "knock-in" mice, one expressing a mutation in tyrosine 145 (Y145F) and a second harboring two point mutations at tyrosines 112 and 128 (Y112-128F). We show here that although thymocyte development requires both Y145- and Y112-128-generated signals, selection was more dependent upon Y145. Although several proximal TCR signaling events were defective in both mutant mice, phosphorylation of the guanine nucleotide exchange factor, Vav1, and activation of Itk-dependent pathways were differentially affected by mutations at Y112-128 and Y145, respectively. Analysis of mice expressing one Y145F and one Y112-128F allele revealed that these mutants could complement one another in trans, demonstrating cooperativity between two or more SLP76 molecules. Thus, the N-terminal tyrosines of SLP76 are required for thymocyte selection but can function on separate molecules to support TCR signaling.

Intrahepatic endothelial and Kupffer cells involved in immunosuppressive cytokines and natural killer (NK)/NK T cell disorders in viral acute hepatitis

During acute viral hepatitis, the intrahepatic tolerance sustained by immunosuppressive cytokines such as interleukin (IL)-4, IL-10, transforming growth factor (TGF)-beta and prostaglandin E2 (PGE2), produced by Kupffer cells (KC), liver sinusoidal endothelial cells (LSEC), natural killer (NK) T cells and natural regulatory T cells may be disturbed. NK cells are recruited normally in the liver and produce interferon (IFN)-gamma to control viral replication. The use of mouse hepatitis virus type 3 (MHV3) attenuated variants showing selected tropisms for KC or LSEC have allowed determining their roles in the disturbances of immune tolerance during viral hepatitis. Groups of C57BL/6 mice were infected with the pathogenic L2-MHV3 (KC+, LSEC+), low attenuated 51.6-MHV3 (KC+, LSEC-) or high attenuated CL12-MHV3 (KC-, LSEC-) variants for the first 3 days. Results showed that IL-10, TGF-beta and PGE2 production in the liver decreased in L2-MHV3-infected mice and increased in 51.6-MHV3- and CL12-MHV3-infected mice. The ratio of IFN-gamma/IL-4 in liver decreased in L2-MHV3-infected mice, while it was not (or low) altered in mice infected with the attenuated MHV3 variant mice. Phenotypic analysis of intrahepatic mononuclear cells revealed that apoptotic NK and NK T cells increased in mice infected with the L2-MHV3, but were minor in 51.6-MHV3- and CL12-MHV3-infected mice. The numbers of CD4+ forkhead box P3+ cells increased in the livers from low pathogenic CL12-MHV3 and YAC-MHV3-infected mice. These results indicate that viral permissivity of KC and LSEC is involved in the decrease of IL-10 and PGE2, while KC may play an additional role in the apoptosis of NK and NK T cells during acute viral hepatitis.

Critical role for CXC chemokine ligand 16 (SR-PSOX) in Th1 response mediated by NKT cells

The transmembrane chemokine CXCL 16 (CXCL16), which is the same molecule as the scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX), has been shown to mediate chemotaxis and adhesion of CXC chemokine receptor 6-expressing cells such as NKT and activated Th1 cells. We generated SR-PSOX/CXCL16-deficient mice and examined the role of this chemokine in vivo. The mutant mice showed a reduced number of liver NKT cells, and decreased production of IFN-gamma and IL-4 by administration of alpha-galactosylceramide (alphaGalCer). Of note, the alphaGalCer-induced production of IFN-gamma was more severely impaired than the production of IL-4 in SR-PSOX-deficient mice. In this context, SR-PSOX-deficient mice showed impaired sensitivity to alphaGalCer-induced anti-tumor effect mediated by IFN-gamma from NKT cells. NKT cells from wild-type mice showed impaired production of IFN-gamma, but not IL-4, after their culture with alphaGalCer and APCs from mutant mice. Moreover, Propionibacterium acnes-induced in vivo Th1 responses were severely impaired in SR-PSOX-deficient as well as NKT KO mice. Taken together, SR-PSOX/CXCL16 plays an important role in not only the production of IFN-gamma by NKT cells, but also promotion of Th1-inclined immune responses mediated by NKT cells.

Intrahepatic lymphocyte expression of dipeptidyl peptidase I-processed granzyme B and perforin induces hepatocyte expression of serine proteinase inhibitor 6 (Serpinb9/SPI-6)

Human proteinase inhibitor 9 (PI-9/serpinB9) and the murine ortholog, serine proteinase inhibitor 6 (SPI-6/serpinb9) are members of a family of intracellular serine proteinase inhibitors (serpins). PI-9 and SPI-6 expression in immune-privileged cells, APCs, and CTLs protects these cells against the actions of granzyme B, and when expressed in tumor cells or virally infected hepatocytes, confers resistance to killing by CTL and NK cells. The present studies were designed to assess the existence of any correlation between granzyme B activity in intrahepatic lymphocytes and induction of hepatic SPI-6 expression. To this end, SPI-6, PI-9, and serpinB9 homolog expression was examined in response to IFN-alpha treatment and during in vivo adenoviral infection of the liver. SPI-6 mRNA expression increased 10- to 100-fold in the liver after IFN-alpha stimulation and during the course of viral infection, whereas no significant up-regulation of SPI-8 and <5-fold increases in other PI-9/serpinB9 homolog mRNAs was observed. Increased SPI-6 gene expression during viral infection correlated with influxes of NK cells and CTL. Moreover, IFN-alpha-induced up-regulation of hepatocyte SPI-6 mRNA expression was not observed in NK cell-depleted mice. Additional experiments using genetically altered mice either deficient in perforin or unable to process or express granzyme B indicated that SPI-6 is selectively up-regulated in hepatocytes in response to infiltration of the liver by NK cells that express perforin and enzymatically active granzyme B.

Primary infection of C57BL/6 mice with Plasmodium yoelii induces a heterogeneous response of NKT cells

NKT cells are a population of innate-like lymphocytes that display effector functions and immunoregulatory properties. We characterized the NKT cell response induced in C57BL/6 mice during a primary infection with Plasmodium yoelii sporozoites. We observed a heterogeneous NKT cell response that differed between liver and spleen. Hepatic NKT cells found in infected livers consisted mainly of CD1d-dependent CD4+ and double-negative (DN) NKT cells, whereas CD1d-independent NKT cells exhibiting a TCR(high) CD4(high) phenotype were prominent among splenic NKT cells during the infection. Hepatic and splenic NKT cells isolated from infected mice were activated and secreted mainly gamma interferon and tumor necrosis factor alpha in response to stimulation. Finally, P. yoelii-activated hepatic DN NKT cells inhibited the parasite's liver stage in a CD1d-dependent manner in vitro. However, experiments using B6.CD1d-deficient mice showed that CD1d and CD1d-restricted NKT cells are not necessary to control the parasite's development in vivo during neither the preerythrocytic stage nor the erythrocytic stage. Thus, our results show that a primary P. yoelii infection induces a heterogeneous and organ-specific response of NKT cells and that CD1d-dependent NKT cells play a minor role in the control of the development of Plasmodium in vivo in our model.

Role of interferon-gamma in Valpha14+ natural killer T cell-mediated host defense against Streptococcus pneumoniae infection in murine lungs

Previously, we demonstrated that Valpha14+ NKT cells and IFN-gamma are important upstream components in neutrophil-mediated host defense against infection with Streptococcus pneumoniae. In the present study, we extended these findings by elucidating the role of IFN-gamma in this Valpha14+ NKT cell-promoted process. Administration of recombinant IFN-gamma to Jalpha18KO mice prolonged the shortened survival, promoted the attenuated clearance of bacteria and improved the reduced accumulation of neutrophils and synthesis of MIP-2 and TNF-alpha in the lungs, in comparison to wild-type (WT) mice. In addition, intravenous transfer of liver mononuclear cells (LMNC) from WT mice into Jalpha18KO mice resulted in complete recovery of the depleted responses listed above, whereas such effects were not detected when LMNC were obtained from IFN-gammaKO or Jalpha18KO mice. Activation of Valpha14+ NKT cells by alpha-galactosylceramide (alpha-GalCer) significantly enhanced the clearance of bacteria, accumulation of neutrophils and synthesis of MIP-2 and TNF-alpha in the infected lungs; this effect was significantly inhibited by a neutralizing anti-IFN-gamma antibody. Finally, in a flow cytometric analysis, TNF-alpha synthesis was detected largely by CD11b(bright+) cells in the infected lungs. Our results demonstrated that IFN-gamma plays an important role in the neutrophil-mediated host protective responses against pneumococcal infection promoted by Valpha14+ NKT cells.

Preferential involvement of Tim-3 in the regulation of hepatic CD8+ T cells in murine acute graft-versus-host disease

Tim-3, a member of the T cell Ig mucin (TIM) family regulates effector Th1 responses. We examined Tim-3 and its ligand expression as well as the effects of anti-Tim-3 mAb treatment in a murine model of acute graft-vs-host disease (aGVHD). In mice with aGVHD, Tim-3 expression was markedly up-regulated on splenic and hepatic CD4+ and CD8+ T cells, dendritic cells (DCs), and macrophages, and this was especially dramatic in hepatic CD8+ T cells. Both donor- and host-derived CD8+ T cells induced similar levels of Tim-3. Tim-3 ligand expression was also up-regulated in splenic T cells, DCs, and macrophages, but not in the hepatic lymphocytes. The administration of anti-Tim-3 mAbs accelerated aGVHD, as demonstrated by body weight loss, reduction in total splenocyte number, and infiltration of lymphocytes in the liver. IFN-gamma expression by splenic and hepatic CD4+ and CD8+ T cells was significantly augmented by anti-Tim-3 mAb treatment. In addition, the cytotoxicity against host alloantigen by donor CD8+ T cells was enhanced. These results demonstrate that the anti-Tim-3 treatment in aGVHD augmented the activation of effector T cells expressing IFN-gamma or exerting cytotoxicity. Our results suggest that Tim-3 may play a crucial role in the regulation of CD8+ T cells responsible for the maintenance of hepatic homeostasis and tolerance.

CCR5 is essential for NK cell trafficking and host survival following Toxoplasma gondii infection

The host response to intracellular pathogens requires the coordinated action of both the innate and acquired immune systems. Chemokines play a critical role in the trafficking of immune cells and transitioning an innate immune response into an acquired response. We analyzed the host response of mice deficient in the chemokine receptor CCR5 following infection with the intracellular protozoan parasite Toxoplasma gondii. We found that CCR5 controls recruitment of natural killer (NK) cells into infected tissues. Without this influx of NK cells, tissues from CCR5-deficient (CCR5-/-) mice were less able to generate an inflammatory response, had decreased chemokine and interferon gamma production, and had higher parasite burden. As a result, CCR5-/- mice were more susceptible to infection with T. gondii but were less susceptible to the immune-mediated tissue injury seen in certain inbred strains. Adoptive transfer of CCR5+/+ NK cells into CCR5-/- mice restored their ability to survive lethal T. gondii infection and demonstrated that CCR5 is required for NK cell homing into infected liver and spleen. This study establishes CCR5 as a critical receptor guiding NK cell trafficking in host defense.

Neutrophil depletion protects against murine acetaminophen hepatotoxicity

We previously reported that liver natural killer (NK) and NKT cells play a critical role in mouse model of acetaminophen (APAP)-induced liver injury by producing interferon gamma (IFN-gamma) and modulating chemokine production and subsequent recruitment of neutrophils into the liver. In this report, we examined the role of neutrophils in the progression of APAP hepatotoxicity. C57BL/6 mice were given an intraperitoneal toxic dose of APAP (500 mg/kg), which caused severe acute liver injury characterized by significant elevation of serum ALT, centrilobular hepatic necrosis, and increased hepatic inflammatory cell accumulation. Flow cytometric analysis of isolated hepatic leukocytes demonstrated that the major fraction of increased hepatic leukocytes at 6 and 24 hours after APAP was neutrophils (Mac-1+ Gr-1+). Depletion of neutrophils by in vivo treatment with anti-Gr-1 antibody (RB6-8C5) significantly protected mice against APAP-induced liver injury, as evidenced by markedly reduced serum ALT levels, centrilobular hepatic necrosis, and improved mouse survival. The protection was associated with decreased FasL-expressing cells, cytotoxicity against hepatocytes, and respiratory burst in hepatic leukocytes. In intracellular adhesion molecule (ICAM)-1-deficient mice, APAP caused markedly reduced liver injury when compared with wild-type mice. The marked protection in ICAM-1-deficient mice was associated with decreased accumulation of neutrophils in the liver. Hepatic GSH depletion and APAP-adducts showed no differences among the antibody-treated, ICAM-1-deficient, and normal mice. In conclusion, accumulated neutrophils in the liver contribute to the progression and severity of APAP-induced liver injury.

Isolation of neutrophils from mouse liver: A novel method to study effector leukocytes during inflammation

Neutrophils are phagocytic leukocytes that represent one of the first lines of defense during infection and injury. Neutrophils emigrate into tissues during inflammation and are phenotypically different compared to cells in the circulation. To further understand the biology of tissue-recruited neutrophils, we have developed a reliable method to isolate these cells from inflamed liver. Acute liver inflammation was induced in mice by systemic treatment with adenovirus vectors. Two hours following adenovirus treatment, livers were enzymatically digested and leukocytes isolated by Percoll density gradient centrifugation. Neutrophils were then purified by negative immunomagnetic separation. Neutrophils isolated in this manner were 95% pure as determined by flow cytometry and more than 97% viable by propidium iodide staining. In order to carry out molecular studies, we extracted high quality genomic DNA and RNA from isolated neutrophils. PCR was used to successfully amplify sample genes from isolated neutrophil DNA. Isolated neutrophil RNA was used in a ribonuclease protection assay to evaluate chemokine gene expression. Neutrophils were shown to express multiple chemokine mRNA transcripts including MIP-1 beta, MIP-2 and IP-10. This work describes a novel method to isolate highly pure, viable neutrophils from pathologically inflamed tissue for subsequent detailed cellular and molecular analysis.

Defining the role of T cell-derived leptin in the modulation of hepatic or intestinal inflammation in mice

The role of leptin in the immune system has been well established. While adipocytes represent the major source, leptin production by lymphocytes, infiltrating at the site of inflammation, was recently demonstrated. However, the significance of this locally released leptin remains unresolved. In the present study, two models in which absence of leptin-signalling is associated with protection were employed: the model of ConA-induced hepatitis and the CD4(+)CD45Rb(high) transfer model of colitis. For the ConA model, scid mice were reconstituted with either WT or leptin-deficient (ob/ob) CD4(+) T cells. Eight weeks post transfer, ConA was injected and serum ALT, TNFalpha, leptin as well as liver mononuclear cell activation and histological signs of inflammation were evaluated. No difference between recipients of WT or ob/ob cells was observed for any of the parameters evaluated. In the second model, either WT or ob/ob CD4(+)CD45Rb(high) cells were transferred into scid mice. No histological differences were detected, although recipients of ob/ob cells showed higher weight loss compared to recipients of WT cells. Spontaneous production of IL-6 from colon cultures obtained from recipients of ob/ob cells was reduced compared to recipients of WT cells, whereas stimulation of lamina propria lymphocytes with leptin resulted in a higher IFNgamma release in recipients of ob/ob cells compared to recipients of WT cells. In conclusion, the present study provides evidence that T cell-derived leptin does not play a major role in the regulation of the inflammatory process, indicating that the adipose tissue is the critical player in the immune-modulating effects of leptin.

CXCL16 participates in pathogenesis of immunological liver injury by regulating T lymphocyte infiltration in liver tissue

AIM: To investigate the role of CXCL16 in the pathogenesis of immunological liver injury and to explore the possible mechanism of T lymphocyte infiltration regulated by CXCL16.

METHODS: Immunological liver injury in murine model was induced by Bacille Calmette-Guerin and lipopolysaccharide. Expression pattern and distribution of CXCL16 were examined by real-time quantitative RT-PCR and immunohistochemical analysis. Anti-CXCL16 antibody was administrated in vivo to investigate its effect on T-cell recruitment and acute hepatic necrosis. The survival of murine model was also evaluated.

RESULTS: The murine immunological liver injury model was successfully established. CXCL16 expression increased and predominantly distributed in periportal areas and vascular endothelia in injured liver tissues. Administration of anti-CXCL16 Ab protected the mice from death and acute liver damage. Approximately 70% of the mice survived for 72 h in the anti-CXCL16 Ab treatment group, whereas 80% died within 72 h in control Ab group. The number of liver-infiltrating T lymphocytes was significantly reduced from 1.01×10⁷ to 3.52×10⁶/liver, compared with control Ab treatment.

CONCLUSION: CXCL16 is involved in immunological liver injury by regulating T lymphocyte infiltration in liver tissue.

The role of TNF in hepatic histopathological manifestations and hepatic CD8+ T cell alloresponses in murine MHC class I disparate GVHD

Transfer of B6 T cells to major histocompatibility complex (MHC) class I disparate bm1 x B6 F1 mice leads to the development of hepatic graft-versus-host disease (GVHD) characterized by an active hepatitis with portal and lobular inflammation as well as bile duct inflammation and venulitis. The present studies determined the role of tumor necrosis factor (TNF) in hepatic GVHD. B6 responder cells were cultured with irradiated MHC class I disparate bm1 or syngeneic spleen cells (SpC) in the presence or absence of TNF receptor inhibitor [TNFR-immunoglobulin (Ig)]. Recipient bm1 x B6 F1 mice were irradiated (600 cGy) and reconstituted with 5 x 10(6) T cell-depleted B6 bone marrow cells and 1 x 10(7) B6 SpC. Mice were injected with an adenovirus encoding TNFR-Ig [TNF inhibitor-encoding adenovirus (Adv-TNFi)] or beta-galactosidase (Adv-betagal). Severity of liver GVHD was assessed by a composite histopathological score consisting of the sum of scores for venulitis, lobular hepatitis, and bile duct inflammation. Addition of TNFR-Ig reduced cell proliferation in mixed lymphocyte cultures using B6 responder SpC by 71% +/- 12.8% and interferon-gamma responses by 78% +/- 18%. GVHD-induced "wasting disease" was reduced in Adv-TNFi recipients [4.4%+/-5.2% weight loss (n=11)] compared with Adv-betagal recipients [16.1%+/-7.6% weight loss (n=11; P=0.0004)] 9 days post-transplant. Composite histopathological scores and individual venulitis scores were reduced with the addition of Adv-TNFi. Hepatic CD8+ T cells in the recipients of Adv-TNFi were reduced as compared with recipients of Adv-betagal. In conclusion, Adv-TNFi reduces MHC class I disparate alloproliferative responses and hepatic GVHD.

Involvement of up-regulated CXC chemokine ligand 16/scavenger receptor that binds phosphatidylserine and oxidized lipoprotein in endotoxin-induced lethal liver injury via regulation of T-cell recruitment and adhesion

A murine model of endotoxin-induced lethal liver injury induced by Mycobacterium bovis BCG plus lipopolysaccharide (LPS) has been widely accepted and used. It has been reported that T cells play an important role in the pathogenesis of liver damage in this model. However, the precise mechanisms involved in regulation of the trafficking of effector T cells need to be elucidated. In the present study, we first reported that CXCL16/SR-PSOX (CXC chemokine ligand 16/scavenger receptor that binds phosphatidylserine and oxidized lipoprotein), a chemokine containing both membrane-anchored and soluble forms, was strongly up-regulated and predominantly distributed in the vascular endothelium in the injured liver tissue in the model. The secretory and membrane-anchored CXCL16/SR-PSOX functioned as a chemokine and an adhesive molecule, respectively, to attract T cells to a tumor necrosis factor alpha-activated endothelial cell line (SVEC) in vitro. To further identify the pathophysiological roles of CXCL16/SR-PSOX in the liver injury, the anti-CXCL16 antibody was administered to the BCG-primed mice before LPS challenge in vivo. Significant protection effects were observed with 70% of mice regarding lethality, the massive necrosis in the liver was reduced, and the intrahepatic infiltrating T cells were significantly inhibited. Taken together, these findings strongly suggest that functional CXCL16/SR-PSOX, as both a chemokine and an adhesion molecule, may be involved in the pathogenesis of the endotoxin-induced lethal liver injury via recruitment and adhesion of activated T cells to the vascular endothelium.

A strong CD8+ T cell response is elicited using the synthetic polypeptide from the C-terminus of the circumsporozoite protein of Plasmodium berghei together with the adjuvant QS-21: quantitative and phenotypic comparison with the vaccine model of irradiated sporozoites

Stable protective immunity can be achieved against malaria by the injection of radiation-attenuated sporozoites (gamma-spz) and is mediated by IFN-gamma producing CD8+ T cells targeting the pre-erythrocytic stages. An efficient malaria vaccine should mimic this immunity. We compared the immune response specific for the circumsporozoite protein (CSP) of Plasmodium berghei (P. berghei), an important target of this protective response, elicited in mice immunized with the long synthetic polypeptide (LSP) PbCS 242-310, representing the C-terminus of the CSP of P. berghei, with the adjuvant QS-21 or injected with gamma-spz. The ex vivo evaluation of the CD8+ T cell response by IFN-gamma ELISPOT assay revealed that the injection of LSP with QS-21 induced, compared to gamma-spz, a similar frequency of peptide-specific lymphocytes in the spleen but a eight-fold increase in the draining lymph-nodes. A very high frequency of CD8+ T cells, specific for the sequence PbCS 245-253, a H-2Kd-restricted CTL epitope, was obtained in the liver and spleen of mice immunized with the two regimens. Even though the frequency of H-2Kd PbCS 245-253 multimer+, CD8+ T cells was higher in gamma-spz immunized mice, the frequency of IFN-gamma producing CD8+ T cells was comparable. The phenotype of the CD8+ T cell responses was characterized with the help H-2Kd PbCS 245-253 multimer and most of the CSP-specific CD8+ T cells represented an intermediate subset between effector and central memory with CD44(high), CD45RB(high), CD62L(low) and CD122(high). The number of memory CD8+ T cells decreased after the last LSP immunization but could be boosted to higher level with live spz. The unique combination of LSP PbCS 242-310 and the adjuvant QS-21 induced an immune response that was comparable in terms of quality to the one generated with gamma-spz. This confirmed the potential of LSP as malaria vaccine candidates as well as for the study of the repertoire of targets of protective immunity in the gamma-spz vaccine model.

The inhibitory effects of synthetic short peptides, mimicking MICA and targeting at NKG2D receptors, on function of NK cells

NKG2D is an activating receptor expressed on most of human NK cells, one of whose ligands is MICA. Based on the crystal structure of NKG2D-MICA complex, we synthesized three short peptides (P1, P2 and P3), mimicking functional alpha1 and alpha2 domain of MICA. The inhibitory effects of three peptides on NK-92 cells, a human NK cell line against Hela cells were observed and the inhibitory percentage was 38% at maximum for P1+P2+P3 in concentration of 1nM. The same peptides had no effect on NK-92 cell against target cells lacking MICA (K562 cells line). The unrelated peptides as controls had no effect on the system. Two peptides (P2 and P3) were prolonged at one or both ends, and the longer forms of peptides exerted stronger inhibitory effects than their shorter forms. Each combination of two peptides exerted a stronger function than single peptide (P1, P2, P3), indicating that shedding of longer amino acid sequence of alpha1 domain or more domain sites of MICA are better than shorter sequence and fewer sites. P1+P2+P3 revealed the almost same inhibitory rate as the soluble MICA (sMICA). P1+P2+P3 were also able to alleviate the concanavalin A-induced murine autoimmune hepatitis in vivo, conforming the similarity of NKG2D between human and mice. The results demonstrate that MICA-mimicking peptides will be useful to search the specific functional sites for NKG2D-MICA interaction, but also promising in explaining NKG2D-related autoimmunity.

Isolation, purification and flow cytometric analysis of human intrahepatic lymphocytes using an improved technique

Intrahepatic lymphocytes (IHL) with their diverse and distinctive subsets emphasise the importance of the liver as a site of immunological activity, but special care is required for their isolation and characterisation. Protocols for IHL isolation, purification and FACS analysis were devised and compared with published extraction protocols. We have reduced the time that IHL are exposed to potentially damaging enzymes during extraction and purified specific subsets using monoclonal antibody (mAb)-coated magnetic microbeads. This has yielded IHL populations with higher viability than previously described protocols (92-95%, compared with 39-86%). Flow cytometric characterisation of IHL subset immunophenotypes was optimised by combining CD45 staining (fluorescence gating) with traditional light scatter properties. Using a panel of mAb and liver biopsies obtained from 23 cadaveric liver transplant donors, we show that the normal liver contains a heterogeneous IHL population with distinctive phenotypes. CD8+ IHL was the predominant population with a mean CD4/CD8 ratio of 1:1.7. Up to 40% of IHL expressed gammadeltaTCR and a third expressed CD56 NK marker; indicating a site of intense immunological activity. The techniques described will allow these cell types to be isolated, fully characterised and their physiological functions to be determined. The histologically normal liver contains heterogeneous and diverse IHL with large numbers of CD8+, NK, NKT and gammadelta+ cells.

Innate immune system plays a critical role in determining the progression and severity of acetaminophen hepatotoxicity

BACKGROUND & AIMS

Inflammatory mediators released by nonparenchymal inflammatory cells in the liver have been implicated in the progression of acetaminophen (APAP) hepatotoxicity. Among hepatic nonparenchymal inflammatory cells, we examined the role of the abundant natural killer (NK) cells and NK cells with T-cell receptors (NKT cells) in APAP-induced liver injury.

METHODS

C57BL/6 mice were administered a toxic dose of APAP intraperitoneally to cause liver injury with or without depletion of NK and NKT cells by anti-NK1.1 monoclonal antibody (MAb). Serum alanine transaminase (ALT) levels, liver histology, hepatic leukocyte accumulation, and cytokine/chemokine expression were assessed.

RESULTS

Compared with APAP-treated control mice, depletion of both NK and NKT cells by anti-NK1.1 significantly protected mice from APAP-induced liver injury, as evidenced by decreased serum ALT level, improved survival of mice, decreased hepatic necrosis, inhibition of messenger RNA (mRNA) expression for interferon-gamma (IFN-gamma), Fas ligand (FasL), and chemokines including KC (Keratinocyte-derived chemokine); MIP-1 alpha (macrophage inflammatory protein-1 alpha); MCP-1 (monocyte chemoattractant protein-1); IP-10 (interferon-inducible protein); Mig (monokine induced by IFN-gamma) and decreased neutrophil accumulation in the liver. Hepatic NK and NKT cells were identified as the major source of IFN-gamma by intracellular cytokine staining. APAP induced much less liver injury in Fas-deficient (lpr) and FasL-deficient (gld) mice compared with that in wild-type mice.

CONCLUSIONS

NK and NKT cells play a critical role in the progression of APAP-induced liver injury by secreting IFN-gamma, modulating chemokine production and accumulation of neutrophils, and up-regulating FasL expression in the liver, all of which may promote the inflammatory response of liver innate immune system, thus contributing to the severity and progression of liver injury downstream of the metabolism of APAP and depletion of reduced glutathione (GSH) in hepatocytes.