Production of neutralizing antibody to rabies and vesicular stomatitis viruses by hybrid cell lines

Hybrid cell lines were obtained following fusion of P 3 × 63 Ag-8 myeloma cells with spleen cells derived from BALB/c mice immunized either with rabies virus or with vesicular stomatitis virus. Hybrid cell lines were selected which continued to secrete rabies virus or vesicular stomatitis virus neutralizing antibody specifically directed against coat glycoprotein of respective viruses.     

Mosquito cells infected with vesicular stomatitis virus yield unsialylated virions of low infectivity.

Vesicular stomatitis virus propagated in and released from Aedes albopictus cells had the normal complement of viral proteins; the glycoprotein contained carbohydrate but no sialic acid. These virions had markedly reduced hemagglutinating activity and exhibited a very high ratio of physical particles to infectious virus. In vitro sialylation of vesicular stomatitis virions grown in mosquito cells resulted in a 100-fold increase in both infectivity and hemagglutination titers to levels approaching those of virus grown in BHK-21 cells. These experiments provide an example of host-controlled modification of viral infectivity.     

Effects of chloroquine and cytochalasin B on the infection of cells by Sindbis virus and vesicular stomatitis virus

The effects of cytochalasin B and chloroquine on the process of endocytosis of Sindbis virus particles and polystyrene spheres were determined by electron microscopy. The effects of these agents on the process of infection (attachment, penetration, and uncoating) of BHK-21 cells by Sindbis virus and vesicular stomatitis virus were also determined. Cytochalasin B completely blocked ingestion of Sindbis virus particles or latex spheres by BHK cells but had no effect on the ability of Sindbis virus or vesicular stomatitis virus to infect or replicate in BHK cells. Chloroquine did not inhibit the ingestion of either latex spheres or virus particles but greatly reduced the yields of virus produced. These data suggest that endocytosis is not essential for the infection of cultured cells by Sindbis virus or vesicular stomatitis virus.     

Infective Virus Substructure from Vesicular Stomatitis Virus

Treatment of suspensions of vesicular stomatitis virus with Tween-ether results in a rapid and considerable loss of infectivity (ca. 4 logs in 2 min), but the residual infectivity is comparatively stable to further treatment with ether. The infectivity remaining after the short exposure to Tween-ether is not due to virus for the following reasons. (i) It is much less infective for tissue cultures than for mice, whereas the intact virion is equally infective for both hosts. (ii) The residual infectivity is much less stable than virus infectivity in both sucrose and tartrate gradients. (iii) Virus immune serum does not neutralize its activity. (iv) The infectivity is associated with material which sediments further in sucrose gradients and has a greater buoyant density in tartrate gradients than the virion. Experiments with (32)P-labeled virion showed that the infective substructure contains ribonucleic acid with the same sedimentation characteristics as that extracted from the virion. Electron microscopy shows that the infective component has the same overall bullet-like structure as the virion but lacks the outer envelope and fringe structure.     

Selective restriction of Nef-defective human immunodeficiency virus type 1 by a proteasome-dependent mechanism

The Nef protein enhances human immunodeficiency virus type 1 (HIV-1) infectivity by facilitating an early postentry step in the virus life cycle. We report here that the addition of MG132 or lactacystin, each a specific inhibitor of cellular proteasome activity, preferentially enhances cellular permissiveness to infection by Nef-defective versus wild-type HIV-1. Pseudotyping by the glycoprotein of vesicular stomatitis virus rendered Nef-defective HIV-1 particles minimally responsive to the enhancing effects of proteasome inhibitors. These results suggest that Nef enhances the infectivity of HIV-1 particles by reducing their susceptibility to proteasomal degradation in target cells.     

Effects of protein kinase C inhibitors on viral entry and infectivity.

The protein kinase C inhibitor H-7 (2-20 microM) inhibited dose-dependently the infectivity of the vesicular stomatitis virus on cultured human fibroblasts. Electron microscopy showed that H-7 inhibited the viral entry. H-7 also inhibited the infectivity of four other enveloped viruses, herpes simplex I, turkey herpes, vaccinia and Sindbis. Similar results were obtained using staurosporine (2.5 nM), tamoxifen (40 microM), phloretin (140 microM), or W-7 (40 microM). However, the infectivity of non-enveloped viruses (e.g. poliomyelitis I) was not inhibited by H-7. These results show that protein kinase C is critically involved in the infectivity of enveloped viruses, most probably at the level of viral entry (receptor-mediated endocytosis).     

Low infectivity of vesicular stomatitis virus (VSV) particles released from interferon-treated cells is related to glycoprotein deficiency

We have investigated the mechanism for the low infectivity of vesicular stomatitis virus (VSV) released from interferon (IFN) -treated cells. With 10-30 units/ml of IFN there was an approximately 5-30 fold reduction in the production of virus particles, as measured by VSV proteins; however, the infectivity of the VSV released from IFN-treated mouse LB, JLS-V9R, or human GM2504 was drastically reduced (2 to 4 logs). The low infectivity of VSV was directly related to a deficiency in virion glycoprotein (G). IFN treatment did not change the specific infectivity of the VSV particles released by HeLa cells; their G protein was also not reduced. A further effect of IFN to reduce the amount of virion M protein appeared to be secondary and was probably not related to the reduced infectivity of VSV.     

HIV-1 selectively infects a subset of nonmaturing BDCA1-positive dendritic cells in human blood

The infection of cultured monocyte-derived dendritic cells (DCs) with HIV-1 involves CD4 and CCR5 receptors, while transmission to T cells is enhanced at least in part by the lectin DC-SIGN/CD209. In the present study, we studied BDCA-1+ myeloid DCs isolated directly from human blood. These cells express CD4 and low levels of CCR5 and CXCR4 coreceptors, but not DC-SIGN. The myeloid DCs replicate two R5 viruses, BaL and YU2, and transfer infection to activated T cells. The virus productively infects a small fraction of the blood DCs that fail to mature in culture, as indicated by the maturation markers CD83 and DC-LAMP/CD208, and the expression of high CD86 and MHC class II, in contrast to many noninfected DCs. A greater proportion of BDCA-1+ DCs are infected when the virus is pseudotyped with the vesicular stomatitis envelope VSV-G (5-15%), as compared with the R5 virus (0.3-3.5%), indicating that HIV-1 coreceptors may limit the susceptibility of DCs to become infected, or the endocytic route of viral entry used by HIV/vesicular stomatitis virus enhances infectivity. When infected and noninfected cells are purified by cell sorting, the former uniformly express HIV p24 gag and are virtually inactive as stimulators of the allogeneic MLR, in contrast to potent stimulation by noninfected DCs from the same cultures. These results point to two roles for a small fraction of blood DCs in HIV-1 pathogenesis: to support productive infection and to evade the direct induction of T cell-mediated immunity.     

Inactivation by gamma irradiation of animal viruses in simulated laboratory effluent.

Several animal viruses were treated with gamma radiation from a 60Co source under conditions which might be found in effluent from an animal disease laboratory. Swine vesicular disease virus, vesicular stomatitis virus, and blue-tongue virus were irradiated in tissues from experimentally infected animals. Pseudorabies virus, fowl plague virus, swine vesicular disease virus, and vesicular stomatitis virus were irradiated in liquid animal feces. All were tested in animals and in vitro. The D10 values, that is, the doses required to reduce infectivity by 1 log10, were not apparently different from those expected from predictions based on other data and theoretical considerations. The existence of the viruses in pieces of tissue or in liquid feces made no difference in the efficacy of the gamma radiation for inactivating them. Under the "worst case" conditions (most protective for virus) simulated in this study, no infectious agents would survive 4.0 Mrads.     

Inactivation by gamma irradiation of animal viruses in simulated laboratory effluent

Several animal viruses were treated with gamma radiation from a 60Co source under conditions which might be found in effluent from an animal disease laboratory. Swine vesicular disease virus, vesicular stomatitis virus, and blue-tongue virus were irradiated in tissues from experimentally infected animals. Pseudorabies virus, fowl plague virus, swine vesicular disease virus, and vesicular stomatitis virus were irradiated in liquid animal feces. All were tested in animals and in vitro. The D10 values, that is, the doses required to reduce infectivity by 1 log10, were not apparently different from those expected from predictions based on other data and theoretical considerations. The existence of the viruses in pieces of tissue or in liquid feces made no difference in the efficacy of the gamma radiation for inactivating them. Under the "worst case" conditions (most protective for virus) simulated in this study, no infectious agents would survive 4.0 Mrads.     

Extreme fitness differences in mammalian and insect hosts after continuous replication of vesicular stomatitis virus in sandfly cells.

Continuous, persistent replication of a wild-type strain of vesicular stomatitis virus in cultured sandfly cells for 10 months profoundly decreased virus replicative fitness in mammalian cells and greatly increased fitness in sandfly cells. After persistent infection of sandfly cells, fitness was over 2,000,000-fold greater than that in mammalian cells, indicating extreme selective differences in the environmental conditions provided by insect and mammalian cells. The sandfly-adapted virus also showed extremely low fitness in mouse brain cells (comparable to that in mammalian cell cultures). It also showed an attenuated phenotype, requiring a nearly millionfold higher intracranial dose than that of its parent clone to kill mice. A single passage of this adapted virus in BHK-21 cells at 37 degrees C restored fitness to near neutrality and also restored mouse neurovirulence. These results clearly illustrate the enormous capacity of RNA viruses to adapt to changing selective environments.     

Biological differences between vesicular stomatitis virus Indiana and New Jersey serotype glycoproteins: identification of amino acid residues modulating pH-dependent infectivity

We previously generated recombinant vesicular stomatitis viruses (VSV) based on the Indiana serotype genome which contained either the homologous glycoprotein gene from the Indiana serotype (VSIV-GI) or the heterologous glycoprotein gene from the New Jersey serotype (VSIV-GNJ). The virus expressing the GNJ gene was more pathogenic than the parental VSIV-GI virus in swine, a natural host (26). For the present study, we investigated the biological differences between the GI and GNJ proteins that may be related to the differences in pathogenesis between VSIV-GI and VSIV-GNJ. We show that the capacities of viruses with either the GNJ or GI glycoprotein to infect cultured cells differ depending on the pH. VSIV-GNJ could infect cells at acidic pHs, while the infectivity of VSIV-GI was severely reduced. VSIV-GNJ infection was also more sensitive to inhibition by ammonium chloride, indicating that the GNJ protein had a lower pH threshold for membrane fusion. We applied selective pressure to VSIV-GI by growing it at successively lower pH values and isolated variant viruses in which we identified amino acid changes that conferred low-pH-resistant infectivity. Repeated passage in cell culture at pH 6.8 resulted in the selection of a VSIV-GI variant (VSIV-6.8) that was similar to VSIV-GNJ regarding its pH- and ammonium chloride-dependent infectivity. Sequence analysis of VSIV-6.8 revealed that it had a single amino acid substitution in the amino-terminal region of the glycoprotein (F18L). This alteration was shown to be responsible for the observed phenotype by site-directed mutagenesis of a VSIV-GI full-length cDNA and analysis of the recovered engineered virus. A further adaptation of VSIV-6.8 to pHs 6.6 and 6.4 resulted in additional amino acid substitutions in areas of the glycoprotein that were not previously implicated in attachment or fusion.     

Comparative Membrane Microviscosity of Fish and Mammalian Rhabdoviruses Studied by Fluorescence Depolarization

The microviscosity of the hydrophobic region of the membrane of infectious hematopoietic necrosis virus was determined using fluorescence depolarization analysis of the probe 1,6-diphenyl-1,3,5-hexatriene and was found to be much lower at 37 C than that of another rhabdovirus, vesicular stomatitis virus. However, the microviscosity of this fish virus at 18 C, the temperature at which it was grown, corresponded to the microviscosity of vesicular stomatitis virus at 37 C. Data obtained with the fish virus host cell (chinook salmon embryo cells) grown at 18 C suggest that its membranes have a lower microviscosity than either L-929 or BHK-21 cells (the vesicular stomatitis virus host cells) grown at 37 C.     

Growth of enveloped RNA viruses in a line of chinese hamster ovary cells with deficient N-acetylglucosaminyltransferase activity.

Sindbis and vesicular stomatitis viruses were grown in a line (termed 15B) of Chinese hamster ovary (CHO) cells that is deficient in a specific UDP-N-acetyl-glucosamine:glycoprotein N-acetylglucosaminyltransferase. Both viruses replicated normally in the cell line, but the glycoproteins of the released virus migrated faster on sodium didecyl sulfate-polyacrylamide gels than did glycoproteins of virus grown in parent CHO cells. Digestion of the viral glycoproteins with Pronase followed by gel filtration demonstrated that the glycoproteins with Pronase followed by gel filtration demonstrated that the glycopeptides of Sinbis-15B virus were much smaller than the glycopeptides of Sindbis-CHO virus. In addition, Sindbis-15B viral glycopeptides but not Sindbis-CHO viral glycopeptides contained terminal alpha-mannose residues as shown by their susceptibility to alpha-mannosidase digestion. These findings demonstrate that the oligosaccharide units of the glycoproteins of vesicular stomatitis and Sinbis viruses are altered when the viruses are grown in 15B cells. We conclude that the N-acetylglucosaminyltransferase that is missing in 15B cells normally participates in the biosynthesis of the oligosaccharide units of the viral glycoproteins, and in the absence of this enzyme incomplete oligosaccharide chanis are produced. Viruses released from 15B cells appear to retain full infectivity; Sindbis-15B virus, however, showed a significant decrease in hemagglutination titer compared with that of Sindbis-CHO virus.     

Sequence Determination of the (+) Leader RNA Regions of the Vesicular Stomatitis Virus Chandipura, Cocal, and Piry Serotype Genomes

Using 3'-end-labeled genome probes, cells infected with vesicular stomatitis virus Chandipura, Cocal, and Piry serotypes were shown to contain (+) leader RNAs of approximately 50 nucleotides in length. The nucleotide sequence of the leader RNA regions of these genomes was determined and compared with the previously reported sequences of both the (+) and (-) leader RNA regions of other vesicular stomatitis virus serotypes. Regions of strong conservation of nucleotide sequence among the various vesicular stomatitis virus serotypes suggest those nucleotides thought to be involved in control functions during vesicular stomatitis virus replication.     

Ebola virus glycoprotein: proteolytic processing, acylation, cell tropism, and detection of neutralizing antibodies

Using the vesicular stomatitis virus (VSV) pseudotype system, we studied the functional properties of the Ebola virus glycoprotein (GP). Amino acid substitutions at the GP cleavage site, which reduce glycoprotein cleavability and viral infectivity in some viruses, did not appreciably change the infectivity of VSV pseudotyped with GP. Likewise, removal of two acylated cysteine residues in the transmembrane region of GP showed no discernible effects on infectivity. Although most filoviruses are believed to target endothelial cells and hepatocytes preferentially, the GP-carrying VSV showed greater affinity for epithelial cells than for either of these cell types, indicating that Ebola virus GP does not necessarily have strong tropism toward endothelial cells and hepatocytes. Finally, when it was used to screen for neutralizing antibodies against Ebola virus GP, the VSV pseudotype system allowed us to detect strain-specific neutralizing activity that was inhibited by secretory GP (SGP). This finding provides evidence of shared neutralizing epitopes on GP and SGP molecules and indicates the potential of SGP to serve as a decoy for neutralizing antibodies.     

Inactivation of vesicular stomatitis virus by photosensitization following incubation with a pyrene-fatty acid

Vesicular stomatitis virus (VSV) was incubated with pyrene dodecanoic acid (P12), a fluorescent derivative of a medium-chain length fatty acid, and subjected to irradiation with a long wavelength ultra-violet light source at 366 nm (UVA). This inactivated the virus, resulting in a drastic decrease of its infectivity. The virus inactivation was proportional to the concentration of the pyrene-fatty acid, the length of exposure of the virus to P12 and the irradiation dose.     

Functional importance of the coiled-coil of the Ebola virus glycoprotein

Ebola virus contains a single glycoprotein (GP) that is responsible for receptor binding and membrane fusion and is proteolytically cleaved into disulfide-linked GP1 and GP2 subunits. The GP2 subunit possesses a coiled-coil motif, which plays an important role in the oligomerization and fusion activity of other viral GPs. To determine the functional significance of the coiled-coil motif of GP2, we examined the effects of peptides corresponding to the coiled-coil motif of GP2 on the infectivity of a mutant vesicular stomatitis virus (lacking the receptor-binding/fusion protein) pseudotyped with the Ebola virus GP. A peptide corresponding to the C-terminal helix reduced the infectivity of the pseudotyped virus. We next introduced alanine substitutions into hydrophobic residues in the coiled-coil motif to identify residues important for GP function. None of the substitutions affected GP oligomerization, but some mutations, two in the N-terminal helix and all in the C-terminal helix, reduced the ability of GP to confer infectivity to the mutant vesicular stomatitis virus without affecting the transport of GP to the cell surface, its incorporation into virions, and the production of virus particles. These results indicate that the coiled-coil motif of GP2 plays an important role in facilitating the entry of Ebola virus into host cells and that peptides corresponding to this region could act as efficient antiviral agents.