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Volume 81,
Issue 3,
2000
Volume 81, Issue 3, 2000
- Animal: RNA Viruses
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Development of a genetically marked recombinant rinderpest vaccine expressing green fluorescent protein
More LessIn order to effectively control and eliminate rinderpest, a method is required to allow serological differentiation between animals that have been vaccinated and those which have recovered from natural infection. One way of doing this would be to engineer the normal vaccine to produce a genetically marked rinderpest virus (RPV) vaccine. We constructed two modified cDNA clones of the RPV RBOK vaccine strain with the coding sequence of the green fluorescent protein (GFP) gene inserted as a potential genetic marker. RPVINS-GFP virus was designed to produce independent and high level expression of GFP inside infected cells, whilst the GFP expressed by RPVSIG-GFP virus was designed to be efficiently secreted. Infectious recombinant virus was rescued in cell culture from both constructs. The effectiveness of these viruses in stimulating protective immunity and antibody responses to the marker protein was tested by vaccination of cattle and goats. All of the vaccinated animals were completely protected when challenged with virulent virus: RPV in cattle or peste-des-petits ruminants virus in the goats. ELISA showed that all of the animals produced good levels of anti-RPV antibodies. Three of the four cattle and the two goats vaccinated with RPVSIG-GFP produced detectable levels of anti-GFP antibodies. In contrast, no anti-GFP antibodies were produced in the four cattle and two goats vaccinated with RPVINS-GFP. Therefore, secretion of the GFP marker protein was absolutely required to elicit an effective humoral antibody response to the marker protein.
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An amino acid in the heptad repeat 1 domain is important for the haemagglutinin–neuraminidase-independent fusing activity of simian virus 5 fusion protein
More LessA canine isolate (strain T1) of simian virus 5 (SV-5) performed multiple replication in BHK cells but did not induce cell fusion for up to 3 days. In contrast, a prototype strain (WR) provoked extensive cell fusion within 2 days during the course of its replication. Accordingly, the fusion (F) protein of the T1 strain did not cause cell fusion even when co-expressed with the SV-5 haemagglutinin–neuraminidase (HN) protein, whereas the WR F protein induced cell fusion in the presence of the HN protein. Differences in the predicted amino acid sequences of the T1 and WR F proteins were found at 12 positions and it was proved that the T1 F protein had a longer cytoplasmic tail than the WR F protein. By reducing the length of the cytoplasmic tail or by replacing the tail with the WR F counterpart, the T1 F protein partly restored its HN-dependent fusing activity. Chimeric and mutational analyses between the T1 F protein and the mutant F protein (L22P) suggested that Glu-132 in the heptad repeat 1 domain was involved in the HN-independent fusing activity in addition to the previously identified Pro-22 at the F2 N terminus. It was also shown that Ala-290 in the heptad repeat 3 domain contributed to the HN-independent fusing activity to some extent.
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Neutralization of measles virus wild-type isolates after immunization with a synthetic peptide vaccine which is not recognized by neutralizing passive antibodies
The sequence H379–410 of the measles virus haemagglutinin (MV-H) protein forms a surface-exposed loop and contains three cysteine residues (Cys-381, Cys-386 and Cys-394) which are conserved among all measles isolates. It comprises the minimal sequential B cell epitope (BCE) (H386–400) of the neutralizing and protective MAb BH6 that neutralizes all wild-type viruses tested. The aim of this study was to design synthetic peptides which induce neutralizing antibodies against MV wild-type isolates. Peptides containing one or two copies of T cell epitopes (TCE) and BCEs of different lengths (H386–400, BCC; H379–400, BCCC), in different combinations and orientations were produced and iteratively optimized for inducing neutralizing antibodies. Peptides with the shorter BCE induced sera that cross-reacted with MV but did not neutralize. The longer BCE containing the three cysteines (BCCC) and two homologous TCE were required for neutralization activity. These sera neutralized wild-type strains of different clades and geographic origins. Neutralizing serum was also obtained after immunization with human promiscuous TCEs. Furthermore BCCC-based peptides were fully immunogenic even in the presence of pre-existing MV-specific antibodies. The results suggest that subunit vaccines based on such peptides could potentially be used to actively protect infants against wild-type viruses irrespective of persisting maternal antibodies.
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Reduced levels of neuraminidase of influenza A viruses correlate with attenuated phenotypes in mice
We have previously obtained four transfectant influenza A viruses containing neuraminidase (NA) genes with mutated base pairs in the conserved double-stranded RNA region of the viral promoter by using a ribonucleoprotein transfection system. Two mutant viruses (D2 and D1/2) which share a C-G→A-U mutation at positions 11 and 12 of the 3′ and 5′ ends, respectively, of the NA gene, showed an approximate 10-fold reduction of NA-specific mRNA and protein levels (Fodor et al., Journal of Virology 72, 6283–6290, 1998). These viruses have now allowed us to determine the effects of decreased NA levels on virus pathogenicity. Both D2 and D1/2 viruses were highly attenuated in mice, and their replication in mouse lungs was highly compromised as compared with wild-type influenza A/WSN/33 virus. The results highlight the importance of the level of NA activity in the biological cycle and virulence of influenza viruses. Importantly, mice immunized by a single intranasal administration of 103 infectious units of D2 or D1/2 viruses were protected against challenge with a lethal dose of wild-type influenza virus. Attenuation of influenza viruses by mutations resulting in the decreased expression of a viral protein represents a novel strategy which could be considered for the generation of live attenuated influenza virus vaccines.
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Nucleotide sequences and phylogeny of the nucleocapsid gene of Oropouche virus
The nucleotide sequence of the S RNA segment of the Oropouche (ORO) virus prototype strain TRVL 9760 was determined and found to be 754 nucleotides in length. In the virion-complementary orientation, the RNA contained two overlapping open reading frames of 693 and 273 nucleotides that were predicted to encode proteins of 231 and 91 amino acids, respectively. Subsequently, the nucleotide sequences of the nucleocapsid genes of 27 additional ORO virus strains, representing a 42 year interval and a wide geographical range in South America, were determined. Phylogenetic analyses revealed that all the ORO virus strains formed a monophyletic group that comprised three distinct lineages. Lineage I contained the prototype strain from Trinidad and most of the Brazilian strains, lineage II contained six Peruvian strains isolated between 1992 and 1998, and two strains from western Brazil isolated in 1991, while lineage III comprised four strains isolated in Panama during 1989.
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Recombinant Semliki Forest virus particles expressing louping ill virus antigens induce a better protective response than plasmid-based DNA vaccines or an inactivated whole particle vaccine
More LessLouping ill virus (LIV) infection of mice was used as a model to evaluate the protective efficacy of Semliki Forest virus (SFV)-based vaccines in comparison to a standard DNA vaccine and a commercial chemically inactivated vaccine. The recombinant SFV-based vaccines consisted of suicidal particles and a naked layered DNA/RNA construct. The nucleic acid vaccines expressed the spike precursor prME and the nonstructural protein 1 (NS1) antigens of LIV. Three LIV strains of graded virulence for mice were used for challenge. One of these was a naturally occurring antibody escape variant. All vaccines tested induced humoral immunity but gave varying levels of protection against lethal challenge. Only recombinant SFV particles administered twice gave full protection against neuronal degeneration and encephalitis induced by two of the three challenge strains, and partial protection against the highly virulent strain, whereas the other vaccines tested gave lower levels of partial protection.
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Biochemical characterization of a hepatitis C virus RNA-dependent RNA polymerase mutant lacking the C-terminal hydrophobic sequence
The RNA-dependent RNA polymerase activity of hepatitis C virus is carried out by the NS5B protein. The full-length protein was previously purified as a non-fusion protein from insect cells infected with a recombinant baculovirus. The characterization is now described of a C-terminal hydrophobic domain deletion mutant of NS5B purified from E. coli. In addition to increased solubility, deletion of this sequence also positively affected the polymerase enzymatic activity. The efficiency of nucleotide polymerization of both the full-length and the C-terminal truncated enzymes were compared on homopolymeric template–primer couples as well as on RNA templates with heteropolymeric sequences. The largest difference in the polymerase activity was observed on the latter. On all the templates, the increased activity could be ascribed, at least in part, to enhanced template turnover of the deletion mutant with respect to the full-length enzyme. The elongation rates of the two enzyme forms were compared under single processive cycle conditions. Under these conditions, both the full-length and the deletion mutant were able to incorporate about 700 nt/min.
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Phylogenetic analysis of GBV-C/hepatitis G virus
Comparison of 33 epidemiologically distinct GBV-C/hepatitis G virus complete genome sequences suggests the existence of four major phylogenetic groupings that are equally divergent from the chimpanzee isolate GBV-Ctro and have distinct geographical distributions. These four groupings are not consistently reproduced by analysis of the virus 5′-noncoding region (5′-NCR), or of individual genes or subgenomic fragments with the exception of the E2 gene as a whole or of 200–600 nucleotide fragments from its 3′ half. This region is upstream of a proposed anti-sense reading frame and contains conserved potential RNA secondary structures that may be capable of directing the internal initiation of translation. Phylogenetic analysis of this region from certain South African isolates is consistent with previous analysis of the 5′-NCR suggesting that these belong to a fifth group. The geographical distribution of virus variants is consistent with a long evolutionary history that may parallel that of pre-historic human migrations, implying that the long-term evolution of this RNA virus is extremely slow.
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Phylogeny of the genus Flavivirus using complete coding sequences of arthropod-borne viruses and viruses with no known vector
Attempts to define the evolutionary relationships and origins of viruses in the genus Flavivirus are hampered by the lack of genetic information particularly amongst the non-vectored flaviviruses. Using a novel protocol for sequence determination, the first complete coding sequence of St Louis encephalitis virus and those of two representative non-vectored flaviviruses, Rio Bravo (isolated from bat) and Apoi (isolated from rodent), are reported. The encoded polyproteins of Rio Bravo and Apoi virus are the smallest described to date within the genus Flavivirus. The highest similarities with other flaviviruses were found in the NS3 and NS5 genes. The proteolytic cleavage sites for the viral serine protease were highly conserved among the flaviviruses completely sequenced to date. Comparative genetic amino acid alignments revealed that p-distance cut-off values of 0·330–0·470 distinguished the arthropod-borne viruses according to their recognized serogroups and Rio Bravo and Apoi virus were assigned to two distinct non-vectored virus groups. Within these serogroups, cladogenesis based on the complete ORF sequence was similar to trees based on envelope and NS5 sequences. In contrast, branching patterns at the deeper nodes of the tree were different from those reported in the previous study of NS5 sequences. The significance of these observations is discussed.
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Leader switching occurs during the rescue of defective RNAs by heterologous strains of the coronavirus infectious bronchitis virus
More LessA defective RNA (D-RNA), CD-61, derived from the Beaudette strain of the avian coronavirus infectious bronchitis virus (IBV), was rescued (replicated and packaged) using four heterologous strains of IBV as helper virus. Sequence analysis of the genomic RNA from the four heterologous IBV strains (M41, H120, HV10 and D207) identified nucleotide differences of up to 17% within the leader sequence and up to 4·3% within the whole of the adjacent 5′ untranslated region (UTR). Analysis of the 5′ ends of the rescued D-RNAs showed that the Beaudette leader sequence, present on the initial CD-61, had been replaced with the corresponding leader sequence from the helper IBV strain but the adjacent 5′ UTR sequence of the rescued D-RNAs corresponded to the original CD-61 Beaudette sequence. These results demonstrated that the phenomenon of leader switching previously identified for the coronaviruses murine hepatitis virus and bovine coronavirus (BCoV) also occurred during the replication of IBV D-RNAs. Three predicted stem–loop structures were identified within the 5′ UTR of IBV. Stem–loop I showed a high degree of covariance amongst the IBV strains providing phylogenetic evidence that this structure exists and is potentially involved in replication, supporting previous observations that a BCoV stem–loop homologue was essential for replication of BCoV defective interfering RNAs.
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Molecular epidemiology of coxsackievirus B4 and disclosure of the correct VP1/2Apro cleavage site: evidence for high genomic diversity and long-term endemicity of distinct genotypes
More LessGenetic diversity among 107 coxsackievirus B4 field isolates has been studied. These isolates included clinical and environmental isolates originating from Finland, the Netherlands and France, and also from several other countries, including the USA. Three genomic regions were used for phylogenetic analyses: the VP1/2A junction, the entire VP1 and the VP4/VP2 region. Alignment of the deduced amino acid sequence in the VP1/2A junction revealed extensive sequence variation at the previously proposed cleavage site. MS analysis of proteolytic fragments from VP1 revealed that the exact cleavage site is situated between amino acid residues Thr-849 and Gly-850. At least seven distinct genetic lineages, or genotypes, had been circulating in Europe during the period 1959–1998. Two genotypes were endemic in the Netherlands during most of the investigated period. Genetically closely related strains could be found in different countries, and different genotypes co-circulated at the same time in a given country. Clustering patterns were identical in the three genomic intervals. In the VP4/VP2 region, the intraserotypic variation approached interserotype variation. Sequence comparisons of the entire VP1 gene gave a reliable genetic identification of enterovirus serotype. It is suggested that, for genotype classification of previously serotyped coxsackievirus B4 isolates, comparison of VP1/2A sequences is sufficient, but for more detailed investigation of genetic relationships, and for ‘genetic serotyping’, the entire VP1 gene should be used. The VP4/VP2 region is less reliable for genetic serotyping and genotyping, although the primers are able to amplify many different serotypes.
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Biochemical characterization of salmon pancreas disease virus
Salmon pancreas disease virus (SPDV) has been shown to cause severe economic losses in farmed Atlantic salmon (Salmo salar) and has been reported to occur in Europe, Scandinavia and the United States. This paper describes the biochemical characterization of SPDV in terms of its RNA and protein composition. SPDV was purified by precipitation from infected Chinook salmon embryo (CHSE-214) cell-culture supernatant and sucrose density-gradient centrifugation. Fractions containing virus were identified by an immunodot blot assay using an SPDV-specific MAb. Two major proteins with molecular masses of approximately 55 and 50 kDa, putatively identified as the E1 and E2 alphavirus glycoproteins respectively, were detected when purified virus preparations were analysed by PAGE. Radiolabelling experiments indicated that SPDV infection of CHSE-214 cells did not shut-off host-cell protein synthesis, making attempts to identify virus-specific proteins unsuccessful. However, radioimmunoprecipitation assay (RIPA) experiments showed that two SPDV-specific MAbs reacted with a protein in the 50–55 kDa range. Northern blot hybridization with cloned cDNA probes indicated that infected cells contained RNA species of approximately 11·4 and 4 kb, which correspond to the genomic and subgenomic RNAs specified by SPDV. The results described are consistent with SPDV being characterized as an alphavirus.
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The C-terminal domain of rotavirus NSP5 is essential for its multimerization, hyperphosphorylation and interaction with NSP6
Rotavirus NSP5 is a non-structural phosphoprotein with putative autocatalytic kinase activity, and is present in infected cells as various isoforms having molecular masses of 26, 28 and 30–34 kDa. We have previously shown that NSP5 forms oligomers and interacts with NSP6 in yeast cells. Here we have mapped the domains of NSP5 responsible for these associations. Deletion mutants of the rotavirus YM NSP5 were constructed and assayed for their ability to interact with full-length NSP5 and NSP6 using the yeast two-hybrid assay. The homomultimerization domain was mapped to the 20 C-terminal aa of the protein, which have a predicted α-helical structure. A deletion mutant lacking the 10 C-terminal aa (ΔC10) failed to multimerize both in yeast cells and in an in vitro affinity assay. When transiently expressed in MA104 cells, NSP5 became hyperphosphorylated (30–34 kDa isoforms). In contrast, the ΔC10 mutant produced forms equivalent to the 26 and 28 kDa species, but was poorly hyperphosphorylated, suggesting that multimerization is important for this proposed activity of the protein. The interaction domain with NSP6 was found to be present in the 35 C-terminal aa of NSP5, overlapping the multimerization domain of the protein, and suggesting that NSP6 might have a regulatory role in the self-association of NSP5. NSP6 was also found to interact with wild-type NSP5, but not with its mutant ΔC10, in cells transiently transfected with plasmids encoding these proteins, confirming the relevance of the 10 C-terminal aa for the formation of the heterocomplex.
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Identification and differentiation of the nine African horse sickness virus serotypes by RT–PCR amplification of the serotype-specific genome segment 2
More LessThis paper describes the first RT–PCR for discrimination of the nine African horse sickness virus (AHSV) serotypes. Nine pairs of primers were designed, each being specific for one AHSV serotype. The RT–PCR was sensitive and specific, providing serotyping within 24 h. Perfect agreement was recorded between the RT–PCR and virus neutralization for a coded panel of 56 AHSV reference strains and field isolates. Serotyping was achieved successfully with live and formalin-inactivated AHSVs, with isolates of virus after low and high passage through either tissue culture or suckling mouse brain, with viruses isolated from widely separated geographical areas and with viruses isolated up to 37 years apart. Overall, this RT–PCR provides a rapid and reliable method for the identification and differentiation of the nine AHSV serotypes, which is vital at the start of an outbreak to enable the early selection of a vaccine to control the spread of disease.
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Subterminal viral DNA nucleotides as specific recognition signals for human immunodeficiency virus type 1 and visna virus integrases under magnesium-dependent conditions
More LessMany reports describe the characteristics of susceptible viral DNA substrates to various retroviral integrases during in vitro reactions in which manganese serves as the divalent cation cofactor for site-specific nicking. However, manganese is known to alter the specificity of some endonucleases and magnesium may be the divalent cation used during retroviral integration in vivo. To address these concerns, we identified conditions under which the integrases of human immunodeficiency virus type 1 and visna virus were optimally active with magnesium (the first time such activity was shown for visna virus integrase) and used these conditions to test the susceptibility of a series of oligodeoxynucleotide substrates. The data show that two base pairs immediately internal to the conserved CA dinucleotide near the termini of retroviral DNA are selectively recognized by the two integrases and that the final six base pairs of viral DNA contain sufficient sequence information for specific recognition and cleavage by each enzyme. The results validate the importance of the subterminal viral DNA positions even in the presence of magnesium and identify viral DNA positions that functionally interact with integrase. The data obtained under magnesium-dependent conditions, which were obtained with substrates containing single and multiple base-pair substitutions and two different retroviral integrases, are consistent with those previously obtained with manganese. Thus, the large body of manganese-dependent data identifying terminal viral DNA positions that are important in substrate recognition by various integrases likely reflects interactions that are biologically relevant.
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- Animal: DNA Viruses
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The non-essential UL50 gene of avian infectious laryngotracheitis virus encodes a functional dUTPase which is not a virulence factor
More LessThe DNA sequence of the infectious laryngotracheitis virus (ILTV) UL50, UL51 and UL52 gene homologues was determined. Although the deduced UL50 protein lacks the first of five conserved domains of the corresponding proteins of mammalian alphaherpesviruses, the ILTV gene product was also shown to possess dUTPase activity. The generation of UL50-negative ILTV mutants was facilitated by recombination plasmids encoding green fluorescent protein (GFP), and expression constructs of predicted transactivator proteins of ILTV (αTIF, ICP4) were successfully used to increase the infectivity of viral genomic DNA. A GFP-expressing UL50-deletion mutant of ILTV showed reduced cell-to-cell spread in vitro, and was attenuated in vivo. A similar deletion mutant without the foreign gene, however, propagated like wild-type ILTV in cell culture and was pathogenic in chickens. We conclude that the viral dUTPase is not required for efficient replication of ILTV in the respiratory tract of infected animals. The replication defect of the GFP-expressing ILTV recombinant is most likely caused by toxic effects of the reporter gene product, since spontaneously occurring inactivation mutants exhibited wild-type-like growth.
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Resistance of herpes simplex virus type 1 against different phosphonylmethoxyalkyl derivatives of purines and pyrimidines due to specific mutations in the viral DNA polymerase gene
More LessDrug-resistant strains of herpes simplex virus type 1 (HSV-1) were selected under the pressure of (S)-3-hydroxy-2-phosphonylmethoxypropyl (HPMP) derivatives of cytosine (HPMPC, cidofovir) and adenine (HPMPA) and 2-phosphonylmethoxyethyl (PME) derivatives of adenine (PMEA, adefovir) and 2,6-diaminopurine (PMEDAP). HPMPC-resistant (HPMPCr) and HPMPAr strains were cross-resistant to one another, but they remained sensitive to foscarnet (PFA), acyclovir (ACV) and the PME derivatives, while the PMEAr and PMEDAPr strains showed cross-resistance to PFA and ACV. The PMEAr, PMEDAPr and PFAr mutants all revealed a single nucleotide change resulting in a Ser-724 to Asn mutation within the conserved region II of the DNA polymerase. Two HPMPAr clones and one HPMPCr clone possessed single amino acid changes in the DNA polymerase (HPMPAr clone D1, Leu-1007 to Met; HPMPAr clone B5, Ile-1028 to Thr; HPMPCr clone C3, Val-573 to Met). The HPMPCr clone A4 contained two mutations, Ala-136 to Thr and Arg-700 to Met. The mutation at position 136, located outside the catalytic domain of the enzyme, was not detected in other HPMPCr clones, suggesting that this mutation may not be responsible for the resistant phenotype. Residue 573 is located within the 3′→5′ exonuclease editing domain close to the catalytically important residues Tyr-577 and Asp-581. Similarly, residue 700 is located in the palm subdomain of the catalytic domain, adjacent to the Asp residues 717, 886 and 888 that are vital for polymerase activity. The HPMPAr mutations at residues 1007 and 1028, beyond the last conserved region, still fall within the thumb subdomain of the catalytic domain. The different drug-resistant mutants varied in neurovirulent behaviour, the HPMPCr strains showing reduced neurovirulence compared with the wild-type.
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Expression from the herpes simplex virus type 1 latency-associated promoter in the murine central nervous system
More LessHerpes simplex virus type 1 (HSV-1) establishes latency in neurones of both the central (CNS) and peripheral nervous system and can be used to drive long-term expression of the lacZ reporter gene by insertion of an encephalomyocarditis virus IRES-linked gene 1·5 kb downstream of the latency-associated transcript (LAT) start site. However, the kinetics of LAT promoter (LAP) activity, and its ability to function in all neuronal types within the CNS has not been studied in detail. In order to address these issues, mice were infected via the ear pinna with 2×106 p.f.u. of either SC16-LβA, which contains an IRES-linked lacZ under the control of LAP, or SC16-C3b, which expresses LacZ under the control of the human cytomegalovirus immediate early (HCMV-IE) promoter. Three to five animals from each group were sampled over a time-course from 5 days to 1 year post-infection (p.i.), and brainstem and spinal cord sections were examined histochemically for LacZ expression. We found that HCMV-IE promoter activity could be detected within distinct CNS regions from 5 to 15 days p.i. In contrast, LAP-driven LacZ expression was first detected at 7 days p.i. and persisted for at least 1 year. At times up to 34 days p.i., LAP activity was seen in similar regions of the CNS as those which were positive for HCMV-IE promoter activity during the acute stage of infection. After 34 days, however, the numbers of cells in which the LAP was active decreased and labelled motorneurones were predominantly detected in the facial and hypoglossal nuclei and occasionally also in the ventral spinal cord. These results suggest that following the establishment of latency in the CNS, the efficiency of long-term LAP-mediated gene expression may be influenced by the neuronal cell type in which latency is established.
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Suppressive effects of human herpesvirus-6 on thrombopoietin-inducible megakaryocytic colony formation in vitro
Two clinical observations, the association of human herpesvirus-6 (HHV-6) with delayed engraftment after stem cell transplantation and thrombocytopenia concomitant with exanthema subitum, prompted us to evaluate the suppressive effects of HHV-6 on thrombopoiesis in vitro. Different culture conditions for thrombopoietin (TPO)-inducible colonies in semi-solid matrices were examined. Using cord blood mononuclear cells as the source of haematopoietic progenitors, two types of colonies, megakaryocyte colony-forming units (CFU-Meg) and non-CFU-Meg colonies, were established. The former colonies were identified by the presence of cells with translucent cytoplasm and highly refractile cell membrane, most of which were positive for the CD41 antigen. Although the plating efficiency of both types was much higher under serum-containing conditions than under serum-free conditions, the proportion of CFU-Meg to non-CFU-Meg colonies was consistently higher under serum-free conditions. The plating efficiency of CFU-Meg colonies was doubled by adding stem cell factor to the serum-free matrix. The effects of two variants of HHV-6 (HHV-6A and 6B) and human herpesvirus-7 (HHV-7) on TPO-inducible colonies were then compared. HHV-6B inhibited both CFU-Meg and non-CFU-Meg colony formation under serum-free and serum-containing conditions. HHV-6A had similar inhibitory effects. In contrast, HHV-7 had no effect on TPO-inducible colony formation. Heat-inactivation and ultra-filtration of the virus sample completely abolished the suppressive effect. After infection of CD34+ cells with HHV-6, the viral genome was consistently detected by in situ hybridization. These data suggest that the direct effect of HHV-6 on haematopoietic progenitors is one of the major causes of the suppression of thrombopoiesis.
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Morphogenesis and release of fowlpox virus
More LessRelease of fowlpox virus (FWPV) as extracellular enveloped virus (EEV) appears to proceed both by the budding of intracellular mature virus (IMV) through the plasma membrane and by the fusion of intracellular enveloped virus (IEV) with the plasma membrane. Based on the frequency of budding events compared to wrapping events observed by electron microscopy, FWPV FP9 strain seems to exit chick embryo fibroblast cells predominantly by budding. In contrast to vaccinia virus (VV), the production of FWPV extracellular virus particles is not affected by N 1-isonicotinoyl-N 2-3-methyl-4-chlorobenzoylhydrazine (IMCBH). Comparison of the sequence of the VV F13L gene product with its FWPV orthologue showed a mutation, in the fowlpox protein, at the residue involved in IMCBH resistance in a mutant VV. Glucosamine, monensin or brefeldin A did not have any specific effect on FWPV extracellular virus production. Cytochalasin D, which inhibits the formation of actin filaments, reduces the production of extracellular virus particles by inhibiting the release of cell-associated enveloped virus (CEV) particles from the plasma membrane. Involvement of actin filaments in this mechanism is further supported by the co-localization of actin with viral particles close to the plasma membrane in the absence of cytochalasin D. Actin is also co-localized with virus factories.
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