The 1:1 N-NS protein complex of vesicular stomatitis virus is essential for efficient genome replication

We studied the effect pH had on the N-NS protein complex to determine its role in vesicular stomatitis virus (VSV) genome replication, as we had previously shown that VSV genome replication in vitro requires the interaction of the viral N and NS proteins into a 1:1 complex. A previous report showed that the growth of VSV in L cells was sensitive to the pH of the environment (M. Fiszman, J. B. Leaute, C. Chany, and M. Girard, J. Virol. 13:801-808, 1974). We hypothesized that low pH might disrupt the N-NS protein complex, and so we investigated the molecular events leading to inhibition of viral RNA replication in vitro from extracts that were prepared from VSV-infected cells incubated at pH 6.6. We found that viral genome RNA synthesis in vitro was reduced when infected cells were maintained at pH 6.6. Through immunoprecipitation analysis of the viral soluble protein pool, we found that a complex that usually exists between the N and NS proteins at pH 7.4 was altered in extracts from infected cells maintained at pH 6.6, and this was responsible for the observed effects on viral replication. The effect of low pH on the N-NS protein complex could not be abolished by increasing the concentration of the altered complex, indicating that the effects is more than simply a decrease in the level of the protein complex in the cell. Our data provide additional evidence that the 1:1 N-NS protein complex, and not the N protein alone, serves as the substrate for viral RNA replication in vivo.

Avian cells expressing the Newcastle disease virus hemagglutinin-neuraminidase protein are resistant to Newcastle disease virus infection

The cDNA derived from the Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) gene was inserted into a replication-competent Schmidt-Ruppin Rous sarcoma virus-derived vector. Chick embryo cells transfected with this vector expressed HN-sized protein which could be precipitated with anti-HN antibody. These cells adsorbed avian red blood cells and the cell surfaces exhibited neuraminidase activity while cells transfected with an antisense version of the gene were negative for hemadsorption and neuraminidase. The cells transfected with the retroviral vector containing the HN gene were resistant to infection by NDV and influenza virus, viruses which bind to sialic acid containing receptors, but sensitive to vesicular stomatitis virus (VSV). Cells transfected with the antisense version of the HN gene were sensitive to NDV, influenza virus, and VSV infection. Thus the HN protein-expressing cells are likely resistant to NDV and influenza virus due to the destruction of the cellular receptors by the neuraminidase of the HN protein. The expression of the influenza virus HA protein using the same retrovirus vector has been reported previously (L. A. Hunt, D. W. Brown, H. L. Robinson, C. W. Naeve, and R. G. Webster, 1988, J. Virol. 62, 3014-3019). Cells infected with this vector were sensitive to infection with influenza virus, NDV, and VSV. Thus expression of a viral surface protein does not necessarily confer resistance of the cell to the homologous virus.

Efficient medium for impingement and storage of enveloped viruses

Airborne infections with pathogenic viruses play an important role in the transmission of diseases amongst men and animals. We compared several media intended for impingement of viruses from virus-contaminated air and for their preserving effect for two enveloped viruses. Sindbis (SINV) and vesicular stomatitis virus (VSV), members of the families Toga- and Rhabdoviridae, respectively, were chosen as indicator agents. Amongst the media tested, a sampling fluid consisting of phosphate buffered saline, pH 7.2, 0.5% bovine serum albumin, 0.5% gelatine (PBSplus) was most efficient to minimize the sampling stress during impingement and to preserve the infectivity SINV and VSV under stringent conditions at 37 degrees C. About 50% of virus infectivity was recovered 15.7 or 30 hours, respectively, after the beginning of storage. Thus the recommended medium is also suitable for shipment and storage of diagnostic virus samples.

Isolation of Chinese hamster ovary cell lines temperature conditional for the cell-surface expression of integral membrane glycoproteins

A procedure is described to select mutants of Chinese hamster ovary cells that are conditionally defective for the cell-surface expression of integral membrane glycoproteins, including the hemagglutinin (HA) of influenza virus. Using a combination of cell sorting and biochemical screening, seven cell lines were obtained that express more cell-surface HA at 32 degrees C than at 39 degrees C. The production of infectious vesicular stomatitis virus, whose growth requires insertion of an integral membrane protein into the plasma membrane, was also temperature conditional in the majority of these mutant cell lines. Five of the lines synthesized apparently normally core-glycosylated HA at the elevated temperature but the protein was neither displayed on the cell surface nor accumulated intracellularly. In these cell lines, little or no terminally glycosylated HA molecules were observed after synthesis at 39 degrees C. By contrast, the core glycosylation of HA and several other integral membrane proteins was abnormal in the remaining two cell lines at both permissive and restrictive temperatures, due to a lesion in a cellular gene(s) that affects the formation of and/or the addition of mannose-rich oligosaccharide chains to newly synthesized polypeptides. Although HA was transported to the plasma membrane at both 32 and 39 degrees C, it did not accumulate on the cell surface at the higher temperature, apparently because of an increased rate of degradation.

Possible involvement of virus-induced protein kinase in the antiviral state induced with interferon-gamma against Sindbis virus

The kinetics of induction of the antiviral state against two RNA viruses, vesicular stomatitis virus (VSV) and Sindbis virus, by human interferons (IFNs)-alpha, -beta, and -gamma was measured and compared with that of 2',5'-oligoadenylate (2-5A) synthetase and protein kinase in cells treated with IFNs. Both enzymes were induced in similar time courses and the induction by IFN-gamma was slower than IFN-alpha or beta. The time course of the induction of antiviral state against VSV almost paralleled with that of the enzyme induction by each IFN species. In contrast, the induction of antiviral state against Sindbis virus with IFN-gamma was as fast as that induced with IFN-alpha or beta, in spite of the slower enzyme induction by IFN-gamma. The addition of actinomycin D at the time of virus challenge did not substantially affect the induction of the antiviral state against VSV, but markedly retarded the establishment of IFN-gamma-induced antiviral state against Sindbis virus. These results suggest that the antiviral machinery against VSV is induced solely by IFN during the pretreatment, but the one against Sindbis virus involves additional cellular component(s) induced shortly after virus infection, especially in the case of IFN-gamma. Sindbis virus, but not VSV, induced a cellular double-stranded (ds) RNA-dependent protein kinase at an early stage of virus replication. The kinase appeared to phosphorylate the same protein as IFN-induced kinase in the IFN-gamma-treated and Sindbis virus-infected cells, leading to an increased phosphorylation level. These results are consistent with the idea that the Sindbis virus-induced protein kinase may be involved in the IFN-gamma-induced antiviral state against Sindbis virus.

Antiviral activity of tumour necrosis factor. Synergism with interferons and induction of oligo-2',5'-adenylate synthetase

Tumour necrosis factor (TNF) induces antiviral activity in HEp-2 cells. Virus yield reduction assays with vesicular stomatitis virus as challenging virus demonstrated that the antiviral state was more pronounced in confluent cultures under low serum conditions. A significant enhancement of the antiviral state was obtained by combining TNF with low concentrations of either interferon (IFN)-beta 1 or IFN-gamma. The reduction in virus yield was significantly higher than that expected from summation of the independent antiviral activities of either substance alone, i.e. TNF and IFN acted synergistically as antiviral agents. Synergism of TNF with IFN-beta or IFN-gamma appeared to be mediated by different pathways, since different requirements for pretreatment and different effects on oligo-2',5'-adenylate synthetase (2-5AS) induction were observed. Induction of 2-5AS by TNF could be shown to be an indirect event that was sensitive to an antiserum against natural IFN-beta 1.

Non-lethal infection of aminergic reticular core neurons: age-dependent spread of ts mutant vesicular stomatitis virus from the nose

In order to induce a non-lethal infection restricted to central aminergic neurons projecting to the olfactory bulbs a series of temperature sensitive (ts) and G-protein monoclonal antibody escape mutants of vesicular stomatitis virus (VSV) were instilled into the nasal cavity of mice. In three-week (wk)-old NMRI mice four monoclonal antibody escape mutants caused an extensive infection of the olfactory epithelium and, like a wild type strain, a lethal brain infection after spread along olfactory pathways. Three ts mutant strains showed an attenuated pathogenic potential. Strain G31 caused a lethal infection with a somewhat prolonged course while the strain G11 failed to invade the nervous system. Strain G41 showed minimal invasion of central nervous system in three-wk-old mice and caused a lethal infection in newborn and one-wk-old mice. In contrast, two-wk-old mice survived infection with this mutant, which spread along olfactory pathways and rather selectively affected aminergic reticular core neurons in the diagonal band, the locus ceruleus and the raphe nuclei in the brainstem. Thus, an age-dependent virus infection of the olfactory pathways can cause restricted lesions in the brain providing a model for studies of virus-induced changes in aminergic neurotransmission.

Reovirus type 3 synthesizes proteins in interferon-treated HeLa cells without reversing the antiviral state

Treatment of HeLa cells with human lymphoblastoid interferon (IFN-alpha) does not inhibit reovirus type 3 protein synthesis during virus infection. In contrast, reovirus translation is blocked by treatment of L cells with mouse IFN-alpha. The (2'-5')A synthetase activity is induced in HeLa cells by IFN-alpha treatment and is activated after reovirus infection, since cell lysates from these cells synthesize in vitro (2'-5')A oligonucleotides. The IFN-induced protein kinase activity is also triggered in those lysates upon dsRNA addition. Thus, contrary to DNA-containing viruses, such as vaccinia virus or adenovirus, reovirus infection does not destroy or reverse the IFN-induced antiviral state. In support of this conclusion, superinfection with poliovirus or vesicular stomatitis virus of reovirus-infected HeLa cells treated with IFN leads only to a blockade of translation of the former viruses. These results provide a remarkable example where in the same cells doubly infected with two different viruses, the antiviral state induced by IFN-alpha is manifested by selectively inhibiting translation of one kind of virus (poliovirus or vesicular stomatitis virus) without affecting the translation of reovirus type 3. In addition, these results indicate that the resistance of reovirus translation to inhibition by IFN is different from the mechanism of resistance induced by DNA-containing viruses.

Vaccinia virus stimulates the growth of vesicular stomatitis virus at the level of protein synthesis in mouse L cells

Coinfection with vaccinia virus increases the growth of vesicular stomatitis virus (VSV) in mouse L cells by 10- to 20-fold. Although vaccinia has no significant effect on RNA synthesis by VSV, VSV protein synthesis is dramatically stimulated by double infection. The enhancement of VSV growth is correlated with the ability of vaccinia to inhibit the VSV-mediated damage to the host translational machinery. Coinfection with vaccinia fails to stimulate the growth of a VSV mutant which is deficient in its ability to shut off protein synthesis during infection.

Activation of vesicular stomatitis virus fusion with cells by pretreatment at low pH

Fusion of vesicular stomatitis virus (VSV) with Vero cells was measured after exposure of the virus to low pH under a variety of experimental conditions. The method of relief of fluorescence self-quenching of the probe octadecylrhodamine was used to monitor fusion. Incubation of the virus at pH 5.5 prior to binding to cells led to significant enhancement of fusion at the plasma membrane, whereas fusion via the endocytic pathway was inhibited. Fusion of pH 5.5-pretreated VSV showed a similar pH threshold for fusion as nontreated virus, and it was blocked by antibody to VSV G protein. Activation of VSV by pretreatment at low pH was only slightly dependent on temperature. In contrast, when VSV was first bound to target cells and subsequently exposed at 4 degrees C to the low pH, activation of the fusion process did not occur. The pH 5.5-mediated activation of VSV could be reversed by returning the pH to neutral in the absence of target membranes. The low pH pretreatment also led to aggregation of virus; large aggregates could be pelleted by low speed centrifugation and only the effects of the supernatant, which consist of single virions and/or microaggregates, were considered. The data were analyzed in the framework of an allosteric model according to which viral spike glycoproteins undergo a pH-dependent conformational transition to an active (fusion-competent) state. Based on that analysis we conclude that the conformational transition to the active state is rate-limiting for fusion and that the viral spike glycoproteins are fusion-competent only in their protonated form.

Delayed formation of defective interfering particles in vesicular stomatitis virus-infected cells: kinetic studies of viral protein and RNA synthesis during autointerference

The time course of defective interfering (DI) particle and B particle release from vesicular stomatitis virus-infected BHK-21 cells was studied at different multiplicities of defective and infective particles. Particle release was progressively delayed in cells infected with an increasing DI-to-B particle ratio. The delayed particle release during interference was found to be connected with a reduced but prolonged synthesis of viral proteins, a slower accumulation of viral proteins, and a delayed shutoff of cellular protein synthesis. The relative synthesis of M and G proteins was reduced during interference, whereas the relative synthesis of N and NS proteins was increased. On the level of genomic RNA replication, we found that DI RNA was replicated more slowly during interference than the standard genomic RNA was during acute infection. The ratio of DI particles to B particles which were released increased throughout the infectious cycle. At a given time in the infectious cycle, this ratio was independent of the multiplicity of infecting DI and B particles. On the basis of the kinetic studies, we argue that cells infected with higher amounts of DI particles compared with B particles synthesize a higher DI-to-B particle ratio and release these progeny particles later than cells infected with a low DI-to-B particle ratio.

Interferon-gamma is not an antiviral, but a growth-promoting factor for T lymphocytes

The effects of interferon (IFN)-gamma or IFN-alpha/beta on virus yield, (2'-5')oligo(A) synthetase activation, H-2 antigen expression and proliferation of T lymphocytes have been investigated. Under the culture conditions used, vesicular stomatitis virus or Semliki Forest virus replication in T cells was not impaired by the addition of IFN-gamma, whereas it was completely inhibited by the addition of IFN-alpha/beta. In contrast, B cell lines, macrophage-transformed cell lines and fibroblasts were fully protected by both IFN-gamma as well as IFN-alpha/beta following virus infection. The lack of sensitivity of T lymphocytes to the antiviral effects of IFN-gamma was not due to absence of specific membrane receptors, since in saturation binding experiments with 125I-labeled murine IFN-gamma most T cell lines displayed a number of binding sites and a degree of affinity comparable to those found on B cells, which are fully sensitive to IFN-gamma antiviral activity. Analysis of IFN-induced dsRNA-dependent (2'-5')oligo(A) synthetase activity, one of the biochemical markers for cellular responses to IFN, showed that it was not induced in T lymphocytes after IFN-gamma treatment, whereas IFN-alpha/beta induced high levels. Both IFN-gamma and IFN-alpha/beta enhanced H-2 antigen expression on T cells as well as on cells of different histological type. Moreover, when IFN-gamma was tested for its antiproliferative activity on T cells, it was found to consistently potentiate the response of these cells to mitogens or growth factors, rather than inhibit their proliferation. Taken as a whole these results suggest that on T lymphocytes IFN-gamma should not be regarded as an antiviral agent, but rather as a modulator of T cell growth and functional differentiation, transducing intracellular signals dissimilar to those observed with target cells of different origin.

Induction of an antiviral state by interferon in the absence of elevated levels of 2,5-oligo(A) synthetase and eIF-2 kinase

A series of clones has been derived from an interferon-resistant murine cell line, Ltk- aprt-, and their antiviral properties have been characterized. In the parental Ltk- aprt- line interferon is unable to establish antiviral properties or to increase the levels of 2,5-oligo(A) synthetase, the 2,5-oligo(A)-activated endonuclease F, 2',5'-phosphodiesterase, or eIF-2 kinase. However, interferon did prevent replication of vesicular stomatitis, Mengo virus, and reovirus in some of the derivative cell lines. The effect of interferon on the levels of the enzymes of the 2,5-oligo(A) and eIF-2 kinase pathways did not correlate directly with the antiviral properties of these cell clones. Greatly increased levels of 2,5-oligo(A) synthetase occurred in one clone without activation of an antiviral state. Another clone exhibited antiviral activity without detectably increased 2,5-oligo(A) synthetase activity. Changes in the levels of endonuclease F and 2',5'-phosphodiesterase were slight in all the clones examined. Neither 2,5-oligo(A) synthetase nor eIF-2 kinase levels were altered by interferon in another clone and yet an antiviral state was established and prevented replication of vesicular stomatitis, Mengo virus, and reovirus. The results show that mechanisms other than the 2,5-oligo(A) and eIF-2 kinase pathways are likely to contribute to the antiviral effects of interferon.

The action of recombinant bovine interferons on influenza virus replication correlates with the induction of two Mx-related proteins in bovine cells

Recombinant bovine interferon-alpha and -gamma differ in their action against influenza virus on bovine cells. Bovine IFN-alpha severely impairs early protein synthesis and replication of influenza virus in bovine cells in contrast to bovine IFN-gamma which fails to induce an antiviral state against influenza virus. Otherwise the IFN system seems to function normally in bovine cells since both bovine IFN-alpha and -gamma induce an antiviral state against vesicular stomatitis virus. The establishment of the specific antiviral state against influenza virus correlates with the induction by bovine IFN-alpha, but not -gamma, of two cytoplasmic proteins related to the IFN-induced mouse protein Mx involved in the mechanism of resistance of mice to influenza virus infection. This study suggests that bovines possess a system for resistance to influenza virus similar to the mouse Mx system.

Vesicular stomatitis virus in Drosophila melanogaster cells: regulation of viral transcription and replication

Vesicular stomatitis virus RNA synthesis was investigated during the establishment of persistent infection in Drosophila melanogaster cells. The transcription rate declined as early as 5 h after infection and was strongly inhibited after 7 h, leading to a decrease in viral mRNA levels and in viral protein synthesis rates. Full-length plus-strand antigenomes and minus-strand genomes were detected after a 3-h lag time and accumulated until 15 h after infection. Short encapsidated plus-strand molecules were also generated corresponding to the 5' end of viral defective antigenomes. Assembly and release of virions were not restricted, but their infectivity was extremely reduced. In persistently infected cells, an equilibrium was reached where the level of intracellular genomes maintained was constant and maximal even after the rate of all viral syntheses had decreased. These results are discussed with regard to the establishment of persistent infection.

Inhibition of the phosphorylation of the regulatory non-structural protein of vesicular stomatitis virus by an antiviral xanthate compound

The growth of vesicular stomatitis virus (VSV) can be inhibited by the antiviral compound tricyclo-decane-9-yl-xanthogenate (D609). On analysing the antiviral mechanism we found no effect on the primary transcription of infecting VSV genomes. In contrast, the processes of replication and transcription during late stages of infection were inhibited. Despite the synthesis of all five virus-coded proteins (41% to 56% of the uninhibited control), as shown by labelling with [35S]methionine, the phosphorylation of the non-structural (NS) protein was reduced in the presence of the xanthate by a factor of at least 17. The pattern of phosphorylation of the bulk of cellular proteins remained unaltered under the same conditions. A relation between a possible loss of biological activity of the NS protein owing to the lack of phosphorylation and the decreased VSV RNA synthesis is suggested.

Physical dependence to morphine diminishes the interferon response in mice

Morphine pellet implantation in mice was demonstrated to diminish resistance to encephalomyocarditis virus infections. The variations in the response to three different interferon (IFN) inducers--Newcastle disease virus, Escherichia coli lipopolysaccharide and a tilorone analogue--were evaluated. A close relationship between morphine dependence and IFN response was detected. A clear inhibition in IFN induction appeared as a concomitant phenomenon with the syndrome of morphine dependence. In the response intensity, the mice strain tested was more important than the total drug dose in the pellet. This effect of morphine on IFN responses presented a characteristic age-related pattern and, perhaps, may also be influenced by the H-2 murine phenotype.

Identification and characterization of a mouse cell mutant defective in the intracellular transport of glycoproteins

We have isolated a mutant line of mouse L cells, termed gro29, in which the growth of herpes simplex virus (HSV) and vesicular stomatitis virus (VSV) is defective. The block occurs late in the infectious cycle of both viruses. We demonstrate that HSV and VSV enter gro29 cells normally, negotiate the early stages of infection, yet are impaired at a late stage of virus maturation. During VSV infection of the mutant cell line, intracellular transport of its glycoprotein (G protein) is slowed. Pulse-chase experiments showed that oligosaccharide processing is impeded, and immunofluorescence localization revealed an accumulation of G protein in a juxtanuclear region that contains the Golgi complex. We conclude that export of newly made glycoproteins is defective in gro29 cells, and speculate that this defect may reflect a lesion in the glycoprotein transport apparatus.

Interferon inducibility and sensitivity of human teratocarcinoma-derived cell lines

Three cell lines tera I, tera II, and PA1, derived from human teratocarcinomas were tested for their capacity to produce interferon (IFN) and for their sensitivity to both human IFN-alpha and IFN-beta. When treated with Newcastle disease virus or Sendai virus, or a synthetic polyribonucleotide, poly(rI):poly(rC), tera I cells produced no IFN and the 2',5'-oligoadenylate (2-5A) synthetase enzymatic pathway was not activated, although there was an increase in protein kinase. In contrast, tera II and PA1 cells produced IFN and both enzymatic activities were detected. IFN treatment has no effect on the growth of any of the cell lines. Tera I and PA1 cells did not develop resistance to challenge with vesicular stomatitis virus or encephalomyocarditis virus, but the growth of a type-C baboon retrovirus was inhibited. Tera II cells were protected against all three viruses. It appears that human teratocarcinoma cell lines can thus differ greatly in their ability to produce IFN and to respond to it.

A mutated membrane protein of vesicular stomatitis virus has an abnormal distribution within the infected cell and causes defective budding

Two temperature-sensitive (ts) mutants of the M protein of vesicular stomatitis virus (tsG31 and tsG33) are defective in viral assembly, but the exact nature of this defect is not known. When infected cells are switched from nonpermissive (40 degrees C) to permissive (32 degrees C) temperatures in the presence of cycloheximide, tsG33 virus release increased by 100-fold, whereas tsG31 release increased only by 10-fold. Thus, the tsG33 defect is more reversible than that of tsG31. Therefore, we investigated how the altered synthesis and cellular distribution of tsG33 M protein correlates with the viral assembly defect. At 32 degrees C tsG33 M protein is stained diffusely in the cell cytoplasm and later at the budding sites. In contrast, at 40 degrees C the mutant M protein formed unusual aggregates mostly located in the perinuclear regions of virus-infected cells and partially colocalized with G protein in this region. In temperature shift-down experiments, M can be disaggregated and used to some extent for nucleocapsid coiling and budding, which correlates with the virus titer increase. M aggregates also formed after shift-up from 32 to 40 degrees C, indicating a complete dependence of M aggregation on the temperature. Biochemical analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting revealed that at 40 degrees C M protein is detected exclusively in pellet fractions (nuclear and cytoskeleton components), whereas at 32 degrees C M protein is mainly in the cytoplasmic soluble fractions. Furthermore, when the temperature is raised from 32 to 40 degrees C, the distribution of M protein tends to shift from the soluble to the pellet and cytoskeletal fractions. Electron micrographs of immunoperoxidase-labeled M protein showed that at 40 degrees C M aggregates are often associated with the outer nuclear membranes as well as with vesicular structures. No nucleocapsid coiling was observed in these cells, whereas coiling and budding were seen at 32 degrees C in cells where M protein was partly associated with the plasma membrane. We suggest that the tsG33 M protein mutation may produce a reversible conformational alteration which causes M protein to aggregate at 40 degrees C, therefore inhibiting the proper association of M protein with nucleocapsids and budding membranes.

CSF-1-induced resistance to viral infection in murine macrophages

Murine peritoneal thioglycollate-elicited macrophages were cultured for 3 days in the presence or absence of highly purified human macrophage colony stimulating factor (CSF-1). The cells were then challenged with vesicular stomatitis virus (VSV) for 24 hr. Ability to resist viral infection was measured in two ways. First, macrophage viability after infection with VSV was measured by washing to remove dead cells, staining the remaining cells with crystal violet, and reading absorbance. Second, a yield reduction assay was used to measure viral replication in the macrophage cultures. Cells treated with CSF-1 (500 to 2000 U/ml) and infected with VSV looked similar microscopically to uninfected cells and had absorbance values twofold to threefold higher than those of infected cultures not treated with CSF-1. The CSF-1-treated cultures also had a virus titer one log lower than that of the untreated cultures. Treatment with partially purified murine CSF-1 induced a similar reduction in virus titer, whereas other murine CSF tested (purified murine GM-CSF, lung-conditioned medium that contains GM-CSF and G-CSF, and WEHI-3B-conditioned medium as a source of IL 3) had little to no effect on virus titer. Antibody to murine IFN-alpha/beta added to the macrophage cultures inhibited the protective effect of CSF-1, indicating that the CSF-1 effect was due to induction of endogenous IFN. Treatment with lipopolysaccharide (1 ng/ml) had some protective effect, which was blocked with polymyxin B. Polymyxin B did not inhibit the effect of CSF-1.

Natural infection of humans, animals, and phlebotomine sand flies with the Alagoas serotype of vesicular stomatitis virus in Colombia

Five isolations of the Alagoas serotype of vesicular stomatitis virus (Rhabdoviridae: Vesiculovirus) were made from naturally infected phlebotomine sand flies (Lutzomyia spp.) collected in Colombia. These are the first isolations of Alagoas virus from an arthropod. Replication of the virus occurred in laboratory-reared sand flies (Lutzomyia longipalpis) after inoculation. Bite and transovarial transmission of the virus was also demonstrated in experimentally infected sand flies. Alagoas virus neutralizing antibodies were found in sera of humans and animals living near the insect collection site; antibody rates among human residents of two nearby towns were 63% and 83%, respectively. Results of comparative serologic studies demonstrated that Alagoas virus is closely related antigenically to Indiana, Cocal, and Maraba viruses and that these four agents form a complex within the vesicular stomatitis virus serogroup. The antigenic similarity among these four viruses makes their differentiation difficult; it also raises doubts about the accuracy of current laboratory methods used for identifying isolates in this serogroup. A discussion follows on the significance of human antibodies to these agents and on the role of sand flies in their ecology.

Adenovirus early region 1A modulation of interferon antiviral activity

Human adenovirus type 5 (Ad5) is a DNA virus which replicates as efficiently in human A549 cells treated with human interferon-alpha 2 (IFN) as in untreated cells. Vesicular stomatitis virus (VSV), on the other hand, is a negative-strand RNA virus which is very sensitive to the effects of IFN treatment in A549 cells. The IFN-mediated inhibition of VSV replication was not observed in cells coinfected with Ad5. Abrogation of IFN-mediated antiviral activity was maximal when Ad5 infection preceded VSV infection by at least 36 h, but did not require adenovirus DNA synthesis for manifestation. Coinfection experiments with VSV and deletion variants of adenovirus demonstrated that neither virus-associated RNA synthesis nor expression of adenovirus early regions E1B, E2A, E3, or E4 are required for abrogation of IFN-mediated inhibition of VSV replication. However, expression of early region E1A was essential, suggesting that E1A products can modulate, either directly or indirectly, IFN activity in adenovirus-infected cells.

Selective infections of olfactory and respiratory epithelium by vesicular stomatitis and Sendai viruses

Following intranasal instillation of vesicular stomatitis virus (VSV) in mice there was an extensive infection of the olfactory epithelium in contrast to a minimal involvement of the respiratory epithelium. Sendai virus (SV), on the other hand, caused an extensive infection of the respiratory epithelium and only minimal infection of the olfactory mucous membrane. VSV budded from basolateral surfaces of supporting cells and olfactory neurons, but not from their apical surfaces or the ciliated bulbous endings of the olfactory neuron dendrites. This asymmetric release of VSV favoured neuroinvasion. The virus spread along the olfactory nerves to the glomeruli in the olfactory bulbs after which it propagated transneuronally into the rest of the brain. SV budded only from the apical surface of respiratory epithelial cells, was released into the air passages, and there were no signs of invasion into the olfactory bulbs. Inoculation of the olfactory mucous membrane is a useful procedure for studies on selectivity of attack on peripheral neurons by viruses and on mechanisms of virus invasion of the nervous system in vivo.

Inhibition of vesicular stomatitis viral mRNA synthesis by interferons

Interferon (IFN) treatment inhibited the replication of vesicular stomatitis virus (VSV) in human GM2767 and mouse JLSV-11 cells. The replication of this virus in either human RD-114 or mouse A402 cells was insensitive to IFN treatment. We analyzed various steps in the VSV life cycle as they occurred under different conditions of IFN treatment to identify the point(s) at which IFN was exerting its inhibitory effect. IFN treatment led to strong inhibition of viral protein synthesis and accumulation of viral RNA in both lines of IFN-sensitive cells. No such effect was observed in the IFN-resistant cells. Using a temperature-sensitive mutant (tsG41) and wild-type VSV that were not undergoing protein synthesis, we determined that the major site of action of IFN against VSV replication in JLSV-11 and GM2767 cells was at the level of primary viral transcription. The accumulation of primary viral transcripts was strongly inhibited in these cells by IFN treatment. This effect was not a consequence of any effect of IFN on virus entry and uncoating. Thus, it appears that IFN exerts a direct effect on the VSV transcriptional process in GM2767 and JLSV-11 cells.

Antiproliferative assay of human leucocyte interferon

An in vitro microtitration system of the antiproliferative effect of human leucocyte interferon (IFN-alpha(Le)) was investigated. The preliminary experiments suggested that the antiproliferative effect of IFN-alpha(Le) was increased by prolonging the incubation period, by reducing the target cell concentration, and might be prescribed by the total IFN amounts in the challenge medium. By employing a system consisted of 1.5 X 10(4) Daudi cells in 0.2 ml of medium containing IFN dilutions and an incubation period of 3 days at 37 degrees C, the antiproliferative effects of twenty-one lots of partially purified IFN-alpha(Le) (PIF-alpha(Le)) preparations were titrated. The interassay variations in the antiproliferative titers of three PIF-alpha(Le) established in the present system were found to be in the same range as those in the antiviral titers estimated by a standard macroplaque reduction assay. The each titration curve was parallel, and the antiproliferative titers, assessed by the reciprocals of the IFN dilutions which suppress the cell growth in 50%, were significantly (p less than 0.01) correlated to the antiviral international units of them.

Macrophages from endotoxin-hyporesponsive (Lpsd) C3H/HeJ mice are permissive for vesicular stomatitis virus because of reduced levels of endogenous interferon: possible mechanism for natural resistance to virus infection

The C3H/HeJ mouse strain bears an autosomal gene defect, Lpsd, which results in a greatly diminished capacity to respond to endotoxin, the ubiquitous lipopolysaccharide derived from the cell walls of gram-negative bacteria. These mice also exhibit greater susceptibility to a variety of viral and bacterial infections than syngeneic, fully lipopolysaccharide-responsive (Lpsn) mouse strains and possess macrophages with defects in differentiation which are reversed by treatment with exogenous interferon (IFN). To test directly the hypothesis that C3H/HeJ macrophages are deficient in endogenous IFN levels, macrophages from C3H/HeJ (Lpsd) and C3H/OuJ (Lpsn) mice were compared for sensitivity to vesicular stomatitis virus. At a multiplicity of infection of 0.1, C3H/OuJ macrophages were completely refractory to infection, whereas C3H/HeJ macrophages were permissive for replication, and infection resulted in 100% cytopathic effect. These findings were confirmed with a second inbred Lpsn and Lpsd strain pair. Levels of 2',5'-oligoadenylate synthetase were significantly higher in Lpsn cells. C3H/HeJ macrophages, derived from bone marrow precursors under the influence of macrophage colony-stimulating factor, shown previously to induce IFN in macrophages, were as refractory as C3H/OuJ macrophages. Exposure of nonpermissive macrophages to anti-IFN-alpha/beta antibody prior to infection rendered cells permissive. Our findings suggest that endotoxin provides a primary stimulus for the maintenance of normal macrophage differentiation and innate resistance via the induction of endogenous IFN by macrophages.

The mechanism of the antiviral effect of interferon differs in two strains of a rabbit kidney cell line

Two variant strains of a rabbit kidney cell line, RK-13, differ markedly in their interferon (IFN)-mediated antiviral mechanism. Both strains are permissive for the growth of vesicular stomatitis (VSV) and vaccinia viruses. Following treatment with 100 U/ml of rabbit IFN, both cell strains restrict VSV yield about a 1000-fold; vaccinia is not inhibited by IFN in either cell strain. However, vaccinia is able to rescue VSV from the inhibitory effects of IFN in one strain (RK-13), but not in the other strain of cells (RK-13-37). Investigation of the mechanism of this phenomenon reveals that VSV growth is blocked at different levels in the two cell strains. In the strain in which vaccinia can rescue VSV from the effects of IFN (RK-13), the major IFN-mediated restriction of VSV growth is at the level of protein synthesis; in the other strain in which vaccinia is unable to rescue VSV (RK-13-37), IFN restricts VSV at earlier steps, including penetration and primary transcription. The two cell strains provide useful models for studying the multifaceted nature of IFN-mediated antiviral effects.

Interferon level in human normal sera

Interferon (IFN) level in the sera of normal humans was determined by their protective effect on a KB cell culture against the cytopathic effect (CPE) induced by vesicular stomatitis virus. The technique revealed all the three known types of IFN. In the investigated population 15 of 37 sera (40%) were found to protect against the CPE at 1/10 dilution, 11 of 37 (30%) still protect at 1/20 dilution, and 7 of 37 sera (19%) still protect at a dilution of 1/40. No serum was found to have detectable IFN levels at 1/80 dilution. We can thus consider that the normal serum level ranges up to a 1/20 dilution i.e., up to 20 IU/ml. The above titers are slightly higher than the normal IFN level reported by other investigators in other human populations, although no clear reasons can be given to account for the differences.

The influence of high temperature on human cells in culture, their sensitivity to viruses and their interferon-producing capacity

The influence of extremely high temperatures on the course of virus infection in vitro was studied. It has been shown that exposure of human cells (continuous cell line of embryonal skin-muscle tissue, donor blood leukocytes) to 43 degrees C leads to a significant increase in their sensitivity to cytopathic action of the viruses tested. Noteworthy, the reproduction of these viruses under tested conditions did not differ from their reproduction in control cells. A dramatic inhibitory effect of high temperatures on the interferon-producing capacity of cells was observed.

Serum protein masking of the thermal sensitivity of the antiviral activity of purified human beta interferon: implications for clinical studies

Human beta-interferon (HuIFN-beta) exhibits antiproliferative and antiviral properties. Successful clinical application of this drug depends on knowledge of the thermal stability of these activities under physiological conditions. In the present study, both the antiproliferative and antiviral activities were stabilized by the addition of very small quantities of serum proteins. This supplement was sufficient to mask the slightly higher thermosensitivity of the antiviral activity. In the absence of serum proteins, the values of both the half-life and the energy of activation were higher for the antiproliferative activity than for the antiviral function. Each had a half-life of at least 24 h and identical values for the energy of activation in the presence of proteins furnished by 1% fetal bovine serum. This study provides additional evidence to support a thesis recently advanced by Carter et al. that the antiproliferative domain of glycosylated beta interferon may be separable from the antiviral domain. It is concluded that the efficacy of HuIFN-beta, under clinical conditions, will not be seriously impaired by thermal inactivation. Antiviral assays of serum may be freely substituted for antiproliferative assays during pharmacological studies.

Interferon-mediated self-limiting growth of respiratory syncytial virus in mouse embryo cells

The growth of respiratory syncytial (RS) virus in primary mouse embryo (ME) cells was investigated. The virus yields in ME cells were markedly lower if compared with those in HEp-2 cells, which are fully permissive for RS virus, and a remarkable production of interferon (IFN) was found in the early period of infection of the former cells. The virus yields in ME cells were enhanced when antimouse IFN serum was added to the medium. Indirect immunofluorescent staining of infected ME cells showed that the infection spread in the entire monolayer in the presence of antiserum, whereas it was markedly restricted throughout in the absence of the serum. All the major viral polypeptides were synthesized in the absence of the serum. However, their synthesis rates were greatly enhanced if the antiserum was added. These results suggest that the virus growth in ME cells is self-limiting and that this limited growth is due to autointerference by endogenously produced IFN during the course of infection. Further, this type of growth restriction of RS virus appears to be characteristic of cells of mouse origin by comparative studies that used other cells of different origin.

Properties of natural and hybrid murine alpha interferons

Four natural murine interferon-alpha genes (MuIFN-alpha 1, -alpha 2, -alpha 4 and -alpha 6) and four hybrid genes (alpha 1 alpha 4, alpha 2 alpha 4, alpha 4 alpha 1 and alpha 4 alpha 2) were transiently expressed in monkey COS cells under the transcriptional control of the simian virus 40 early promoter. The proteins were labelled with [35S]methionine during a 16 h incubation and proteins secreted by the cells during this period were separated by polyacrylamide gel electrophoresis and subsequently visualized by fluorography. Under the conditions used, the IFNs represented 5 to 10% of the total amount of secreted proteins. All genes were found to encode biologically active IFN subspecies, including alpha 4 which has a deletion of five amino acids. When the specific activities of the proteins were compared, it appeared that the specific antiviral activity of alpha 4 on mouse cells was three- to sixfold higher than the activities of the other natural IFN subspecies. The specific activities of the hybrid proteins were similar to those of the natural proteins, except for the alpha 2 alpha 4 hybrid which had a higher specific activity than the original proteins. The ability of the natural and hybrid subspecies to protect hamster cells against viral infection was determined using MuIFN-alpha 1 as a standard. Large differences in activity were found, with alpha 6 as the most and alpha 4 as the least active subspecies.

An antiviral state induced in HeLa cells by microinjected poly(rI).poly(rC)

The direct introduction with micropipettes of poly(rI).poly(rC) into the cytoplasm of several human cell lines inhibited the multiplication of vesicular stomatitis virus. This antiviral activity was at least partly due to interferon (IFN) production and secretion from the injected cells since it was species-specific, partly neutralized by IFN antibodies and was transmissible to non-adjacent cells. This suggests a mechanism of IFN induction involving the internalization of poly(rI).poly(rC) and its interaction with an intracellular target.

Biological activities and receptor binding of two human recombinant interferons and their hybrids

Two human recombinant lymphoblastoid interferon-alpha subtypes, LyIFN-B (alpha 8) and LyIFN-D (alpha 1), and 10 hybrids generated therefrom were produced in Escherichia coli and purified. The antiviral and antiproliferative activities and the induction of (2'-5')oligoadenylate synthetase were compared to their receptor binding affinities. The IFN subtypes and their hybrids had similar specific antiviral activities on bovine cells. On human cells both the specific antiviral and antiproliferative activities of LyIFN-B were about 30-fold higher than those of LyIFN-D. This difference in activity could be attributed partly to the N-terminal amino acids 1 to 60 and partly to amino acids 61 to 92. A third domain affecting the biological activities was found within the carboxy-proximal segment from amino acids 93 to 150. The differences in these activities were found to correlate with their ability to bind the receptor, suggesting that the differences in activity might be due to altered binding of the IFNs to the cellular receptors. In contrast, the induction of (2'-5')oligoadenylate synthetase did not follow the same activity profile. On mouse cells, the efficiency of the hybrids was affected by at least four sites on the IFN protein. A hybrid with the N-terminal segment 1 to 60 from IFN-B and amino acids 61 to 166 from IFN-D had a specific antiviral activity on mouse cells as high as on human cells corresponding to a 500- and 5000-fold increase in specific activity compared to IFN-D and IFN-B, respectively. We suggest that on mouse cells the IFN activity may be more dependent on conformational differences than on human cells, which in turn might reflect a less precise fit to the mouse receptor than to the human receptor.

Study of receptors for vesicular stomatitis virus in vertebrate and invertebrate cells

Early interactions between vesicular stomatitis virus (VSV) and susceptible cells were examined in cell lines of mammalian (HeLa), bird (CER), piscine (EPC) and arthropod (Aedes albopictus) origin showing different permissiveness to VSV growth. The chemical nature of receptors was investigated either by modification of cell surfaces with different enzymes or by competition for VSV binding between extracted membrane components and whole cells. Results obtained indicate that in all cell models, membrane lipid components show receptor activity whereas glycid groups participate to the in virus binding to a different extent.

Antiviral effect of two aryl-oligopeptides, FR41565 and FR48217

Macrophages from mice pretreated with two chemically synthesized immunostimulating aryl-oligopeptides, FR41565 and FR48217, inhibited the multiplication of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in monkey Vero cells, and that of vesicular stomatitis virus (VSV) in murine L929 cells. In addition, the aryl-oligopeptides protected mice against a lethal HSV-1 infection. In particular, when treated with FR48217 at 6 mg/kg, all mice survived, whereas all control mice died from the HSV-1 infection.

An enzyme-linked immunosorbent assay for the detection of bovine antibodies to vesicular stomatitis virus

An indirect enzyme-linked immunosorbent assay (ELISA) was developed to detect bovine antibody to vesicular stomatitis virus (VSV). Serum samples from cows experimentally infected with the New Jersey serotype of VSV (VSV-NJ) were assayed by the ELISA and serum-neutralization (SN) assay. The ELISA was as sensitive as the SN assay in detecting bovine antibody to VSV. The correlation between SN titers and ELISA values at absorbance at 405 nm was statistically significant. The ELISA was not specific for VSV-NJ, however, and could detect serum samples positive to the Indiana serotype of VSV that had SN titers of greater than or equal to 480. Nonspecific reactions were due to cross-reactive group-specific viral proteins that are shared by both serotypes. The cross-reactivity allows the use of a single rapid test in identifying both serotypes of VSV from the other exotic vesicular diseases, especially foot-and-mouth disease. The ELISA titers of serum samples positive for VSV-NJ were comparable with the corresponding SN titers of each sample. The sensitivity, rapidity, and ease of the ELISA system and the use of a single test in identifying both serotypes of VSV from the other exotic vesicular diseases make this ELISA suitable as a rapid diagnostic assay for VS.

Very rapid generation/amplification of defective interfering particles by vesicular stomatitis virus variants isolated from persistent infection

Multiply cloned variants of vesicular stomatitis virus (VSV) were found to generate/amplify defective interfering (DI) particles at a rate greatly exceeding the rates normally observed for wild-type VSV (or for other mutants of VSV). A single undiluted passage of the first clonal pool of this variant virus produced concentrated visible bands of DI particles on sucrose gradients whereas wild-type and other mutant strains of VSV required from three to six or more serial undiluted passages. Since DI particle amplification by wild-type VSV at each undiluted passage can exceed 10,000-fold enrichment, these variant virus clones were generating/amplifying DI particles many millions of times more rapidly than were wild-type and other mutant strains of VSV. This rate of generation/amplification is so high that it was not feasible to obtain accurate estimates of the rates of generation (or amplification) of these DI particles.

Increased resistance to the anticellular effect of interferon in an ultraviolet light-resistant human cell line, UVr-1

Interferon (alpha, beta and gamma) susceptibility was tested in a human cell line, UVr-1, a u.v. light-resistant variant of RSa cells; the latter have high sensitivity to both u.v. lethality and the cell proliferation inhibition (anticellular) effect of human interferon (HuIFN) preparations. UVr-1 cells were less sensitive than the parental RSa cells to the inhibitory effects of HuIFN preparations, as measured by cell proliferation and the incorporation of [3H]deoxythymidine and [3H]deoxyadenosine into acid-insoluble cellular material. Nevertheless, UVr-1 cells exposed to HuIFN showed almost the same enhanced levels of antiviral activity and pppA(2'p5'A)n synthetase activity as similarly treated RSa cells. Further, UVr-1 cells had much the same binding capacity for 125I-labelled HuIFN-alpha A. Thus, it seems likely that the variant has an increased resistance to the anticellular effect but not to the antiviral effect of HuIFN preparations. UVr-1 cells showed no significant difference from RSa cells in u.v.-induced DNA repair synthesis. However, when a comparison was made between the susceptibility of normal fibroblasts and fibroblasts from patients with Cockayne's syndrome, characterized by an altered u.v. sensitivity but no alteration of DNA repair replication synthesis, the Cockayne's syndrome fibroblasts, CCK-3 and CCK-4, were more susceptible to HuIFN-beta as judged by cell proliferation and deoxythymidine incorporation tests.

Interferon induction with polyinosinic:polycytidylic acid in the newborn piglet

Newborn piglets were treated with various doses of polyinosinic:polycytidylic acid intravenously and their serum interferon responses determined by a plaque reduction assay with vesicular stomatitis virus in Madin-Darby bovine kidney cells. A single dose of 5 mg of polyinosinic:polycytidylic acid was found consistently to induce detectable levels of interferon in serum, while the response to lower doses was inconsistent and higher doses produced clinical signs of toxicity. Piglets receiving 5 mg of polyinosinic:polycytidylic acid had maximum serum interferon titers between four and eight hours after treatment, and interferon was no longer detected at 72 hours after treatment. Following treatment with polyinosinic:polycytidylic acid leukopenia was observed, coincident with peak serum interferon titers. Elevated levels of serum glutamic oxaloacetic transaminase and blood urea, indicative of hepatic and renal dysfunction respectively, were also observed following interferon induction with polyinosinic:polycytidylic acid. Piglets treated with polyinosinic:polycytidylic acid also demonstrated antiviral activity in their intestinal mucosal tissues and intestinal washes, but the antiviral activity in the intestinal wash was not characterizable as interferon. A factor in the intestinal washes from newborn piglets was found to antagonize the antiviral effects of interferon by enhancing the plaque forming ability of vesicular stomatitis virus.

Mouse peritoneal cells confer an antiviral state on mouse cell monolayers: role of interferon

Vesicular stomatitis virus and encephalomyocarditis virus do not multiply in the majority of peritoneal macrophages freshly explanted from 4- to 8-week-old male or female mice. However, when peritoneal macrophages were cultivated in vitro for 3 to 5 days, these cells became permissive for both viruses. The loss of antiviral state in "aged" macrophages paralleled a significant decrease in the intracellular levels of (2'-5')oligo-adenylate synthetase activity. Although biologically active interferon was not detected in the nutrient medium of macrophage cultures, freshly harvested peritoneal cells could confer an antiviral state on monolayer cultures of mouse cells (aged macrophages, embryonic fibroblasts, and L cells) but not on heterologous chicken embryo, rabbit kidney, or human cells infected with vesicular stomatitis virus or encephalomyocarditis virus. The conferred antiviral state required at least 7 h to develop in target cells and was totally inhibited by the presence of antibody to mouse interferon alpha/beta but not to interferon gamma in the cocultures. Heterologous guinea pig and rabbit peritoneal cells could not transfer an antiviral state to target mouse cells. Donor peritoneal cells from mice preinjected with antibody to interferon alpha/beta could not transfer an antiviral state to target mouse cells. This ensemble of results indicating that freshly harvested peritoneal cells transfer interferon (which is responsible for inducing an antiviral state in susceptible mouse target cells) adds further experimental evidence that interferon is spontaneously expressed in normal mice and plays an important role in maintaining some host cells in an antiviral state.

Polarized plasma membrane domains in cultured endothelial cells

To determine whether distinct plasma membrane domains exist in endothelial cells, we infected monolayer cultures of macro- and microvascular endothelial cells with enveloped RNA viruses known to bud selectively from either the apical or basal surface in polarized epithelial cells. We found that vesicular stomatitis (VSV) and Sendai virus emerge asymmetrically from cultured endothelial cells. This provides direct evidence for the existence of polarized plasma membrane domains in vascular endothelial cells.

In vivo and in vitro models of demyelinating diseases. XII. Persistence and expression of corona JHM virus functions in RN2-2 Schwannoma cells during latency

The coronavirus JHMV persistently infects rat Schwannoma cells RN2-2 at 32.5 degrees C and enters a host-imposed reversible, latent state at 39.5 degrees C. JHMV can remain up to 20 days in the latent state and about 14 days before the cultures lose the capacity to resume virus production upon return to 32.5 degrees C. Although persistently and latently infected RN2-2 cells display resistance to superinfection by a heterologous agent VSV, these cells do not release detectable soluble mediators (e.g., interferon) of the antiviral state. Nevertheless, RN2-2 cells are competent to synthesize and release interferon when treated with the appropriate inducers. These observations suggest that interferon does not play any role or may not be the major factor in the control of latency in the Schwannoma cell. Hybridization with virus-specific cDNAs shows that all viral mRNAs are present during latency and that viral mRNAs are present in the polysomes of infected cells at 39.5 degrees C. Western immunoblotting with hybridoma antibodies demonstrates that viral specific proteins are produced at the restrictive temperature. These results suggest that despite the absence of production of infectious virus at 39.5 degrees C, there is active transcription and translation into virus-specified products.

Glucocorticoid-mediated establishment of an antiviral state coincident with other glucocorticoid-induced biochemical activities in L929 cells

Incubation of L929 cells with three different glucocorticoids, hydrocortisone, dexamethasone and triamcinolone acetonide, rendered the cells unable to support plaque formation by several unrelated DNA and RNA viruses. The establishment of this antiviral state by dexamethasone coincided with an inhibition of cell growth and induction of glutamine synthetase activity. These steroid-mediated activities occurred only in cultures of L929 cells and not in cultures of rabbit skin or rat glioma cells.

Effect of monensin on the synthesis, maturation and secretion of vesicular stomatitis virus proteins in a monensin-resistant Chinese hamster ovary cell line

We compared the effects of the cationic ionophore, monensin, on the synthesis, maturation and release of vesicular stomatitis virus (VSV) in cultures of Chinese hamster ovary (CHO) cells and the monensin-resistant clone, MonR-31. Our results depended on the dose and time of the addition of monensin to the infected cells, from 1 h prior to VSV infection to 1 h after infection. VSV production was more resistant in MonR-31 than in CHO cells when the ionophore was added 1 h prior to VSV infection. Monensin added 1 h after VSV infection showed the opposite phenomenon; release of virus particles into the medium was 10- to 10(5)-fold less in MonR-31 cells than in CHO cells, and the intracellular virus number in the resistant cells was one-third to one-fourth of that in the parental CHO cells. Syntheses of all virus-associated G, N and M proteins were inhibited in both cell lines by monensin, but especially so in the MonR-31 cells. There were no marked qualitative changes in the biochemical properties of viral glycoprotein G in virus-infected CHO and MonR-31 cells treated with monensin after virus infection. An endoglycosidase H-resistant G with a molecular weight smaller than that of normal G and attachments of palmitate or fucose on the truncated G protein appeared. Alteration of the secretion of as well as the synthesis of the enveloped virus is discussed in relation to the monensin susceptibility of the resistant MonR-31 clone.

Monensin-resistant mouse Balb/3T3 cell mutant with aberrant penetration of vesicular stomatitis virus

A mutant (MO-5) resistant to monensin (an ionophoric antibiotic) derived from the mouse Balb/3T3 cell line, was a poor host for vesicular stomatitis virus (VSV) or semliki forest virus (SFV) multiplication. The yield of VSV particles in MO-5 is one 100-fold reduced as is VSV-dependent RNA synthesis. In contrast to a pH-remedial mutant, the abortive production of infectious VSV particles in MO-5 cells was not restored by low pH treatment. The pH values in the endosome and the lysosome of MO-5 cells were 5.2 and 5.4, respectively, values that were comparable to the pH value in Balb/3T3 cells. Assays with [3H]uridine-labeled VSV indicated similar binding of VSV in MO-5: percoll gradient centrifugation analysis of [35S]methionine-labeled VSV-infected Balb/3T3 showed accumulation of VSV in the lysosome fraction 20 min after VSV infection, whereas VSV can be found mainly in endosome/Golgi fraction of MO-5 cells after 40 to 60 min on the percoll gradients. Degradation of [35S]methionine-labeled VSV was observed at a significant rate in Balb/3T3 cells, but not in MO-5 cells. The monensin-resistant somatic cell may thus provide a genetic route to study the mechanism of endocytosis or transport of enveloped viruses.

Pharmacokinetic study of a human recombinant interferon (Re-IFN-alpha A) in cynomolgus monkeys by 2'-5' oligoadenylate synthetase assay

We evaluated 2'-5'Oligoadenylate (2-5 A) synthetase assay for pharmacokinetic study of human interferon (IFN) in cynomolgus monkeys. The enzyme was induced in primary cultures of cynomolgus monkey kidney (PMK) cells as well as in FL cells in response to human recombinant IFN-alpha A treatment. The enzyme activity increased with IFN dose and, in parallel with the enzyme elevation, developed the antiviral state of the cells. The enzyme activity induced in the peripheral blood lymphocytes peaked at 6 to 12 hr after iv or im administration. The peak level of the enzyme activity depended on the IFN concentration of the blood and the activity rapidly decreased as serum IFN was cleared from the blood. These results indicate that human recombinant IFN-alpha A induces 2-5 A synthetase in monkey cells both in vitro and in vivo, and that the enzyme assay can be used to quantitatively monitor the host response after IFN administration.