Two clones obtained from Urabe AM9 mumps virus vaccine differ in their replicative efficiency in neuroblastoma cells

A high rate of post-vaccinal aseptic meningitis for Urabe AM9 mumps virus strain is well documented. This strain is composed of two virus variants differing at the nt 1081 (A/G) region in the hemagglutinin-neuraminidase (HN) gene. An association of HN-A(1081) variant with neurovirulence has been proposed. In order to test for neurotropism we isolated the HN-A(1081) and HN-G(1081) virus variants from Urabe AM9 mumps virus vaccine. Sequential passages were performed in monkey kidney Vero cells and human neuroblastoma SH-SY5Y cells. Viral replication was determined by conventional and real-time RT-PCR. The results show that clone HN-A(1081) can replicate efficiently in both cell types. However, a defective replication of clone HN-G(1081), lacking its genetic marker, was observed after the third passage in neuroblastoma cells. Kinetics assays showed that clone HN-A(1081) replicates faster than clone HN-G(1081). Viral clones were also inoculated into the brains of newborn rats. Clone HN-A(1081) replicated 14 times, while clone HN-G(1081) merely duplicated its level over the initial inoculum. These results suggest that there is a selective replication of HN-A(1081) mumps virus variants in cells of nervous origin.     

Dissociation of interferon effects on murine leukemia virus and encephalomyocarditis virus replication in mouse cells.

Two subclones of Swiss mouse cells infected with Moloney murine leukemia virus (M-MuLV) were tested for their response to interferon (IFN). Whereas M-MuLV production in the two subclones was inhibited to the same extent, one of the subclones was significantly more sensitive to IFN when the antiviral effect was measured by replication of encephalomyocarditis (EMC) virus. The same subclone was also more sensitive to the anticellular activities of IFN. Additionally, NIH 3T3 cells infected with M-MuLV were completely resistant to IFN actions when EMC virus replication or the anticellular activities were tested. However, under the same conditions, M-MuLV production was completely inhibited by IFN. These results indicate that IFN may affect cell growth functions and EMC replication through mechanisms different from those by which MuLV production is inhibited.     

The reactogenicity and immunogenicity of the Urabe Am 9 live mumps vaccine and persistence of vaccine induced antibodies in healthy young children

The immunogenicity and reactogenicity of the Urabe Am 9 mumps virus vaccine strain were studied after the administration of different doses of the vaccine to 197 children ranging in age from seven and a half months to nine years and without a history of mumps. There was no effect of dose on the response in serum neutralizing antibodies in the range of 10(2.9) to 10(4.7) TCID50/dose. In the 90 subjects without detectable serum neutralization antibodies before vaccination seroconversion was obtained in 94.4% after 42 days. Half of a group of 34 seropositive children who were tested also showed a fourfold or greater rise in antibodies. Persistence of vaccine-enhanced haemagluttinin-inhibition (EHI) antibodies was satisfactory as only two of 46 vaccinees followed-up for between 27 and 32 months had undetectable levels of EHI antibodies and the geometric mean titre of vaccine-induced EHI antibodies had only fallen to about one-third by 32 months after vaccination. Although there was serological evidence of a subclinical re-infection in three subjects, to date none of the vaccinees has had clinical mumps indicating that the vaccine confers protection against disease. The vaccine was well tolerated. Furthermore, the majority of the few 'reactions' reported were probably not vaccine-related. It is concluded that the Urabe Am 9 is an acceptable strain for use in live mumps vaccines.     

Differential effects of mutations in NS4B on West Nile virus replication and inhibition of interferon signaling

West Nile virus (WNV) is a human pathogen that can cause symptomatic infections associated with meningitis and encephalitis. Previously, we demonstrated that replication of WNV inhibits the interferon (IFN) signal transduction pathway by preventing the accumulation of phosphorylated Janus kinase 1 (JAK1) and tyrosine kinase 2 (Tyk2) (J. T. Guo et al., J. Virol. 79:1343-1350, 2005). Through a genetic analysis, we have now identified a determinant on the nonstructural protein 4B (NS4B) that controls IFN resistance in HeLa cells expressing subgenomic WNV replicons lacking the structural genes. However, in the context of infectious genomes, the same determinant did not influence IFN signaling. Thus, our results indicate that NS4B may be sufficient to inhibit the IFN response in replicon cells and suggest a role for structural genes, or as yet unknown interactions, in the inhibition of the IFN signaling pathway during WNV infections.     

Alpha/Beta interferon and gamma interferon synergize to inhibit the replication of herpes simplex virus type 1

In vivo evidence suggests that T-cell-derived gamma interferon (IFN-gamma) can directly inhibit the replication of herpes simplex virus type 1 (HSV-1). However, IFN-gamma is a weak inhibitor of HSV-1 replication in vitro. We have found that IFN-gamma synergizes with the innate IFNs (IFN-alpha and -beta) to potently inhibit HSV-1 replication in vitro and in vivo. Treatment of Vero cells with either IFN-beta or IFN-gamma inhibits HSV-1 replication by <20-fold, whereas treatment with both IFN-beta and IFN-gamma inhibits HSV-1 replication by approximately 1,000-fold. Treatment with IFN-beta and IFN-gamma does not prevent HSV-1 entry into Vero cells, and the inhibitory effect can be overcome by increasing the multiplicity of HSV-1 infection. The capacity of IFN-beta and IFN-gamma to synergistically inhibit HSV-1 replication is not virus strain specific and has been observed in three different cell types. For two of the three virus strains tested, IFN-beta and IFN-gamma inhibit HSV-1 replication with a potency that approaches that achieved by a high dose of acyclovir. Pretreatment of mouse eyes with IFN-beta and IFN-gamma reduces HSV-1 replication to nearly undetectable levels, prevents the development of disease, and reduces the latent HSV-1 genome load per trigeminal ganglion by approximately 200-fold. Thus, simultaneous activation of IFN-alpha/beta receptors and IFN-gamma receptors appears to render cells highly resistant to the replication of HSV-1. Because IFN-alpha or IFN-beta is produced by most cells as an innate response to virus infection, the results imply that IFN-gamma secreted by T cells may provide a critical second signal that potently inhibits HSV-1 replication in vivo.     

Modified model for the switch from Sendai virus transcription to replication

RNase mapping was used to estimate the levels of unencapsidated Sendai virus plus-strand RNAs which cross the leader-NP junction relative to NP mRNA. Significant amounts of leader readthrough RNAs were found in Z strain-infected cells, similar to that described for the polR mutant of vesicular stomatitis virus, even though this strain is considered wild type. The levels of the readthrough RNAs detected fell sharply when progressively longer probes were used, unlike that of NP mRNA. These studies suggest that polymerases which read through the first junction terminate shortly afterwards in the absence of concurrent assembly of the nascent chain, whereas those which reinitiate at NP continue efficiently to the next junction. Reinitiation appears to be necessary to convert the polymerase to a mode in which elongation is independent of concurrent assembly. Concurrent assembly appears to be required not only for the polymerase to read through the junction efficiently, but also for it to continue elongation between junctions.     

Differential sensitivity to detergents of actin cytoskeleton from nerve endings

Detergent-resistant membranes (DRM), an experimental model used to study lipid rafts, are typically extracted from cells by means of detergent treatment and subsequent ultracentrifugation in density gradients, Triton X-100 being the detergent of choice in most of the works. Since lipid rafts are membrane microdomains rich in cholesterol, depletion of this component causes solubilization of DRM with detergent. In previous works from our group, the lack of effect of cholesterol depletion on DRM solubilization with Triton X-100 was detected in isolated rat brain synaptosomes. In consequence, the aim of the present work is to explore reasons for this observation, analyzing the possible role of the actin cytoskeleton, as well as the use of an alternative detergent, Brij 98, to overcome the insensitivity to Triton X-100 of cholesterol-depleted DRM. Brij 98 yields Brij-DRM that are highly dependent on cholesterol, since marker proteins (Flotillin-1 and Thy-1), as well as actin, appear solubilized after MCD treatment. Pretreatment with Latrunculin A results in a significant increase in Flotillin-1, Thy-1 and actin solubilization by Triton X-100 after cholesterol depletion. Studies with transmission electron microscopy show that combined treatment with MCD and Latrunculin A leads to a significant increase in solubilization of DRM with Triton X-100. Thus, Triton-DRM resistance to cholesterol depletion can be explained, at least partially, thanks to the scaffolding action of the actin cytoskeleton, without discarding differential effects of Brij 98 and Triton X-100 on specific membrane components. In conclusion, the detergent of choice is important when events that depend on the actin cytoskeleton are going to be studied.     

Comparative replication of natural,attenuated, and laboratory strains of mumps virus

Natural, Laboratory and attenuated strains of mumps virus replicate in similar fashion in chicken embryonic heart, lung and liver cells. Heart cells are maximally suceptible to all three strains of virus, and liver cells are the least susceptible. Infection of the immature chicken embryo results in the multiplication of both the natural and laboratory strain to highest titet in the heart near hatch. However, the attenuated Jeryl Lynn virus possesses limited capacity for persistent replication in chicken embryonic tissues.     

Mutational robustness of an RNA virus influences sensitivity to lethal mutagenesis

The ability to extinguish a viral population of fixed reproductive capacity by causing small changes in the mutation rate is referred to as lethal mutagenesis and is a corollary of population genetics theory. Here we show that coxsackievirus B3 (CVB3) exhibits reduced mutational robustness relative to poliovirus, manifesting in enhanced sensitivity of CVB3 to lethal mutagens that is dependent on the size of the viral population. We suggest that mutational robustness may be a useful measure of the sensitivity of a virus to lethal mutagenesis.     

Persistence of mumps virus in mouse L929 cells

The characteristics of a persistent infection of L929 cells with mumps virus (MuV) is presented. The persistent infection (L-MuV cells) was regulated by interferon (IFN) produced endogenously and almost all the properties showed that the carrier culture was maintained by horizontal transmission of the virus. Small-plaque mutants, but not temperature-sensitive variants, were selected during the persistent infection. MuV released from L-MuV cells (MuV-pi) replicated efficiently in L929 cells, while infection of L929 cells with the original MuV-o resulted in an abortive infection. The efficient replication of MuV-pi in L929 cells can be explained by the findings that MuV-pi induced IFN more slowly and had lower susceptibility to IFN in L929 cells than MuV-o did. M protein was synthesized to a considerable degree in MuV-pi-infected cells, while it could not be detected in MuV-o-infected cells. By contrast, MuV-pi formed small plaques in Vero cell monolayers and the yield of MuV-pi in Vero cells was lower than that of MuV-o. M protein induced by MuV-pi decayed easily in Vero cells. M protein was considered to be a limiting factor for MuV replication in both cell lines.     

Differential effects of nerve growth factor and dexamethasone on herpes simplex virus type 1 oriL- and oriS-dependent DNA replication in PC12 cells.

The herpes simplex virus type 1 (HSV-1) genome contains three origins of DNA replication, one copy of oriL and two copies of oriS. Although oriL and oriS are structurally different, they have extensive nucleotide sequence similarity and can substitute for each other to initiate viral DNA replication. A fundamental question that remains to be answered is why the HSV-1 genome contains two types of origin. We have recently identified a novel glucocorticoid response element (GRE) within oriL that is not present in oriS and have shown by gel mobility shift assays that purified glucocorticoid receptor (GR), as well as GR present in cellular extracts, can bind to the GRE in oriL. To determine whether glucocorticoids and the GRE affect the efficiency of oriL-dependent DNA replication, we performed transient DNA replication assays in the presence and absence of dexamethasone (DEX). Because HSV-1 is a neurotropic virus and establishes latency in cells of neural origin, these tests were conducted in PC12 cells, which assume the properties of sympathetic neurons when differentiated with nerve growth factor (NGF). In NGF-differentiated PC12 cells, oriL-dependent DNA replication was enhanced 5-fold by DEX, whereas in undifferentiated cells, DEX enhanced replication approximately 2-fold. Notably, the enhancement of oriL function by DEX was abolished when the GRE was mutated. NGF-induced differentiation alone had no effect. In contrast to oriL, oriS-dependent DNA replication was reduced approximately 5-fold in NGF-differentiated PC12 cells and an additional 4-fold in differentiated cells treated with DEX. In undifferentiated PC12 cells, DEX had only a minor inhibitory effect (approximately 2-fold) on oriS function. Although the cis-acting elements that mediate the NGF- and DEX-specific repression of oriS-dependent DNA replication are unknown, a functional GRE is critical for the DEX-induced enhancement of oriL function in NGF-differentiated PC12 cells. The enhancement of oriL-dependent DNA replication by DEX in differentiated PC12 cells suggests the possibility that glucocorticoids, agents long recognized to enhance reactivation of latent herpesvirus infections, act through the GRE in oriL to stimulate viral DNA replication and reactivation in terminally differentiated neurons in vivo.