- Volume 81, Issue 5, 2000
Volume 81, Issue 5, 2000
- Animal: DNA Viruses
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Agnoprotein 1a and agnoprotein 1b of avian polyomavirus are apoptotic inducers
More LessAvian polyomavirus (APV) causes an acute fatal disease in a variety of avian species. DNA laddering indicating apoptosis was demonstrated in APV-infected chicken embryo (CE) cells. DNA laddering, however, was not observed in Vero cells infected with mammalian polyomavirus simian virus 40. Expression of APV agnoprotein 1a and agnoprotein 1b induced apoptosis in insect cells and CE cells. An APV full-length plasmid transfected in CE cells induced apoptosis, and infectious virus was produced. After transfection of CE cells with a plasmid containing a mutated initiation codon for agnoprotein 1a and agnoprotein 1b, however, a considerably lower number of apoptotic cells was observed, and no infectious progeny was produced.
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Evolution of human polyomavirus JC
More LessMore than 20 near full-length genome sequences have been reported for human polyomavirus JC (JCV). These have previously been classified into seven genotypes, and additional subtypes, which exhibit geographical associations. One of these genotypes, Type 4, has been suggested to be a recombinant of Types 1 and 3. We have investigated the pattern of diversity, and evolutionary relationships, among these sequences. In direct contradiction of a recent report, we found that different phylogenetic methods gave consistent results for the phylogenetic relationships among strains. The single known strain representing Type 5 was shown to be a mosaic of sequences from Types 2 and 6, although whether this recombination occurred in vivo or in vitro is not clear. In contrast, there was no substantial evidence that Type 4 strains are recombinant; rather they seem to be simply divergent examples of Type 1. On the assumption that the major genotypes of JCV diverged with human populations, the rate of synonymous nucleotide substitution was estimated to be around 4×10−7 per site per year, about 10 times higher than a previous estimate for primate polyomaviruses.
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Neuronal pathways for the propagation of herpes simplex virus type 1 from one retina to the other in a murine model
More LessHerpetic retinitis in humans is characterized by a high frequency of bilateral localization. In order to determine the possible mechanisms leading to bilateral retinitis, we studied the pathways by which herpes simplex virus type 1 (HSV-1) is propagated from one retina to the other after intravitreal injection in mice. HSV-1 strain SC16 (90 p.f.u.) was injected into the vitreous body of the left eye of BALB/c mice. Animals were sacrificed 1, 2, 3, 4 and 5 days post-inoculation (p.i.). Histological sections were studied by immunochemical staining. Primary retinitis in the inoculated eye (beginning 1 day p.i.) was followed by contralateral retinitis (in the uninoculated eye) starting at 3 days p.i. Infected neurons of central visual pathway nuclei (lateral geniculate nuclei, suprachiasmatic nuclei and pretectal areas) were detected at 4 days p.i. Iris and ciliary body infection was minimal early on, but became extensive thereafter and was accompanied by the infection of connected sympathetic and parasympathetic pathways. The pattern of virus propagation over time suggests that the onset of contralateral retinitis was mediated by local (non-synaptic) transfer in the optic chiasm from infected to uninfected axons of the optic nerves. Later, retinopetal transneuronal propagation of the virus from visual pathways may have contributed to increase the severity of contralateral retinitis.
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Detection of lymphocytes productively infected with Epstein–Barr virus in non-neoplastic tonsils
Epstein–Barr virus (EBV) persists for life in the infected host. Little is known about EBV reactivation and regulation of virus persistence in healthy individuals. We examined tonsils of chronic tonsillitis patients to detect EBV transcripts, EBV genomes and lytic proteins. LMP1 transcripts were observed in 11 of 15 specimens and BZLF1 transcripts were detected in six. Multiple copies of EBV genome equivalents per cell, and ZEBRA- and viral capsid antigen-positive cells were also detected in tonsillar lymphocytes. These results indicate that EBV productively infected cells may survive in the face of immune surveillance in the tonsils. Thus, EBV replication may occur in tonsillar lymphocytes, and tonsillar lymphoid tissues may play a role in the maintenance of EBV load in vivo.
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Molecular characterization of Kaposi’s sarcoma-associated herpesvirus/human herpesvirus-8 strains from Russia
We report the molecular characterization, with subtyping of both K1 and K14.1/K15 genomic regions, of seven new human herpesvirus-8 (HHV-8) strains from Russian patients with classical Kaposi’s sarcoma. Phylogenetic studies, based on the complete K1 gene/protein analysis, indicate that six of these strains belong to the A subtype, with one belonging to the A4 group and exhibiting a unique deletion of 19 amino acids in the VR2 region at position 186–204. PCR-based studies of the K14.1/K15 genomic region indicate that four of the new strains were of the M subtype while three belonged to the P subtype. Our study indicates an important genetic diversity of the HHV-8 strains currently present in Russia, including a new peculiar strain possessing a unique deletion in the VR2 segment, and confirms the absence of correlation between the K1 and K14.1/K15 molecular subtypes, as M and P genotypes can be observed in the A K1 subtype.
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Ectromelia, vaccinia and cowpox viruses encode secreted interleukin-18-binding proteins
More LessInterleukin-18 (IL-18) is a proinflammatory cytokine that plays a key role in the activation of natural killer and T helper 1 cell responses principally by inducing interferon-γ (IFN-γ). Human and mouse secreted IL-18-binding proteins (IL-18BPs) have recently been described which block IL-18 activity but have no sequence similarity to membrane IL-18 receptors. Several poxvirus genes encode proteins with sequence similarity to IL-18BPs. Here we show that vaccinia, ectromelia and cowpox viruses secrete from infected cells a soluble IL-18BP (vIL-18BP) that may modulate the host antiviral response. The ectromelia virus protein was found to block NF-κB activation and induction of IFN-γ in response to IL-18. The highly attenuated vaccinia virus modified virus Ankara encodes IL-18-binding activity, and thus deletion of the vIL-18BP may improve further the safety and immunogenicity of this promising human vaccine candidate. We confirm that molluscum contagiosum virus, a molluscipoxvirus that produces small skin tumours in immunocompetent individuals and opportunistic infections in immunodeficient AIDS patients, also encodes a related, larger vIL-18BP (gene MC54L). This protein may contribute to the lack of inflammatory response characteristic of molluscum contagiosum virus lesions. The expression of vIL-18BPs by distinct poxvirus genera that cause local or general viral dissemination, or persistent or acute infections in the host, emphasizes the importance of IL-18 in response to viral infections.
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The punctate sites of accumulation of vaccinia virus early proteins are precursors of sites of viral DNA synthesis
More LessSeveral vaccinia virus early proteins (encoded by genes B1R, H5R and I3L) synthesized in the presence of an inhibitor of DNA synthesis localize, at least in part, to punctate inclusions that are visible by immunofluorescence in the cytoplasm of poxvirus-infected cells. It is shown that these inclusions contain DNA (visualized by DAPI staining of the infected cells) and that the number of inclusions is proportional to the amount of input virus. Their mean diameter (about 680 nm) was larger than that of purified vaccinia virus particles. When the inhibition of DNA synthesis was reversed, incorporation of BrdU into the B1R particles was demonstrated after labelling for 30 min, suggesting that these cytoplasmic focal sites correspond to viral DNA replication complexes that have initiated normally but are inhibited at the step of DNA chain elongation. These experiments suggest strongly that these inclusions are the precursors of the virosomes.
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- Insect
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Mutagenesis of the active site coding region of the Autographa californica nucleopolyhedrovirus chiA gene
More LessThe chitinase of Autographa californica nucleopolyhedrovirus (AcMNPV) is required for the characteristic liquefaction of baculovirus-infected insect larvae. Alignments of the putative active sites of a range of chitinases revealed two highly conserved residues, glutamate and aspartate, which have been proposed to constitute the catalytic residues of the active site. These residues were mutated in the AcMNPV chitinase. Three recombinant viruses were generated, AcchiA D311G, AcchiA E315G and AcchiA D311G E315G, which contained mutations at either the glutamate, the aspartate or both. It was demonstrated that chitinase protein production was unaffected by the mutation of these residues. However, mutation of both residues resulted in the attenuation of chitinolytic activity and the cessation of liquefaction of Trichoplusia ni larvae infected with AcchiA D311G E315G. Mutagenesis of the glutamate residue led to a reduction in exochitinase activity and a delay in the appearance of endochitinase activity. In addition, larvae infected with this virus, AcchiA E315G, liquefied more slowly than those larvae infected with wild-type AcMNPV. Mutagenesis of the aspartate residue resulted in a reduction of exochitinase activity but an unexpected enhancement of endochitinolytic activity. Liquefaction of AcchiA D311G-infected larvae was observed at the same time as that of AcMNPV-infected larvae.
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