Cell killing by spleen necrosis virus is correlated with a transient accumulation of spleen necrosis virus DNA.

Spleen necrosis virus productively infects avian and rat cells. The average number of molecules of unintegrated and integrated viral DNA in cells at different times after infection was determined by hybridization and transfection assays. Shortly after infection, there was a transient accumulation of an average of about 150 to 200 molecules of unintegrated linear spleen necrosis virus DNA per chicken, turkey, or pheasant cell. No such accumulation was seen in infected rat cells. Soon after infection there was in chicken cells, but not inturkey, pheasant, or rat cells, also a transient integration of an average of 35 copies of viral DNA per cell. By 10 days after infection, the majority of this integrated viral DNA was lost from the population of infected chicken cells. At the same time, the majority of the unintegrated viral DNA was also lost from infected chicken, turkey, and pheasant cells. The transient cytopathic effect seen in these infected cells also occurred at this time. Late after infection about five copies of apparently nondefective spleen necrosis proviruses were stably integrated at multiple sites in chicken, turkey, pheasant, and rat DNA. These results demonstrate a correlation between the transient accumulation of large numbers of spleen necrosis virus DNA molecules and the transient occurrence of cytopathic effects.     

A double hairpin structure is necessary for the efficient encapsidation of spleen necrosis virus retroviral RNA.

We conducted a mutational analysis within the previously defined encapsidation sequence (E) for spleen necrosis virus (SNV), an avian retrovirus. We found that two regions are necessary for efficient SNV replication. The first region is a double hairpin structure as proposed by Konings et al. (1992, J. Virol., 66, 632-640); the second region is located downstream of the hairpins. We showed further that the double hairpin structure is required for efficient SNV RNA encapsidation. Our work is the first to demonstrate, via linker-scanning and site-directed mutagenesis, that a specific RNA secondary structure is required for the encapsidation of retroviral RNA. Analysis of a series of mutations within the E region indicates (i) that preserving the secondary structure of the two hairpins is important for efficient encapsidation and (ii) that the stem regions of the hairpins contain specific sequences critical for encapsidation. Within the hairpins, the presence of at least one of the two conserved GACG four-residue loops, but not the moderately conserved bulge sequence of the first hairpin, is crucial for function. The function of the hairpins is independent of the relative order of the two hairpins. However, the two hairpins are not redundant and are not functionally identical. Replacement of SNV double hairpin sequences with those of Moloney murine leukemia virus (M-MLV) has no detectable effect on the replication of SNV-based retrovirus vectors with reticuloendotheliosis virus strain A (REV-A) helper virus. Furthermore, replacement of the entire E sequence of SNV with that of Moloney murine sarcoma virus (M-MSV) and M-MLV results in retroviral vectors that replicate as well as SNV vectors with wild type SNV E. This result indicates that the encapsidation sequences of M-MSV/M-MLV and SNV are not virus specific and that, during packaging of SNV and MLV RNA with viral proteins from REV-A, the encapsidation sequences are recognized largely by their secondary or tertiary structures.     

ICOS-B7 homologous protein interactions are necessary for mercury-induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we explore the role of one of the members of the CD28-B7 costimulation families, ICOS-B7 homologous protein (B7h), in the regulation of mercury-induced autoimmunity. The expression of ICOS on T cells was more enhanced in susceptible A.SW mice than in non-responsive C57BL/6 and DBA/2 mice after HgCl(2) treatment. Furthermore, in A.SW mice treated with HgCl(2), administration of a blocking anti-ICOS Ab effectively inhibited anti-nucleolar autoantibodies and total serum IgE production. Taken together, these results indicate that the ICOS-B7h costimulation pathway is required for this autoimmune syndrome and suggest that targeting this pathway might have therapeutic benefits for human autoimmune diseases.     

Polypeptide composition of spleen necrosis virus, a reticuloendotheliosis virus.

The polypeptide composition of virions of spleen necrosis virus, a reticuloendotheliosis virus, was determined using electrophoresis on sodium dodecyl sulfate-containing, 10 percent polyacrylamide gels. Ten polypeptides were resolved. Four of these were present in minor and somewhat variable amounts. Two proteins, gp71 and gp22, contained D-glucosamine and were located on the outer surface of the lipid envelope, as demonstrated by lactoperoxidase-catalyzed iodination and by bromelain digestion. The results suggest that two of the minor proteins, p36 and p26, were also located on the outer surface, although they lacked D-glucosamine. Treatment of the virus with 0.25 percent Nonidet P-40 and 1 percent dithiothreitol produced a subparticle with a buoyant density of approximately 1.31 g/cm-3. This particle was relatively enriched with polypeptides p77, p62, and p50 and contained small amounts of three other polypeptides.     

The ribosomal fraction mediates the translational enhancement associated with the 5''-leader of tobacco mosaic virus.

The omega sequence at the 5'-terminus of tobacco mosaic virus (TMV) RNA acts as a translational enhancer. The differential in omega-associated translational enhancement between the in vitro translation system derived from wheat germ (WG) and that from rabbit reticulocytes (MDL) was exploited to identify that lysate component which was responsible for a lysate's characteristic response to omega. Using fractionated MDL and WG lysates, which were reconstituted in various combinations, the high salt-washed ribosomal fraction was determined to be the responsive element in a lysate. Analysis of omega's ability to enhance translation was greatest at low mRNA and high ribosomal concentrations and to occur in the early phase of an in vitro translation assay. Translation of omega-containing CAT mRNA was more sensitive to the presence of micrococcal nuclease than CAT mRNA without an omega. In substitution experiments, WG ribosomes functioned at much reduced efficiency in MDL as did MDL ribosomes in WG lysate. The initiation factor-containing fraction of one system could not, as a whole, functionally replace that of the other and actually acted to inhibit translation in the heterologous system.     

Ribonucleotides in unintegrated linear spleen necrosis virus DNA.

The structure of unintegrated spleen necrosis virus DNA was characterized by using various chemical and enzymatic treatments in conjunction with denaturing gels and nucleic acid hybridization probes. Throughout the course of the viral infection, the predominant species of viral DNA was that of a linear double-stranded molecule containing ribonucleotides covalently joined to the DNA. The majority of both - and + strands were continuous. The ribonucleotide linkages appeared to be relatively short, and the base composition and distribution of the ribonucleotide linkages were heterogeneous. On the average, the - strand had fewer of the ribonucleotide linkages than did the strand. Viral DNA containing ribonucleotide linkages was infectious in DNA transfection assays. The structure of spleen necrosis virus DNA was different from that of Schmidt-Ruppin Rous sarcoma virus-D, and mixed infections demonstrated that the observed differences are a result of cis-acting functions.     

Glycoproteins required for entry are not necessary for egress of pseudorabies virus

In the current perception of the herpesvirus replication cycle, two fusion processes are thought to occur during entry and nuclear egress. For penetration, glycoproteins gB and gH/gL have been shown to be essential, whereas a possible role of these glycoproteins in nuclear egress remains unclear. Viral envelope glycoproteins have been detected by immunolabeling in the nuclear membrane as well as in primary enveloped particles in several herpesviruses, indicating that they might be involved in the fusion process. Moreover, a herpes simplex virus type 1 mutant simultaneously lacking gB and gH was described to be deficient in nuclear egress (A. Farnsworth, T. W. Wisner, M. Webb, R. Roller, G. Cohen, R. Eisenberg, and D. C. Johnson, Proc. Natl. Acad. Sci. USA 104:10187-10192, 2007). To analyze the situation in the related alphaherpesvirus pseudorabies virus (PrV), mutants carrying single and double deletions of glycoproteins gB, gD, gH, and gL were constructed and characterized. We show here that the simultaneous deletion of gB and gD, gB and gH, gD and gH, or gH and gL has no detectable effect on PrV egress, implying that none of these glycoproteins either singly or in the tested combinations is required for nuclear egress. In addition, immunolabeling studies using different mono- or polyclonal sera raised against various PrV glycoproteins did not reveal the presence of viral glycoproteins in the inner nuclear membrane or in primary virions. Thus, our data strongly suggest that different fusion mechanisms are active during virus entry and egress.     

Cap-independent translational enhancement of turnip crinkle virus genomic and subgenomic RNAs

The presence of translational control elements and cap structures has not been carefully investigated for members of the Carmovirus genus, a group of small icosahedral plant viruses with positive-sense RNA genomes. In this study, we examined both the 5' and 3' untranslated regions (UTRs) of the turnip crinkle carmovirus (TCV) genomic RNA (4 kb) as well as the 5' UTR of the coat protein subgenomic RNA (1.45 kb) for their roles in translational regulation. All three UTRs enhanced translation of the firefly luciferase reporter gene to different extents. Optimal translational efficiency was achieved when mRNAs contained both 5' and 3' UTRs. The synergistic effect due to the 5'-3' cooperation was at least fourfold greater than the sum of the contributions of the individual UTRs. The observed translational enhancement of TCV mRNAs occurred in a cap-independent manner, a result consistent with the demonstration, using a cap-specific antibody, that the 5' end of the TCV genomic RNA was uncapped. Finally, the translational enhancement activity within the 5' UTR of 1.45-kb subgenomic RNA was shown to be important for the translation of coat protein in protoplasts and for virulent infection in Arabidopsis plants.     

Antiviral antibodies are necessary for control of simian immunodeficiency virus replication

To better define the role of B cells in the control of pathogenic simian immunodeficiency virus (SIV) replication, six rhesus monkeys were depleted of B cells by intravenous infusion of rituximab (anti-CD20) 28 days and 7 days before intravaginal SIVmac239 inoculation and every 21 days thereafter until AIDS developed. Although the blood and tissues were similarly depleted of B cells, anti-SIV immunoglobulin G (IgG) antibody responses were completely blocked in only three of the six animals. In all six animals, levels of viral RNA (vRNA) in plasma peaked at 2 weeks and declined by 4 weeks postinoculation (PI). However, the three animals prevented from making an anti-SIV antibody response had significantly higher plasma vRNA levels through 12 weeks PI (P = 0.012). The remaining three B-cell-depleted animals made moderate anti-SIV IgG antibody responses, maintained moderate plasma SIV loads, and showed an expected rate of disease progression, surviving to 24 weeks PI without developing AIDS. In contrast, all three of the B-cell-depleted animals prevented from making anti-SIV IgG responses developed AIDS by 16 weeks PI (P = 0.0001). These observations indicate that antiviral antibody responses are critical in maintaining effective control of SIV replication at early time points postinfection.     

Analysis of translational products of Friend strain of spleen focus-forming virus.

We have analyzed normal rat kidney cells nonproductively infected with the Friend strain of spleen focus-forming virus (SFFV) for the presence of murine leukemia virus-specific type C viral proteins. SFFV was found to code for the p15 and p12 proteins of Friend-murine leukemia virus as determined by immunological typing of their antigenic determinants. Molecular-size analysis of p15 and p12 proteins in SFFV nonproductively infected normal rat kidney cells indicated that these proteins are translated as parts of polyprotein molecules. The apparent molecular weights of the polypeptides bearing p12 antigenic determinants revealed the presence of translational products of the SFFV genome that could not be accounted for by know type C virus helper structural proteins.     

Purification and properties of spleen necrosis virus DNA polymerase.

DNA polymerase was purified to apparent electrophoretic homogeneity from virions of spleen necrosis virus (SNV). (SNV is a member of the reticuloendotheliosis group of avian ribodeoxyviruses). The SNV DNA polymerase appears to consist of a single polypeptide with a molecular weight of 68,000. The SNV DNA polymerase has a preference for Mn2+ for DNA synthesis with an RNA template and Mg2+ for DNA synthesis with a deoxyribohomopolymer template. At the optimum concentrations of divalent cation, the relative rates of DNA synthesis by SNV DNA polymerase with different template.primers were similar to the relative rates of DNA synthesis by an avian leukosis virus DNA polymerase, with the exception of a lower relative rate of DNA synthesis by SNV DNA polymerase with SNV RNA. However, in contrast to DNA synthesized by the avian leukosis virus DNA polymerase with a SNV RNA template, DNA synthesized by SNV DNA polymerase with an SNV RNA template did not hybridize to the SNV RNA. SNV DNA polymerase has RNase H activity which is antigenically distinct from the RNase H activity of avian leukosis-sarcoma virus DNA polymerase.     

Smallpox vaccine-induced antibodies are necessary and sufficient for protection against monkeypox virus

Vaccination with live vaccinia virus affords long-lasting protection against variola virus, the agent of smallpox. Its mode of protection in humans, however, has not been clearly defined. Here we report that vaccinia-specific B-cell responses are essential for protection of macaques from monkeypox virus, a variola virus ortholog. Antibody-mediated depletion of B cells, but not CD4+ or CD8+ T cells, abrogated vaccine-induced protection from a lethal intravenous challenge with monkeypox virus. In addition, passive transfer of human vaccinia-neutralizing antibodies protected nonimmunized macaques from severe disease. Thus, vaccines able to induce long-lasting protective antibody responses may constitute realistic alternatives to the currently available smallpox vaccine (Dryvax).