Expression of perforin and Fas ligand mRNA in the liver of viral hepatitis

Foxp3 expression in liver correlates with the degree but not the cause of inflammation

Patients with chronic viral hepatitis display increased expression of Foxp3 in liver, suggesting that Tregs expansion contributes to persistent infection. The purpose of this study was to elucidate whether the expression of Foxp3 relates not to the viral infection but to the resulting liver inflammation. Liver biopsies obtained from 69 individuals (26 chronic HBV hepatitis, 14 chronic HCV hepatitis, 11 nonalcoholic fatty liver disease, 8 autoimmune diseases, 2 methotrexate-related toxicity, and 8 controls) were examined, by qRT-PCR, for the mRNA expression of Foxp3, IL-10, TGF-β1, Fas, FasL, TRAIL, caspase-3, TNF-α, IFN-γ, and IL-1β. Significant increase of Foxp3 was observed in all disease groups compared to controls, which was positively correlated with the intensity of inflammation. The expression of the apoptosis mediators Fas, FasL, and TRAIL, but not of IL-10 and TGF-β1, was also significantly elevated. Our findings indicate that, independently of the initial inducer, liver inflammation is correlated with elevated expression of apoptosis mediators and is followed by local Treg accumulation. Further research towards the elucidation of the underlying casual relationships is required, in order to clarify whether our results signify the existence of a uniform Treg-mediated regulatory mechanism of apoptosis-induced inflammation.

Apoptosis as a mechanism for liver disease progression

Hepatocyte injury is ubiquitous in clinical practice, and the mode of cell death associated with this injury is often apoptosis, especially by death receptors. Information from experimental systems demonstrates that hepatocyte apoptosis is sufficient to cause liver hepatic fibrogenesis. The mechanisms linking hepatocyte apoptosis to hepatic fibrosis remain incompletely understood, but likely relate to engulfment of apoptotic bodies by professional phagocytic cells and stellate cells, and release of mediators by cells undergoing apoptosis. Inhibition of apoptosis with caspase inhibitors has demonstrated beneficial effects in murine models of hepatic fibrosis. Recent studies implicating Toll-like receptor 9 in liver injury and fibrosis are also of particular interest. Engulfment of apoptotic bodies is one mechanism by which the TLR9 ligand (CpG DNA motifs) could be delivered to this intracellular receptor. These concepts suggest therapy focused on interrupting the cellular mechanisms linking apoptosis to fibrosis would be useful in human liver diseases.

HBV X protein: elucidating a role in oncogenesis

Chronic HBV infection is associated with the development of hepatocellular carcinoma (HCC). HBV contributes to tumorigenesis by encoding hepatitis B x antigen (HBxAg), which is a trans-regulatory protein that appears to contribute to HCC by altering patterns of host gene expression. In this review, recent data is presented that outlines some of the putative mechanisms whereby HBxAg contributes to HCC. With the development of animal models of HBxAg-mediated HCC, the relevance and temporal order of putative steps in this process can now be dissected to elucidate what is rate limiting and when. This will have a profound impact on the design of novel and specific therapeutics for HCC.

Clinical significance of intrahepatic perforin expression in patients with chronic hepatitis B

AIM: To investigate the clinical significance of intrahepatic perforin expression in patients with chronic hepatitis B virus (HBV) infection.

METHODS: The hepatic biopsies were performed in 47 patients with chronic hepatitis B, and out of them, 35 patients subsequently received interferon α-2b antiviral therapy. The expression of perforin in liver tissues was detected by immunohistochemistry, and the HBV DNA loads, the serum HBV immunologic markers and transaminases were also determined in peripheral blood samples.

RESULTS: The expression of intrahepatic perforin was positive in 37 patients (13 cases strongly positive). The intensity of perforin showed a significant accordance with serum alanine aminotransferase (ALT) level (χ² = 8.004, P = 0.018) and histological inflammation grades (χ² = 8.532, P = 0.014), but did not correlate with the degrees of liver fibrosis (χ² = 0.865, P = 0.649). The data showed a significantly negative correlation between perforin and the HBV DNA loads (χ² = 7.902, P = 0.019), and there was almost significantly correlation between perforin and the level of HBeAg (χ² = 5.283, P = 0.071). Among the 35 patients accepted interferon antiviral therapy, there were 12 cases with complete responses, 14 cases with partial responses and 9 without responses at the end of treatment. The intensity of perforin expression was positively correlated with the interferon responses (χ² = 7.533, P = 0.023).

CONCLUSION: The expression of intrahepatic perforin can mediate the liver cell injury, contribute to the clearance of hepatitis B virus, and enhance the antiviral efficacy of interferon, and it may be a predictor to interferon antiviral therapy.

Apoptosis of activated CD4+ and CD8+ T cells is enhanced by co-culture with hepatocytes expressing hepatitis C virus (HCV) structural proteins through FasL induction

A central unresolved issue in hepatitis C virus (HCV) infection is how the virus establishes chronic infection. Recent studies suggest that the liver microenvironment leads to apoptosis of activated T cells, which may be involved in the tolerance to liver allograft. Here, We report that murine hepatocytes expressing a transgene encoding the HCV structural proteins core, envelope 1 (E1) and envelope 2 (E2) enhance apoptosis of activated T cells. Unlike normal liver, which appears to selectively remove only activated CD8+ T cells, enhanced apoptosis was seen for both CD4+ and CD8+ T cells. Enhanced apoptosis of activated T lymphocytes was associated with upregulation of FasL by HCV transgenic hepatocytes and was specifically inhibited by anti-FasL blocking antibody. Increased apoptosis of activated T cells induced by HCV structural proteins could amplify the ability of the liver to down-modulate T cell responses, leading to attenuation of anti-viral responses and facilitating viral persistence.

Rescue of in vivo FAS-induced apoptosis of hepatocytes by corticosteroids either associated with alcohol consumption by mice or provided exogenously

The pathogenic effects of many hepatic viral infections are mediated, at least in part, by the immune response to the infected hepatocyte. The immune response in the infected liver involves the interaction of cytotoxic T cells (CTL) with the hepatocytes through the interaction of FAS-ligand on the CTL and FAS on the hepatocyte. The initial hypothesis for this study was that alcohol consumption by mice would sensitize the liver to apoptosis induced by ligation of FAS. C57Bl/6 mice fed ethanol in a liquid diet did show an increased percentage of apoptotic cells 2 h after injection with anti-FAS as compared with the percentage in the control mice. However, 4 and 6 h after anti-FAS injection, control mice showed high percentages of apoptotic cells (20% to 41%) compared with 5% and 4% apoptotic cells in the ethanol-fed mice. The decreased apoptosis of ethanol-fed mice correlated closely with corticosterone levels in the sera. This was confirmed by the finding that adrenalectomized (ADX) mice provided a high level of corticosterone in drinking water were protected against FAS-induced hepatocyte apoptosis. Ethanol-fed mice showed a significant elevation of serum alanine aminotransferase (ALT) levels indicating the development of hepatitis in spite of the relatively low proportion of apoptotic cells in the liver. In conclusion, high levels of corticosterone protect hepatocytes from FAS-mediated apoptosis, but do not prevent the ultimate development of liver damage. In experiments where mice were provided ethanol chronically in drinking water, where stress is minimal, higher levels of ALT were noted in animals in the ethanol group as compared with animals in the control group. These data support the suggestion that ethanol increases hepatocyte sensitivity to FAS-mediated damage.

Apoptotic pathway related to oval cell proliferation

BACKGROUND AND AIM

Oval cells, liver stem cell-derived cells, are generated from the liver periportal region and spread into the parenchyma by an autocrine signaling pathway. The mechanism behind how oval cells take their place among packed silent hepatocytes, however, is not well understood. We hypothesized that apoptosis involves a decrease in hepatocytes surrounding oval cells.

METHODS

Male Fisher rats were treated using the AAF/PH protocol to induce oval cells in the liver. Apoptosis was assessed by measuring the activity of caspase-3, -8 and -9, and apoptosis-related molecules such as caspase-3, Fas, Fas-L and Bax were also assessed by immunohistochemical analysis and reverse transcriptase-polymerase chain reaction (RT-PCR). Apoptosis was confirmed by TUNEL staining. Regarding antiapoptotic factors, nuclear factor-kappaB (NF-kappaB) DNA binding activity and proliferating cell nuclear antigen (PCNA) expression were examined.

RESULTS

NF-kappaB elevated at the early stage of oval cell proliferation. Conversely, caspase activity increased after NF-kappaB elevation. The mRNA of caspase-3, Fas, Fas-L and Bax was induced during and after AAF/PH treatment. Immunohistochemically, oval cells lacked the expression of these proteins, whereas the hepatocytes, particularly those surrounding oval cells, expressed strongly.

CONCLUSIONS

The present study suggests that the apoptosis in hepatocytes through both extrinsic and intrinsic pathways mediates oval cell proliferation.

Pervasive influence of hepatitis C virus on the phenotype of antiviral CD8+ T cells

Recent studies using MHC class I tetramers have shown that CD8(+) T cell responses against different persistent viruses vary considerably in magnitude and phenotype. At one extreme, hepatitis C virus (HCV)-specific CD8(+) T cell responses in blood are generally weak and have a phenotype that is perforin low and CCR7 high (early memory). At the other, specific responses to CMV are strong, perforin high, and CCR7 low (mature or effector memory). To examine the potential mechanisms behind this diversity, we compared CMV-specific responses in HCV-infected and healthy individuals. We find a striking difference in the phenotype of CMV-specific CD8(+) T cells between these groups. In the HCV-infected cohort, CMV-specific CD8(+) T cells lost markers associated with maturity; they had increased expression of CCR7 and reduced expression of Fas and perforin. They nevertheless responded to Ag in vitro in a manner similar to controls, with strong proliferation and appropriate acquisition of effector memory markers. The reduction in mature CD8 T cells in HCV-infected individuals may arise through either impairment or regulation of T cell stimulation, or through the early loss of mature T cells. Whatever the mechanism, HCV has a pervasive influence on the circulating CD8(+) T cell population, a novel feature that may be a hallmark of this infection.

Expression of FasL and perforin/granzyme B mRNA in chronic hepatitis B virus infection

Cytotoxic T lymphocytes are essential components of immune responses during chronic hepatitis B (CHB). It has been known that Fas ligand (FasL) and perforin/granzyme B-based mechanisms account for all T cell-mediated cytotoxicity. In the present work, we examined the correlation between injury of the hepatocytes and mRNA expression of FasL and perforin/granzyme B in liver tissue to investigate the roles of both the FasL and the perforin/granzyme B pathways in CHB. Reverse transcription-polymerase chain reaction was used to identify intrahepatic expression of FasL and perforin/granzyme B in liver biopsy specimens from 24 patients with hepatitis B virus (HBV) infection. In addition, the transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) method was used to determine the degree of apoptosis. The degree of mRNA expression and apoptosis were compared with the histologic activity index (HAI) and serology, including alanine aminotransferase (ALT). Intrahepatic mRNA expression rates of FasL, perforin and granzyme B were seen in 79.2, 62.5 and 33.3% of patients, respectively, and correlated with ALT levels (P < 0.05). Intrahepatic expression of FasL and perforin mRNA were significantly correlated with HAI (P < 0.05). Also, apoptosis documented by the TUNEL assay was correlated with HAI and intrahepatic mRNA expression of FasL and perforin (P < 0.05). Our results show that the T-cell mediated perforin death pathway as well as the Fas system play important roles in liver cell injury in HBV infection and that apoptosis mediated by the Fas/FasL system is closely correlated with HAI in chronic HBV infection.

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Hemophagocytic lymphohistiocytosis is associated with deficiencies of cellular cytolysis but normal expression of transcripts relevant to killer-cell-induced apoptosis

In 65 patients with hemophagocytic lymphohistiocytosis (HLH), we found an as yet undescribed heterogeneity of defects in cellular cytotoxicity when assay conditions were modified by the incubation time, the presence of mitogen, or interleukin-2 (IL-2). The standard 4-hour natural killer (NK) test against K562 targets was negative in all patients. In patients deficient in type 1 (n = 21), type 2 (n = 5), and type 4 (n = 8) HLH, negative NK function could be reconstituted by mitogen, by IL-2, or by prolongation of the incubation time (16 hours), respectively. Most patients (n = 31) displayed the type 3 defect, defined by a lack of any cellular cytotoxicity independent of assay variations. The characteristic hypercytokinemia also concerned counterregulatory cytokines, such as proinflammatory interferon-gamma (IFN-gamma), simultaneously elevated with suppressive IL-10 in 38% of types 1-, 2-, and 4-deficient patients and in 71% of type 3-deficient patients. Elevated IFN-gamma alone correlated with high liver enzymes, but sCD95-ligand and sCD25 did not-though these markers were expected to indicate the extent of histiocytic organ infiltration. Outcome analysis revealed more deaths in patients with type 3 deficiency (P =.017). Molecular defects were associated with homozygously mutated perforin only in 4 patients, but other type 3 patients expressed normal transcripts of effector molecules for target-cell apoptosis, including perforin and granzyme family members, as demonstrated by RNase protection analysis. Thus, target-cell recognition or differentiation defects are likely to explain this severe phenotype in HLH. Hyperactive phagocytes combined with NK defects may imply defects on the level of the antigen-presenting cell.

In situ expression of Granzyme B and Fas-ligand in the liver of viral hepatitis

BACKGROUND/AIMS

The molecular mechanism involved in hepatocellular injury in viral hepatitis remains to be clarified.

METHODS

We investigated the in situ expression of effector molecules of cytotoxic T lymphocytes such as Fas-ligand (Fas-L), perforin and Granzyme B (Gr-B) immunohistochemically in liver tissues from 20 patients with chronic hepatitis B (CHB) and C (CHC). The degree of cell infiltration was analysed semi-quantitatively and compared with the histological activity index (HAI). Fas-L was expressed in both CD4 and CD8 T-cells in the portal tract as well as in the parenchyma.

RESULTS

Immunostaining of serial sections demonstrated that mononuclear cells at interface hepatitis and focal necrosis were mainly Fas-L positive CD8 T-cells. On the other hand, the expression of perforin or Gr-B was limited to a few mononuclear cells in the portal tract and parenchyma. Semi-quantitative analysis showed a positive correlation between HAI and the grade of infiltration of CD8 T-cells or Fas-L-positive cells, while the correlation was not apparent between HAI and the number of Gr-B positive cells. The expression of these molecules was not different between types of viruses.

CONCLUSIONS

These results suggest that Fas-L-positive CD8 T-cells play a major role in the pathogenesis of liver cell injury in chronic hepatitis.

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.