- Volume 73, Issue 5, 1992

After immunization of mice with isolated Borna disease virus (BDV)-specific proteins having M rs of 38/39K and 24K, monoclonal antibodies (MAbs) were obtained which were specific for one of the antigens in Western blot analysis. However, in immunoprecipitation assays it was found that some MAbs of each specificity reacted exclusively with their respective antigen from BDV-infected cells, whereas other MAbs coprecipitated the heterologous protein. The relationship between the 38/39K and 24K proteins was demonstrated by two-dimensional peptide mapping, which revealed four identical peptides. Additionally, it was found that neither the 38/39K nor the 24K protein is glycosylated, but that the 24K protein is phosphorylated at serine residues. Experiments employing various cell separation protocols revealed that the 38/39K and the 24K proteins are evenly distributed within infected cells; this was confirmed by immunofluorescence techniques using 38/39K- or 24K-specific MAbs. Iodination experiments clearly demonstrated that only the 38/39K protein is expressed on the surface of virus-infected cells.

A cDNA encoding the spike (S) protein of the neurovirulent murine coronavirus JHMV variant c1-2 was isolated and sequenced. Analysis of the cDNA revealed that the S protein consists of 1376 amino acids, as does the S protein of mouse hepatitis virus 4. We inserted the cDNA into the genome of vaccinia virus to obtain a recombinant vaccinia virus (rVV). The S protein expressed in RK13 cells infected by the rVV was shown to be electrophoretically and immunologically indistinguishable from the S protein produced in DBT cells infected with c1-2 virus. RVV infection of rats and mice induced S protein-specific antibody production detectable by immunofluorescence and neutralization. Moreover, the S protein expressed by the rVV induced syncytium formation not only in mouse DBT and L cells, which are susceptible to c1-2 virus infection, but also in rabbit RK13 cells, which are not susceptible to c1-2 virus infection. This result suggests the possibility that RK13 cells have binding sites for the c1-2 virus S protein.

The structural proteins of rubella virus consist of a nucleocapsid protein (C) and two membrane-embedded spike glycoproteins (E1 and E2). Since many reports have suggested that rubella virus buds intracellularly, we have examined the intracellular transport of the structural proteins in the absence of virion formation, particularly whether the membrane glycoproteins are retained inside the cell or are transported to the cell surface. We have expressed the structural proteins from cloned cDNA either alone or in different combinations, have examined the intracellular location of the proteins by immunofluorescence and using biochemical methods, and have looked for plasma membrane-localized E1 or E2 using a cell surface biotinylation assay. The C protein was found in the Golgi complex when expressed with E2 and E1; without the membrane glycoproteins, C appeared to remain in the endoplasmic reticulum (ER). When expressed alone, E1 was retained in a pre-Golgi compartment, and was not detected at the cell surface in any cell line. When E2 was expressed alone a small fraction could be detected at the cell surface, but the majority was retained intracellularly, apparently in the ER and the Golgi. Both proteins were transported to the surface when they were expressed together, albeit with low efficiencies in all cell lines. These data suggest that, although neither glycoprotein carries a dominant intracellular retention signal, E2 and E1 are largely retained in the Golgi even when present as a transport-competent heterodimer.

Retrovirus-like particles were secreted in a steroid-dependent manner by the human mammary carcinoma cell line T47D. The particles exhibited typical retroviral properties such as their electron microscopic appearance (95 nm in diameter) and occasional budding, sedimentation at 1.14 g/ml, reverse transcriptase activity and genomic RNA. The T47D particles were related to mouse mammary tumour virus (MMTV) as shown by their ultrastructural appearance (B type-like eccentric dense cores and budding), Mg2+ dependence of the reverse transcriptase activity; immunological reactivity with MMTV-directed antibodies (revealing proteins of 63K, 52K, 26K and 18K), and hybridization of particle RNA with MMTV DNA under stringent conditions. Purified particles were able to incorporate deoxynucleoside triphosphates in the absence of an exogenous primer and template, thus indicating the existence of a complete and biochemically functional reverse transcription apparatus (reverse transcriptase, RNA and primer) and the ability to direct endogenous cDNA synthesis. Labelled particle cDNA hybridized strongly to human genomic DNA but not to mouse and cat DNA, thus indicating the human origin of the T47D particles. Furthermore all human DNAs, hybridized with the labelled particle cDNA, showed a uniform hybridization pattern of restriction fragments, indicating the endogenous origin and distribution of the proviral particle DNA in the human genome.

Chimpanzees infected with human immunodeficiency virus type 1 produce antibodies against the variable regions of the external envelope glycoprotein gp120. All five variable regions contain an epitope which is recognized by at least one of five chimpanzee sera. Each of the sera recognized a different pattern of epitopes. It is suggested that this varying response contributes to the emergence of variant viruses in the host. In contrast with the variability of the chimpanzees’ response to replicating virus, that of baboons to a candidate recombinant vaccine is more uniform. Baboons injected with recombinant gp120 produced high levels of antibodies to epitopes within both the variable and conserved regions which coincided with epitopes previously shown to induce neutralizing antibodies.

The mechanism for the gradual loss of CD4+ T lymphocytes and the development of the slowly progressive inflammatory/degenerative lesions that accompany human immunodeficiency virus infection are poorly understood. Using the Simian immunodeficiency virus (SIVmac) macaque model of AIDS, we found that persistently infected primary macrophages fuse with primary activated CD4+ lymphocytes and that this interaction results in production of tumour necrosis factor-α (TNFα) and interleukin 6 (IL-6). An earlier report had shown that SIV-infected macaque macrophages fuse with CEM174 cells (a human CD4+ cell line) and cause their lysis. In the present report, we have shown that TNF-α and IL-6 are also produced during the early stages of this interaction. Data from cocultivation of infected macrophages with several CD4+ T cell lines, including CEM174, suggested that the cytokines are produced by the T cells, and that cytokine production is restricted to those cells which not only express CD4, but are also capable of fusing with the infected macrophages. These data suggest that infected macrophages in vivo could fuse with and eliminate activated CD4+ lymphocytes and, during this interaction, release cytokines, which would contribute to the degenerative and inflammatory lesions characteristic of this disease.

Cytotoxic T (Tc) cells were generated in mice of five H-2 haplotypes against the flaviviruses Kunjin and West Nile (WNV). A panel of recombinant vaccinia viruses which between them expressed cDNA of the entire Kunjin virus genome were used to infect targets. Anti-Kunjin virus responses to determinants derived from non-structural proteins, especially NS3, NS4A and NS4B, were dominant in most mouse strains; usually only one class I major histocompatibility complex (MHC) restriction element was involved. WNV-immune Tc cells showed similar but not identical patterns of antigen recognition to Kunjin virus-immune Tc cells. The extent to which WNV-immune Tc cells recognized Kunjin virus-encoded determinants varied considerably between mice of different MHC haplotypes.

Eight monoclonal antibodies (MAbs) derived using yellow fever (YF) virus (French viscerotropic virus strain) labelled the nuclei (wild-type strains) and/or the nucleoli (vaccine strains) of cells infected with different strains of YF virus. The specificity of these antibodies for YF virus-infected cells was confirmed using MAbs that bind only the YF virus envelope glycoprotein. The characteristics of fluorescent labelling in the nuclei and nucleoli of both normal cells and of nuclei separate from cell cytoplasm confirmed that the antigen was inside the nucleus rather than on the outer surface of the nuclear membrane. Virus-specific antigen was also observed in the cytoplasm of infected cells. One additional virus envelope-specific antibody, derived at the same time, identified cytoplasmic antigen exclusively. The eight antibodies that identified nuclear antigen showed no activity in neutralization, haemagglutination inhibition or mouse protection tests. Analysis of their molecular specificities by radio-immunoprecipitation of virus-infected cell lysates showed that they identified the non-structural NS5 antigen of YF virus. These results support the possibility of nuclear involvement in the replicative stages of YF virus infection.

Sequences obtained in the 5′ non-coding region (5′NCR) of hepatitis C virus (HCV) were obtained from Scottish blood donors and compared with previously published HCV sequences. Phylogenetic analysis revealed the existence of three distinct groups of sequences; two of these corresponded to the recently described HCV types 1 and 2 variants, while viral sequences detected in around a third of the blood donors formed a separate phylogenetic group that probably represents infection with a novel virus species. Nucleotide sequences of this latter group differed from all previously published 5′NCR sequence variants by at least 9%. This new virus type also differed considerably from previously published variants in other regions of the viral genome (core, NS-3 and NS-5), with corrected nucleotide distances of 15, 43 and 49% respectively from the prototype HCV-1 sequence. Formal phylogenetic analysis of each of the coding regions confirmed that HCV type 1 variants could be clearly differentiated into regional variants (Far East and U.S.A./European), in contrast to the clearly overlapping geographical distributions of the main HCV types in U.K. blood donors. We discuss the evidence for and against the hypothesis that the three main phylogenetic groups identified in this study represent separate species of HCV.

This paper describes isolation and identification of a virus (termed strain 87A) which has the cytopathic effect and haemagglutination properties of hepatitis E virus (HEV). This virus was isolated by tissue culture from the faeces of a patient with acute non-A, non-B enteric hepatitis in Xinjiang, China. The isolated virus was neutralized by acute phase sera obtained from other patients with acute non-A, non-B enteric hepatitis. The virus particles also could be specifically aggregated with acute phase sera from patients with known HEV hepatitis in China, Burma, India and the U.S.S.R., and with acute and convalescent sera from an HEV-infected chimpanzee. Crystalline arrangements of virus particles in the cytoplasm were observed by electron microscopy in ultrathin sections of infected cells. The sedimentation coefficient of the strain 87A virus particles in sucrose gradients was 176S. Purified virus particles revealed a protein band of about 76K on SDS-PAGE and Western blotting. The evidence indicates that the strain 87A virus is an HEV. Our ability to propagate HEV in cell culture should facilitate research on this hepatotropic virus.

A molecular epidemiological study of the rabies virus currently prevalent in France was carried out by directly sequencing polymerase chain reaction-amplified genes. The rabies virus pseudogene Ψ was chosen as the most divergent genomic area, and as such the best ‘clock’ for measuring virus evolution. Sequence comparisons between 12 wild rabies virus isolates indicated strong conservation whatever the host and wherever the virus had been isolated. This holds true for a unique wild reservoir, the fox. On the other hand, a good correlation between genetic and geographical criteria indicates a slow evolution of the wild virus in parallel with the spatio-temporal progression of the epizootic. In contrast to their intrinsic homogeneity (about 2% divergence), the wild isolate sequences showed a marked divergence from those of vaccine seed strains (about 14.7%). This finding invites world-wide molecular epidemiological studies, particularly in countries in which vaccination failures have been reported.

Primary isolation of type A influenza (H3N2) virus in mammalian Madin Darby canine kidney (MDCK) cells results in a virus with haemagglutinin (HA) identical to that of the virus replicating in the infected individual, whereas similar isolation of virus in the embryonated egg results in the selection of variants with amino acid substitutions in the globular head region of the HA molecule. To determine whether other mammalian and avian host cells routinely used in laboratory isolation of influenza viruses also impose a selective pressure on the replicating virus population, the HA of viruses isolated in several different primary or continuous mammalian cells or avian cells has been characterized. The HAs of H3N2 viruses isolated in monkey kidney LLC-MK2 and primary guinea-pig kidney cell culture were antigenically identical to MDCK cell-grown virus isolated from the same patient. The deduced amino acid sequence over the region of HA1 encoding residues implicated in host cell-mediated sequence variation revealed that the HA sequences of viruses isolated and passaged in these mammalian cell types, and in a human lung continuous cell line (MRC-5), were identical to that of the virus present in the infected individual. In addition, isolation of virus in avian primary chick kidney (CK) cells yielded a predominant virus with HA identical to that of mammalian cell-grown virus and the virus present in the original clinical material. However, passage of CK cell-grown virus in chicken embryos (eggs) resulted in the predominance of viruses with amino acid substitutions in HA, a minority of which resulted in antigenic variation. Since CK cell culture is used in the development of live attenuated influenza vaccines, the sequence identity between CK cell-grown virus and the virus present in the infected individual is reassuring. Nevertheless, subsequent passage of virus strains in eggs, necessary for vaccine production, must be monitored closely.

The majority of neutralizing monoclonal antibodies (MAbs) to the haemagglutinin-neuraminidase (HN) glycoprotein of Newcastle disease virus prevent attachment of the virus to cellular receptors and inhibits virion-induced fusion from without (FFWO) and fusion from within (FFWI) mediated by the virus glycoprotein-laden infected cell surface. For these antibodies, the inhibition of fusion is presumed to be the result of the prevention of HN-mediated bridging of potential fusion partners. MAbs against antigenic sites 3 and 4 neutralize virus infectivity, but by a mechanism other than the prevention of attachment, the exact nature of which remains to be established. Antibodies to both of these sites effectively inhibit virion-induced FFWO, even when the inducing virus is not infectious. This is consistent with the mechanism of neutralization of these MAbs involving the inhibition of an early, post-attachment step in infection. MAbs to site 3 also inhibit FFWI, but those to site 4 do not, even when added at high concentrations. This suggests that the requirement for HN may be different in the two modes of fusion. The epitopes recognized by MAbs to sites 3 and 4 have been delineated by the identification of individual nucleotide substitutions in the HN genes of neutralization escape variants. Some of the deduced amino acid substitutions result in additional N-linked glycosylation sites in HN, which are utilized and presumably account for the escape from neutralization.

The intracellular processing and transport of the respiratory syncytial virus (RSV) fusion (F) glycoprotein was examined by comparing the maturation and stability of wild-type F, uncleaved mutant F and chimeric F glycoproteins expressed by recombinant vaccinia viruses to that of F protein expressed by RSV. One of the recombinant viruses, vF317, expressed F protein (F317) that was processed like the RSV F glycoprotein. F317 was synthesized initially as F0, the uncleaved glycosylated precursor of mature F protein, and formed stable oligomeric structures that were maintained following cleavage of F0 to form the disulphide bond-linked F1 and F2 subunits. Most of the newly synthesized F0 expressed by either RSV or by vF317 was sensitive to treatment with endoglycosidase H (Endo H). Following cleavage of F0, F1 was resistant to Endo H, suggesting that conversion to complex-type sugars, which takes place in the medial Golgi apparatus, occurred simultaneously with or immediately prior to cleavage of F0 into F1 and F2. Another recombinant virus, vF313, synthesized only uncleaved F protein (F313) that comigrated with F0. Uncleaved F313 was expressed as a stable glycosylated protein; however, unlike cleaved F317, its oligosaccharides were not modified to complex forms, as determined from its Endo H sensitivity, and uncleaved F313 did not assemble into stable oligomeric structures. Nucleotide sequence analysis of the cDNA clones encoding F313 and F317 revealed four predicted amino acid sequence differences, none of which were located at the cleavage site. Expression of chimeric F proteins obtained by restriction fragment exchange between the two cDNA clones indicated that two amino acid changes in the F1 domain, located at amino acid residues 301 (Val to Ala) and 447 (Val to Met), resulted in the expression of uncleaved F protein. A change at either of these two amino acid residues, 301 or 447, resulted in the expression of inefficiently cleaved F protein, defining an additional F protein phenotype. Pulse-chase analyses to examine the association of recombinant F glycoproteins with gradient-purified fractionated membranes or with GRP78-BiP, a protein resident in the endoplasmic reticulum (ER) which binds to nascent proteins, revealed that uncleaved F protein (F313) is associated with GRP78-BiP in the ER for a longer time than F317, and little if any F313 was transported to the cell surface. In addition, the uncleaved F protein (F313) was not recognized by a panel of F protein-specific monoclonal antibodies in ELISA or indirect immunofluorescence assays, suggesting that F313 was misfolded and, as a result, not transported properly or cleaved.

Generation of a set of cDNA clones covering the N, P/V/C, M, F, H and part of the L gene of phocine distemper virus (PDV) has been described. The gene order of PDV determined from a physical as well as a transcriptional map, was identical to that of the other morbilliviruses so far studied. The H gene sequence (1951 nucleotides) contains one large open reading frame which encodes a protein of 607 amino acids, identical in length to that of the H protein of the Convac strain of canine distemper virus (CDV). Nucleotide and protein sequence comparisons between PDV and the other morbilliviruses provide further evidence in favour of PDV’s inclusion in the morbillivirus genus as a distinct species closely related to CDV and more distantly to measles virus and rinderpest virus.

The nucleotide sequence of the P gene of the porcine paramyxovirus La-Piedad-Michoacan-Mexico virus (LPMV) was analysed. Three long open reading frames (ORFs) were found in the mRNA sense. Insertion of two G residues is necessary to obtain an ORF encoding the P protein, which gives a P protein of 404 amino acids with a calculated M r of 42475. This form of editing was demonstrated, two non-templated G residues being added in a portion of the mRNA transcripts. The LPMV V protein, which has a conserved cysteine-rich C-terminal region, is encoded by an exact copy of the P gene. The third ORF has the capacity to encode a protein of 126 amino acids, which may resemble the C proteins found in some paramyxoviruses. The ORF starts from an AUG codon down-stream of the first AUG codon of the P/V ORF.

The surface (S) genes of 12 hepatitis B viruses (HBVs) encoding nine different serotypes of hepatitis B surface antigen (HBsAg) were amplified by the polymerase chain reaction and sequenced. These represented the eight strains of HBV, P1 to P8, defined at an international workshop on HBsAg subtypes in Paris in 1975, and the adrq − subtype. The S genes from additional HBV strains, one ayw4, one adw4 and one ayw1, of sub-Saharan African origin, were also sequenced. The relationship of these 12 new S gene sequences to those of the 20 published previously was investigated by constructing a phylogenetic tree, which confirmed a previous classification into four groups, designated A to D, based on 18 complete HBV genomes. When relating our sequenced S genes to these genomic groups, ayw1 of African origin and P6 (adw2) were both allocated to group A, the reference P1 (ayw1 of Vietnamese origin) was allocated to group B, P5 (ayr), P8 (adr) and adrq − were all related to group C, and P2 (ayw2) and P3 (ayw3) could both be allocated to group D. Interestingly, the S genes of w4 serotype viruses, i.e. P4 (ayw4) and P7 (adw4q −), differed by 4% or more from both previous groups and from each other, suggesting their classification into two new groups, for which the designations E and F are proposed. Genomes specifying ayw were also found in groups A and B; previously sequenced genomes specifying the ayw subtype have all been confined to group D. There were indications that the epitope for subdeterminants of w resided at amino acid positions 125 to 127. Thus, at positions 125 and 127, ayw1, ayw2 and adw2 had T and P residues, respectively, whereas M and T residues were at the corresponding positions of ayw3. Both ayw4 and adw4 had L at residue 127, and all strains expressing r, apart from P5, had an I instead of a T residue at position 126.

Simian varicella virus (SVV) causes a varicella-like disease in non-human primates. In this study, SVV virions were purified from SVV-infected BSC-1 cells by zonal and differential gradient centrifugation and the virion polypeptide composition was analysed by SDS-PAGE. SVV virions had a buoyant density of 1.21 g/ml, identical to the value obtained for varicella-zoster virus (VZV) virions purified by the same method. Electron microscopy of the concentrated SVV virions revealed characteristic herpesvirus morphology. SVV virions consisted of at least 30 polypeptide species ranging from 16K to >200K. The electrophoretic profiles of radiolabelled SVV and VZV virion polypeptides were very similar. Immunoprecipitations of solubilized SVV-infected cell preparations using SVV immune sera revealed at least 18 viral polypeptides with an M r range of 12K to 142K and six glycoproteins ranging from 46K to 115K. In addition, extensive cross-reactivity between SVV and VZV proteins and glycoproteins was demonstrated by immunoprecipitation with heterologous immune sera. The high degree of antigenic relatedness between SVV and VZV provides further support for simian varicella as a model for VZV infections.

The molecular structure of the genome of simian herpes B virus (SHBV) was determined by restriction endonuclease mapping studies. Genomic DNA was cleaved with restriction endonucleases BamHI and SalI into 41 and 58 fragments, respectively. Most of these fragments were cloned into the plasmid vector pACYC184; uncloned fragments were identified following isolation from agarose gels. Terminal fragments were identified by exonuclease digestion and radioactive end-labelling, and linkage of fragments was deduced by a combination of single and double digest experiments and cross-blot hybridizations. The genome is larger than that of herpes simplex virus type 1 (HSV-1), being approximately 165 kilobase pairs. Like that of HSV-1, the SHBV genome is composed of a long and a short unique region each flanked by inverted repeat sequences, which allow the unique regions to invert relative to one another, resulting in four possible isomeric arrangements of the molecule. Genome locations of several SHBV genes were compared with their HSV-1 homologues.