Transcriptional activation of the interleukin-2 promoter by hepatitis C virus core protein

Most patients infected with hepatitis C virus (HCV) become chronic carriers. Viruses that efficiently establish persistent infections must have effective ways of evading host defenses. In the case of HCV, little is known about how chronic infections are established or maintained. Besides hepatocytes, several reports suggest that HCV can infect T and B lymphocytes. Since T cells are essential for viral clearance, direct or indirect effects of HCV on T-cell function could influence the outcome of infection. Given that T-cell growth and differentiation require the cytokine interleukin 2 (IL-2), we asked whether HCV might modulate synthesis of IL-2. Portions of the HCV polyprotein were expressed in Jurkat cells under a variety of conditions. We found that the highly conserved HCV core protein, in combination with other stimuli, was able to dramatically activate transcription from the IL-2 promoter. The carboxy-terminal hydrophobic portion of the core protein was required for this activity. Activation was dependent on nuclear factor of activated T cells (NFAT), occurred in cells deficient in the tyrosine kinase p56(lck), and could be blocked by addition of cyclosporin A and by depletion of calcium. These results suggest that the HCV core protein can activate transcription of the IL-2 promoter through the NFAT pathway. This novel activity may have consequences for T-cell development and establishment of persistent infections.

Efficient initiation of HCV RNA replication in cell culture

Hepatitis C virus (HCV) infection is a global health problem affecting an estimated 170 million individuals worldwide. We report the identification of multiple independent adaptive mutations that cluster in the HCV nonstructural protein NS5A and confer increased replicative ability in vitro. Among these adaptive mutations were a single amino acid substitution that allowed HCV RNA replication in 10% of transfected hepatoma cells and a deletion of 47 amino acids encompassing the interferon (IFN) sensitivity determining region (ISDR). Independent of the ISDR, IFN-alpha rapidly inhibited HCV RNA replication in vitro. This work establishes a robust, cell-based system for genetic and functional analyses of HCV replication.

Efficient initiation of HCV RNA replication in cell culture

Hepatitis C virus (HCV) infection is a global health problem affecting an estimated 170 million individuals worldwide. We report the identification of multiple independent adaptive mutations that cluster in the HCV nonstructural protein NS5A and confer increased replicative ability in vitro. Among these adaptive mutations were a single amino acid substitution that allowed HCV RNA replication in 10% of transfected hepatoma cells and a deletion of 47 amino acids encompassing the interferon (IFN) sensitivity determining region (ISDR). Independent of the ISDR, IFN-alpha rapidly inhibited HCV RNA replication in vitro. This work establishes a robust, cell-based system for genetic and functional analyses of HCV replication.

An SNP map of human chromosome 22

The human genome sequence will provide a reference for measuring DNA sequence variation in human populations. Sequence variants are responsible for the genetic component of individuality, including complex characteristics such as disease susceptibility and drug response. Most sequence variants are single nucleotide polymorphisms (SNPs), where two alternate bases occur at one position. Comparison of any two genomes reveals around 1 SNP per kilobase. A sufficiently dense map of SNPs would allow the detection of sequence variants responsible for particular characteristics on the basis that they are associated with a specific SNP allele. Here we have evaluated large-scale sequencing approaches to obtaining SNPs, and have constructed a map of 2,730 SNPs on human chromosome 22. Most of the SNPs are within 25 kilobases of a transcribed exon, and are valuable for association studies. We have scaled up the process, detecting over 65,000 SNPs in the genome as part of The SNP Consortium programme, which is on target to build a map of 1 SNP every 5 kilobases that is integrated with the human genome sequence and that is freely available in the public domain.

Mechanism of action of a pestivirus antiviral compound

We report here the discovery of a small molecule inhibitor of pestivirus replication. The compound, designated VP32947, inhibits the replication of bovine viral diarrhea virus (BVDV) in cell culture at a 50% inhibitory concentration of approximately 20 nM. VP32947 inhibits both cytopathic and noncytopathic pestiviruses, including isolates of BVDV-1, BVDV-2, border disease virus, and classical swine fever virus. However, the compound shows no activity against viruses from unrelated virus groups. Time of drug addition studies indicated that VP32947 acts after virus adsorption and penetration and before virus assembly and release. Analysis of viral macromolecular synthesis showed VP32947 had no effect on viral protein synthesis or polyprotein processing but did inhibit viral RNA synthesis. To identify the molecular target of VP32947, we isolated drug-resistant (DR) variants of BVDV-1 in cell culture. Sequence analysis of the complete genomic RNA of two DR variants revealed a single common amino acid change located within the coding region of the NS5B protein, the viral RNA-dependent RNA polymerase. When this single amino acid change was introduced into an infectious clone of drug-sensitive wild-type (WT) BVDV-1, replication of the resulting virus was resistant to VP32947. The RNA-dependent RNA polymerase activity of the NS5B proteins derived from WT and DR viruses expressed and purified from recombinant baculovirus-infected insect cells confirmed the drug sensitivity of the WT enzyme and the drug resistance of the DR enzyme. This work formally validates NS5B as a target for antiviral drug discovery and development. The utility of VP32947 and similar compounds for the control of pestivirus diseases, and for hepatitis C virus drug discovery efforts, is discussed.

Molecular virology of hepatitis C virus: an update with respect to potential antiviral targets

Hepatitis C virus (HCV), a positive-strand enveloped RNA virus, is a major cause of chronic liver disease worldwide. Cis-acting RNA elements and virus-encoded polypeptides required for HCV replication represent attractive targets for the development of antiviral therapies. Internal ribosome entry site-directed translation of HCV genome RNA produces a long polyprotein which is co- and post-translationally processed to yield at least 10 viral proteins. A host signal peptidase is responsible for maturation of the structural proteins located in the N-terminal one-third of the polyprotein. Thus far, four enzymatic activities encoded by the non-structural (NS) proteins have been reported. The NS2-3 region encodes an autoproteinase responsible for cleavage at the 2/3 site. The N-terminal one-third of NS3 functions as the catalytic subunit of a serine proteinase which cleaves at the 3/4A, 4A/4B, 4B/5A and 5A/5B sites, and NS4A is an essential cofactor for some of these cleavages. NS3 also encodes an RNA-stimulated NTPase/RNA helicase at its C terminus, and NS5B has been shown to possess an RNA-dependent RNA polymerase activity. To date, no functions have been reported for NS4B or NS5A in RNA replication, however, NS5A has been implicated in modulating the sensitivity of HCV to interferon. Sequence and structural conservation within the 3' terminal 98 bases of genomic RNA suggest a functional importance in the virus life-cycle and hence another target for antiviral intervention. Recently, HCV infection was shown to be initiated in chimpanzees following intrahepatic inoculation of RNA transcribed from cloned HCV cDNA. The ability to generate large quantities of infectious HCV RNA may facilitate the development of reliable cell culture replication systems useful for the evaluation of antiviral drugs.

From long range mapping to sequence-ready contigs on human chromosome 6

Our aim is to construct physical clone maps covering those regions of chromosome 6 that are not currently extensively mapped, and use these to determine the DNA sequence of the whole chromosome. The strategy we are following involves establishing a high density framework map of the order of 15 markers per Megabase using radiation hybrid (RH) mapping. The markers are then used to identify large-insert genomic bacterial clones covering the chromosome, which are assembled into sequence-ready contigs by restriction enzyme fingerprinting and sequence tagged site (STS) content analysis. Contig gap closure is performed by walking experiments using STSs developed from the end sequences of the clone inserts.

The Chromosome 6 database at the Sanger Centre

The Sanger Centre Chromosome 6 Database (6ace) has been developed as the primary means of release of annotated sequencing and mapping information for human chromosome 6 from the Sanger Centre. It is also being used to curate global data from published and unpublished external sources. The rationale behind the development of 6ace is described, together with information as to how to access the database.

Subcellular localization, stability, and trans-cleavage competence of the hepatitis C virus NS3-NS4A complex expressed in tetracycline-regulated cell lines

A tetracycline-regulated gene expression system and a panel of novel monoclonal antibodies were used to examine the subcellular localization, stability, and trans-cleavage competence of the hepatitis C virus (HCV) NS3-NS4A complex in inducible cell lines. The NS3 serine protease domain and the full-length NS3 protein expressed in the absence of the NS4A cofactor were diffusely distributed in the cytoplasm and nucleus. Coexpression of NS4A, however, directed NS3 to the endoplasmic reticulum (ER) or an ER-like modified compartment, as demonstrated by colocalization with 3,3'-dihexyloxacarbocyanine iodide, protein disulfide isomerase, and calnexin, as well as subcellular fractionation analyses. In addition, coexpression with NS4A dramatically increased the intracellular stability of NS3 (mean protein half-life of 26 versus 3 h) and allowed for NS4A-dependent trans-cleavage at the NS4B-NS5A junction. Deletion analyses revealed that the hydrophobic amino-terminal domain of NS4A was required for ER targeting of NS3. These results demonstrate the importance of studying HCV proteins in their biological context and define a well-characterized cell culture system for further analyses of the NS3-NS4A complex and the evaluation of novel antiviral strategies against hepatitis C.

Hepatitis C virus-encoded enzymatic activities and conserved RNA elements in the 3' nontranslated region are essential for virus replication in vivo

Hepatitis C virus (HCV) infection is a widespread major human health concern. Significant obstacles in the study of this virus include the absence of a reliable tissue culture system and a small-animal model. Recently, we constructed full-length HCV cDNA clones and successfully initiated HCV infection in two chimpanzees by intrahepatic injection of in vitro-transcribed RNA (A. A. Kolykhalov et al., Science 277:570-574, 1997). In order to validate potential targets for development of anti-HCV therapeutics, we constructed six mutant derivatives of this prototype infectious clone. Four clones contained point mutations ablating the activity of the NS2-3 protease, the NS3-4A serine protease, the NS3 NTPase/helicase, and the NS5B polymerase. Two additional clones contained deletions encompassing all or part of the highly conserved 98-base sequence at the 3' terminus of the HCV genome RNA. The RNA transcript from each of the six clones was injected intrahepatically into a chimpanzee. No signs of HCV infection were detected in the 8 months following the injection. Inoculation of the same animal with nonmutant RNA transcripts resulted in productive HCV infection, as evidenced by viremia, elevated serum alanine aminotransferase, and HCV-specific seroconversion. These data suggest that these four HCV-encoded enzymatic activities and the conserved 3' terminal RNA element are essential for productive replication in vivo.

Mutagenesis of the signal sequence of yellow fever virus prM protein: enhancement of signalase cleavage In vitro is lethal for virus production

Proteolytic processing at the C-prM junction in the flavivirus polyprotein involves coordinated cleavages at the cytoplasmic and luminal sides of an internal signal sequence. We have introduced at the COOH terminus of the yellow fever virus (YFV) prM signal sequence amino acid substitutions (VPQAQA mutation) which uncoupled efficient signal peptidase cleavage of the prM protein from its dependence on prior cleavage in the cytoplasm of the C protein mediated by the viral NS2B-3 protease. Infectivity assays with full-length YFV RNA transcripts showed that the VPQAQA mutation, which enhanced signal peptidase cleavage in vitro, was lethal for infectious virus production. Revertants or second-site mutants were recovered from cells transfected with VPQAQA RNA. Analysis of these viruses revealed that single amino acid substitutions in different domains of the prM signal sequence could restore viability. These variants had growth properties in vertebrate cells which differed only slightly from those of the parent virus, despite efficient signal peptidase cleavage of prM in cell-free expression assays. However, the neurovirulence in mice of the VPQAQA variants was significantly attenuated. This study demonstrates that substitutions in the prM signal sequence which disrupt coordinated cleavages at the C-prM junction can impinge on the biological properties of the mutant viruses. Factors other than the rate of production of prM are vitally controlled by regulated cleavages at this site.

A single nucleotide change in the 5' noncoding region of Sindbis virus confers neurovirulence in rats

Two pairs of Sindbis virus (SV) variants that differ in their neuroinvasive and neurovirulent traits in mice have been isolated. Recently, we mapped the genetic determinants responsible for neuroinvasiveness in weanling mice. Here, we extend this study to newborn and adult rats and to rat neuronal cultures. Remarkably, certain aspects of the pathogenesis of these strains in rats were found to be quite distinct from the mouse model. Suckling rats were susceptible to all four isolates, and replication in the brain was observed after both intraperitoneal and intracranial (i.c.) inoculation. None of the isolates was neuroinvasive in adult rats, although all replicated after i.c. inoculation. For the isolate pair that was highly neurovirulent in mice, SVN and SVNI, only SVNI caused death after i.c. inoculation of adult rats. Similarly, only SVNI was cytotoxic for primary cultures of mature neurons. The genetic determinants responsible for the pathogenic properties of SVNI were mapped to the E2 glycoprotein and the 5' noncoding region (5'NCR). Substitution of two amino acids in SVN E2 with the corresponding residues of SVNI (Met-190 and Lys-260) led to paralysis in 3- and 5-week-old rats. More dramatically, a single substitution in the 5'NCR of SVN (G at position 8) transformed the virus into a lethal pathogen for 3-week-old rats like SVNI. In 5-week-old rats, however, this recombinant was attenuated relative to SVNI by 2 orders of magnitude. Combination of the E2 and 5'NCR determinants resulted in a recombinant with virulence properties indistinguishable from those of SVNI. These data indicate that the 5'NCR and E2 play an instrumental role in determining the age-dependent pathogenic properties of SV in rats.

Mutagenesis of the NS2B-NS3-mediated cleavage site in the flavivirus capsid protein demonstrates a requirement for coordinated processing

Analysis of flavivirus polyprotein processing has revealed the presence of a substrate for the virus-encoded NS2B-NS3 protease at the carboxy-terminal end of the C (capsid or core) protein. Cleavage at this site has been implicated in the efficient generation of the amino terminus of prM via signal peptidase cleavage. Yellow fever virus has four basic residues (Arg-Lys-Arg-Arg) in the P1 through P4 positions of this cleavage site. Multiple alanine substitutions were made for these residues in order to investigate the substrate specificity and biological significance of this cleavage. Mutants were analyzed by several methods: (i) a cell-free trans processing assay for direct analysis of NS2B-NS3-mediated cleavage; (ii) a trans processing assay in BHK-21 cells, using a C-prM polyprotein, for analysis of prM production; (iii) an infectivity assay of full-length transcripts to determine plaque-forming ability; and (iv) analysis of proteins expressed from full-length transcripts to assess processing in the context of the complete genome. Mutants that exhibited severe defects in processing in vitro and in vivo were incapable of forming plaques. Mutants that contained two adjacent basic residues within the P1 through P4 region were processed more efficiently in vitro and in vivo, and transcripts bearing these mutations were fully infectious. Furthermore, two naturally occurring plaque-forming revertants were analyzed and shown to have restored protein processing phenotypes in vivo. Finally, the efficient production of prM was shown to be dependent on the proteolytic activity of NS3. These data support a model of two coordinated cleavages, one that generates the carboxy terminus of C and another that generates the amino terminus of prM. A block in the viral protease-mediated cleavage inhibits the production of prM by the signal peptidase, inhibits particle release, and eliminates plaque formation.

Identification of the major phosphorylation site of the hepatitis C virus H strain NS5A protein as serine 2321

The hepatitis C virus (HCV) NS5A protein is phosphorylated by a cellular, serine/threonine kinase. To identify the major site(s) of NS5A phosphorylation, radiolabeled HCV-H NS5A phosphopeptides were purified and subjected to phosphoamino acid analysis and Edman degradation. These data identified the major intracellular phosphorylation site in the HCV-H NS5A protein as Ser(2321), a result verified by two additional, independent methods: (i) substitution of Ala for Ser(2321) and the concomitant disappearance of the major in vivo phosphorylated peptides and corresponding in vitro phosphorylated peptides; and (ii) comigration of the digestion products of a synthetic peptide phosphorylated on Ser(2321) with the major in vivo phosphorylated NS5A peptides. Site-directed mutagenesis of Ser(2321) suggested that phosphorylation of NS5A is dispensable for previously described interactions with NS4A and PKR, a cellular, antiviral kinase that does not appear to catalyze NS5A phosphorylation. The proline-rich nature of the amino acid sequence flanking Ser(2321) (PLPPPRS(2321) PPVPPPR) suggests that a proline-directed kinase is responsible for the majority of HCV NS5A phosphorylation, consistent with previous kinase inhibitor studies.

The role of host immunocompetence in neuroinvasion of Sindbis virus

Viral infections of the central nervous system (CNS) following peripheral inoculation of Sindbis viruses were studied. The use of viral strains, which vary in their neuroinvasive and neurovirulent properties, and various strains of mice, which differ in immunocompetence, revealed several pathways of viral neuroinvasion in adult mice. A genetic-trait dependent mechanism was exhibited by the neuroinvasive viruses, showing a similar pattern in all mice strains tested. A second mechanism, dependent on a prolonged high viral load, was exhibited by a noninvasive variant in Severe Combined ImmunoDeficient (SCID) mice. The absence of antiviral antibodies in SCID mice allowed the maintenance of a long-term high viremia, leading to a random entry to the CNS and proliferation in brain tissue. An additional pathway for neuroinvasion was induced upon disruption of the blood-brain barrier activity by exogenous reagents and was demonstrated in cases of short lived high viremia of noninvasive viruses.

Genetic interaction of flavivirus nonstructural proteins NS1 and NS4A as a determinant of replicase function

Nonstructural protein 1 (NS1) of yellow fever virus (YF) is a glycoprotein localized to extracytoplasmic compartments within infected cells. We have previously shown that NS1 can be supplied in trans and is required for viral RNA replication, a process thought to occur in membrane-bound cytoplasmic complexes. Here we report that the NS1 gene from a related virus, dengue virus (DEN), is unable to function in the process of YF RNA replication. This virus-specific incompatibility leads to a lack of initial minus-strand accumulation, suggesting that DEN NS1 is unable to productively interact with the YF replicase. Based on a YF deletion mutant that requires NS1 in trans, a genetic screen for suppressor mutants was used to select virus variants able to utilize DEN NS1. In three independent selections, a single mutation was mapped to the NS4A gene, which encodes a putative transmembrane replicase component. This mutation, as well as several additional mutations, was engineered into the NS1-deficient genome and confirmed a genetic interaction between NS1 and NS4A. These findings suggest a potential mechanism for integrating NS1 into the cytoplasmic process of RNA replication.

Selection of RNA replicons capable of persistent noncytopathic replication in mammalian cells

The natural life cycle of alphaviruses, a group of plus-strand RNA viruses, involves transmission to vertebrate hosts via mosquitoes. Chronic infections are established in mosquitoes (and usually in mosquito cell cultures), but infection of susceptible vertebrate cells typically results in rapid shutoff of host mRNA translation and cell death. Using engineered Sindbis virus RNA replicons expressing puromycin acetyltransferase as a dominant selectable marker, we identified mutations allowing persistent, noncytopathic replication in BHK-21 cells. Two of these adaptive mutations involved single-amino-acid substitutions in the C-terminal portion of nsP2, the viral helicase-protease. At one of these loci, nsP2 position 726, numerous substitution mutations were created and characterized in the context of RNA replicons and infectious virus. Our results suggest a direct correlation between the level of viral RNA replication and cytopathogenicity. This work also provides a series of alphavirus replicons for noncytopathic gene expression studies (E. V. Agapov, I. Frolov, B. D. Lindenbach, B. M. Prágai, S. Schlesinger, and C. M. Rice, Proc. Natl. Acad. Sci. USA 95:12989-12994, 1998) and a general strategy for selecting RNA viral mutants adapted to different cellular environments.

Long-term follow-up of chimpanzees inoculated with the first infectious clone for hepatitis C virus

Two chimpanzees (Ch1535 and Ch1536) became infected with hepatitis C virus (HCV) following intrahepatic inoculation with RNA transcribed from a full-length cDNA clone of the virus. Both animals were persistently infected and have been followed for 60 weeks. They showed similar responses to infection, with transient liver enzyme elevations and liver inflammatory responses, which peaked at weeks 17 (Ch1535) and 12 (Ch1536) postinoculation (p.i.). Antibody responses to structural and nonstructural proteins were first detected at weeks 13 (Ch1535) and 10 (Ch1536) p.i. Serum RNA titers increased steadily during the first 10 to 13 weeks but decreased sharply in both animals following antibody and inflammatory responses. Despite direct evidence of humoral immune responses to multiple viral antigens, including hypervariable region 1 (HVR1), both animals remained chronically infected. Detailed sequence analysis of serum HCV RNA revealed no change in the majority HVR1 sequence in Ch1535 and a single-amino-acid mutation in Ch1536, with very little clonal variation in either animal. Full-length genome analysis at week 60 revealed several amino acid substitutions localized to antigens E1, E2, p7, NS3, and NS5. Of these, 55.6 and 40% were present as the majority sequence in serum RNA isolated at week 26 p.i. (Ch1535) and week 22 p.i. (Ch1536), respectively, and could represent immune escape mutations. Mutations accumulated at a rate of 1.57 x 10(-3) and 1.48 x 10(-3) nucleotide substitutions/site/year for Ch1535 and Ch1536, respectively. Taken together, these data indicate that establishment of a persistent HCV infection in these chimpanzees is not due to changes in HVR1; however, the possibility remains that mutations arising in other parts of the genome contributed to this persistence.

Yellow fever/Japanese encephalitis chimeric viruses: construction and biological properties

A system has been developed for generating chimeric yellow fever/Japanese encephalitis (YF/JE) viruses from cDNA templates encoding the structural proteins prM and E of JE virus within the backbone of a molecular clone of the YF17D strain. Chimeric viruses incorporating the proteins of two JE strains, SA14-14-2 (human vaccine strain) and JE Nakayama (JE-N [virulent mouse brain-passaged strain]), were studied in cell culture and laboratory mice. The JE envelope protein (E) retained antigenic and biological properties when expressed with its prM protein together with the YF capsid; however, viable chimeric viruses incorporating the entire JE structural region (C-prM-E) could not be obtained. YF/JE(prM-E) chimeric viruses grew efficiently in cells of vertebrate or mosquito origin compared to the parental viruses. The YF/JE SA14-14-2 virus was unable to kill young adult mice by intracerebral challenge, even at doses of 10(6) PFU. In contrast, the YF/JE-N virus was neurovirulent, but the phenotype resembled parental YF virus rather than JE-N. Ten predicted amino acid differences distinguish the JE E proteins of the two chimeric viruses, therefore implicating one or more residues as virus-specific determinants of mouse neurovirulence in this chimeric system. This study indicates the feasibility of expressing protective antigens of JE virus in the context of a live, attenuated flavivirus vaccine strain (YF17D) and also establishes a genetic system for investigating the molecular basis for neurovirulence determinants encoded within the JE E protein.

In vitro human Th-cell responses to a recombinant hepatitis C virus antigen: failure in IL-2 production despite proliferation

Hepatitis C Virus (HCV) causes chronic infection in 80-90% of those exposed and persists despite evidence of immune recognition. To understand the immunological basis of this phenomenon, we have synthesized a non structural (NS) protein that is critical to HCV infection and replication, NS3, and used it to study in vitro helper T-cell responses from infected individuals. Strong proliferative responses were generated by peripheral T-cells isolated from a subset of chronically infected patients, but not by normal, non-infected controls. Interestingly, though gamma-interferon (gammaIfn) and IL-10 were both secreted in response to stimulation by NS3 antigen, IL-2 was not. In contrast, IL-2 was secreted in response to influenza virus vaccine antigen. Lack of IL-2 induction was confirmed by a failure to amplify IL-2 mRNA upon NS3 antigen stimulation, whereas IL-4, IL-15, and gammaIfn mRNA were seen as early as 24 h. The predominance of IL-4 and IL-10 and the lack of IL-2 suggests that in vitro responses to at least some HCV antigens are biased towards a Th2 phenotype, which may be conducive to viral persistence.

Functionally distinct T-cell epitopes within the hepatitis C virus non-structural 3 protein

Clearance of Hepatitis C Virus (HCV) infection is an uncommon phenomenon. To understand the mechanism of viral persistence despite active cellular and humoral responses, we examined the in vitro cytokine response of PBMC from an HCV sero-positive, asymptomatic individual to recombinant intact antigen and sixty-nine overlapping peptides of the HCV non-structural (NS) 3 protein. Whereas, intact antigen induced strong proliferation and significant levels of gammaIFN and IL-10, little or no IL-2 was produced. Only 7% of peptides induced IL-2, which also coincided with their ability to stimulate proliferation. In contrast, 38% of the peptides induced gammaIFN while 35% induced IL-10. All IL-2 stimulating peptides also induced significant levels of gammaIFN and among these, a peptide corresponding to residues 358-375 was the strongest. In addition, 16% of the peptides induced both gammaIFN and IL-10. Exogenous recombinant IL-10 inhibited proliferation and IL-2 induction in response to peptide 358-375. Furthermore, neutralization of IL-10 with an anti-IL-10 antibody resulted in enhanced IL-2 production in response to recombinant NS3 protein. We suggest that IL-10 inducing epitopes within HCV NS3 may thus down-regulate IL-2 dependent T-cell responses.

Class I MHC molecule-mediated inhibition of Sindbis virus replication

The threshold for systemic viral infection relies on the amplification of virus at a primary infection site. We have identified that class I MHC molecules can trigger the inhibition of replication of Sindbis virus in a haplotype- and allele-specific manner. Class I MHC molecules of H-2d haplotypes exhibit a strong inhibitory effect whereas H-2k haplotypes show minimal inhibition of Sindbis viral replication. By a single gene transfection of H-2d class I MHC molecules, into cells that express class I MHC molecules of H-2k haplotype and are susceptible to viral replication, these cells became resistant to viral replication. The inhibition of viral replication by class I MHC molecules occurs neither during the stage of virus entry/endocytosis nor during virus maturation. Rather, viral-specific RNA replication, as well as viral gene expression, are inhibited in cells expressing inhibitory class I MHC molecules. This class I MHC molecule-mediated inhibition requires newly synthesized host gene products, implying the activation of an intracellular signaling mechanism that is triggered by specific class I MHC molecules.