Characterization of virulent isolates of vesicular stomatitis virus in relation to interference by defective particles

Mutagenesis-mediated virus extinction: virus-dependent effect of viral load on sensitivity to lethal defection

BACKGROUND

Lethal mutagenesis is a transition towards virus extinction mediated by enhanced mutation rates during viral genome replication, and it is currently under investigation as a potential new antiviral strategy. Viral load and virus fitness are known to influence virus extinction. Here we examine the effect or the multiplicity of infection (MOI) on progeny production of several RNA viruses under enhanced mutagenesis.

RESULTS

The effect of the mutagenic base analogue 5-fluorouracil (FU) on the replication of the arenavirus lymphocytic choriomeningitis virus (LCMV) can result either in inhibition of progeny production and virus extinction in infections carried out at low multiplicity of infection (MOI), or in a moderate titer decrease without extinction at high MOI. The effect of the MOI is similar for LCMV and vesicular stomatitis virus (VSV), but minimal or absent for the picornaviruses foot-and-mouth disease virus (FMDV) and encephalomyocarditis virus (EMCV). The increase in mutation frequency and Shannon entropy (mutant spectrum complexity) as a result of virus passage in the presence of FU was more accentuated at low MOI for LCMV and VSV, and at high MOI for FMDV and EMCV. We present an extension of the lethal defection model that agrees with the experimental results.

CONCLUSIONS

(i) Low infecting load favoured the extinction of negative strand viruses, LCMV or VSV, with an increase of mutant spectrum complexity. (ii) This behaviour is not observed in RNA positive strand viruses, FMDV or EMCV. (iii) The accumulation of defector genomes may underlie the MOI-dependent behaviour. (iv) LCMV coinfections are allowed but superinfection is strongly restricted in BHK-21 cells. (v) The dissimilar effects of the MOI on the efficiency of mutagenic-based extinction of different RNA viruses can have implications for the design of antiviral protocols based on lethal mutagenesis, presently under development.

Interferon induction by viruses. XXI. Vesicular stomatitis virus: interferon inducibility as a phylogenetic marker

Forty-five vesiculovirus isolates were systematically compared for their capacity to induce interferon (IFN) in chick embryo cells under conditions such that the maximum (quantum) yield of IFN per cell and the titer of IFN-inducing particles (IFP) could validly be determined. Twelve isolates of the New Jersey (NJ) serotype of vesicular stomatitis virus (VSV) were good inducers, yielding amounts of IFN that ranged in a continuum from 300 to more than 8,000 units per 10(7) cells. These must reflect genetic differences between the closely related viruses. These differences were not reflected in the nucleotide sequence of the viral 3' leader RNA, for analysis of eight of the NJ isolates showed no correlation with the IFN yields. As found in previous smaller surveys, 28 out of 32 VSV isolates of the Indiana (IN) serotype produced little or no IFN, or even suppressed its induction. However, four exceptional IN strains were isolated during 1984 and 1985 from cattle within a relatively circumscribed geographical area in Costa Rica and Panama; all belonged to Indiana virus, type 1, subtype IV, in the proposed G-protein gene evolutionary tree. This is the first example of an IFN-inducing phenotype serving as a phylogenetic marker.

Interferon induction by viruses. XVIII. Vesicular stomatitis virus-New Jersey: a single infectious particle can both induce and suppress interferon production

In contrast to wild-type vesicular stomatitis virus (VSV) of Indiana (Ind.) origin which express interferon (IFN) inducing- and IFN induction-suppressing activities as mutually exclusive properties, individual particles of wild-type VSV of the New Jersey (N.J.) serotype (Hazelhurst [H] isolate) paradoxically can both induce IFN and suppress its induction in cells coinfected with a potent inducer of IFN. The properties of IFN induction, and its suppression, appear to reside in the particle that manifests infectivity. Analyses of IFN induction dose-response curves to measure IFN-inducing particles (IFP), and IFN yield-reduction curves to measure IFN induction-suppressing particles (ISP) generated by VSV-N.J.(H) in aged chick embryo cells revealed that (i) a single particle per cell sufficed to induce a quantum (full) yield of IFN, or to suppress fully IFN production by a coinfecting inducing virus, and (ii) the addition of one or more IFP per cell did not suppress the yield of IFN beyond the plateau level. The time-course of IFN production in chick cells infected with VSV-N.J. (H) revealed about a 4-h lag, even when the cells were coinfected with a potent inducer that normally induced IFN 1 or 2 h sooner. Thus, VSV-N.J.(H) appears to regulate the production of IFN in cells--even that initiated by other inducers. Expression of IFP and ISP activities both required primary transcription, with respective genomic targets similar to those reported for VSV-Ind. N.J.(H) is the first wild-type VSV observed to express IFP and ISP activities concomitantly. A model is presented to suggest how these two antagonistic properties might be expressed by a single infectious particle.

Interferon induction by viruses. XIX. Vesicular stomatitis virus--New Jersey: high multiplicity passages generate interferon-inducing, defective-interfering particles

The infectious particles of plaque-derived, low multiplicity passaged wild-type VSV of New Jersey origin consistently induce about 1800 units of interferon (IFN)/10(7) aged chick embryo cells. This inducing capacity is sensitive to both uv radiation and heat (50 degrees). Virus obtained after two successive high multiplicity passages in GMK-Vero cells consistently induced over 25,000 units of IFN/10(7) cells. The IFN induction dose-response curve showed that one IFN-inducing particle (IFP) per cell sufficed to produce a quantum yield of IFN, but infection with two or more IFPs led initially to a marked suppression in the yield of IFN. IFN induction was attributed to two distinct defective particles that differed in size, both containing snap-back RNA, i.e., covalently linked, self-complementary [+/-]RNA. The IFN-inducing capacity of these defective-interfering particles was not inactivated by uv or heat. However heat did eliminate the IFN suppressing activity observed at higher multiplicities, implicating a heat-sensitive component in the virion as a regulator of IFN yield, and involving possibly the virion transcriptase and 3'-leader RNA product.