An RBM10 and NF-κB interacting host lncRNA promotes JEV replication and neuronal cell death

IMPORTANCE

Central nervous system infection by flaviviruses such as Japanese encephalitis virus, Dengue virus, and West Nile virus results in neuroinflammation and neuronal damage. However, little is known about the role of long non-coding RNAs (lncRNAs) in flavivirus-induced neuroinflammation and neuronal cell death. Here, we characterized the role of a flavivirus-induced lncRNA named JINR1 during the infection of neuronal cells. Depletion of JINR1 during virus infection reduces viral replication and cell death. An increase in GRP78 expression by JINR1 is responsible for promoting virus replication. Flavivirus infection induces the expression of a cellular protein RBM10, which interacts with JINR1. RBM10 and JINR1 promote the proinflammatory transcription factor NF-κB activity, which is detrimental to cell survival.

Evaluating the competence of the primary vector, Culex tritaeniorhynchus, and the invasive mosquito species, Aedes japonicus japonicus, in transmitting three Japanese encephalitis virus genotypes

Japanese encephalitis virus (JEV) is maintained in an enzootic cycle between swine, water birds, and mosquitoes. JEV has circulated indigenously in Asia, with Culex tritaeniorhynchus as the primary vector. In some areas where the primary vector is scarce or absent, sporadic cases of Japanese encephalitis have been reported, with Aedes japonicus japonicus presumed to have the potential as a secondary vector. As one of the world's most invasive culicid species, Ae. j. japonicus carries a considerable health risk for spreading diseases to wider areas, including Europe and North America. Thus, evaluation of its competency as a JEV vector, particularly in a native population, will be essential in preventing potential disease spread. In this study, the two mosquito species' vector competence in transmitting three JEV genotypes (I, III, and V) was assessed, with Cx. tritaeniorhynchus serving as a point of reference. The mosquitoes were virus-fed and the infection rate (IR), dissemination rate (DR), and transmission rate (TR) evaluated individually by either RT-qPCR or focus forming assay. Results showed striking differences between the two species, with IR of 95% (261/274) and 9% (16/177) in Cx. tritaeniorhynchus and Ae. j. japonicus, respectively. Both mosquitoes were susceptible to all three JEV genotypes with significant differences in IR and mean viral titer. Results confirm the primary vector's competence, but the fact that JEV was able to establish in Ae. j. japonicus is of public health significance, and with 2%-16% transmission rate it has the potential to successfully transmit JEV to the next host. This may explain the human cases and infrequent detection in primary vector-free areas. Importantly, Ae. j. japonicus could be a relevant vector spreading the disease into new areas, indicating the need for security measures in areas where the mosquito is distributed or where it may be introduced.

Identifying optimal capsid duplication length for the stability of reporter flaviviruses

ABSTRACT Mosquito-transmitted flaviviruses cause widespread disease across the world. To provide better molecular tools for drug screens and pathogenesis studies, we report a new approach to produce stable NanoLuc-tagged flaviviruses, including dengue virus serotypes 1-4, Japanese encephalitis virus, yellow fever virus, West Nile virus, and Zika virus. Since the reporter gene is often engineered at the capsid gene region, the capsid sequence must be duplicated to flank the reporter gene; such capsid duplication is essential for viral replication. The conventional approach for stabilizing reporter flaviviruses has been to shorten or modify the duplicated capsid sequence to minimize homologous recombination. No study has examined the effects of capsid duplication length on reporter virus stability. Here we report an optimal length to stabilize reporter flaviviruses. These viruses were stable after ten rounds of cell culture passaging, and in the case of stable NanoLuc-tagged Zika virus (ZIKV C38), the virus replicated to 107 FFU/ml in cell culture and produced robust luciferase signal after inoculation in mosquitoes. Mechanistically, the optimal length of capsid duplication may contain all the cis-acting RNA elements required for viral RNA replication, thus reducing the selection pressure for recombination. Together, these data describe an improved method of constructing optimal reporter flaviviruses.

Establishment and characterization of the pig tonsil epithelial (PT) cell line as a new model for persist infection of Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) causes a serious zoonotic disease worldwide, pig is the reservoir and amplifying host of JEV. JEV can persist infect tonsil in pig, but the relation between persist infection in tonsil and reservoir are not clear until now. A stable pig tonsil cell line is necessary for JEV persist infection research. In this study, we established a continuous epithelial cell line, named PT cell, from the pig tonsil. This cell is susceptible to JEV. We determined the growth characteristics, molecular properties, microstructure profiles of PT cell. JEV is easy to enter PT cell which may partly explain the reason of persist infection. We further determined that LMAN2L, a mannose lectin proteins, is the primary viral receptors for JEV entry in PT cell. IFITM3, an cellular surface antiviral factor, is underexpression in PT cell after JEV infection. All these results provide solid evidence that PT cell will promote additional research on JEV persist infection in pig tonsil.

The emerged genotype I of Japanese encephalitis virus shows an infectivity similar to genotype III in Culex pipiens mosquitoes from China

Japanese Encephalitis virus (JEV) is a zoonotic flavivirus that represents the most significant etiology of childhood viral neurological infections throughout the Asia. During the last 20 years, JEV genotype dominance has shifted from genotype III (GIII) to genotype I (GI). To date, the exact mechanism of this displacement is still not known. Culex (Cx.) mosquitoes are the most common species in China and play an essential role in maintaining JEV enzootic transmission cycle. In this study, we used Cx. pipiens mosquitoes from China as an in vivo mosquito model to explore if mosquitoes played a potential role in JEV genotype shift. We exposed female Cx. pipiens mosquitoes orally to either GI or GIII JEV strains. Midgut, whole mosquitoes, secondary organs, and salivary glands of JEV-infected mosquitoes were collected at 7 and 14 days of post infection (dpi) and subjected to measure the infection rate, replication kinetics, dissemination rate and transmission potential of the infected JEV strains in Cx. pipiens mosquitoes by 50% tissue culture infective dose assay. We found that Cx. pipiens mosquito was competent vector for both GI and GIII JEV infection, with similar infection rates and growth kinetics. After the establishment of infection, Cx. pipiens mosquitoes disseminated both JEV genotypes to secondary organs at similar rates of dissemination. A few GI-infected mosquito salivary glands (16.2%) were positive for GI virus, whereas GIII virus was undetectable in GIII-infected mosquito salivary glands at 7 dpi. However, 29.4% (5/17) and 36.3% (8/22) were positive for GI- and GIII-infected mosquito salivary glands at 14 dpi, respectively, showing an increase in JEV positive rate. No statistical difference in the transmission rate between GI- and GIII-infected mosquitoes was detected. Our experiment data demonstrated that GI and GIII viruses have similar infectivity in Cx. pipiens mosquitoes, suggesting that Cx. pipiens mosquitoes from China may not play a critical role in JEV genotype shift. Although the current data were obtained solely from Cx. pipiens mosquitoes, it is likely that the conclusion drawn could be extrapolated to the role of mosquitoes in JEV genotype shift.

Genetic and neuroattenuation phenotypic characteristics and their stabilities of SA14-14-2 vaccine seed virus

Japanese encephalitis (JE) live attenuated vaccine SA14-14-2 is the most widely used JE vaccine in the world. Large-scale clinical trials have demonstrated satisfactory safety and efficacy profiles. The establishment of genetic and attenuated neurovirulence characteristics and their stabilities of SA14-14-2 virus are important in relation to vaccine safety in humans. Therefore, several researchers have studied and analyzed the full-length gene sequences of the SA14-14-2 virus strain. However, sequencing results have shown a significant difference. Here, we further studied the full-length sequence of three class seed virus banks of the vaccine as well as two vaccine viruses with different passages in primary hamster kidney cells, and compared them with our original stored SA14 parent virus (low passage in mouse brain). The full-length gene sequence determined in this study indicates there were 57 nucleotide and 25 amino acid substitutions of the SA14-14-2 strain compared to its parental SA14 virus strain. The full-length sequences of the three class seed bank viruses and the vaccine virus PHKC8 were completely identical among them, but the working seed virus passaged in primary hamster kidney cells for 17 generations (PHKC17) had a single nucleotide change at the 5' NCR. Both KM and ICR mice tested by intracerebral (i.c.) or subcutaneous (s.c.) routes with the three class seed viruses and vaccine viruses with ≥5.7 lgpfu/mL remained healthy, but all the mice inoculated with the SA14 parental virus strain died as early as day 5 post-inoculation. The present study provided new information on the full-length gene sequence and attenuated neurovirulence of SA14-14-2. They can be used as a reference sequence for vaccine quality control and surveillance of neurovirulence reversion following vaccination. Moreover, the present results further demonstrated the high genetic and phenotypic stabilities of the SA14-14-2 virus, suggesting the neurovirulence reversion of the vaccine strain will be highly unlikely.

Identification and characterization of differentially expressed genes from human microglial cell samples infected with Japanese encephalitis virus

BACKGROUND & OBJECTIVES

Limited studies have been reported on Japanese encephalitis (JE) with reference to microarray data analysis. The present study involved an in silico approach for identification and characterization of differentially expressed genes in human microglial cell (CHME3) samples, infected with P20778 strain of Japanese encephalitis virus (JEV).

METHODS

Gene expression data (GSE57330) belonging to mRNA expression profile of CHME3 cells infected with JEV, was downloaded from the gene expression omnibus (GEO) database, processed and normalized by robust multichip averaging (RMA) method using affy packages of R. The Bayes method was used to correct multiple testing. The log fold change (logFC > 1) and p< 0.05 were used as cut-off to identify differentially expressed genes (DEGs). The newly identified hub genes were set at the centre for construction of protein-protein interaction network using search tool for the retrieval of interacting genes/proteins (STRING) database considering human genome as reference. Gene ontology and pathway enrichment analysis of the hub gene and its associated genes were performed using STRING and DAVID tool.

RESULTS

Microarray data analysis revealed that STAT1 gene was down-regulated during JEV infection. STAT1 gene was found to interact with tyrosine protein kinase family members, and showed strong interaction with JAK1 and JAK2 genes.

INTERPRETATION & CONCLUSION

The identified transcription factors and the binding sites in the promoter region of STAT1 gene might act as potential drug targets in near future.

In vitro growth, pathogenicity and serological characteristics of the Japanese encephalitis virus genotype V Muar strain

The characteristics of genotype V Japanese encephalitis virus (GV JEV) remain poorly understood as only two strains have been isolated to date. In this study, we examined the effects of the GV JEV Muar strain on in vitro growth and pathogenicity in mice; we also evaluated the efficacy of inactivated JEV vaccines against the Muar strain. Although growth of the Muar strain in mouse neuroblastoma N18 cells was clearly worse than that of the GIII Beijing-1 and GI Mie/41/2002 strains, neuroinvasiveness of the Muar strain was similar to that of the Beijing-1 strain and significantly higher than that of the Mie/41/2002 strain. The results of a plaque reduction neutralization test suggested that the neutralization ability of the JEV vaccines against the Muar strain was reduced compared with the GI and GIII strains. However, the protection potency of the JEV vaccine against the Muar strain was similar to that for the Beijing-1 strain in mice. Our data indicate that GV JEV has unique growth, virulence and antigenicity features.

Genetic differences of E gene of a Thai strain of Japanese encephalitis virus that determine small plaque size phenotype but not neurovirulence in suckling mice

Two small plaque variants of Japanese encephalitis virus (JEV), S4P9 and S9P10, were recovered from the wild type of JEV strain KE-093 using plaque purification in combination with the temperature-shift induction technique. Growth patterns of the S4P9 and S9P10 in BHK-21 cells as well as neurovirulence in suckling mice were similar to that of KE-093. An amino acid substitution, lysine for glutamic acid, was present in envelope protein at residue E-83 in the small plaque variants. This study shows that small plaque phenotype is not always associated with attenuation in vivo.

Plaque formation by Japanese encephalitis virus bound to mosquito C6/36 cells after low pH exposure on the cell surface

Japanese encephalitis virus (JEV) formed plaques in mosquito C6/36 cell layers after adsorption on the cell surface and exposure to pH values lower than 6.2. The number of plaques decreased within pH ranges from 7.4 to 6.4, but increased within pH ranges from 6.2 to 5.8. Plaque formation was prevented by treatment of the virus with a JEV-neutralizing monoclonal antibody, 503, after virus adsorption. Plaque formation was not affected by pretreatment with a specific V-ATPase inhibitor, bafilomycin A1. The results indicate that JEV successfully fused with the C6/36 cell membrane under acidic conditions below pH 6.2, which in turn led to plaque formation in C6/36 cell layers. These results suggest that productive JEV infection occurs at the C6/36 cell surface via the fusion between JEV and the cell membrane.

Replication of Japanese encephalitis virus in mouse brain induces alterations in lymphocyte response

The experimental model using intracerebral (i.c.) challenge was employed in many studies evaluating the protection against disease induced by Japanese encephalitis virus (JEV). We investigated alterations in peripheral lymphocyte response caused by i.c. infection of mice with JEV. Splenocytes from the i.c.-infected mice showed suppressed proliferative response to concanavalin A (con A) and anti-CD3 antibody stimulation. At the same time, the expression of CD25 (IL-2R) and production of IL-2 was inhibited. Addition of anti-CD28 antibody restored the decreased anti-CD3 antibody-mediated proliferation in the splenocytes. Moreover, the number of con A-stimulated cells secreting IL-4 was significantly reduced in splenocytes from i.c.-infected mice. These studies suggested that the i.c. infection with JEV might involve additional immune modulation effects due to massive virus replication in the brain.

Mosquito cells infected with Japanese encephalitis virus release slowly-sedimenting hemagglutinin particles in association with intracellular formation of smooth membrane structures

Arthropod-borne flaviviruses can grow in both arthropod and mammalian cells. Virion morphogenesis, though well studied in mammalian cells, is still unclear in arthropod cells. Here, we compared a mosquito cell line C6/36 and a mammalian cell line Vero in extracellular virus particles and intracellular ultrastructures triggered by infection with Japanese encephalitis virus (JEV). Sedimentation analyses of virion and slowly-sedimenting hemagglutinin (SHA) particles released by infection with the Nakayama strain revealed that C6/36 cells produced higher envelope (E) antigen levels in the SHA than the virion fraction in contrast to Vero cells that showed the opposite pattern. Specific infectivities per ng of E were similar in both cells, whereas specific hemagglutinating activities in the SHA fraction were lower in C6/36 than Vero cells. The precursor membrane protein was less efficiently cleaved to the membrane protein in SHA particles released from C6/36 than Vero cells. Ultrastructural studies showed more remarkable production of smooth membrane structures (SMSs) in C6/36 than in Vero cells. The differences in sedimentation patterns of extracellular virus particles between Nakayama-infected C6/36 and Vero cells were consistently observed in 5 other strains (Beijing P1, Beijing P3, JaTH-160, KE-093 and JaGAr-O1), except for KE-093-infected C6/36 cells which exhibited the Vero-type sedimentation profile under conditions of open cultivation. By electron microscopy, the production of SMSs from KE-093-infected C6/36 cells under open conditions was markedly less than that under closed conditions where the cells exhibited the C6/36-type sedimentation profile. Thus, intracellular SMS formations were associated with extracellular SHA production in JEV-infected mosquito cells.

[Research on Culex tritaeniorhynchus and Culex pipiens quinquefasciatus intrathoracically infected with attenuated Japanese encephalitis virus SA14-14-2 vaccine strain]

BACKGROUND

To determine if the attenuated Japanese encephalitis (JE) virus SA14-14-2 vaccine strain interacts efficiently with Culex tritaeniorhynchus and Culex pipiens quinquefasciatus, and further to acquire a new knowledge of its characteristics and safety for human beings.

METHODS

Laboratory colonies of the two species of mosquitoes were set up and were inoculated intrathoracically with the attenuated vaccine virus and wild JE virus (Nak), both of which were used with different dilution from 10(-1) to 10(-9). Subsequently, the virus titers in the mosquitoes were detected by the plaque assay.

RESULTS

Inoculated with the vaccine strain, two species of mosquitoes were infected with the titers ranged from 10(0)-10(-3), and the maximum titers in Culex tritaeniorhynchus and Culex pipiens quinquefasciatus were 4.48 logPFU/ml and 5.63 logPFU/ml, respectively. Inoculated with wild JE virus, Culex pipiens quinquefasciatus was infected with titers ranged from 10(0)-10(-5), and the maximum titer in the mosquitoes was 6.59; Culex tritaeniorhynchus was infected with titers ranged from 10(0)-10(-4) and the maximum titer was 5.74 logPFU/ml.

CONCLUSION

By intrathoracic infection, the attenuated JE virus SA14-14-2 vaccine strain can replicate in both species of mosquitoes.

[Further studies of continuous human and animal cell lines for the manufacture of viral vaccines and diagnostic kits]

Long-term experiments have provided conditions for the optimal conditions for reproduction of vaccine strains of poliomyelitis, measles, tick-borne and Japan encephalitis on the continuous cell lines. This makes it possible to solve one of the most urgent problems of modern biotechnology, namely to refuse to use primary cell cultures in vaccinology and to apply a more accessible, safe, and reference biological substrate that are stable cell lines.

Nuclear localization of Japanese encephalitis virus core protein enhances viral replication

Japanese encephalitis virus (JEV) core protein was detected in both the nucleoli and cytoplasm of mammalian and insect cell lines infected with JEV or transfected with the expression plasmid of the core protein. Mutation analysis revealed that Gly(42) and Pro(43) in the core protein are essential for the nuclear and nucleolar localization. A mutant M4243 virus in which both Gly(42) and Pro(43) were replaced by Ala was recovered by plasmid-based reverse genetics. In C6/36 mosquito cells, the M4243 virus exhibited RNA replication and protein synthesis comparable to wild-type JEV, whereas propagation in Vero cells was impaired. The mutant core protein was detected in the cytoplasm but not in the nucleus of either C6/36 or Vero cell lines infected with the M4243 virus. The impaired propagation of M4243 in mammalian cells was recovered by the expression of wild-type core protein in trans but not by that of the mutant core protein. Although M4243 mutant virus exhibited a high level of neurovirulence comparable to wild-type JEV in spite of the approximately 100-fold-lower viral propagation after intracerebral inoculation to 3-week-old mice of strain Jcl:ICR, no virus was recovered from the brain after intraperitoneal inoculation of the mutant. These results indicate that nuclear localization of JEV core protein plays crucial roles not only in the replication in mammalian cells in vitro but also in the pathogenesis of encephalitis induced by JEV in vivo.

Fitness of Japanese encephalitis virus to Neuro-2a cells is determined by interactions of the viral envelope protein with highly sulfated glycosaminoglycans on the cell surface

Genetically different subpopulations were identified and purified from Japanese Encephalitis virus (JEV). Those with small plaques (SPs; <2 mm in diameter), derived from strains of T1P1, CJN, and CC27, were more competent than those with large plaques (LPs; >5 mm in diameter) when passaged in Neuro-2a cells. Differences in amino acids between SPs and LPs from each strain were shown in the viral envelope (E) protein. The amino acid at E-306 was Glu in LP but was substituted by Lys in SP in the T1P1 strain. A similar substitution occurred at E-138 in the CJN strain. However, the amino acid was Asp in LP but was substituted by Asn in SP at E-389 in the CC27 strain. All SPs were shown to have a higher affinity to the cellular membrane when compared to LPs, and this resulted in more-efficient infection of Neuro-2a cells, suggesting that the differential fitness of JEV variants to Neuro-2a cells appeared in the early phase of infection. In addition, glycosaminoglycans (GAGs) on the surface of many mammalian cells have been demonstrated to be critical for infection by JEV, especially SP variants. The present results suggest that T1P1-SP1 viruses infected Neuro-2a cells more efficiently in spite of the sparse distribution of cell surface GAGs. We conclude that highly sulfated forms of GAGs expressed by Neuro-2a cells play an important role in selecting JEV variants with specific mutations in the E glycoprotein.

Flavivirus isolations from mosquitoes collected from Saibai Island in the Torres Strait, Australia, during an incursion of Japanese encephalitis virus

Adult mosquitoes (Diptera: Culicidae) were collected in January and February 2000 from Saibai Island in the Torres Strait of northern Australia, and processed for arbovirus isolation during a period of Japanese encephalitis (JE) virus activity on nearby Badu Island. A total of 84 210 mosquitoes were processed for virus isolation, yielding six flavivirus isolates. Viruses obtained were single isolates of JE and Kokobera (KOK) and four of Kunjin (KUN). All virus isolates were from members of the Culex sitiens Weidemann subgroup, which comprised 53.1% of mosquitoes processed. Nucleotide sequencing and phylogenetic analysis of the pre-membrane region of the genome of JE isolate TS5313 indicated that it was closely related to other isolates from a sentinel pig and a pool of Cx. gelidus Theobald from Badu Island during the same period. Also molecular analyses of part of the envelope gene of KUN virus isolates showed that they were closely related to other KUN virus strains from Cape York Peninsula. The results indicate that flaviviruses are dynamic in the area, and suggest patterns of movement south from New Guinea and north from the Australian mainland.

Common E protein determinants for attenuation of glycosaminoglycan-binding variants of Japanese encephalitis and West Nile viruses

Natural isolates and laboratory strains of West Nile virus (WNV) and Japanese encephalitis virus (JEV) were attenuated for neuroinvasiveness in mouse models for flavivirus encephalitis by serial passage in human adenocarcinoma (SW13) cells. The passage variants displayed a small-plaque phenotype, augmented affinity for heparin-Sepharose, and a marked increase in specific infectivity for SW13 cells relative to the respective parental viruses, while the specific infectivity for Vero cells was not altered. Therefore, host cell adaptation of passage variants was most likely a consequence of altered receptor usage for virus attachment-entry with the involvement of cell surface glycosaminoglycans (GAG) in this process. In vivo blood clearance kinetics of the passage variants was markedly faster and viremia was reduced relative to the parental viruses, suggesting that affinity for GAG (ubiquitously present on cell surfaces and extracellular matrices) is a key determinant for the neuroinvasiveness of encephalitic flaviviruses. A difference in pathogenesis between WNV and JEV, which was reflected in more efficient growth in the spleen and liver of the WNV parent and passage variants, accounted for a less pronounced loss of neuroinvasiveness of GAG binding variants of WNV than JEV. Single gain-of-net-positive-charge amino acid changes at E protein residue 49, 138, 306, or 389/390, putatively positioned in two clusters on the virion surface, define molecular determinants for GAG binding and concomitant virulence attenuation that are shared by the JEV serotype flaviviruses.

Differential binding efficiency between the envelope protein of Japanese encephalitis virus variants and heparan sulfate on the cell surface

Japanese encephalitis (JE) virus infects a number of host cells, either mosquitoes or vertebrates, in nature. The viral envelope (E) protein is known to interact with molecule(s) on the cell membrane during the early stage of virus infection. In this study, two sets of virus variants including T1P1-L4/T1P1-S1 and CJN-L1/CJN-S1 derived from two strains (T1P1 and CJN) of the JE virus were used to evaluate the effects of genomic variations on virus entry. Each set of virus variant (T1P1-L4/T1P1-S1 or CJN-L1/CJN-S1) possessed a single amino acid variation in the E protein. The variation of Glu/Lys at E-306 was found between T1P1-L4 and T1P1-S1 whereas the same variation at E-138 was seen between CJN-L1 and CJN-S1. The results showed that heparan sulfate (HS) differentially expressed on the surface of different types of host cells was essential for JE virus infection as shown in an evident difference in attachment efficiency between CHO-K1 cells and its mutant with defects in GAG biosynthesis. Furthermore, differential interaction of heparin with the envelope protein of JE virus variants implies the significance of virus mutations (especially Lys for E-138 and/or E306 in this case) that are rather likely involved in determining efficiencies of viral attachment, penetration, and eventual infection.

Study on persistent infection of Japanese encephalitis virus Beijing-1 strain in serum-free Sf9 cell cultures

Sf9 cells have obvious advantages for the conventional production technology of vaccine. They are useful tools for high concentration and large-scale cultures. Sf9 cells were grown to maximal concentration, 8 x 10(6) cells/ml in a 500ml spinner flask, with a doubling time at the exponentially growing phase of 24.5 hours, using serum-free media. To explore the ability of Sf9 cells to be infected by the Japanese encephalitis (JE) virus Beijing-1 strain, Sf9 cells were infected with the virus. By 4-5 days post-infection, 10-15% of the Sf9 cells showed cytopathic effect (CPE), from granularity to the formation of syncytia and multinucleated giant cells continuously observed over a period of 35 days. Positive fluorescent reactions were detected in 30-40% of cells infected with the JE virus Beijing-1 strain, and the uninfected Sf9 cells were completely negative. Virus particles, propagated in Sf9 and Vero cells, were concentrated by sedimentation on 40% trehalose cushions by ultracentrifugation, and showed identical patterns of viral morphogenesis. Complete virus particles, 40 to 50 nm in diameter, were observed, and JE virus envelope (E) proteins, at 53 kDa, were found in the western blot analysis to the anti-JE virus E protein monoclonal antibody and reacted as a magenta band in the same position to the glycoprotein staining. To evaluate whether the infectious virus was produced in Sf9 cells inoculated with the JE virus Beijing-1 stain, Sf9 cells were inoculated with the virus, and sample harvested every 5 days. The titers of the JE virus Beijing-1 strain rose from 1.0 x 10(5) to 1.5 x 10(6) pfu/ml. The infected Sf9 cells could be sub-cultured in serum-free medium, with no change in the plaque sizes formed by the JE virus Beijing-1 strain in the plaque assay. It is suggested that the ability of the JE virus Beijing-1 strain to infect Sf9 cells in serum-free media will provide a useful insect cell system, where the JE virus replication, cytopathogenicity and vaccine immunogen can be studied.

Climate variability and transmission of Japanese encephalitis in eastern China

A time-series analysis was conducted to study the impact of climate variability on the transmission of Japanese encephalitis in eastern China. Correlation and regression analyses were used to examine the relationship between monthly climatic variables and monthly incidence of Japanese encephalitis in Jieshou County, China over the period 1980-96. Spearman's correlation analysis showed that maximum and minimum temperatures and rainfall were all associated with the transmission of Japanese encephalitis in the county. Regression analysis suggested that monthly mean minimum temperature and monthly precipitation had a significant relationship with the transmission of Japanese encephalitis, with a 1-month lag effect. The results indicated that these climatic variables might be treated as possible predictors for regions with similar geographic, climatic, and socio-economic conditions to Jieshou County.

Mosquito host-feeding patterns and implications for Japanese encephalitis virus transmission in northern Australia and Papua New Guinea

Japanese encephalitis (JE) virus spread to northern Australia during the 1990s, transmitted by Culex annulirostris Skuse and other mosquitoes (Diptera: Culicidae). To determine the relative importance of various hosts for potential vectors of JE virus, we investigated the host-feeding patterns of mosquitoes in northern Australia and Western Province of Papua New Guinea, with particular attention to pigs, Sus scrofa L. - the main amplifying host of JE virus in South-east Asia. Mosquitoes were collected by CDC light traps baited with dry ice and 1-octen-3-ol, run 16.00-08.00 hours, mostly set away from human habitations, if possible in places frequented by feral pigs. Bloodmeals of 2569 mosquitoes, representing 15 species, were identified by gel diffusion assay. All species had fed mostly on mammals: only <10% of bloodmeals were from birds. The predominant species was Cx. annulirostris (88%), with relatively few (4.4%) bloodmeals obtained from humans. From all 12 locations sampled, the mean proportion of Cx. annulirostris fed on pigs (9.1%) was considerably lower than fed on other animals (90.9%). Highest rates of pig-fed mosquitoes (>30%) were trapped where domestic pigs were kept close to human habitation. From seven of eight locations on the Australian mainland, the majority of Cx. annulirostris had obtained their bloodmeals from marsupials, probably the Agile wallaby Macropus agilis (Gould). Overall proportions of mosquito bloodmeals identified as marsupial were 60% from the Gulf Plains region of Australia, 78% from the Cape York Peninsula and 64% from the Daru area of Papua New Guinea. Thus, despite the abundance of feral pigs in northern Australia, our findings suggest that marsupials divert host-seeking Cx. annulirostris away from pigs. As marsupials are poor JE virus hosts, the prevalence of marsupials may impede the establishment of JE virus in Australia.

Cell-adhesion and morphological changes are not sufficient to support anchorage-dependent cell growth via non-integrin-mediated attachment

Cell-adhesion and spread are important for cell survival. Although extensive studies have suggested several potential mechanisms of action, it is not yet clear how important cell-morphological change per se contributes to the cell-surviving signal. We employed a non-integrin-mediated cell-adhesion system to explore this question. BHK-Japanese encephalitis virus (JEV) cells (BHK21 cells that are persistently infected with JEV) express a large amount of JEV-envelope protein (JEV E) on their surfaces, and can attach and form pseudopodia on the anti-JEV E antibody-coated substrates. However, cells that adhered on the antibody substrate underwent a caspase-3-mediated apoptosis together with a down-regulation of mitogen-activated protein kinase activity within 20 h after adhesion, which indicates that viral-protein-mediated cell-adhesion and cell-spread are not sufficient for supporting cell survival. This provides a different perspective for the study of the relationships between the cell-morphological change and the cell-survival signal.

Isolation of Japanese encephalitis and Getah viruses from mosquitoes (Diptera: Culicidae) collected near Camp Greaves, Gyonggi Province, Republic of Korea, 2000

As part of an evaluation of the ecology of arthropod-borne diseases in the Republic of Korea (ROK), we examined 8,765 mosquitoes captured in Paju County, Gyonggi Province, ROK, for the presence of viruses. Mosquitoes were captured in propane lantern/human-baited Shannon traps, Mosquito Magnet traps, or American Biophysics Corporation (East Greenwich, RI) miniature light traps with or without supplemental octenol bait and/or dry ice. Mosquitoes were identified to species, placed in pools of up to 40 mosquitoes each, and tested on Vero cells for the presence of virus. A total of 15 virus isolations were made from 293 pools of mosquitoes. Viruses were identified by reverse transcriptase-polymerase chain reaction and sequencing and consisted of 14 isolations of Japanese encephalitis (JE) virus and one isolation of Getah (GET) virus. All JE isolates were from Culex tritaeniorhynchus Giles, and the isolate of GET was from Aedes vexans (Meigen). The minimum field infection rate for JE in Cx. tritaeniorhynchus was 3.3 per 1,000, whereas the GET virus infection rate for Ae. vexans was 0.2 per 1,000. Isolation of JE and GET indicated that both viruses were actively circulating in northern Gyonggi Province, ROK. The lack of human cases of JE among the Korean population probably is because of an effective government-mandated vaccination program. The reason for no cases among >10,000 United States military and others that reside or train nearby is unknown, but may be related to personnel protection measures (permethrin-impregnated uniforms and use of deet repellent), adult mosquito control, mosquito selection of nonhuman hosts (unpublished data), and the low symptomatic to asymptomatic ratio of disease in adults.

Phenotypic and genotypic characterization of the neurovirulence and neuroinvasiveness of a large-plaque attenuated Japanese encephalitis virus isolate

The virulent phenotypes of Japanese encephalitis virus (JEV) can be divided into neuroinvasiveness (NI) and neurovirulence (NV). In this study, two JEV antigenic variants, CH2195LA (large-plaque, attenuated) and CH2195SA (small-plaque, non-attenuated), were passaged in suckling mice by intracerebral inoculation. Viruses at passage two and four were characterized in terms of NV and NI in weaning mice, as well as their in vitro growth characteristics in six cell lines. Following two brain-brain passages in mice, the attenuated variant CH2195LA was found to significantly restore the NV and NI by approximately 90% and 20-40%, respectively. The increased titers in THP-1 monocytic cells but not IMR-32 and Neuro-2A neuroblastoma cells were more correlated with the phenotypic changes of NI and NV in mice. Entire genomic sequencing was further performed to demonstrate that 14 nucleotides were altered in the attenuated variant CH2195LA following four brain-brain passages in mice, giving 12 amino acid changes, in prM-73, prM-80, E-161, E-170, E-276, NS2A-136, NS2A-215, NS3-346, NS4A-128, NS4B-196, NS4B-197, NS4B-198. This study indicated a cluster of amino acids which is involved in NV and NI of the JEV for mice and, perhaps, for humans. Elucidating the molecular basis of virulence of flaviviruses can provide valuable information for live-attenuated vaccine development.

Inhibition of Japanese encephalitis virus maturation and transport in PS cells to cell surface by brefeldin A

A brefeldin A (BFA) treatment of porcine stable kidney (PS) cells resulted in inhibition of Japanese encephalitis virus (JEV) maturation and its transport to the cell surface. Intrestingly, the antigenicity of the virus, in contrast, remained unaffected as no difference in epitope presentation/expression was observed in BFA-treated and control (untreated) infected cells even though in the former cells a loss of hemagglutinating (HA) activity was recorded. Thus it seems that the BFA treatment did not affect the glycoprotein E (gpE) synthesis and folding essentially required for the epitope presentation/expression in cells.

Application of cDNA microarray technique to detection of gene expression in host cells infected with viruses

cDNA microarray technique was used to monitor changes in mRNA levels in cells after Hantaan virus (HTNV) infection. The values of the ratio of medians for HTNV and Japanese encephalitis virus (JEV) at the early stage of infection were compared and found similar, suggesting that the same or similar genes are associated with the early events of infection with either virus. The reproducibility of values of the "ratio of medians" for HTNV was examined. We found that applying cluster analysis to the gene expression data groups efficiently together genes with the same function. Therefore, in analyzing the effects of viral infection on host cells by the cDNA microarray technique, clustering data appear to be necessary for gaining biological meaning from a dump of gene expression profiles obtained from virus-infected cells.

Neuropathogenesis of Japanese encephalitis virus

In the central nervous system, the Japanese encephalitis virus can replicate only in neurons. The mechanism of the type of neurotropism was analyzed. The susceptibility to Japanese encephalitis virus infection in the rat brain was closely associated with neuronal immaturity. The initial specific binding of the virus to cells is one of the reasons for neurotropism of the Japanese encephalitis virus. The treatment of Japanese encephalitis virus infection with the neutralizing monoclonal antibody against the E protein did not inhibit the virus from binding to the cell surfaces, but strongly inhibited Japanese encephalitis virus-induced cell fusion and internalization of the virus into the host cells. One of the genome regions responsible for neuropathogenesis of the Japanese encephalitis virus was located on the E protein-coding region. The 138th amino acid of the E protein was important for neuropathogenesis expression of the Japanese encephalitis virus. The cell fusion activity of the E protein was closely correlated with neuropathogenesis of the virus.

Detection and stability of Japanese encephalitis virus RNA and virus viability in dead infected mosquitoes under different storage conditions

A semi-nested polymerase chain reaction (PCR) was evaluated for detection of Japanese encephalitis (JE) virus in infected mosquitoes stored under simulated northern Australian summer conditions. The effect of silica gel, thymol, and a combination of the two on RNA stability and virus viability in dead mosquitoes were also examined. While JE virus RNA was relatively stable in mosquitoes held for up to 14 days after death, viable virus was not detected after day 1. Thymol vapor inhibited fungal contamination. Detection of single mosquitoes infected with JE virus in large pools of mosquitoes was also investigated. Single laboratory-infected mosquitoes were detected in pools of < or = 200 mosquitoes and in pools diluted to 0.2/100 and 0.1/100 mosquitoes, using the semi-nested PCR. However, the ability to detect live virus decreased as pool size increased. The semi-nested PCR proved more expensive than virus isolation for pools of 100 mosquitoes. However, the semi-nested PCR was faster and more economical using larger pools. Results indicate that surveillance of JE virus in mosquitoes using the semi-nested PCR is an alternative to monitoring seroconversions in sentinel pigs.

Stationary and microcarrier cell culture processes for propagating Japanese encephalitis virus

Inactivated mouse-brain-derived vaccines for Japanese encephalitis virus (JEV) have been used for many years. Recently, attempts have been made to employ cultured Vero cells to replace mouse brain tissues for developing cell-culture-derived vaccines that will be more suitable for worldwide usage. In this study, JEV replication processes in Vero and BHK cells and between stationary and microcarrier culture systems were investigated. Our results demonstrated that a stationary Vero cell culture system produced higher viral titers of JEV, including the Beijin-1 vaccine strain and the attenuated strain CH2195LA, than microcarrier culture did. BHK cells showed less significant differences in their replication kinetics between stationary and microcarrier cultures. Reducing serum concentration during infection led to an overall decrease of JEV production in Vero cells but an increase in BHK cells. By establishing a complete serum-free Vero cell culture, the microcarrier system resulted in a more than 4-log lowered yield compared to that of the stationary culture for JEV production. Thus, the stationary culture is the most efficient system for JEV production from cultured Vero cells.

A 'minimal' approach in design of flavivirus infectious DNA

The 'infectious DNA' approach, which is based on in vivo transcription of (+)RNA virus genome cDNA cassettes from eukaryotic promoters in transfected cells, became a popular alternative to the classical scheme in the infectious clone methodology. Its use, however, is often limited by the instability of plasmids due to a transcriptional activity of eukaryotic promoters in Escherichia coli resulting in synthesis of products toxic for the bacterial host. Using a highly unstable representative infectious clone of Japanese encephalitis (JE) flavivirus, we tested a new approach in design of such problematic 'infectious DNA' constructs, which is based on minimizing unwanted transcription in the bacterial host. A plasmid containing full genome size JE cDNA under control of the minimal cytomegalovirus (CMV) promoter can be propagated in E. coli with growth and stability characteristics similar to that of constructs controlled by the T7 promoter. Transfection of this plasmid into susceptible cells leads to the establishment of a productive infectious cycle. Reinsertion of the CMV enhancer at the 3'-end of the JE cassette substantially increased the specific infectivity without affecting the stability and growth characteristics of the construct. This approach can be useful when stabilization of infectious clones by modification of a viral cDNA cassette is not the feasible or suitable alternative.

Mutations in the NS3 gene and 3'-NCR of Japanese encephalitis virus isolated from an unconventional ecosystem and implications for natural attenuation of the virus

The T1P1 strain of Japanese encephalitis (JE) virus was recently isolated from paddy-free Liu-Chiu Islet in which natural JE antibody has been prevalent. In mouse neuroblastoma-derived Neuro-2a cells, T1P1 appeared significantly lower in virus productivity than another local isolate, CH1392. It implied that this new isolate possesses a characteristic viral replication pattern other than that of CH1392. T1P1 has also shown lower neurovirulence, which was reflected by a significantly higher LD(50) (2.44 x 10(6) PFU) than CH1392 (2.87 x 10(2) PFU). In comparison of the full-length RNA sequences between T1P1 and CH1392, a total of 7 nucleotides, including 1 in preM/M and 2 each in NS3, NS5, and the 3'-end noncoding region (NCR), appeared different. Of them, only the changes in NS3 (position 325, T for CH1392, A for T1P1; and position 364, G for CH1392 and A for T1P1) resulted in substitutions of deduced amino acids. There were two additional nucleotide changes appearing in the 3'-NCR. The amino acids 109 Phe and 122 Glu in NS3 of CH1392 were substituted by Ile and Lys, respectively, in T1P1. The unique growth properties and low virulence of T1P1 presented in this report were likely related to abnormal enzymatic activity due to mutations of the NS3 gene (especially position 364) and possibly to the mutations in the 3'-NCR. The natural attenuation of T1P1 that has been circulating in paddy-free Liu-Chiu Islet may account for the absence of clinical JE cases in past years.

Effects of organic and inorganic fertilisers on mosquito populations in rice fields of southern India

The effects of nitrogenous (inorganic) fertilisers, organic manures and blue-green algae (BGA) biofertiliser on mosquito populations (Diptera: Culicidae) were studied in rice fields of Madurai, Tamil Nadu, south India, with particular attention to Culex vishnui Theobald, Cx. pseudovishnui Colless and Cx. tritaeniorhynchus Giles, the vectors of Japanese encephalitis (JE). The application of urea, a nitrogenous fertiliser, in rice fields significantly increased the grain yield and the population densities of mosquito larvae and pupae (anophelines as well as culicines) in a dose-related manner. Fields treated with inorganic fertilisers (N, P, K) had significantly higher population densities of mosquito immatures than fields treated with organic manures (farmyard manure and green manure). Without nitrogenous fertiliser, BGA increased paddy yield without enhancing mosquito production. Therefore, the use of BGA with less nitrogenous fertiliser is recommended, which is beneficial economically and agronomically to the farming community and also significantly reduces mosquito production in rice fields. Increased use of nitrogenous fertiliser over the past two decades may have contributed to the increased severity of Japanese encephalitis epidemics, vectors of which breed in rice fields.

Growth characteristics of the chimeric Japanese encephalitis virus vaccine candidate, ChimeriVax-JE (YF/JE SA14--14--2), in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes

The Japanese encephalitis (JE) virus vaccine candidate, ChimeriVax-JE, which consists of a yellow fever (YF) 17D virus backbone containing the prM and E genes from the JE vaccine strain JE SA14--14--2, exhibits restricted replication in non-human primates, producing only a low-level viremia following peripheral inoculation. Although this reduces the likelihood that hematophagous insects could become infected by feeding on a vaccinated host, it is prudent to investigate the replication kinetics of the vaccine virus in mosquito species that are known to vector the viruses from which the chimera is derived. In this study ChimeriVax-JE virus was compared to its parent viruses, as well as to wild-type JE virus, for its ability to replicate in Culex tritaeniorhynchus, Aedes albopictus, and Aedes aegypti mosquitoes. Individual mosquitoes were exposed to the viruses by oral ingestion of a virus-laden blood meal or by intrathoracic (IT) virus inoculation. ChimeriVax-JE virus did not replicate following ingestion by any of the three mosquito species. Additionally, replication was not detected after IT inoculation of ChimeriVax-JE in the primary JE virus vector, Cx. tritaeniorhynchus. ChimeriVax-JE exhibited moderate growth following IT inoculation into Ae. aegypti and Ae. albopictus, reaching titers of 3.6-5.0 log(10) PFU/mosquito. There was no change in the virus genotype associated with replication in mosquitoes. Similar results were observed in mosquitoes of all three species that were IT inoculated or had orally ingested the YF 17D vaccine virus. In contrast, all mosquitoes either IT inoculated with or orally fed wild-type and vaccine JE viruses became infected, reaching maximum titers of 5.4-7.3 log(10) PFU/mosquito. These results indicate that ChimeriVax-JE virus is restricted in its ability to infect and replicate in these mosquito vectors. The low viremia caused by ChimeriVax-JE in primates and poor infectivity for mosquitoes are safeguards against secondary spread of the vaccine virus.

Molecular characterization of an Indian isolate of Japanese encephalitis virus that shows an extended lag phase during growth

The biological properties of an Indian isolate (GP78) of Japanese encephalitis virus (JEV) were characterized in tissue-cultured cells and mice and these were compared with the JaOArS982 strain from Japan. The GP78 strain had a markedly extended lag phase during its growth in porcine stable kidney (PS) cells. There were no obvious defects in the penetration of GP78 into PS cells. However, viral RNA and protein synthesis were significantly delayed in GP78-infected PS cells. Fusion-from-within assays carried out in C6/36 cells indicated that GP78 was less fusogenic than the JaOArS982 strain of JEV. Moreover, maximum fusion in GP78-infected cells occurred at pH 5.5, whereas JaOArS982-infected cells showed maximum fusion at pH 6.0. These results suggested that there may be a lesion in the virus-cell fusion process. The GP78 strain also showed delayed growth in brains of 1-week-old BALB/c mice. Although JEV GP78 was as virulent as the JaOArS982 strain in these mice, the appearance of clinical symptoms of JEV infection was delayed by a day in mice infected with the GP78 strain and these animals showed an increased average survival time. Comparison of the nucleotide sequences of the GP78 and the JaOArS982 strains of JEV identified a number of amino acid substitutions in structural proteins. Of these, a Thr --> Met substitution at residue 76 of the envelope protein is predicted to be causally associated with the altered biology of the GP78 strain during growth.

Recombinant, chimaeric live, attenuated vaccine (ChimeriVax) incorporating the envelope genes of Japanese encephalitis (SA14-14-2) virus and the capsid and nonstructural genes of yellow fever (17D) virus is safe, immunogenic and protective in non-human primates

Yellow fever 17D virus, a safe and effective live, attenuated vaccine, was used as a vector for genes encoding the protective antigenic determinants of a heterologous member of the genus Flavivirus, Japanese encephalitis (JE) virus, the leading cause of acute viral central nervous system infection and death throughout Asia. The viral envelope (prM and E) genes of a full-length cDNA clone of YF 17D virus were replaced with the corresponding genes of JE SA14-14-2, a strain licensed as a live, attenuated vaccine in China. Full-length RNA transcripts of the YF/JE chimaera were used to transfect Vero cells. The progeny virus (named 'ChimeriVax-JE'), was used to define safety after intracerebral (i.c.) inoculation of rhesus monkeys. Monkeys (N = 3) inoculated with a high dose (6.6 log10 pfu) developed a brief viremia, showed no signs of illness, developed high titers of anti-JE neutralizing antibody, and had minimal brain and spinal cord lesion scores according to criteria specified in the WHO monkey neurovirulence test. A control group of 3 monkeys that received a lower dose (4.2 log10 pfu) of commercial YF 17D vaccine had slightly higher lesion scores. To develop a lethal monkey model of JE for vaccine protection tests, we inoculated groups of monkeys i.c. or intranasally (i.n.) with a JE virus strain found to be highly neurovirulent and neuroinvasive for mice. Monkeys inoculated i.c., but not i.n., developed severe encephalitis after an incubation period of 8-13 days. The ChimeriVax-JE virus was passed in a cell line acceptable for human use (diploid fetal rhesus lung) and 4.3 or 5.3 log10 pfu were inoculated into groups of 3 monkeys by the subcutaneous route. All 6 animals developed brief viremias (peak titer < 2.0 log10 pfu/ml) and subsequently had anti-JE but no yellow fever neutralizing antibodies. On day 64, the monkeys were challenged i.c. with 5.5 log10 pfu of virulent JE virus. The immunized animals had no detectable viremia post-challenge, whereas 4 unimmunized controls became viremic. Only 1 of 6 (17%) vaccinated monkeys but 4 of 4 (100%) unvaccinated controls developed encephalitis. Histopathological examination 30 days after challenge confirmed that the protected, immunized animals had no or minimal evidence of encephalitis. These data demonstrated the ability of the ChimeriVax-JE to induce a rapid humoral immune response and to protect against a very severe, direct intracerebral virus challenge. Target areas of neuronal damage and inflammation in monkeys infected IC with wild-type JE, the chimaeric virus and YF 17D were similar, indicating that the histopathological scoring system used for the WHO yellow fever monkey neurovirulence test will be applicable to control testing of chimaeric seed viruses and vaccines.

Effect of bafilomycin A1 on the growth of Japanese encephalitis virus in Vero cells

We studied the effect of bafilomycin A1 (Baf-A1), a novel and highly specific inhibitor for vacuolar-type proton (V-H+) pump, on the growth of Japanese Encephalitis virus (JEV) in Vero cells. Viral fluorescence microscopic study showed that Baf-A1 induced the complete disappearance of acidified compartments such as endosomes and lysosomes in Vero cells by the treatment with 0.1 microM Baf-A1 for 1 h at 37 degrees C. In proportion to the disappearance of acidified compartments, virus growth was inhibited when Baf-A1 was present from 1 h before infection to the end of incubation in a dose-dependent manner, or added within as early as 5 min after infection. Conversely, the virus growth was recovered in correlation with the reappearance of acidified compartments after removal of Baf-A1. These results suggest that a low pH condition, which is regulated by Baf-A1-sensitive V-H+ pumps, is essential for the early stage of JEV growth.

Susceptibility of three laboratory strains of Aedes albopictus (Diptera: Culicidae) to Japanese encephalitis virus from Taiwan

The susceptibility of 3 laboratory strains of Aedes albopictus (Skuse) (Sanhsia [SH], Yungho [YH], Liyang [LY], and 1 strain of Culex tritaeniorhynchus Giles from northern and central Taiwan were compared for susceptibility to the MQ1-2 strain of Japanese encephalitis (JE) virus. The median infective dose (MID50) by intrathoracic inoculation was 0.23, 0.76, 1.60, and -0.03 log10 WMICLD50 (50% weanling mice intracranial lethal dose) with Ae. albopictus SH, YH, LY, and Cx. tritaeniorhynchus, respectively. After feeding on a sweetened blood-virus mixture, the oral MID50 was 2.03, 4.32, and 4.98 log10 WMICLD50 for SH, YH, and LY, respectively, and 1.02 log10 WMICLD50 for Cx. tritaeniorhynchus. The SH Ae. albopictus strain transmitted virus to normal mice after 14 d. with an average transmission rate of 45%. Based on these results, the SH strain was the most susceptible and important potential vector among 3 Ae. albopictus strains for the sympatric MQ1-2 strain of JE.

Assessment of neutralizing antibodies elicited by a vaccine (Nakayama) strain of Japanese encephalitis virus in Taiwan

A total of 368 blood specimens were resampled from a serum collection containing 2914 blood samples which were collected by a random sampling in Taiwan in 1991. The plaque reduction neutralization test was applied to evaluate the neutralizing ability to two strains of Japanese encephalitis viruses, i.e. Nakayama (the present vaccine strain) and JE5 (a Taiwan isolate). The result revealed that antibodies against JE virus were present in each stratified age group. Antibody positive rates were both highest in the group older than 70 years although the lowest rates were located in different groups. In addition, the result showed that the immunogenicity potency of the antibody induced by the vaccine strain did not have a good coverage against JE5. The rate of neutralizing antibodies above the level of protective efficacy of the present vaccine was limited as low as 37.93%. Efficacy of the vaccine used at present was apparently not efficient. Consideration of a more promising vaccine may be necessary.

Inhibition of Japanese encephalitis virus infection by nitric oxide: antiviral effect of nitric oxide on RNA virus replication

The antiviral effects of nitric oxide (NO) on Japanese encephalitis virus (JEV), a member of the family Flaviviridae, were investigated in this study. In vitro, inhibition of replication of JEV in gamma interferon-activated RAW 264.7 murine macrophages was correlated to cellular NO production. When cocultured with infected murine neuroblastoma N18 cells, gamma interferon-activated RAW 264.7 cells also efficiently hindered JEV replication in contiguous bystanders, and this anti-JEV effect could be reversed by an NO synthase (NOS) inhibitor, N-monomethyl-L-arginine acetate. In vivo, the mortality rate increased as the NOS activity of JEV-infected mice was inhibited by its competitive inhibitor, N-nitro-L-arginine methyl ester. Moreover, when an organic donor, S-nitro-N-acetylpenicillamine (SNAP), was used, the NO-mediated antiviral effect was also observed in primarily JEV-infected N18, human neuronal NT-2, and BHK-21 cells, as well as in persistently JEV-infected C2-2 cells. These data reaffirm that NO has an effective and broad-spectrum antimicrobial activity against diversified intracellular pathogens. Interestingly, the antiviral effect of NO was not enhanced by treatment of N18 cells with SNAP prior to JEV infection, a measure which has been shown to greatly increase the antiviral effect of NO in infection by vesicular stomatitis virus. From biochemical analysis of the impact of NO on JEV replication in cell culture, NO was found to profoundly inhibit viral RNA synthesis, viral protein accumulation, and virus release from infected cells. The results herein thus suggest that NO may play a crucial role in the innate immunity of the host to restrict the initial stage of JEV infection in the central nervous system.

In vitro antiviral activity of indigenous glycyrrhizin, licorice and glycyrrhizic acid (Sigma) on Japanese encephalitis virus

Glycyrrhizin, a triterpenoid glycoside and Licorice from Glycyrrhiza glabra and Ammonium salt of Glycyrrhizic acid (Sigma) were tested for antiviral activity on three strains of Japanese encephalitis virus (JEV), Nakayama, P-20778 and 821564 XY48. Purified glycyrrhizin (M.w. 822.92) inhibited plaque formation in all the three strains of JEV at a concentration of 500 micrograms/ml at 96 hrs, Similar effect was observed at 1000 micrograms/ml concentration with Licorice and Ammonium salt of glycyrrhizic acid. The minimal inhibitory concentrations were not toxic to porcine stable kidney (PS) and human cervical carcinoma (HeLa) cell lines. Cyctotoxicity of these chemicals was evaluated by trypan blue dye exclusion test which indicated subtoxic concentrations at 5,000 micrograms/ml at 96 hrs and toxic concentrations were 10,000 micrograms/ml at the same time period for the host cells PS. Thus the indigenously purified glycyrrhizin seems to be more potent antiviral agent than Licorice and ammonium salt of glycyrrhizic acid (Sigma) for JEV 'in vitro'.

Nutrient composition for cultivation of Japanese encephalitis virus in vitro

Effects of certain groups of nutrients such as glucose, essential amino acids (AA), nonessential AA, vitamins and trace nutrients on the multiplication of various strains of Japanese encephalitis virus (JEV) were studied with an aim to optimise the conditions for cultivation of the virus in porcine stable (PS) kidney cell cultures. Eagle's Minimal Essential Medium (MEM) was modified by addition of the nutrients in different concentrations and combinations. Glucose was found the most important single nutrient in promoting significantly the virus multiplication. Essential AA alone did not influence the virus yield, while in combination with glucose they caused its marked increase. Vitamins and other nutrients did not stimulate significantly virus multiplication. The study revealed that the extent of the glucose effect depends on the virus strain used.

Growth and cytopathic effect of Japanese encephalitis virus in astrocyte-enriched cell cultures from neonatal mouse brains

Neuron-free, astrocyte-enriched brain cell cultures from newborn mice could be infected with Japanese encephalitis virus (JEV) as evidenced by immunofluorescence (IF), viral replication and cytopathic effect (CPE). Virus-specific cytoplasmic fluorescence was detectable in astrocytes first after 18 hrs, released infectious progeny virus in the culture fluid after 24 hrs, and CPE after 11 days post infection (p.i.).

Cytotoxic T lymphocytes raised against Japanese encephalitis virus: effector cell phenotype, target specificity and in vitro virus clearance

Several H-2 defined cell lines were examined for their ability to support infection and replication of Japanese encephalitis virus (JEV) before their use in in vitro and in vivo stimulation protocols for generating cytotoxic T lymphocytes (CTLs) against JEV. Among 11 different cell lines tested, two H-2d macrophage tumour lines (P388D1, RAW 264.7), an H-2d hybridoma (Sp2/0), an H-2KkDd neuroblastoma (Neuro 2a), and H-2k fibroblast cell line (L929) were found to support JEV infection and replication. These cell lines were used to generate anti-JEV CTLs by using in vivo immunization followed by in vitro stimulation of BALB/c mice. We observed that not only syngeneic and allogeneic infected cells but also JEV-infected xenogeneic cells could prime BALB/c mice for the generation of JEV-specific CTLs upon subsequent in vitro stimulation of splenocytes with JEV-infected syngeneic cells. Although infected xenogeneic cells were used for immunization, the anti-JEV effectors that were generated lysed infected syngeneic targets but not JEV-infected xenogeneic or allogeneic target cells in a 5 h 51Cr release assay. These anti-JEV effectors recognized syngeneic target cells infected with West Nile virus to a lesser extent and were shown to be Lyt-2.2+ T cells. The results of unlabelled cold target competition studies suggested alterations in the cell surface expression of viral antigenic determinants recognized by these CTLs. We further demonstrate that the JEV-specific CTLs generated could virtually block the release of infectious virus particles from infected P388D1 and Neuro 2a cells in vitro.

Morphogenesis of the protein secretory system in PC12 cells infected with Japanese encephalitis virus

Infection of PC12 cells with Japanese encephalitis (JE) virus caused marked proliferation of the protein secretory system. Accordingly, in this study the morphogenesis of the secretory organelles, i.e., rough endoplasmic reticulum (RER) and the Golgi apparatus, in JE virus-infected PC12 cells was analyzed by electron microscopical observation. Starting 24 h postinoculation (p.i.), a structure that represented nascent RER appeared in the cytoplasm in the form of rows of ribosomes which surrounded membrane-unbounded, electron-lucent lacunae in a reticular, honey-comb pattern (reticular RER). Although the reticular RER lacked membrane components, its lacunae contained progeny virions, indicating that the rows of ribosomes synthesized the viral proteins and discharged them into the lacunae for the viral assembly. The reticular RER apparently transformed into the familiar lamellar RER during the RER morphogenesis as the lacunae coalesced to form flat cisternae and RER membrane assembled to border the cisternae. These findings indicated that the proliferating RER was the site of not only active protein synthesis but also active membrane biogenesis. The proliferating RER released a large number of membrane vesicles including virion-carrying vesicles into the cytoplasm. These vesicles congregated in the juxtanuclear region, especially around the centrioles, and fused to existing Golgi complexes for enlargement or fused among themselves to form new Golgi complexes. The present study, therefore, indicated that (a) nascent RER was formed by polysomes that arranged themselves in rows of ribosomes without participation of a preexisting membrane framework of endoplasmic reticulum (ER), (b) membrane components of RER were assembled de novo within the structure during the RER morphogenesis, and (c) RER released membrane vesicles that moved to the Golgi apparatus and contributed to the morphogenesis of the Golgi apparatus. Possible causative mechanisms involved in the proliferation of the secretory system in JE virus-infected PC12 cells are discussed.

Detection of viral antigens on the surface of cells infected with Japanese encephalitis virus by modified immunofluorescent technique

A modified immunofluorescent method employing anti-Japanese encephalitis (JE) virus monoclonal (MoAbs) and polyclonal (immune PF) antibodies was evaluated for the detection of viral antigens expressed on the surface of porcine stable kidney cells infected with JE virus (733913, India). The infected cells showed granular immunofluorescence on the surface with both the MoAbs, Hs-1 and Hx-3 and immune PF 24 hr and 48 hr post virus infection. Interestingly, two strains of JE virus viz. Yoken (Japan) and 755468 (India) which did not react with the MoAb Hs-1 in the standard indirect fluorescent antibody (FA) technique, were positive for surface immunofluorescence (IF) with the same MoAb. Thus, the modified technique will be useful for the detection of more labile and conformational-dependent epitopes which might get lost or denatured by prior fixation of infected cells with acetone.

Japanese encephalitis virus latency in peripheral blood lymphocytes and recurrence of infection in children

In a study group of 40 children who had been admitted to hospital with acute encephalitis, the disease was due to infection with Japanese encephalitis virus (JEV). Three children developed recurrence of disease 8-9 months later. No virus had been isolated from these three patients during the acute stage of their illness, but virus was recovered from all during the recurrence phase by co-cultivation of their peripheral blood mononuclear cells in primary mouse embryo fibroblast cultures. Virus was also recovered by co-cultivation of peripheral blood mononuclear cells collected 8 months after their acute disease from three out of eight randomly selected asymptomatic children within the study group but not from similar cultures set up from JEV-seronegative children used as controls. Virus was also isolated by co-cultivation of T lymphocytes of asymptomatic children as detected by indirect immunofluorescence or by inoculation in mice.

Entry and replication of Japanese encephalitis virus in cultured neurogenic cells

The entry mode and growth pattern of Japanese encephalitis (JE) virus in mouse neuroblastoma N18TG2 cells and mouse neuroblastoma x rat glioma NG108-15 hybrid cells were studied by electron microscopy. At two minutes after inoculation, JE virions adsorbed onto and directly penetrated through the plasma membrane of the hybrid cells, whereas virions did not adsorb nor entered the neuroblastoma cells. Correspondingly, the hybrid cells showed assembling progeny JE virions in the cisternae of rough endoplasmic reticulum (RER) 1 day postinoculation (p.i.) although virions were rarely found on the following days during the experiment. On the other hand, progeny virions did not assemble in the RER cisternae of the neuroblastoma cells throughout the experiment. The morphologic observations, therefore, suggest that (a) the hybrid cells express JE-virus receptors which facilitate the viral attachment onto and entry into the cells, while the neuroblastoma cells do not and (b) JE virus replicates very poorly after the entry into the hybrid cells while it does not replicate at all in the neuroblastoma cells. The virus titrations of the media of the neuroblastoma and hybrid cell cultures showed only titers indicative of residual virus of the inoculum that progressively decreased during the experiment. The present results show therefore that of the two neurogenic cell culture lines studied only the hybrid cell line can be used for the study of viral entry and replication, although it is not suited for virus production. Possible reasons for the poor replication of JE virus in the hybrid cells are discussed.

Evidence for latency of Japanese encephalitis virus in T lymphocytes

Activation of latent Japanese encephalitis virus (JEV) in the spleen has been studied by co-cultivation with allogeneic or syngeneic cells. Activated virus was isolated by co-cultivation from T lymphocytes of spleen, as shown by indirect immunofluorescence or by inoculation into mice. The B lymphocytes and macrophages of latently infected mice did not reactivate the virus. A higher proportion of Lyt 1 cells than Lyt 2 cells were harbouring JEV as shown by indirect immunofluorescence. The spleen cells from latently infected mice elicited the lymphoproliferative response but this was much lower than that observed in the controls. These findings suggest the establishment of latent JEV infection in T lymphocytes.