Basis for Variable Response of Arboviruses to Guanidine Treatment

The effect of guanidine on the replication of the group A arboviruses, Sindbis virus, and Semliki Forest virus (SFV) was studied. Guanidine rapidly, but reversibly, inhibited SFV ribonucleic acid (RNA) synthesis. The synthesis of all species of viral RNA was inhibited, but that of ribonuclease-resistant forms was least affected. This inhibition occurred when the drug was added at any point during the log phase of virus growth. The growth of SFV was also markedly inhibited, but Sindbis virus growth was unimpaired. Infection of guanidine-treated cells with the viruses together resulted in a significant inhibition of the yields of both. It appears that, in the case of Sindbis virus, viral RNA is ordinarily produced in such excess that inhibition of its synthesis does not reduce virus yields. In the case of SFV, guanidine also markedly distorts the pattern of RNA synthesis by greatly decreasing the production of the 26S interjacent RNA form. This may account for the observed inhibition of SFV growth in the presence of guanidine.     

Comparative Effects of β-Propiolactone on Mice, Mouse-derived Cell Cultures, and Venezuelan Equine Encephalomyelitis Virus

Studies were made comparing the toxicity of β-propiolactone (BPL) for mammalian (mouse) cells in vitro and for mice and for Venezuelan equine encephalomyelitis (VEE) virus which is highly cytopathogenic for each. The mammalian cells grown in tissue culture were found to be adversely affected by BPL in concentrations ranging from 0.001 to 0.1 mg/ml of supernatant fluid. The difference in response was influenced by the menstruum in which the BPL was suspended and the difference in cell types tested. Tenfold less BPL appeared to be required to destroy the cells when it was suspended in a balanced salt solution than when it was suspended in protein-containing solutions such as beef heart infusion broth or medium 199 plus 20% horse serum. Secondary embryonic mouse lung cells seemed slightly more adversely affected by BPL than the established embryonic lung or L cells. BPL given to mice by intranasal instillation and by intracerebral injection was lethal to half of the animals within 2 days at doses of 0.31 and 0.39 mg, respectively. Higher concentrations of BPL were required to rapidly inactivate the virus in vitro than were required to kill mice or to cause a toxic effect on cells in culture. It required 10 mg/ml of BPL to completely inactivate a high-titered VEE virus preparation in 5 min and 1 mg/ml to inactivate most, but not all, of the virus in 15 min. A concentration of 0.1 mg/ml of BPL had only a slight effect on the virus after a period as long as 60 min. Evidence is presented indicating that simultaneous inactivation of all of the properties of the VEE virus particles by BPL aerosols did not occur at the same time but that, after treatment, the virus possessed a limited ability to immunize mice despite a loss in infectivity.     

Temperature-sensitive Steps in the Biosynthesis of Venezuelan Equine Encephalitis Virus

In contrast to Eastern equine encephalitis virus, the replication of Venezuelan equine encephalitis (VEE) virus was strongly inhibited at 44 C in chick embryo cells. The inhibited steps were analyzed by shifting the incubating temperatures up or down, and by determining during the shifts the rate and extent of infectious ribonucleic acid (RNA) synthesis, intact virus synthesis, and formation of complement-fixing antigen or of antigen detectable by a direct fluorescent-antibody technique. The inhibition appeared to be due to two temperature-sensitive steps involved in the synthesis of VEE virus in chick embryo cells. The first step of inhibition at 44 C occurred early in virus replication and could be completely reversed simply by transferring cultures to 37 C. The inhibition appeared to take place at some point between the time when the virus entered the cell and was uncoated and the beginning of viral RNA synthesis. The second temperature-sensitive step in VEE virus synthesis was irreversible; it occurred at a point after the synthesis of viral RNA, and before the formation of virus protein measured as complement-fixing antigen or as antigen that could be stained with fluorescent antibody.     

Noncytopathic replication of Venezuelan equine encephalitis virus and eastern equine encephalitis virus replicons in Mammalian cells

Venezuelan equine encephalitis (VEE) and eastern equine encephalitis (EEE) viruses are important, naturally emerging zoonotic viruses. They are significant human and equine pathogens which still pose a serious public health threat. Both VEE and EEE cause chronic infection in mosquitoes and persistent or chronic infection in mosquito-derived cell lines. In contrast, vertebrate hosts infected with either virus develop an acute infection with high-titer viremia and encephalitis, followed by host death or virus clearance by the immune system. Accordingly, EEE and VEE infection in vertebrate cell lines is highly cytopathic. To further understand the pathogenesis of alphaviruses on molecular and cellular levels, we designed EEE- and VEE-based replicons and investigated their replication and their ability to generate cytopathic effect (CPE) and to interfere with other viral infections. VEE and EEE replicons appeared to be less cytopathic than Sindbis virus-based constructs that we designed in our previous research and readily established persistent replication in BHK-21 cells. VEE replicons required additional mutations in the 5' untranslated region and nsP2 or nsP3 genes to further reduce cytopathicity and to become capable of persisting in cells with no defects in alpha/beta interferon production or signaling. The results indicated that alphaviruses strongly differ in virus-host cell interactions, and the ability to cause CPE in tissue culture does not necessarily correlate with pathogenesis and strongly depends on the sequence of viral nonstructural proteins.     

Comparison of the effects of Sindbis virus and Sindbis virus replicons on host cell protein synthesis and cytopathogenicity in BHK cells.

Infection of BHK cells by Sindbis virus leads to rapid inhibition of host cell protein synthesis and cytopathic effects (CPE). We have been studying these events to determine whether the expression of a specific viral gene is required and, in the present study, have focused our attention on the role of the structural proteins--the capsid protein and the two membrane glycoproteins. We tested a variety of Sindbis viruses and Sindbis virus replicons (virus particles containing an RNA that is self-replicating but with some or all of the viral structural protein genes deleted) for their abilities to inhibit host cell protein synthesis and cause CPE in infected BHK cells. Our results show that shutoff of host cell protein synthesis occurred in infected BHK cells when no viral structural proteins were synthesized and also under conditions in which the level of the viral subgenomic RNA was too low to be detected. These results support the conclusion that the early steps in viral gene expression are the ones required for the inhibition of host cell protein synthesis in BHK cells. In contrast, the Sindbis viruses and Sindbis virus replicons were clearly distinguished by the time at which CPE became evident. Viruses that synthesized high levels of the two membrane glycoproteins on the surface of the infected cells caused a rapid (12 to 16 h postinfection) appearance of CPE, and those that did not synthesize the glycoprotein spikes showed delayed (30 to 40 h) CPE.     

Replication of modified vaccinia virus Ankara in primary chicken embryo fibroblasts requires expression of the interferon resistance gene E3L

Highly attenuated modified vaccinia virus Ankara (MVA) serves as a candidate vaccine to immunize against infectious diseases and cancer. MVA was randomly obtained by serial growth in cultures of chicken embryo fibroblasts (CEF), resulting in the loss of substantial genomic information including many genes regulating virus-host interactions. The vaccinia virus interferon (IFN) resistance gene E3L is among the few conserved open reading frames encoding viral immune defense proteins. To investigate the relevance of E3L in the MVA life cycle, we generated the deletion mutant MVA-DeltaE3L. Surprisingly, we found that MVA-DeltaE3L had lost the ability to grow in CEF, which is the first finding of a vaccinia virus host range phenotype in this otherwise highly permissive cell culture. Reinsertion of E3L led to the generation of revertant virus MVA-E3rev and rescued productive replication in CEF. Nonproductive infection of CEF with MVA-DeltaE3L allowed viral DNA replication to occur but resulted in an abrupt inhibition of viral protein synthesis at late times. Under these nonpermissive conditions, CEF underwent apoptosis starting as early as 6 h after infection, as shown by DNA fragmentation, Hoechst staining, and caspase activation. Moreover, we detected high levels of active chicken alpha/beta IFN (IFN-alpha/beta) in supernatants of MVA-DeltaE3L-infected CEF, while moderate IFN quantities were found after MVA or MVA-E3rev infection and no IFN activity was present upon infection with wild-type vaccinia viruses. Interestingly, pretreatment of CEF with similar amounts of recombinant chicken IFN-alpha inhibited growth of vaccinia viruses, including MVA. We conclude that efficient propagation of MVA in CEF, the tissue culture system used for production of MVA-based vaccines, essentially requires conserved E3L gene function as an inhibitor of apoptosis and/or IFN induction.     

Venezuelan equine encephalomyelitis virus structure and its divergence from old world alphaviruses

Although alphaviruses have been extensively studied as model systems for the structural organization of enveloped viruses, no structures exist for the phylogenetically distinct eastern equine encephalomyelitis (EEE)-Venezuelan equine encephalomyelitis (VEE) lineage of New World alphaviruses. Here we report the 25-A structure of VEE virus, obtained from electron cryomicroscopy and image reconstruction. The envelope spike glycoproteins of VEE virus have a T=4 icosahedral arrangement, similar to that observed in Old World Sindbis, Semliki Forest, and Ross River alphaviruses. However, VEE virus has pronounced differences in its nucleocapsid structure relative to nucleocapsid structures repeatedly observed in Old World alphaviruses.     

Kinetics of herpes simplex virus photoinhibition by haematoporphyrin in both diploid and heteroploid cells

The kinetics of inhibition of herpes simplex virus type 1 (HSV 1) on both diploid (CEF) and heteroploid cells (HEp2) by light-irradiated haematoporphyrin (HP) was studied. The inactivation of HSV1 by HP was drug-dose dependent and light-irradiation dependent; the viruses grown in heteroploid cells being in all cases more sensitive to inhibition than viruses grown in diploid cells. Cell toxicity by HP was markedly more evident on HEp2 cells than on CEF. The highest viral sensitivity to photodynamic inactivation by HP was found to be between the 4th and the 5th hour after cell infection, when the viral DNA synthesis is at its peak and before it is incorporated into complete virions. Microfluorometric and spectrofluorometric assays revealed that virus infected cells always take up more HP than uninfected cells, and heteroploid cells incorporated more HP than diploid cells. The possibility that an increased uptake of HP and modifications of the cell micro-environment in virus infected cells could account for the viral-inhibiting properties of HP, is discussed.     

Differential effects of cycloheximide on protein and RNA synthesis as a function of dose

The $\text{in}$$\text{vivo}$ dose response of rat liver protein and DNA synthesis to cycloheximide have been determined. Protein synthesis was quite sensitive to relatively low doses of cycloheximide being inhibited by more than 90% with 1.5 mg/kg. Maximal inhibition of 98% was achieved with 5 mg/kg. There was no inhibition of RNA synthesis with this dose of cycloheximide. Larger doses of cycloheximide did lead to quite marked inhibition of RNA synthesis without any change in the already maximally inhibited rate of protein synthesis. This differential effect of cycloheximide on protein and RNA synthesis as a function of dose indicates that the inhibition of RNA synthesis caused by the antibiotic is not a consequence of the inhibition of protein synthesis but related otherwise to the effects of large doses of cycloheximide.     

Studies on Antiviral and Antitumor Antibiotics

Antiviral activity of geodin obtained from a soil fungus was studied employing the Newcastle disease virus—chick embryo fibroblasts culture system. In a plate assay method, the minimum inhibitory concentration was about 9 μg/ml and cytotoxicity was detected at 36 μg/ml. Hemagglutinin synthesis was completely suppressed in a tube assay method when 4 μg/ml of geodin was added after the infection (50 plaque forming units/cell), but at this concentration cytotoxic effect of the antibiotic was observed. At sub-inhibitory concentrations, a dose response was shown in the yield of hemagglutinin and infective virus at 16 hr after the infection, and at this time cytopathic effect was partially or completely arrested depending on the antibiotic concentrations even when complete inhibition of hemagglutinin synthesis was not observed. Geodin did not have any effect on the activity of free virus particles and their adsorption to host cells. The inhibition site of geodin exists somewhere between viral adsorption and viral maturation.     

Modulation by the src oncogene of the effect of inhibitory diffusible factor IDF45

Density-dependent inhibition of growth has been assumed to be under the control of inhibitory molecules diffusing from dense cell cultures. Growth inhibitory factors have been fractionated or purified from medium conditioned by different cell types. In the present work, it was shown that IDF45 (inhibitory factor diffusing from 3T3 cells) decreased DNA synthesis in chick embryo fibroblasts (CEF) and was an inhibitor of CEF growth; this inhibition was reversible. Since similitudes between oncogene products and growth factors have been observed, it was of interest to compare the inhibitory effect of IDF45 upon the stimulation of DNA synthesis induced either by serum or by pp60-src. CEF infected by Ny68 virus (a mutant of Rous sarcoma virus ts for the expression of transformation) were density-inhibited at 41 degrees C, but were stimulated at this temperature by addition of 1% serum. This stimulation was 94% inhibited by IDF45. The same Ny68-infected cells could also be stimulated by transfer to 37 degrees C, the permissive temperature (in the absence of serum). The stimulation of DNA synthesis by src expression was poorly inhibited by IDF45. From our results, it appears that oncogene expression in CEF induces a loss in their sensitivity to IDF45. This would explain why transformed cells escape DDI of growth.     

Vitamin A inhibition of polyoma virus replication

Vitamin A (retinoic acid) inhibited polyoma virus replication in confluent mouse embryo cells. A significant, dose dependent inhibition was observed when cell monolayers were pretreated with concentrations of vitamin A (10(-8) to 10(-6) M) thought to approximate those found in vivo. This inhibitory effect could be reduced by increasing the input multiplicity of infection. Growth curves of polyoma virus in the presence and absence of vitamin A suggested that vitamin A actually inhibited, and did not simply delay, virus replication. The cell density dependence of this inhibitory effect suggested its association with the prevailing level of cellular DNA synthesis. Vitamin A caused a significant decrease in overall (viral plus cellular) DNA synthesis. Other viruses which do not require induction of host cell DNA synthesis for their replication in confluent, non-dividing cells were not inhibited by vitamin A. These results are consistent with the known inhibitory effects of vitamin A on papovavirus infection in vivo and suggest a mechanism of vitamin A action at the level of the infected cell.     

Inhibition of Sindbis virus maturation after treatment of infected cells with trypsin.

Brief treatment of Sindbis virus-infected BHK-21 or Vero cells with low concentrations of trypsin irreversibly blocked further production of progeny virions after removal of the enzyme. The inhibitory effects of the trypsin treatment could only be demonstrated in cells in which virus infection was established; optimal inhibition occurred at ca. 3 h postinfection. Production of virus structural proteins PE2, E1, and C occurred at normal levels in inhibited cells. PE2 and E1 were also transported to the cell plasma membrane during inhibition; however, PE2 was not cleaved to E2, and little capsid protein became membrane associated relative to control cells. Although trypsin treatment had no effect on Sindbis protein synthesis, the production of both 26S and 42S RNA was greatly reduced. Similar trypsin treatment of BHK cells infected with vesicular stomatitis virus had no detectable effect on the course of virus infection.     

Study of antiviral activity of different drugs against bovine herpes virus and pestivirus]

In vitro antiviral activity of 11 different drugs against the viruses of infectious bovine rhionotracheitis (IBR) and bovine viral diarrhea (BVD) was studied. The ID50 of the drugs were determined in monolayers of cell cultures MDBK and KCT: 20 mcg/ml for anandin, 25 mcg/ml for polyprenole, 50 mcg/ml for bromuridin, methisazone, aciclovir, gossypole, ribavirin and liposomal ribavirin, 100 mcg/ml for eracond, and 200 mcg/ml for phosprenil and argovit. Phosprenil was the only drug that showed virucidal activity against the IBR virus. All the drugs inhibited reproduction of the IBR virus in sensitive cell culture MDBK: 100,000-fold inhibition by bromuridin, aciclovir, ribavirin and methisazone, 1000-10000-fold inhibition by liposomal ribavirin, gossypole, anandin, polyprenole and phosprenil, 100-fold inhibition by eracond and argovit. As for the BVD virus, bromuridin, phosprenil, polyprenole, methisazone, aciclovir, gossypole, argovit, ribavirin and liposomal ribavirin also showed their activity in cell culture KCT (100-10,000-fold inhibition). The other drugs were ineffective.     

Comparative Studies on Large- and Small-Plaque-Forming Clones of Newcastle Disease Virus (Miyadera Strain)

The Miyadera strain of Newcastle disease virus (NDV) consisted predominantly of virus particles forming small plaques on monolayers of chick embryo fibroblasts (CEF), and contained small amounts of virus particles forming large plaques. These large- and small-plaque-forming clones of this virus (NDV-L and NDV-S) were isolated. The small size of the NDV-S plaques did not appear to be due to an agar inhibitor. NDV-L produced a much higher yield of infective virus particles in CEF and they were released more completely from the infected cells than were those produced by NDV-S. The yield of infective virus of NDV-L per cell from cultures of CEF was comparable to the yield from the allantoic cells. The infectivity/hemagglutinin ratio for NDV-L from CEF was as high as the ratio for virus from the allantoic cells, but the ratio for NDV-S from CEF was lower. NDV-S demonstrated an autointerference phenomenon in CEF when infected at high multiplicities, but NDV-L did not. Contrary to virus multiplication, NDV-S exhibited a more rapid and marked cytopathic effect on monolayers of CEF than NDV-L. In the allantoic cavity of eggs NDV-S produced slightly higher virus yields than NDV-L. No correlation existed between plaque size of the two viruses and the capacity to induce interferon synthesis or the susceptibility to the action of interferon. The properties of both distinctive plaque isolates were stable on egg passage.     

Ultrastructural studies on interaction of infectious bursal disease virus (IBDV) and aflatoxin B1 on chick embryo fibroblast cell culture.

Light and electron microscopic evaluation of chick embryo fibroblast (CEF) cell culture inoculated with graded doses (0.25, 2.5 and 25 micrograms/ml medium) of aflatoxin B1 with and without infectious bursal disease virus (IBDV) was undertaken. The light microscopy revealed degeneration, detachment and necrosis of fibroblasts and multiple plaques formation in IBDV infected group without and with (0.25, 2.5 micrograms) aflatoxin B1. The cultures infected with virus, with or without 25 micrograms aflatoxin B1 showed complete detachment from glass surface. Electron microscopy of these cultures showed marked pyknotic or bizarre shaped nuclei, pronounced degenerative changes in the rough endoplasmic reticulum (RER), mitochondria and the presence of multiple vacuoles in the cytoplasm. The viruses were spherical, arrayed, complete, generally closer to nuclei and RER and indistinctly membrane bound. The viruses were either localised or scattered in the cytoplasm. Cultures containing 25 micrograms aflatoxin B1 without or infected with virus showed marked necrosis of cells. In latter group only a few viruses were seen either in infected cells or free in culture. Control cultures failed to show cytopathic changes as observed in the other three groups.     

Preferential Inhibition of Herpes-Group Viruses by Phosphonoacetic Acid: Effect on Virus DNA Synthesis and Virus-Induced DNA Polymerase Activity

In tissue culture phosphonoacetic acid (PAA) specifically inhibited DNA synthesis of human cytomegalovirus (CMV), murine CMV, simian CMV, Epstein-Barr virus, and Herpesvirus saimiri. Fifty to one hundred micrograms per milliliter PAA completely inhibited viral DNA synthesis with no significant damage to host cell DNA synthesis. In vitro DNA polymerization assays showed that 10 μg/ml of PAA specifically inhibited partially purified human CMV-induced DNA polymerase, while little inhibition of host-cell DNA polymerase activity was found. The specific inhibition of herpes-group virus DNA synthesis with little toxicity to host cells suggests that PAA has great potential as an antiherpesvirus therapeutic agent.