Evolution of hepatitis C virus-specific T cell responses and cytokine production in chronic hepatitis C patients treated with high doses of interferon-alpha

OBJECTIVE

To assess the evolution of in vitro T cell response to hepatitis C virus (HCV) Core, E1, E2 and NS3 antigens in 10 patients with chronic hepatitis C, before, during and after a high dose interferon alpha (IFN-alpha) therapy, and to evaluate the influence of IFN-alpha on the in vivo and in vitro production of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma).

METHODS

T cell response to HCV antigens was evaluated by lymphoproliferation assays. In vivo and in vitro cytokine production was evaluated at weeks 0, 4, 8, and 12 of IFN-alpha therapy by enzyme immunoassays.

RESULTS

In general, of all HCV antigens tested throughout the follow-up, those belonging to the Core region were the most immunostiumlatory. This observation was valid in IFN-alpha responders as well as IFN-alpha non-responders. The lymphoproliferative response to HCV antigens increased during IFN-alpha therapy. Serum levels of TNF-alpha were significantly increased in HCV patients, and six out of ten patients showed increased IFN-gamma serum levels. A significant decrease of IFN-gamma levels was observed during therapy and the same trend was seen for TNF-alpha. Mitogen-stimulated TNF-alpha and IFN-gamma production before therapy did not differ from that of normal controls, however, the cytokine production was reduced at week 4 of therapy, corresponding with a clinical improvement. A return to pretreatment values was observed after 8 weeks of therapy.

CONCLUSIONS

a) Core antigens are the most immunostimulatory HCV antigens at the T cell level in chronic hepatitis C patients; b) High dose IFN-alpha therapy induces an increase in lymphoproliferative response to HCV antigens; c) Serum levels of TNF-alpha are increased in HCV patients; d) High dose IFN-alpha therapy induces a decrease in serum levels of IFN-gamma; e) High dose IFN-alpha therapy induces a transiently decreased mitogen-induced TNF-alpha and IFN-gamma production.

Lettuce mosaic virus pathogenicity determinants in susceptible and tolerant lettuce cultivars map to different regions of the viral genome

Full-length infectious cDNA clones were constructed for two isolates (LMV-0 and LMV-E) of Lettuce mosaic virus (LMV), a member of the genus Potyvirus. These two isolates differ in pathogenicity in susceptible and tolerant-resistant lettuce cultivars. In susceptible plants, LMV-0 induces mild mosaic symptoms, whereas LMV-E induces severe stunting, leaf deformation, and a necrotic mosaic. In plants carrying either of the two probably allelic recessive resistance genes mol1 or mol2, LMV-0 is restricted partially to the inoculated leaves. When a systemic invasion does occur, however, symptoms fail to develop. LMV-E overcomes the protection afforded by the resistance genes, resulting in systemic mosaic symptoms. Analysis of the behavior of recombinants constructed between the two virus isolates determined that the HC-Pro protein of LMV-E causes the severe stunting and necrotic mosaic induced by this isolate in susceptible cultivars. In contrast, the ability to overcome mol resistance and induce symptoms in the resistant-tolerant cultivars was mapped to the 3' half of the LMV-E genome. These results indicate that the ability to induce severe symptoms and to overcome the protection afforded by the recessive genes mol1 or mol2 are independent phenomena.

Mutation at codon 130 in hepatitis B virus (HBV) core region increases markedly during acute exacerbation of hepatitis in chronic HBV carriers

Mutations within T-cell or B-cell epitopes are suggested to have some influence on the clinical course of chronic hepatitis B virus (HBV) infection. To investigate the relationship between liver cell injury and heterogeneity of the HBV core gene, we focused on the sequence of codon 130, which is located on both T- and B-cell epitopes, and serially analyzed the proportion of mutant virus (core130Thr) to wild-type virus (core130Pro) during the exacerbation of chronic hepatitis B. Sera obtained serially from five HBV carriers who had exacerbation of hepatitis, and three asymptomatic HBV carriers (ASCs) with persistently normal serum aminotransferase (ALT) values were studied, using the restriction fragment length polymorphism (RFLP) method. Core130Pro predominated in the sera in the remission state, but core130Thr increased markedly in parallel with ALT elevation and decreased again after the ALT peak, followed by the predominance of core130Pro, in all the five patients. In one patient, the ratio of core130Thr/core130Pro (Thr/Pro) was more than 70% at the ALT peak. On the other hand, in sera from the three ASCs core130Pro always predominated, and no divergence was identified in the ratio of Thr/Pro. Our data suggest that codon 130 is one of the most important immunogenic regions in the HBV core gene and that elevation of Thr/Pro could be the result of immune selection.

Selection of a subgroup A avian leukosis virus [ALV(A)] envelope resistant to soluble ALV(A) surface glycoprotein

The host developing resistance to retroviral infection is believed to be a major force in the evolution of multiple receptor usage by retroviruses. The avian leukosis-sarcoma virus (ALV) group of retroviruses provides a powerful system for studying the envelope-receptor interactions involved in retrovirus entry; different members of this group of closely related viruses use distinct cellular receptors. Analysis of the ALV envelope subgroups suggests that the different ALVs evolved from a common ancestor by mutations in the env gene. Cells and animals that express subgroup A ALV envelope glycoproteins are highly resistant to ALV(A) infection due to receptor interference. In this study, we tested whether expression of a soluble form of subgroup A surface glycoprotein (SU) would result in receptor interference and whether this interference would select for resistant viruses with altered receptor usage. Chicken cells expressing the secreted ALV(A) SU immunoadhesin SU(A)-rIgG, which contains the subgroup A SU domain fused to the constant region of a rabbit immunoglobulin (IgG) heavy chain, showed significant receptor interference. A variant virus resistant to SU(A)-rIgG receptor interference was obtained. This virus had a six-amino-acid deletion in the subgroup A hr1 that altered receptor usage. This approach may identify regions of SU that play a critical role in receptor specificity.

[Hepatitis virus and malignant lymphoma]

Hepatitis virus, especially hepatitis C virus(HCV), is suggested to be associated with lymphomagenesis. A high prevalence(33%) of HCV among non-Hodgkin's lymphoma(NHL) patients has been reported mainly in Italy, but the prevalence is low in other countries. HCV-related NHL is varied histopathologically, including diffuse large B cell lymphoma, immunocytoma or follicular lymphoma(REAL). The HCV genotypes involved are 1b, 2a or 2c(Simmonds). Although HCV RNA + strand has been detected in lymphoma tissue in various studies, there are not many studies in which HCV RNA-strand has been detected. Recent studies have shown that BCL-2 plays an important role in lymphoproliferation by suppressing apoptosis, that HCV core protein regulates c-myc transcription and that BCL-2 and c-myc work together in lymphomagenesis. It seems difficult to provide reasonable explanations regarding these puzzling epidemiological findings and lymphomagenesis.

Genotypic differences in the hepatitis B virus core promoter and precore sequences during seroconversion from HBeAg to anti-HBe

Hepatitis B virus (HBV) strains from anti-HBe positive patients often show specific mutations in the precore gene, the core promoter region, or both. The dynamics of seroconversion in relation to the appearance of these mutations has not been studied and compared between defined HBV genotypes. Samples from patients followed during seroconversion from HBeAg to anti-HBe were amplified by polymerase chain reaction (PCR), sequenced and genotyped. Among 16 sets of samples, 6 belonged to genotype A, 6 to genotype D, 2 to genotype B, 1 to genotype C, and 1 to genotype E. Whereas strains from genotypes B, C and E showed changes in the core promoter, precore codon 28 or both, genotype A and D strains displayed a different pattern. In 4 of 6 anti-HBe positive samples from genotype A, the precore had a wild-type sequence while the core promoter sequence showed a specific TGA mutation. In another genotype A strain a precore stop mutation was preceded by a mutation in codon 15, thus conserving base-pairing at the pregenomic RNA level in this region. In contrast, all genotype D strains showed wild-type sequences in both the core promoter and precore codon 28 in pre- and post-seroconversion samples. Thus, in 8 patients with a mean follow-up time of 17 months, wild-type sequences in both the core promoter and precore codon 28 were found after seroconversion to anti-HBe. This study also confirmed, for genotype D, that HBeAg seroconversion often occurs earlier than genomic conversion.

Association between the sigma C protein of avian reovirus and virus-induced fusion of cells

Monoclonal antibodies (MAbs) against a 39 kDa (sigma C) protein of the avian reovirus RAM-1 strain inhibited virus-induced fusion of cells and the protein was expressed on the surface of infected cells. The fusion-inhibiting activity of the three MAbs reacting with the sigma C protein suggest two putative epitopes were involved: one epitope recognised by antibody 6H1 and involved in fusion of both Vero and CK cells and a second epitope recognised by antibody 1G1 involved in fusion of Vero cells but not CK cells. The activity of the MAb 6E2 was intermediate, suggesting it may have been located in an intermediate position between the two putative epitopes and inhibited fusion by steric hindrance.

Differential serological diagnosis of HTLV-I and HTLV-II infection by external membrane protein peptide-based enzyme immunoassays

BACKGROUND

HTLV antibody screening assays detect both antibodies to the etiological agent of adult T-cell leukemia and tropical spastic paraparesis HTLV-I and to the less pathogenic HTLV-II. It is critical to make a differential diagnosis of the two viruses.

OBJECTIVES

To design and evaluate synthetic core and envelope-derived peptide enzyme immunoassays (EIA) for serological differential diagnosis.

STUDY DESIGN

Peptide EIAs were evaluated with a panel of 202 plasma samples comprised of HTLV antibody positive, serologically classified as confirmed, indeterminate, or non confirmed, characterized as HTLV-I, HTLV-II or neither by genomic amplification. The peptide EIA with the best performance was further used to differentiate between HTLV-I and HTLV-II antibodies in 807 samples from 18 countries in four continents and to provide ratios between the two infections.

RESULTS

The gp46 peptide EIA correctly identified 96.5% of HTLV-I and 98.6% of HTLV-II antibody-confirmed samples. HTLV-I was found exclusively in Japan and Caribbean countries; almost exclusively in Africa. HTLV-II represented 10-25% of samples from Canada, Chile and Venezuela and was predominant in the US.

CONCLUSIONS

Differential diagnosis between HTLV-I and HTLV-II can be reliably performed using specific peptides from the gp46 envelope protein of each virus.

Transcriptional repression of p53 promoter by hepatitis C virus core protein

Our previous results have suggested that the putative core protein of hepatitis C virus (HCV) transcriptionally regulates cellular and viral genes, inhibits cisplatin and c-myc-mediated apoptotic cell death under certain conditions, and transforms primary rat embryo fibroblast cells with a cooperative oncogene. Because HCV appears to cause hepatocellular carcinoma, we evaluated the regulatory role of the HCV core protein on p53, a well known tumor suppressor gene, by an in vitro transfection assay. HCV core protein repressed transcriptional activity of the p53 promoter when tested separately in COS7 and HeLa cells. Deletion mutational analysis of the HCV core gene indicated that the regulatory domain involved in the repression of p53 transcriptional activity is located around amino acid residues 80-122 encompassing a putative DNA binding motif and two major phosphorylation sites. Results from this study suggest that the putative core protein may have an important biological role in the promotion of cell growth by repressing p53 transcription, and this appears to be consistent with certain earlier observations about HCV core moving into the nucleus.

Structure of Semliki Forest virus core protein

Alphaviruses are enveloped, insect-borne viruses, which contains a positive-sense RNA genome. The protein capsid is surrounded by a lipid membrane, which is penetrated by glycoprotein spikes. The structure of the Sindbis virus (SINV) (the type virus) core protein (SCP) was previously determined and found to have a chymotrypsin-like structure. SCP is a serine proteinase which cleaves itself from a polyprotein. Semliki Forest virus (SFV) is among the most distantly related alphaviruses to SINV. Similar to SCP, autocatalysis is inhibited in SFCP after cleavage of the polyprotein by leaving the carboxy-terminal tryptophan in the specificity pocket. The structures of two different crystal forms (I and II) of SFV core protein (SFCP) have been determined to 3.0 A and 3.3 A resolution, respectively. The SFCP monomer backbone structure is very similar to that of SCP. The dimeric association between monomers, A and B, found in two different crystal forms of SCP is also present in both crystal forms of SFCP. However, a third monomer, C, occurs in SFCP crystal form I. While monomers A and B make a tail-to-tail dimer contact, monomers B and C make a head-to-head dimer contact. A hydrophobic pocket on the surface of the capsid protein, the proposed site of binding of the E2 glycoprotein, has large conformational differences with respect to SCP and, in contrast to SCP, is found devoid of bound peptide. In particular, Tyr184 is pointing out of the hydrophobic pocket in SFCP, whereas the equivalent tyrosine in SCP is pointing into the pocket. The conformation of Tyr184, found in SFCP, is consistent with its availability for iodination, as observed in the homologous SINV cores. This suggests, by comparison with SCP, that E2 binding to cores causes major conformational changes, including the burial of Tyr184, which would stabilize the intact virus on budding from an infected cell. The head-to-tail contacts found in the pentameric and hexameric associations within the virion utilize in the same monomer surface regions as found in the crystalline dimer interfaces.

Structural analysis of Sindbis virus capsid mutants involving assembly and catalysis

Sindbis virus core protein (SCP) has been isolated from virus and crystallized. The X-ray crystallographic structure showed that the amino-terminal 113 residues appeared to be either disordered or truncated during crystallization and that the carboxy-terminal residues 114 to 264 had a chymotrypsin-like structure. The carboxy-terminal residues 106 to 264 and 106 to 266 of SCP have now been expressed in Escherichia coli. Most crystal forms of the truncated proteins were isomorphous with those of the virally extracted protein. There are only small structural differences between the truncated recombinant protein and the ordered part of the wild-type virus-extracted protein. Hence, E. coli-expressed SCP can be used to study proteolytic properties and the contribution of SCP to nucleocapsid assembly, interaction with the E2 glycoprotein and interaction with RNA. The same dimer that was found in two different crystal forms of the virus-extracted SCP was present also in some of the crystals of the truncated recombinant protein. The monomer-monomer interface is maintained by two pairs of hydrogen bonds and by hydrophobic interactions. Removal of the hydrogen bonds by single substitutions did not prevent dimer formation. However, a mutation that reduced the hydrophobic contacts did inhibit dimer formation. The wild-type truncated SCP is active in E. coli, as evidenced by proteolytic processing of a series of progressively longer precursors that extend beyond residue 264. Unlike the virus-extracted capsid protein, the E. coli-expressed SCP described here is terminated following the carboxy-terminal residue and, therefore, does not require autocatalysis. Nevertheless, the E. coli-expressed protein folds with the carboxy-terminal tryptophan residue in the specificity pocket. Two crystallographically independent molecules of SCP(106 to 266), which had two additional downstream residues and had the essential S215 mutated to alanine, showed two distinct modes of binding the uncleaved carboxy-terminal residues. These may represent successive steps of binding substrate prior to catalytic cleavage. Refinement of the various crystal structures of SCP showed that the amino-terminal arm from residues 107 to 113 was not disordered, but is associated with neighboring molecules. Residues 108 to 111 bind into a hydrophobic pocket composed primarily of Y180, W247 and F166. It had been shown that the double mutant (Y180S; E183G), with the Y180S substitution in this pocket, produced a large number of non-infectious virions, possibly because of modification in the interaction of the glycoprotein spikes with core proteins. The crystal structure of this double mutant showed that there was a large positional change in the side-chain of W247, which moved into the space created by the replacement of Y180 with serine. These conformational changes may alter the stability of the virion and, thus, regulate its functional requirements during cell entry.

Identification of a protein binding site on the surface of the alphavirus nucleocapsid and its implication in virus assembly

BACKGROUND

Many enveloped viruses exit cells by budding from the plasma membrane. The driving force for budding is the interaction of an inner protein nucleocapsid core with transmembrane glycoprotein spikes. The molecular details of this process are ill defined. Alphaviruses, such as Sindbis virus (SINV) and Semliki Forest virus (SFV), represent some of the simplest enveloped viruses and have been well characterized by structural, genetic and biochemical techniques. Although a high-resolution structure of an alphavirus has not yet been attained, cryo-electron microscopy (cryo-EM) has been used to show the multilayer organization at 25 A resolution. In addition, atomic resolution studies are available of the C-terminal domain of the nucleocapsid protein and this has been modeled into the cryo-EM density.

RESULTS

A recombinant form of Sindbis virus core protein (SCP) was crystallized and found to diffract much better than protein extracted from the virus (2.0 A versus 3.0 A resolution). The new structure showed that amino acids 108 to 111 bind to a specific hydrophobic pocket in neighboring molecules. Re-examination of the structures derived from virus-extracted protein also showed this 'N-terminal arm' binding to the same hydrophobic pocked in adjacent molecules. It is proposed that the binding of these capsid residues into the hydrophobic pocket of SCP mimics the binding of E2 (one of two glycoproteins that penetrate the lipid bilayer of the viral envelope) C-terminal residues in the pocket. Mutational studies of capsid residues 108 and 110 confirm their role in capsid assembly.

CONCLUSIONS

Structural and mutational analyses of residues within the hydrophobic pocket suggest that budding results in a switch between two conformations of the capsid hydrophobic pocket. This is the first description of a viral budding mechanism in molecular detail.

New strategies for treating AIDS

To date, the effective management of HIV-1 infection by anti-retroviral drugs has proved remarkably difficult to achieve. This is primarily due to the ease with which HIV-1 becomes resistant to drugs which initially may be very effective at blocking viral replication. In a recent issue of Science, two promising new AIDS treatments were reported. The first described the use of retroviral-type zinc finger structures found in the HIV-1 nucleocapsid protein as targets for antiretroviral drugs. THe second demonstrated the feasibility of the reverse transcriptase inhibitor (R)-9-(2-phosphonylmethoxypropyl) adenine as a postexposure prophylaxis in blocking HIV-1 infection.

IRES-controlled protein synthesis and genome replication of poliovirus

Initiation of translation of the single-stranded genomic RNAs of picornaviruses such as poliovirus (PV) and encephalomyocarditis virus (EMCV) is cap-independent and controlled by a long segment within the 5' non-translated region (5'NTR), termed internal ribosomal entry site (IRES). Cellular RNA-binding proteins have been identified that are involved in IRES function in trans. One of these proteins (p57) has been found to be identical to the polypyrimidine tract binding protein (pPTB), a nuclear protein implicated in various processes involving pre-mRNA. Anti-pPTB antibodies inhibit picornavirus mRNA, but not globin mRNA translation, in vitro. Proof for the 5'-independent initiation of translation in vivo was obtained by inserting the EMCV IRES into the ORF of PV thereby constructing a dicistronic, viable poliovirus with the genotype [PV] 5'NTR-P1-[EMCV] IRES-[PV] P2-P3-3'NTR. Dicistronic polioviruses were also constructed that served as novel expression vectors where a foreign gene has been inserted into the PV genome. Incubation of poliovirus RNA in a HeLa cell-free extract leads to the synthesis and processing of viral proteins, viral RNA replication followed by formation of infectious virions. Cell-free synthesis of PV has nullified the dictum that no virus can multiply in a cell-free medium. The genome replication of poliovirus and the mechanism of recombination in poliovirus replication is still not fully understood. Biochemical evidence has been obtained that the conserved NTP-binding motif in PV protein 2C is essential for RNA replication and virus propagation. Finally by using genetic studies we found that during viral RNA synthesis a poliovirus containing two tandemly arranged VPgs (3A-VPg1-VPg2-3Cpro) led to the removal of the 3C-proximal VPg copy.

Hepadnaviral assembly is initiated by polymerase binding to the encapsidation signal in the viral RNA genome

Hepadnaviruses, as well as other pararetroviruses, express their pol (P) gene product unfused to the preceding core gene implying that these retroelements have developed a mechanism for initiating assembly and replication that is principally different from the one used by retroviruses and retrotransposons. We have analysed this mechanism for the human hepatitis B virus by using a newly developed, highly sensitive detection method based upon radiolabelling of the P protein at newly introduced target sites for protein kinase A. The results obtained demonstrate that polymerase encapsidation depends on the concomittant encapsidation of the HBV RNA pregenome and that packaging of the viral RNA, in turn, depends on the presence of P protein. Loss of P protein encapsidation by mutations inactivating the HBV RNA encapsidation signal epsilon could be compensated by trans-complementation with recombinant RNA molecules carrying the epsilon sequence. Thus, in contrast to retroviral replication, the interaction of the hepadnaviral P protein and the RNA genome at its packaging signal appears to be crucial for initiating the formation of replication-competent nucleocapsids. Furthermore, RNA control of P protein packaging stringently limits the number of polymerase molecules that can be encapsidated.

Serodiagnostic assay of hepatitis C virus infection using viral proteins expressed in Escherichia coli

Infection with hepatitis C virus (HCV) was analyzed by an enzyme-linked immunosorbent assay based on recombinant viral proteins encoded by regions of the putative viral core, NS3, NS4 and NS5, which were expressed in E. coli. Results showed that 106 of 124 cases (85.5%) of non-A, non-B chronic hepatitis and 43 of 45 cases (95.5%) of hepatocellular carcinoma, negative for HBV marker, were positive for antibodies against at least one of these viral proteins. One of 87 healthy individuals with normal alanine aminotransferase activity was positive for antibody against only the viral core, but was negative for HCV RNA. The serum of one patient with chronic hepatitis was positive for one of these proteins, but negative for HCV RNA. These findings in combination with results on detection of HCV RNA in the sera of patients with non-A, non-B chronic hepatitis indicated that 105 of 124 cases (84.6%) were positive for HCV infection. Sera that were negative for HCV antibodies against all these proteins were also negative for HCV RNA assayed by reverse transcription followed by the polymerase chain reaction. Screening of HCV infection by detecting viral antibodies in circulating blood using all these viral proteins is useful for reducing the number of ambiguous results in screening for viral infection. Thus, this assay system may be useful diagnostic purposes.

Induction of an organ-specific autoimmune disease, lymphocytic hypophysitis, in hamsters by recombinant rubella virus glycoprotein and prevention of disease by neonatal thymectomy

Glycosylated, membrane-associated E1 (58-kDa) and E2 (47- to 49-kDa) rubella virus proteins and unglycosylated nucleoprotein C (33 kDa), from separately expressed vaccinia virus recombinants, were injected into golden Syrian hamsters. Rubella virus E1 and E2 glycoproteins consistently induced an organ-specific autoimmune disease, autoimmune lymphocytic hypophysitis, which was evidenced by the induction of autoantibodies against pituitary cells and by lymphocytic infiltration of the pituitary. Neonatal thymectomy prevented the disease. In contrast, rubella virus nucleoprotein C did not induce either autoantibodies against pituitary cells or lymphocytic infiltration of the pituitary. This finding raises the possibility that virus-specific protein itself can induce an organ-specific autoimmune disease in certain circumstances.

The purification and properties of the scaffolding protein of bacteriophage lambda

The Nu3 gene of bacteriophage lambda resides within a cluster of genes that specify structural components of the bacteriophage head. Previous experiments indicate that the Nu3 gene product (gpNu3) is associated with immature proheads but is not detectable in mature proheads or bacteriophage particles, hence its classification as a scaffolding protein. The Nu3 gene has been cloned and overexpressed, and its protein product has been purified. The purified protein is biologically active, as demonstrated by its ability to complement a gpNu3-deficient extract in an in vitro assembly reaction. The sequence of the amino terminus of the protein indicates that translation of Nu3 starts at nucleotide position 5,342 on the standard lambda DNA sequence, yielding a protein with a calculated Mr of 13,396. A combination of gel exclusion chromatography and velocity sedimentation gradient data indicates that gpNu3 possesses an unusually elongated shape.

The complete sequence of the group-specific antigen, VP7, of African horsesickness disease virus serotype 4 reveals a close relationship to bluetongue virus

The complete sequence of the S7 RNA that codes for the major group-specific coat protein. VP7, of African horsesickness virus serotype 4 (AHSV-4) was determined from cDNA analyses and found to be 1179 nucleotides in length. One single open reading frame of 353 codons was observed defining a protein of Mr 38,107 with a net charge of -1.5 at neutral pH. Comparison of the AHSV-4 VP7 sequence with that of bluetongue virus serotype 10 revealed an overall similarity of 44%, with the amino- and carboxy-terminal regions exhibiting the greatest levels of homology. In addition, potential secondary structures of the terminal sequences of the S7 RNA segments of AHSV-4 and BTV serotypes 10, 13 and 17 are presented.