Induction of murine hepatocyte death by membrane-bound CD95 (Fas/APO-1)-ligand: characterization of an in vitro system

The use of biologics in the treatment of autoimmune liver disease

Introduction: Autoimmune liver diseases include autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and juvenile autoimmune hepatitis (JAIH). The pathophysiologic features of each disease vary, but generally include presence of autoantibodies, cytokine abnormalities, and/or T and B cell autoreactivity.Areas covered: This article compares conventional therapy with newer biologics available for treatment of autoimmune liver diseases. Conventional therapy involves the use of immunosuppressive agents, or other treatment modalities for specific autoimmune liver diseases such as ursodeoxycholic acid and fibrates for PBC. Biologics were developed to target the production of autoantibodies by B cells, the presence of proinflammatory cytokines, adhesion molecules or T and B cell activation.Expert opinion: Despite the promise of biologics being able to target specific cellular and humoral pathways, results have been generally poor, and safety has not been as expected. Cases of autoimmune hepatitis have also developed with the use of these biologicals. Reasons for the lack of success of biologics in treating autoimmune liver disease has led to a reevaluation of our understanding of underlying pathogenesis, demonstrating that while our knowledge of the immunity has improved over the past two decades, it is far from complete.

Novel Immunotherapies for Autoimmune Hepatitis

Autoimmune hepatitis (AIH) is a multifactorial autoimmune disease of unknown pathogenesis, characterized by a loss of immunological tolerance against liver autoantigens resulting in the progressive destruction of the hepatic parenchyma. Current treatments are based on non-specific immunosuppressive drugs. Although tremendous progress has been made using specific biological agents in other inflammatory diseases, progress has been slow to come for AIH patients. While current treatments are successful in the majority of patients, treatment discontinuation is difficult to achieve, and relapses are frequent. Lifelong immunosuppression is not without risks, especially in the pediatric population; 4% of patient with type 1 AIH will eventually develop hepatocellular carcinoma with a 2.9% probability after 10 years of treatment. Therefore, future treatments should aim to restore tolerance to hepatic autoantigens and induce long-term remission. Promising new immunotherapies have been tested in experimental models of AIH including T and B cell depletion and regulatory CD4+ T cells infusion. Clinical studies on limited numbers of patients have also shown encouraging results using B-cell-depleting (rituximab) and anti-TNF-α (infliximab) antibodies. A better understanding of key molecular targets in AIH combined with effective site-specific immunotherapies could lead to long-term remission without blanket immunosuppression and with minimal deleterious side effects.

Serum Amyloid A Induces Inflammation, Proliferation and Cell Death in Activated Hepatic Stellate Cells

Serum amyloid A (SAA) is an evolutionary highly conserved acute phase protein that is predominantly secreted by hepatocytes. However, its role in liver injury and fibrogenesis has not been elucidated so far. In this study, we determined the effects of SAA on hepatic stellate cells (HSCs), the main fibrogenic cell type of the liver. Serum amyloid A potently activated IκB kinase, c-Jun N-terminal kinase (JNK), Erk and Akt and enhanced NF-κB-dependent luciferase activity in primary human and rat HSCs. Serum amyloid A induced the transcription of MCP-1, RANTES and MMP9 in an NF-κB- and JNK-dependent manner. Blockade of NF-κB revealed cytotoxic effects of SAA in primary HSCs with signs of apoptosis such as caspase 3 and PARP cleavage and Annexin V staining. Serum amyloid A induced HSC proliferation, which depended on JNK, Erk and Akt activity. In primary hepatocytes, SAA also activated MAP kinases, but did not induce relevant cell death after NF-κB inhibition. In two models of hepatic fibrogenesis, CCl₄ treatment and bile duct ligation, hepatic mRNA levels of SAA1 and SAA3 were strongly increased. In conclusion, SAA may modulate fibrogenic responses in the liver in a positive and negative fashion by inducing inflammation, proliferation and cell death in HSCs.

Experimental models of hepatotoxicity related to acute liver failure

Acute liver failure can be the consequence of various etiologies, with most cases arising from drug-induced hepatotoxicity in Western countries. Despite advances in this field, the management of acute liver failure continues to be one of the most challenging problems in clinical medicine. The availability of adequate experimental models is of crucial importance to provide a better understanding of this condition and to allow identification of novel drug targets, testing the efficacy of new therapeutic interventions and acting as models for assessing mechanisms of toxicity. Experimental models of hepatotoxicity related to acute liver failure rely on surgical procedures, chemical exposure or viral infection. Each of these models has a number of strengths and weaknesses. This paper specifically reviews commonly used chemical in vivo and in vitro models of hepatotoxicity associated with acute liver failure.

Primary hepatocytes and their cultures in liver apoptosis research

Apoptosis not only plays a key role in physiological demise of defunct hepatocytes, but is also associated with a plethora of acute and chronic liver diseases as well as with hepatotoxicity. The present paper focuses on the modelling of this mode of programmed cell death in primary hepatocyte cultures. Particular attention is paid to the activation of spontaneous apoptosis during the isolation of hepatocytes from the liver, its progressive manifestation upon the subsequent establishment of cell cultures and simultaneously to strategies to counteract this deleterious process. In addition, currently applied approaches to experimentally induce controlled apoptosis in this in vitro setting for mechanistic research purposes and thereby its detection using relevant biomarkers are reviewed.

Inducing apoptosis in rolling cancer cells: a combined therapy with aspirin and immobilized TRAIL and E-selectin

Though metastasis is considered an inefficient process, over 90% of cancer related deaths are attributed to the formation of secondary tumors. Thus, eliminating circulating cancer cells could lead to improved patient survival. This study was aimed at exploiting the interactions of cancer cells with selectins under flow to selectively kill captured colon cancer cells. Microtubes functionalized with E-selectin and TRAIL were perfused with colon cancer cell line Colo205 either treated with 1 mM aspirin or untreated for 1 or 2 h. Cells were collected from the microtube and analyzed by flow cytometry. Aspirin treatment alone killed only 3% cells in culture. A 95% difference in the number of cells killed between control and TRAIL + ES surfaces was seen when aspirin treated cells were perfused over the functionalized surface for 2 h. We have demonstrated a novel biomimetic method to capture and neutralize cancer cells in flow, thus reducing the chances for the formation of secondary tumors.

End-organ damage in a mouse model of fulminant liver inflammation requires CD4+ T cell production of IFN-gamma but is independent of Fas

Fulminant inflammation in the liver is often accompanied by the accumulation of IFN-gamma-producing T cells. The BALB/c-Tgfb1(-/-) mouse exhibits extensive, spontaneously developing necroinflammation in the liver, accompanied by the accumulation of IFN-gamma-producing CD4(+) and CD8(+) T cells. Liver damage depends on the presence of an intact Ifng gene. We determined the relevant cellular source(s) of IFN-gamma. In Tgfb1(-/-) liver, CD4(+) T cells were more numerous than CD8(+) T cells and NK cells, and produced more IFN-gamma. Depletion of CD4(+) T cells eliminated both the elevation in plasma IFN-gamma and aspartate aminotransferase, whereas depletion of CD8(+) T cells did not. Rag1(-/-)Tgfb1(-/-) mice exhibited neither IFN-gamma elevation nor tissue damage, indicating that NK cells are not sufficient. IFN-gamma was required for strong overexpression of class II genes but not for CD4(+) T cell activation, oligoclonal expansion, or accumulation in the liver. The T cell inhibitory molecule PD-L1 was strongly expressed in Tgfb1(-/-) livers, ruling out a lack of PD-L1 expression as an explanation for aberrant liver T cell activation. Finally, whereas Tgfb1(-/-) CD4(+) T cells overexpressed Fas ligand, hepatocellular damage was observed in Fas(lpr/lpr)Tgfb1(-/-) mice, indicating that liver pathology is Fas independent. We conclude that liver damage in this model of fulminant autoimmune hepatitis is driven by CD4(+) T cell production of IFN-gamma, is independent of both CD8(+) T cells and the Fas ligand/Fas pathway, and is not explained by a lack of PD-L1 expression.

From biochemical principles of apoptosis induction by TRAIL to application in tumour therapy

The tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily which has been shown to selectively kill tumour cells, while sparing normal tissue. This attribute makes TRAIL an attractive drug candidate for cancer therapy. Although most primary tumour cells turned out to be primarily TRAIL-resistant, recent studies evidenced that a variety of cancers can be sensitised to TRAIL-induced apoptosis upon pre-treatment with chemotherapeutic agents or irradiation, while normal cells remain TRAIL-resistant. However, biomarkers that reliably predict which patients may benefit from such combinatorial therapies are required. Thus, it is essential to better understand the mechanisms underlying TRAIL resistance versus sensitivity. In this chapter, we introduce the signalling events which take place during TRAIL-induced apoptosis, describe the physiological function of TRAIL and summarise pre-clinical and clinical results obtained so far with TRAIL-receptor agonists.

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.

Pathogenesis of autoimmune hepatitis: from break of tolerance to immune-mediated hepatocyte apoptosis

Understanding the pathogenesis and progression of autoimmune hepatitis (AIH) at the molecular level could prove essential in developing new preventive and therapeutic strategies. Recently developed murine models have enabled the identification of various mechanisms involved in the development and perpetuation of this autoimmune disorder. Studies on these models have shown that a peripheral break of tolerance against liver-expressed antigens is sufficient to induce an autoimmune liver disease, which can occur without prior liver damage. Recent data have also shown that the liver selectively recruits and induces the apoptosis of activated CD8+ T cells after an immune response. This process of T-cell trapping involves the expression of specific chemokines and adhesion molecules, and these molecules are believed to play an important role in the initiation and perpetuation of autoimmune hepatitis. Hepatocyte apoptosis, induced by autoreactive T cells, follows specific pathways that could be targeted by new therapeutic agents. Basic research on the break of immune tolerance against liver antigens would be beneficial for patients with autoimmune hepatitis, as well as those suffering from other chronic inflammatory liver diseases, such as primary biliary cirrhosis and graft-versus-host diseases.

Epithelial cell apoptosis by fas ligand-positive myofibroblasts in lung fibrosis

The Fas/Fas ligand (FasL) apoptotic pathway has been shown to be involved in bleomycin-induced lung fibrosis. We examined the hypothesis that myofibroblasts from fibrotic lungs possess a cytotoxic phenotype that causes apoptosis of epithelial cells via the Fas/FasL pathway. We show in vivo epithelial cell apoptosis and associated upregulation of Fas and apoptotic Fas pathway genes in epithelial cells of lungs with bleomycin-induced fibrosis. In addition, we show that FasL surface molecules are overexpressed on alpha-SMA-positive cells in mice with bleomycin-induced fibrosis, and in humans with idiopathic pulmonary fibrosis. This enables the molecules to kill Fas-positive epithelial cells. In contrast, FasL-deficient myofibroblasts lose this myofibroblast cytotoxic phenotype, both in vivo and in vitro. In vivo, there was no bleomycin-induced epithelial cell apoptosis, as assessed by specific M30 staining in chimeric FasL-deficient mice that lacked FasL-positive myofibroblasts. In vitro, FasL-positive, but not FasL-negative myofibroblasts, induce mouse lung epithelial cell apoptosis. Thus myofibroblast cytotoxicity may underlie the absence of re-epithelialization, resulting in persistent lung fibrosis.

Coencapsulation of hepatocytes and bone marrow cells: In vitro and in vivo studies

Bioencapsulation of cells is one of the many areas of artificial cells being extensively investigated by centers around the world. This includes the bioencapsulation of hepatocytes. A number of methods have been developed to maintain the specific function and phenotype of the bioencapsulated hepatocytes for in vitro and in vivo applications. These include supplementation of factors in the culture medium; use of appropriate substrates and the co-cultivation of hepatocytes with other type of cells, the so called "feeder cells". These feeder cells can be of liver origin or non-liver origin. We have recently studied the role of bone marrow cells in the maintenance of hepatocytes viability and phenotype by using the coculture of hepatocytes with bone marrow cells (nucleated cells including stem cells), and the coencapsulation of hepatocytes with bone marrow stem cells. This way, the hepatocytes viability and specific function can be maintained significantly longer. In vivo studies of both syngeneic and xenogeneic transplantation show that the hepatocytes viability can be maintained longer when coencapsulated with bone marrow cells. Transplantation of coencapsulated hepatocytes and bone marrow cells enhances the ability of the hepatocytes in correcting congenital hyperbilirubinmia in Gunn rats. Both in vitro and in vivo studies show that bone marrow cells can enhance the viability and phenotype maintenance of hepatocytes. Thus, bone marrow cells play an important role as a new type of feeder cells for bioencapsulated hepatocytes for the cellular therapy of liver diseases.

Neutralization of tumor necrosis factor abrogates hepatic failure induced by alpha-galactosylceramide without attenuating its antitumor effect in aged mice

BACKGROUND/AIMS

The functions of mouse liver NK1.1+ T (NKT) cells stimulated with alpha-galactosylceramide (alpha-GalCer) are enhanced age dependently, and the antitumor and anti-metastatic effect in the liver is dependent on IFN-gamma. However, hepatic injury is independent of IFN-gamma and Fas/Fas-ligand dependent. The aim of this study is to investigate how tumor necrosis factor is involved in the alpha-GalCer-mediated immune phenomena.

METHODS

C57BL/6 mice were intraperitoneally treated with anti-TNF antibody 1 h before alpha-GalCer injection, and Fas-ligand expression of NKT cells, the serum ALT levels and histopathological findings of the liver, kidney and lung and mortality after alpha-GalCer injection were evaluated. IFN-gamma production and antitumor immunity in the liver after the intravenous injection of EL-4 cells were also assessed.

RESULTS

Serum TNF levels after alpha-GalCer injection increased age dependently in mice. Anti-TNF Ab reduced Fas-ligand (Fas-L) expression of NKT cells while it completely inhibited organ injuries induced by alpha-GalCer and thereby reduced the mortality of old mice, whereas it did not affect the IFN-gamma production from NKT cells, the antitumor immunity in the liver nor the mouse survival after EL-4 injection.

CONCLUSIONS

NKT cells activated by alpha-galactosylceramide participated in either antitumor immunity or hepatic injury using IFN-gamma and TNF/Fas-L, respectively.

Transforming growth factor-beta1, Th1 responses, and autoimmune liver disease

Transforming growth factor-beta1 (TGF-beta1) is released during the storage of blood components, particularly platelet concentrates, and transfusion recipients are exposed to high levels of TGF-beta1. Because TGF-beta1 is one of the most potent immunosuppressive cytokines known, understanding the immunobiologic functions of TGF-beta1 may be relevant for understanding the immunobiologic effects of transfusion. Our laboratory studies the biologic effects of TGF-beta1 in the immune system. Mice deficient in TGF-beta1 spontaneously develop autoimmunity, confirming the important role of this cytokinean an immune regulator. A few years ago, my laboratory made the observation that genetic background strongly affects the phenotype of TGF-beta1-/- mice. TGF-beta1-/- mice on the BALB/c background rapidly develop an aggressive T-cell-mediated hepatitis, whereas TGF-beta1-/- mice on the 129/CF-1 background do not. In this review, I summarize findings published or in press from our laboratory on disease pathogenesis in TGF-beta1-/- mice and then discuss some of the exciting (as-yet-unpublished) directions our laboratory is currently taking.

Anandamide induces necrosis in primary hepatic stellate cells

The endogenous cannabinoid anandamide (AEA) is a lipid mediator that blocks proliferation and induces apoptosis in many cell types. Although AEA levels are elevated in liver fibrosis, its role in fibrogenesis remains unclear. This study investigated effects of AEA in primary hepatic stellate cells (HSCs). Anandamide blocked HSC proliferation at concentrations of 1 to 10 micromol/L but did not affect HSC proliferation or activation at nanomolar concentrations. At higher concentrations (25-100 micromol/L), AEA rapidly and dose-dependently induced cell death in primary culture-activated and in vivo-activated HSCs, with over 70% cell death after 4 hours at 25 micromol/L. In contrast to treatment with Fas ligand or gliotoxin, AEA-mediated death was caspase independent and showed typical features of necrosis such as rapid adenosine triphosphate depletion and propidium iodide uptake. Anandamide-induced reactive oxygen species (ROS) formation, and an increase in intracellular Ca(2+). Pretreatment with the antioxidant glutathione or Ca(2+)-chelation attenuated AEA-induced cell death. Although the putative endocannabinoid receptors CB1, CB2, and VR1 were expressed in HSCs, specific receptor blockade failed to block cell death. Depletion of membrane cholesterol by methyl-beta-cyclodextrin inhibited AEA binding, blocked ROS formation and intracellular Ca(2+)-increase, and prevented cell death. In primary hepatocytes, AEA showed significantly lower binding and failed to induce cell death even after prolonged treatment. In conclusion, AEA efficiently induces necrosis in activated HSCs, an effect that depends on membrane cholesterol and a subsequent increase in intracellular Ca(2+) and ROS. The anti-proliferative effects and the selective killing of HSCs, but not hepatocytes, indicate that AEA may be used as a potential anti-fibrogenic tool.

Differential requirement for c-Jun NH2-terminal kinase in TNFalpha- and Fas-mediated apoptosis in hepatocytes

The c-Jun NH2-terminal kinase (JNK) is involved in the regulation of cell death, but its role in tumor necrosis factor (TNF)-alpha- and Fas-mediated apoptosis in primary cells is not well defined. In primary rat hepatocytes expressing an IkappaB superrepressor, the JNK inhibitor SP600125 strongly decreased TNF-alpha-induced cell death, caspase 3 activation, and DNA laddering. In contrast, SP600125 did not rescue mouse hepatocytes from Fas-induced apoptosis. Apoptosis in mouse hepatocytes, induced by human TNF-alpha, was blocked by SP600125, indicating that TNF-receptor (TNF-R) 1-mediated JNK activation is important for TNF-alpha-induced death. However, mouse TNF-alpha was more efficient than human TNF-alpha in activating JNK and killing mouse hepatocytes, suggesting that TNF-R1 and TNF-R2 cooperate in JNK activation and apoptosis. SP600125 rescued actinomycin D-pretreated hepatocytes and hepatocytes expressing a dominant negative c-Jun from TNF-alpha, indicating that JNK exerts its proapoptotic effect independently of transcription and c-Jun. SP600125 delayed the mitochondrial permeability transition, inhibited cytochrome c release and prevented bid degradation after TNF-alpha, suggesting that JNK-regulated proapoptotic factors act upstream of the mitochondria. Moreover, overexpression of JNK1 activated a mitochondrial death pathway in hepatocytes, albeit less efficiently than TNF-alpha. This study demonstrates that JNK augments TNF-alpha-induced apoptosis in hepatocytes through a signaling pathway that is distinct from the pathway by which it regulates proliferation.

Gap junction-mediated intercellular communication in a long-term primary mouse hepatocyte culture system

Gap junction-mediated intercellular communication (GJIC) is critical for maintaining integral cellular processes including differentiation and growth control. The disruption of GJIC has been correlated with aberrant function in many cell types, including hepatocytes in vivo; therefore it is imperative that cellular model systems support intercellular communication to simulate normal cellular functions. Functional GJIC has been shown in long-term primary rat hepatocyte cultures, which have been implemented widely to study various aspects of hepatocellular function; however, the onset of transgenic technology in murine species has necessitated the development of a primary mouse hepatocyte system. In this report, we analyze GJIC in a dimethylsulfoxide (DMSO)-containing long-term primary mouse hepatocyte culture system. The cells retain morphologic and biochemical characteristics of differentiated hepatocytes through day 30 post plating, including liver-specific gene expression. We further show that connexin32 and connexin26 expression and gap junction plaque formation increase over time in culture concomitant with an increase in GJIC between adjoining primary mouse hepatocytes. In conclusion, the findings described in this study make it possible to maintain differentiated primary mouse hepatocytes that also show GJIC in long-term culture for 30 days. In addition, this system has the potential to be extended to study primary mouse hepatocytes isolated from genetically engineered mice.

Hepatic T cells and liver tolerance

The T-cell biology of the liver is unlike that of any other organ. The local lymphocyte population is enriched in natural killer (NK) and NKT cells, which might have crucial roles in the recruitment of circulating T cells. A large macrophage population and the efficient trafficking of dendritic cells from sinusoidal blood to lymph promote antigen trapping and T-cell priming, but the local presentation of antigen causes T-cell inactivation, tolerance and apoptosis. These local mechanisms might result from the need to maintain immunological silence to harmless antigenic material in food. The overall bias of intrahepatic T-cell responses towards tolerance might account for the survival of liver allografts and for the persistence of some liver pathogens.

Cellular specificity related to monoglyceride-induced cell death

We have recently observed that monoglycerides (MGs), a family of lipids consisting of a single fatty acid moiety attached to a glycerol backbone, induce rapid dose-dependent apoptosis in murine thymocytes. In this work, we evaluated the sensitivity of various normal and malignant immune and non-immune cells to MGs. We demonstrate that the propensity to MG-induced death displayed by both T and B lymphocytes is clearly modulated according to their differentiation and activation status. For instance, the earliest T and B cell precursors are refractory to MG-mediated cell death. In the T-cell lineage, immature thymocytes are the most susceptible to MG treatment, while B cells from peripheral lymphoid organs appear more sensitive than B-cell subsets from the bone marrow. On the other hand, both activated T and B cells are more resistant to MG exposure than their non-activated counterparts. In addition, other hematopoietic lineages such as natural killer cells, macrophages, and erythroid cells are quite resistant to MG-induced death. Furthermore, using various immortalized cell lines from different tissues, we found that lymphomas and thymomas are the most sensitive among all lineages tested, while epithelial cells and fibroblasts are unaffected by MG treatment. Finally, MG-induced death was shown to be independent of Fas/Fas ligand (FasL) interactions. Altogether, our findings indicate that there is a cellular specificity related to MG-mediated cell death biased towards T and B lymphocytes. This suggests that MGs could potentially be used in the treatment of specific lymphoid disorders by bypassing the requirement for the Fas/FasL system.

Cytokine-dependent bystander hepatitis due to intrahepatic murine CD8 T-cell activation by bone marrow-derived cells

BACKGROUND & AIMS

Intrahepatic accumulation of CD8+ T cells following antigen-specific activation has been demonstrated in a number of transgenic models and also in extrahepatic viral infections. In some transgenic models, intrahepatic accumulation of cytotoxic T lymphocytes is associated with hepatitis. This observation suggests that hepatocellular damage may occur in some forms of immune-mediated hepatitis on the basis of a "bystander injury," whereby cytotoxic T lymphocytes accumulating in the liver mediate injury to hepatocytes in a nonspecific manner. Mouse transgenic models were therefore developed to investigate whether bystander damage to non-antigen-bearing hepatocytes occurs in vivo.

METHODS

T cell receptor transgenic T cells were adoptively transferred into transgenic mice ubiquitously expressing the specific antigen, or into bone marrow radiation chimeras in which hepatocytes did not express the antigen.

RESULTS

Selective accumulation of transgenic CD8+ T cells in the liver of intact recipients could be detected within 2 hours of transfer, despite ubiquitous antigenic expression. T cells retained in the liver were activated and induced hepatitis. Similar results were obtained using bone marrow chimeras, suggesting that antigen expression by hepatocytes was not required either for intrahepatic accumulation or for subsequent hepatitis. This "bystander hepatitis" was dependent on tumor necrosis factor alpha and interferon gamma.

CONCLUSIONS

Intrahepatic accumulation of activated CD8+ T cells and subsequent hepatitis can result from primary activation of CD8+ T cells by liver resident bone marrow-derived cells, inducing bystander damage to non-antigen-bearing hepatocytes. This mechanism may play a role in some forms of biologically significant hepatitis, including autoimmune hepatitis and hepatitis associated with extrahepatic diseases.

Ursodeoxycholic acid diminishes Fas-ligand-induced apoptosis in mouse hepatocytes

Ursodeoxycholic acid (UDCA) can protect hepatocytes from apoptosis induced by a variety of stimuli including anti-Fas antibody. However, in vivo the Fas receptor is activated by its natural ligand, Fas-L, whereas anti-Fas antibodies are not a physiologic stimulus. We therefore have assessed the anti-apoptotic effects of UDCA and other bile acids in a novel coculture model where apoptosis is induced in murine hepatocytes by membrane-bound Fas-L expressing fibroblasts. Primary hepatocytes were cultured overnight on collagen-coated coverslips with increasing concentrations of different bile acids and overlaid with either NIH 3T3 Fas-L(+) or Fas-L(-) expressing fibroblasts. After 6 hours cells were fixed and apoptosis was evaluated by TUNEL assay and DAPI staining using digital imaging. Fas-L protein expression and Fas trimerization were evaluated by Western blot analysis. FITC-UDCA and Mitotracker Red were used to evaluate UDCA localization with mitochondria. UDCA (up to 100 micromol/L, P <.0001), TUDCA (up to 400 micromol/L, P <.0001), and TCDCA (up to 200 micromol/L, P <.0001), but not TCA (up to 500 micromol/L), significantly protected hepatocytes in Fas-L(+) cocultures. UDCA had no significant effect on hepatocytes in Fas-L(-) cocultures. TUDCA, 50 micromol/L (P <.001) and TCDCA up to 200 micromol/L (P <.0001) also reduced the hepatocytes apoptotic rate in Fas-L(-) cocultures. Bile acids did not affect Fas-L expression in fibroblasts or Fas trimerization. FITC-UDCA colocalized with the mitochondrial probe. In conclusion, UDCA, TUDCA, and TCDCA but not TCA are capable of protecting hepatocytes from Fas-L-induced apoptosis. This protective effect is not associated with reductions in Fas trimerization, but may be related to a direct effect on the mitochondrial membrane.

Fas counterattack in cholangiocarcinoma: A mechanism for immune evasion in human hilar cholangiocarcinomas

AIM: To investigate FasL expression in hilar cholangiocarcinoma tissues and cultured cholangiocarcinoma cells, and to assess its ability to induce apoptosis.

METHODS: We studied the expression of FasL by human hilar cholangiocaroinomas tissues by immunohistochemistry, and the QBC939 cholangiocarcinoma cell line by RT-PCR, immunohistochemistry, and Western Blot. TUNEL and flow cytometry were used to detect apoptotic cells.

RESULTS: Prevalent expression of FasL was detected in 39 resected hilar cholangiocarcinoma tissues. TUNEL staining disclosed a high level of cell death among lymphocytes infiltrating FasL positive areas of tumor. FasL mRNA and protein expressions in cholangiocarcinoma cells could induce Jurkat cells.

CONCLUSION: Hilar cholangiocarcinomas may elude immunological surveillance by inducing, via Fas/FasL system, the apoptosis of activated lymphocytes.

Apoptosis in diseases of the liver

Apoptosis, or programmed cell death, and the elimination of apoptotic cells are crucial factors in the maintenance of liver health Apoptosis allows hepatocytes to die without provoking a potentially harmful inflammatory response In contrast to necrosis, apoptosis is tightly controlled and regulated via several mechanisms, including Fas/Fas ligand interactions, the effects of cytokines such as tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta), and the influence of pro- and antiapoptotic mitochondria-associated proteins of the B-cell lymphoma-2 (Bcl-2) family. Efficient elimination of apoptotic cells in the liver relies on Kupffer cells and endothelial cells and is thought to be regulated by the expression of certain cell surface receptors. Liver disease is often associated with enhanced hepatocyte apoptosis, which is the case in viral and autoimmune hepatitis, cholestatic diseases, and metabolic disorders. Disruption of apoptosis is responsible for other diseases, for example, hepatocellular carcinoma. Use and abuse of certain drugs, especially alcohol, chemotherapeutic agents, and acetaminophen, have been associated with increased apoptosis and liver damage. Apoptosis also plays a role in transplantation-associated liver damage, both in ischemia/reperfusion injury and graft rejection. The role of apoptosis in various liver diseases and the mechanisms by which apoptosis occurs in the liver may provide insight into these diseases and suggest possible treatments.