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Biomedical subjects

Fritz von Weizsäcker

Publications and source records attributed to Fritz von Weizsäcker.

At least 19 recordsLinked to original sources
PubMed2007

Pathogenesis of hepatitis B virus infection.

Infection with hepatitis B virus (HBV) leads to a wide spectrum of clinical presentations ranging from an asymptomatic carrier state to self-limited acute or fulminant hepatitis to chronic hepatitis with progression to cirrhosis and hepatocellular carcinoma. Infection with HBV is one of the most common viral diseases affecting man. Both viral factors as well as the host immune response have been implicated in the pathogenesis and clinical outcome of HBV infection. In this review, we will discuss the impact of virus-host interactions for the pathogenesis of HBV infection and liver disease. These interactions include the relevance of naturally occurring viral variants for clinical disease, the role of virus-induced apoptosis for HBV-induced liver cell injury and the impact of antiviral immune responses for outcome of infection.

Antibodies, Viral↗
PubMed2006

Analysis of CD127 and KLRG1 expression on hepatitis C virus-specific CD8+ T cells reveals the existence of different memory T-cell subsets in the peripheral blood and liver.

The differentiation and functional status of virus-specific CD8+ T cells is significantly influenced by specific and ongoing antigen recognition. Importantly, the expression profiles of the interleukin-7 receptor alpha chain (CD127) and the killer cell lectin-like receptor G1 (KLRG1) have been shown to be differentially influenced by repetitive T-cell receptor interactions. Indeed, antigen-specific CD8+ T cells targeting persistent viruses (e.g., human immunodeficiency virus and Epstein-Barr virus) have been shown to have low CD127 and high KLRG1 expressions, while CD8+ T cells targeting resolved viral antigens (e.g., FLU) typically display high CD127 and low KLRG1 expressions. Here, we analyzed the surface phenotype and function of hepatitis C virus (HCV)-specific CD8+ T cells. Surprisingly, despite viral persistence, we found that a large fraction of peripheral HCV-specific CD8+ T cells were CD127+ and KLRG1- and had good proliferative capacities, thus resembling memory cells that usually develop following acute resolving infection. Intrahepatic virus-specific CD8+ T cells displayed significantly reduced levels of CD127 expression but similar levels of KLRG1 expression compared to the peripheral blood. These results extend previous studies that demonstrated central memory (CCR7+) and early-differentiated phenotypes of HCV-specific CD8+ T cells and suggest that insufficient stimulation of virus-specific CD8+ T cells by viral antigen may be responsible for this alteration in HCV-specific CD8+ T-cell differentiation during chronic HCV infection.

Acute Disease↗
PubMed2006

Peptide aptamer-mediated inhibition of target proteins by sequestration into aggresomes.

Peptide aptamers (PAs) can be employed to block the intracellular function of target proteins. Little is known about the mechanism of PA-mediated protein inhibition. Here, we generated PAs that specifically bound to the duck hepatitis B virus (HBV) core protein. Among them, PA34 strongly blocked duck HBV replication by inhibiting viral capsid formation. We found that PA34 led to a dramatic intracellular redistribution of its target protein into perinuclear inclusion bodies, which exhibit the typical characteristics of aggresomes. As a result, the core protein is efficiently removed from the viral life cycle. Corresponding findings were obtained for bioactive PAs that bind to the HBV core protein or to the human papillomavirus-16 (HPV16) E6 protein, respectively. The observation that PAs induce the specific sequestration of bound proteins into aggresomes defines a novel mechanism as to how this new class of intracellular inhibitors blocks the function of their target proteins.

Amino Acid Sequence↗
PubMed2006

Dominant influence of an HLA-B27 restricted CD8+ T cell response in mediating HCV clearance and evolution.

Virus-specific CD8+ T cell responses play an important role in the natural course of infection; however, the impact of certain CD8+ T cell responses in determining clinical outcome has not been fully defined. A well-defined cohort of women inoculated with HCV from a single source showed that HLA-B27 has a strong association with spontaneous clearance. The immunological basis for this association is unknown. However, the finding is especially significant because HLA-B27 has also been shown to have a protective role in HIV infection. We report the identification of an HLA-B27 restricted hepatitis C virus (HCV)-specific CD8+ T cell epitope that is recognized in the majority of recovered HLA-B27 positive women. In chronically HCV-infected individuals, analysis of the corresponding viral sequence showed a strong association between sequence variations within this epitope and expression of HLA-B27, indicating allele-specific selection pressure at the population level. Functional analysis in 3 chronically HCV-infected patients showed that the emerging variant viral epitopes represent escape mutations. In conclusion, our results suggest a dominant role of HLA-B27 in mediating spontaneous viral clearance as well as viral evolution in HCV infection and mechanistically link both associations to a dominant novel CD8+ T cell epitope. These results support the central role of virus-specific CD8+ T cells and the genetically determined restriction of the virus-specific T cell repertoire in HCV infection.

Adult↗
PubMed2006

Host cell responses induced by hepatitis C virus binding.

Initiation of hepatitis C virus (HCV) infection is mediated by docking of the viral envelope to the hepatocyte cell surface membrane followed by entry of the virus into the host cell. Aiming to elucidate the impact of this interaction on host cell biology, we performed a genomic analysis of the host cell response following binding of HCV to cell surface proteins. As ligands for HCV-host cell surface interaction, we used recombinant envelope glycoproteins and HCV-like particles (HCV-LPs) recently shown to bind or enter hepatocytes and human hepatoma cells. Gene expression profiling of HepG2 hepatoma cells following binding of E1/E2, HCV-LPs, and liver tissue samples from HCV-infected individuals was performed using a 7.5-kd human cDNA microarray. Cellular binding of HCV-LPs to hepatoma cells resulted in differential expression of 565 out of 7,419 host cell genes. Examination of transcriptional changes revealed a broad and complex transcriptional program induced by ligand binding to target cells. Expression of several genes important for innate immune responses and lipid metabolism was significantly modulated by ligand-cell surface interaction. To assess the functional relevance and biological significance of these findings for viral infection in vivo, transcriptional changes were compared with gene expression profiles in liver tissue samples from HCV-infected patients or controls. Side-by-side analysis revealed that the expression of 27 genes was similarly altered following HCV-LP binding in hepatoma cells and viral infection in vivo. In conclusion, HCV binding results in a cascade of intracellular signals modulating target gene expression and contributing to host cell responses in vivo. Reprogramming of cellular gene expression induced by HCV-cell surface interaction may be part of the viral strategy to condition viral entry and replication and escape from innate host cell responses.

Antigens, Viral↗
PubMed2005

Hepatitis B virus mutations associated with fulminant hepatitis induce apoptosis in primary Tupaia hepatocytes.

Hepatitis B virus (HBV) core promoter mutations have been implicated in the pathogenesis of fulminant hepatitis B. Due to the limited availability of primary human hepatocytes, the functional characterization of HBV mutants has been performed predominantly in transformed cells, which may not represent ideal model systems for studying virus-cell interactions. We and others have shown that primary hepatocytes of the tree shrew Tupaia belangeri support HBV infection and replication. In this study, we used primary Tupaia hepatocytes to analyze the phenotype of two HBV core promoter mutations that have been associated with a clinical outbreak of fatal fulminant hepatitis. Similar to previous findings in human hepatoma cells, the HBV core promoter mutations resulted in enhanced viral replication and core expression. Surprisingly, however, the presence of the mutations had a marked effect on hepatocyte viability not previously observed in hepatoma cells. Reduced cell viability was found to be due to the induction of apoptosis, as evidenced by caspase-3 activation and nuclear fragmentation. In conclusion, HBV mutants exhibit a novel phenotype in primary hepatocytes distinctly different from previous findings in hepatoma cell lines. This phenotype may have important implications for the understanding of the fulminant clinical course associated with HBV mutations.

Animals↗
PubMed2005

APOBEC-mediated interference with hepadnavirus production.

APOBEC3G is a cellular cytidine deaminase displaying broad antiretroviral activity. Recently, it was shown that APOBEC3G can also suppress hepatitis B virus (HBV) production in human hepatoma cells. In the present study, we characterized the mechanisms of APOBEC-mediated antiviral activity against HBV and related hepadnaviruses. We show that human APOBEC3G blocks HBV production in mammalian and nonmammalian cells and is active against duck HBV as well. Early steps of viral morphogenesis, including RNA and protein synthesis, binding of pregenomic RNA to core protein, and self-assembly of viral core protein, were unaffected. However, APOBEC3G rendered HBV core protein-associated full-length pregenomic RNA nuclease-sensitive. Ongoing reverse-transcription in capsids that had escaped the block in morphogenesis was not significantly inhibited. The antiviral effect was not modulated by abrogating or enhancing expression of the accessory HBV X protein, suggesting that HBV X protein does not represent a functional homologue to the HIV vif protein. Furthermore, human APOBEC3F but not rat APOBEC1 inhibited HBV DNA production. Viral RNA and low-level DNA produced in the presence of APOBEC3F or rat APOBEC1 occasionally displayed mutations, but the majority of clones were wild-type. In conclusion, APOBEC3G and APOBEC3F but not rat APOBEC1 can downregulate the production of replication-competent hepadnaviral nucleocapsids. In contrast to HIV and other retroviruses, however, APOBEC3G/3F-mediated editing of nucleic acids does not seem to represent an effective innate defense mechanism for hepadnaviruses.

APOBEC-1 Deaminase↗
PubMed2005

Intrahepatic CD8+ T-cell failure during chronic hepatitis C virus infection.

The precise mechanisms responsible for the failure of intrahepatic hepatitis C virus (HCV)-specific CD8+ T cells to control the virus during persistent infection have not been fully defined. We therefore studied the CD8+ T-cell response in 27 HLA-A2-positive patients using four previously well-defined HLA-A2-restricted HCV epitopes. The corresponding HCV sequences were determined in several patients and compared with the intrahepatic HCV-specific CD8+ T-cell response. The results of the study indicate: (1) intrahepatic HCV-specific CD8+ T cells are present in the majority of patients with chronic HCV infection and overlap significantly with the response present in the peripheral blood. (2) A large fraction of intrahepatic HCV-specific CD8+ T cells are impaired in their ability to secrete interferon gamma (IFN-gamma). This dysfunction is specific for HCV-specific CD8+ T cells, since intrahepatic Flu-specific CD8+ T cells readily secrete this cytokine. (3) T-cell selection of epitope variants may have occurred in some patients. However, it is not an inevitable consequence of a functional virus-specific CD8+ T-cell response, since several patients with IFN-gamma-producing CD8+ T-cell responses harbored HCV sequences identical or cross-reactive with the prototype sequence. (4) The failure of intrahepatic virus-specific CD8+ T cells to sufficiently control the virus occurs despite the presence of virus-specific CD4+ T cells at the site of disease. In conclusion, different mechanisms contribute to the failure of intrahepatic CD8+ T cells to eliminate HCV infection, despite their persistence and accumulation in the liver.

Adult↗
PubMed2005

Chronic infection with hepatitis B viruses and antiviral drug evaluation in uPA mice after liver repopulation with tupaia hepatocytes.

BACKGROUND/AIMS: Transplantation of primary human hepatocytes and establishment of hepatitis B virus (HBV) infection in immunodeficient urokinase plasminogen activator (uPA) transgenic mice was shown. However, the availability of usable primary human hepatocytes is very limited. Therefore, alternative and more accessible sources of hepatocytes permissive for HBV infection are highly desirable. Here we investigated the potential of primary hepatocytes from the tree shrew Tupaia belangeri that were shown to be susceptible to HBV infection. METHODS: Freshly isolated or cryopreserved primary tupaia hepatocytes were transplantated via intrasplenic injection into immunodeficient uPA/RAG-2 mice. Engrafted mice were then infected with HBV and woolly monkey (WM)-HBV positive sera. RESULTS: Extensive proliferation of xenografted cells was demonstrated by the stable production of tupaia alpha1-antitrypsin in serum and liver of transplanted mice. Quantitative PCR assays demonstrated the presence of circulating viral particles as well as intracellular viral DNA, including covalently closed circular (ccc) DNA, in transplanted mice. Viral infection could be serially passaged in mice. Furthermore, viral replication was strongly inhibited by treating mice with adefovir dipivoxil. CONCLUSIONS: uPA mice repopulated with tupaia hepatocytes represent a useful and more accessible model for HBV infection studies, including the evaluation of antiviral therapy and cccDNA.

Adenine↗
PubMed2005

T cells with a CD4+CD25+ regulatory phenotype suppress in vitro proliferation of virus-specific CD8+ T cells during chronic hepatitis C virus infection.

Chronic hepatitis C virus (HCV) infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8(+) T cells that probably contribute significantly to viral persistence. Here, we investigated the potential role of T cells with a CD4(+)CD25(+) regulatory phenotype in suppressing virus-specific CD8(+) T-cell proliferation during chronic HCV infection. In vitro depletion studies and coculture experiments revealed that peptide specific proliferation as well as gamma interferon production of HCV-specific CD8(+) T cells were inhibited by CD4(+)CD25(+) T cells. This inhibition was dose dependent, required direct cell-cell contact, and was independent of interleukin-10 and transforming growth factor beta. Interestingly, the T-cell-mediated suppression in chronically HCV-infected patients was not restricted to HCV-specific CD8(+) T cells but also to influenza virus-specific CD8(+) T cells. Importantly, CD4(+)CD25(+) T cells from persons recovered from HCV infection and from healthy blood donors exhibited significantly less suppressor activity. Thus, the inhibition of virus-specific CD8(+) T-cell proliferation was enhanced in chronically HCV-infected patients. This was associated with a higher frequency of circulating CD4(+)CD25(+) cells observed in this patient group. Taken together, our results suggest that chronic HCV infection leads to the expansion of CD4(+)CD25(+) T cells that are able to suppress CD8(+) T-cell responses to different viral antigens. Our results further suggest that CD4(+)CD25(+) T cells may contribute to viral persistence in chronically HCV-infected patients and may be a target for immunotherapy of chronic hepatitis C.

Adult↗
PubMed2005

Scavenger receptor class B type I and hepatitis C virus infection of primary tupaia hepatocytes.

Hepatitis C virus (HCV) is a major cause of chronic hepatitis worldwide. The study of early steps during HCV infection has been hampered by the lack of suitable in vitro or in vivo models. Primary Tupaia hepatocytes (PTH) have been shown to be susceptible to HCV infection in vitro and in vivo. Human scavenger receptor class B type I (SR-BI) represents an HCV receptor candidate mediating the cellular binding of E2 glycoprotein to HepG2 hepatoma cells. However, the function of SR-BI for viral infection of hepatocytes is unknown. In this study, we used PTH to assess the functional role of SR-BI as a putative HCV receptor. Sequence analysis of cloned tupaia SR-BI revealed a high homology between tupaia and human SR-BI. Transfection of CHO cells with human or tupaia SR-BI but not mouse SR-BI cDNA resulted in cellular E2 binding, suggesting that E2-binding domains between human and tupaia SR-BI are highly conserved. Preincubation of PTH with anti-SR-BI antibodies resulted in marked inhibition of E2 or HCV-like particle binding. However, anti-SR-BI antibodies were not able to block HCV infection of PTH. In conclusion, our results demonstrate that SR-BI represents an important cell surface molecule for the binding of the HCV envelope to hepatocytes and suggest that other or additional cell surface molecules are required for the initiation of HCV infection. Furthermore, the structural and functional similarities between human and tupaia SR-BI indicate that PTH represent a useful model system to characterize the molecular interaction of the HCV envelope and SR-BI on primary hepatocytes.

12E7 Antigen↗
PubMed2004

Hepatitis B virus nucleocapsids formed by carboxy-terminally mutated core proteins contain spliced viral genomes but lack full-size DNA.

The carboxy-terminal sequence of the hepatitis B virus (HBV) core protein constitutes a nucleic acid binding domain that is rich in arginine residues and contains three serine phosphorylation sites. While dispensable for capsid assembly, this domain is involved in viral replication, as demonstrated by the effects of mutations on RNA packaging and/or reverse transcription; however, the underlying mechanisms are poorly understood. Here we tested a series of core protein mutants in which the three serine phosphorylation sites were replaced by glutamic acid, in parallel with a previously described deletion variant lacking the 19 C-terminal amino acid residues, for their ability to support viral replication in transfected hepatoma cells. Replacement of all serines and the deletion gave rise to nucleocapsids containing a smaller than wild-type DNA genome. Rather than a single-stranded DNA intermediate, as previously thought, this was a 2.0-kbp double-stranded DNA molecule derived from spliced pregenomic RNA (pgRNA). Interestingly, full-length pgRNA was associated with nucleocapsids but was found to be sensitive to nuclease digestion, while encapsidated spliced RNA and 3' truncated RNA species were nuclease resistant. These findings suggest that HBV pgRNA encapsidation is directional and that a packaging limit is determined by the C-terminal portion of the core protein.

Amino Acid Sequence↗
PubMed2003

Inhibitory effect of adefovir and lamivudine on the initiation of hepatitis B virus infection in primary tupaia hepatocytes.

Adefovir dipivoxil and lamivudine are two safe and efficacious drugs licensed for the treatment of chronic hepatitis B virus (HBV) infection. Both drugs inhibit the viral polymerase, resulting in a profound suppression of virus production. Blocking the viral polymerase may also affect the initiation of HBV infection, because HBV virions harbor a partially double-stranded genome and productive infection requires completion of viral plus-strand DNA synthesis with subsequent formation of covalently closed circular DNA (cccDNA). To address this issue, we used primary hepatocytes from the tree shrew Tupaia belangeri that were recently shown to be susceptible to HBV infection. Treatment of cells with either drug partially inhibited initial HBV cccDNA formation. Adefovir was more effective than lamivudine, resulting in a 3-fold reduction of RNA synthesis and viral surface antigen production. However, prevention of initial cccDNA formation was incomplete even after combined treatment, whereas de novo synthesis of viral replicative intermediates was completely suppressed. A possible explanation for this observation is the genomic plus-strand gap of less than 200 bases in some virions, limiting the window for antiviral action. In conclusion, nucleos(t)ide analogues can target initial plus-strand DNA repair and reduce but not completely block HBV infection.

Adenine↗
PubMed2002

Pancreatico-mediastinal fistula with a mediastinal mass lesion demonstrated by MR imaging.

Internal pancreatic fistulas are uncommon but well-recognized complications of inflammatory pancreatic disease. A case of a pancreatico-mediastinal fistula with a mediastinal mass lesion in a patient with a documented history of chronic alcohol consumption and previous episodes of acute pancreatitis is described. Since the clinical symptomatology was dominated by pulmonary complaints, magnetic resonance (MR) imaging using a breathhold coronal T2-weighted sequence with spectral fat saturation was essential in clarifying this difficult and rare pathology. Furthermore, the depiction of a fistulous tract between a mediastinal mass lesion and the retroperitoneum posterior to the pancreas, i.e., a pancreatico-mediastinal fistula by MR imaging has not been previously reported, to the best of our knowledge.

Adipose Tissue↗
PubMed2002

Cis-preferential recruitment of duck hepatitis B virus core protein to the RNA/polymerase preassembly complex.

Hepadnaviral replication requires the concerted action of the polymerase and core proteins to ensure selective packaging of the RNA pregenome into nucleocapsids. Virus assembly is initiated by cis-preferential binding of polymerase to the encapsidation signal straightepsilon, present on pregenomic RNA. Using the duck hepatitis B virus (DHBV) model, we analyzed how core protein is recruited to the RNA/polymerase preassembly complex. Two sets of trans-complementation assays were performed in cotransfected hepatoma cells. First, a replication-competent DHBV construct was tested for its ability to rescue replication of genomes bearing mutations within the core region. Self-packaging of wild-type pregenomes was more efficient than cross-packaging of core-deficient pregenomes, and this bias was strongly enhanced if mutant pregenomes coded for self-assembly-competent, but packaging-deficient, core proteins. Second, the site of wild-type core protein translation, i.e., pregenomic RNA (cis) or separate messenger RNA (trans), was analyzed for its effect on the phenotype of a previously described dominant-negative (DN) DHBV core protein mutant. This mutant forms chimeric nucleocapsids with wild-type core proteins and blocks reverse transcription within most, but not all, mixed particles. Strikingly, suppression of viral DNA synthesis by the mutant increased 100-fold when wild-type core protein was provided in trans. Our results suggest that recruitment of core protein to the DHBV preassembly complex occurs in a cis-preferential manner. This mechanism may account for the leakiness of DN DHBV core protein mutants targeting reverse transcription.

Binding Sites↗