Serologic and Virologic Studies of an Imported Dengue Case Occurring in 2014 in Okinawa, Japan

After returning from Bali, Indonesia, in February 2014, a 72-year-old man was hospitalized in Okinawa owing to a high fever and rash. Dengue was clinically suspected, and the patient tested positive for IgM against dengue using a commercial kit. Serologically, the patient showed secondary seroreactivity. Significant increases in neutralization titers (N-titers) against all 4 serotypes of dengue virus (DENV) and Japanese encephalitis virus (JEV) strains were recognized in convalescent-phase sera comparing to acute phase sera. The N-titer against DENV serotype 1 (DENV-1) was the highest among all DENV serotypes. Interestingly, the N-titers against JEV strains were significantly higher than those against all types of DENV comparing to acute phase sera. The virus was isolated from the acute-phase serum and identified as DENV-1 and designated RD14/Okinawa. The patient's symptoms were due to DENV-1 infection. Phylogenetic sequencing analysis indicated that the isolate RD14/Okinawa belonged to genotype I of DENV-1, which is closely related to the Southeast Asian strains and isolates found during the dengue outbreak in Japan in 2014. We should undertake control measures against dengue in Okinawa, which is a subtropical area with Aedes albopictus activity throughout year.

Mucosal vaccination approach against mosquito-borne Japanese encephalitis virus

To investigate the potential applicability of mucosal vaccines against mucosa-unrelated pathogens, a non-parenteral vaccination approach was taken as a prophylactic strategy against mosquito-borne Japanese encephalitis virus (JEV). Intranasal (i.n.) immunization with a mouse brain-derived formalin-inactivated JE vaccine induced a robust virus-neutralizing antibody in mice, and this induction was augmented by co-administration with cholera toxin (CT) and pertussis toxin, but not with killed Bordetella pertussis. The antibody response induced by the i.n. administration of the JE vaccine with bacterial toxins was comparable in intensity to that induced by a parenteral immunization regime, and the former was considerably more effective in terms of delayed-type hypersensitivity and local antibody response. In addition, the adjuvant effects of bacterial toxins were much more prominent for the mucosal than the parenteral route. Two other non-invasive routes, oral and transcutaneous administration, were examined, but the i.n. route was by far the most effective. Finally, the vaccine efficacy of a chimeric fusion protein between the B subunit of CT and the JEV envelope protein showed some promise for the development of non-invasive JE vaccine. Our results suggest that the mucosal vaccination approach is feasible for a non-mucosal pathogen such as JEV, but that the adjuvant, carrier molecule, and administration route must be optimized for construction of an effective vaccine platform.

Construction of human Fab (gamma1/kappa) library and identification of human monoclonal Fab possessing neutralizing potency against Japanese encephalitis virus

A combinatorial human Fab library was constructed using RNAs from peripheral blood lymphocytes obtained from Japanese encephalitis virus hyper-immune volunteers on pComb3H phagemid vector. The size of the constructed Fab library was 3.3x10(8) Escherichia coli transformants. The library was panned 3 times on the purified Japanese encephalitis virus (JEV) virion, and phage clones displaying JEV antigen-specific Fab were enriched. The enriched phage pool was then screened for clones producing Fab molecule with JEV neutralizing activity by the focus reduction-neutralizing test. Among 188 randomly selected clones, 9 Fab preparations revealed neutralizing activities against JEV strain Nakayama. An E. coli transformed with TJE12B02 clone, which produced human monoclonal Fab with the highest neutralizing activity was cultured in a large scale, and the Fab molecule was purified using affinity chromatography. The purified FabTJE12B02 showed the 50% focus reduction endpoint at the concentration of 50.2 microg/ml (ca. 1,000 nM) when JEV strain Nakayama was used. The FabTJE12B02 recognized E protein of JEV strain Nakayama, and the dissociation equilibrium constant (Kd) of the FabTJE12B02 against purified JEV antigen was calculated as 1.21x10(-8) M. Sequence analysis demonstrated that TJE12B02 used a VH sequence homologous to the VH3 family showing 88.8% homology to germline VH3-23, and used a Vkappa sequence homologous to the VkappaII subgroup showing 92.8% homology to germline A17.

Heteropentameric cholera toxin B subunit chimeric molecules genetically fused to a vaccine antigen induce systemic and mucosal immune responses: a potential new strategy to target recombinant vaccine antigens to mucosal immune systems

Noninvasive mucosal vaccines are attractive alternatives to parenteral vaccines. Although the conjugation of vaccine antigens with the B subunit of cholera toxin (CTB) is one of the most promising strategies for vaccine delivery to mucosal immune systems, the molecule cannot tolerate large-protein fusion, as it severely impairs pentamerization and loses affinity for GM1-ganglioside. Here we report a new strategy, in which steric hindrance between CTB-antigen fusion subunits is significantly reduced through the integration of unfused CTB "molecular buffers" into the pentamer unit, making them more efficiently self-assemble into biologically active pentamers. In addition, the chimeric protein took a compact configuration, becoming small enough to be secreted, and one-step affinity-purified proteins, when administered through a mucosal route, induced specific immune responses in mice. Since our results are not dependent on the use of a particular expression system or vaccine antigen, this strategy could be broadly applicable to bacterial enterotoxin-based vaccine design.

Molecular basis for adaptation of a chimeric dengue type-4/Japanese encephalitis virus to Vero cells

The premembrane and envelope (E) genes of a full-length cDNA clone of the dengue type-4 (DEN4) virus 814669 strain were replaced with those of the Japanese encephalitis (JE) virus JaOH0566 strain. The in vitro-synthesized RNA transcripts prepared from chimeric cDNA were used to transfect mosquito C6/36 cells. A viable chimeric virus (designated DEN4/JE) was recovered. Unexpectedly, DEN4/JE exhibited restricted growth in Vero cells. After a serial passage in Vero cells, the Vero-adapted chimeras were obtained (two clones, designated Strain I and Strain II, respectively). The entire genomes of DEN4/JE, Strain I, and Strain II were sequenced and compared. There were multiple mutations, but amino acid substitutions occurred only in E and nonstructural (NS) protein NS4B. Our findings in this study indicate that the 5' nontranslated region, E, and NS4B may be involved in Vero cell adaptation in this chimeric system.

Dengue virus-induced apoptosis in hepatic cells is partly mediated by Apo2 ligand/tumour necrosis factor-related apoptosis-inducing ligand

Although hepatic injury is reported in cases with dengue haemorrhagic fever and dengue shock syndrome, its mechanism remains poorly understood. Several findings suggest that dengue virus (DEN) induces apoptosis of hepatocytes in vivo. In this work, DEN type 2 (DEN-2) strain NGC was shown to induce apoptosis in the hepatic cell line HepG2, and infection of HepG2 cells was found to induce Apo2 ligand (Apo2L, also known as tumour necrosis factor-related apoptosis-inducing ligand or TRAIL) expression. Furthermore, Apo2L/TRAIL induced apoptosis in HepG2 cells, which expressed the Apo2L/TRAIL receptor DR5/TRAIL-R2 on their surface. Analysis of the Apo2L/TRAIL promoter revealed that this gene was activated by DEN-2 infection, whose responsive element was overlapping NF-kappaB- and Sp1-binding sites located at nt -75 to -65. The proteasome inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal (LLnL) inhibited Apo2L/TRAIL mRNA expression, and LLnL and anti-Apo2L/TRAIL antibody inhibited DEN-2-induced apoptosis. It was proposed that DEN infection promotes apoptosis partly through the induction of Apo2L/TRAIL expression.

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.

Apoptosis induced by the histone deacetylase inhibitor FR901228 in human T-cell leukemia virus type 1-infected T-cell lines and primary adult T-cell leukemia cells

Inhibition of histone deacetylase (HDAC) activity induces growth arrest, differentiation, and, in certain cell types, apoptosis. FR901228, FK228, or depsipeptide, is an HDAC inhibitor effective in T-cell lymphomas. Adult T-cell leukemia (ATL) is caused by human T-cell leukemia virus type 1 (HTLV-1) and remains incurable. We examined whether FR901228 is effective for treatment of ATL by assessing its ability to induce apoptosis of HTLV-1-infected T-cell lines and primary leukemic cells from ATL patients. FR901228 induced apoptosis of Tax-expressing and -unexpressing HTLV-1-infected T-cell lines and selective apoptosis of primary ATL cells, especially those of patients with acute ATL. FR901228 also efficiently reduced the DNA binding of NF-kappaB and AP-1 in HTLV-1-infected T-cell lines and primary ATL cells and down-regulated the expression of Bcl-x(L) and cyclin D2, regulated by NF-kappaB. Although the viral protein Tax is an activator of NF-kappaB and AP-1, FR901228-induced apoptosis was not associated with reduced expression of Tax. In vivo use of FR901228 partly inhibited the growth of tumors of HTLV-1-infected T cells transplanted subcutaneously in SCID mice. Our results indicated that FR901228 could induce apoptosis of these cells and suppress the expression of NF-kappaB and AP-1 and suggest that FR901228 could be therapeutically effective in ATL.

Short report: a major genotype of Japanese encephalitis virus currently circulating in Japan

A 240-nucleotide sequence of the capsid/premembrane gene region of 23 Japanese encephalitis virus (JEV) strains isolated in Tokyo and Oita, Japan was determined and phylogenetic analyses were performed. All the strains clustered into two distinct genotypes (III and I). All strains isolated before 1991 belonged to genotype III, while those isolated after 1994 belonged to genotype I. In addition, the strains of the genotype I isolated in Japan showed a close genetic relationship with those from Korea and Malaysia.

The complete genomic sequence of hepatitis delta virus genotype IIb prevalent in Okinawa, Japan

The Miyako Islands, located in the southernmost part of Japan, have been reported to be endemic for hepatitis delta virus (HDV). The majority of HDV patients in this area exhibit a relatively mild course of infection that evolves into a quiescent cirrhotic condition. The entire nucleotide sequence of the Miyako isolate (L215) of HDV obtained from a cirrhotic patient infected with HDV was determined. This isolate, L215, comprises 1682 nt and encodes 213 aa of the hepatitis delta antigen. Phylogenetic analysis showed that L215 is closely related to the Taiwanese genotype IIb HDV isolate. In addition, the predicted folding structure of the antigenomic RNA substrate was different from those of the published genotype II sequences.

Locus of a virus neutralization epitope on the Japanese encephalitis virus envelope protein determined by use of long PCR-based region-specific random mutagenesis

We prepared recombinant Japanese encephalitis (JE) virus populations possessing random mutations at the envelope (E) protein region by a long PCR-based method. Neutralization-resistant mutants were selected from these populations by application of JE-specific virus neutralizing monoclonal antibody (mAb) 503, which possessed a 51,200-fold neutralization titer. We classified the mutants into three groups, each bearing two amino acid alterations at the E protein region: 52, Gln-Arg, and 136, Lys-Glu; 136, Lys-Glu, and 275, Ser-Pro; and 126, Ile-Thr, and 136, Lys-Glu, respectively. Three different genetically engineered variants, each bearing a single mutation, 126, Ile-Thr; 136, Lys-Glu; and 275, Ser-Pro, respectively, showed partial but not complete recovery of reactivity to mAb 503. Our results indicate that the amino acid substitutions at amino acid positions 52, 126, 136, and 275 altered the structure of the neutralization epitope for mAb 503 on the E protein. All these mutations were clustered at the junction of domains I and II of the E protein and it is likely that the epitope for mAb 503 is composed of at least E(0)-e, D(0)-a, and k strands of the E protein. We also demonstrated the efficacy of the long PCR-based recombinant virus technique as a useful tool for the creation of a variety of mutants bearing random mutations at targeted areas of the virus genome.

Health effects of fluoride pollution caused by coal burning

Recently a huge amount of fluoride in coal has been released into indoor environments by the combustion of coal and fluoride pollution seems to be increasing in some rural areas in China. Combustion of coal and coal bricks is the primary source of gaseous and aerosol fluoride and these forms of fluoride can easily enter exposed food products and the human respiratory tract. Major human fluoride exposure was caused by consumption of fluoride contaminated food, such as corn, chilies and potatoes. For each diagnostic syndrome of dental fluorosis, a log-normal distribution was observed on the logarithm of urinary fluoride concentration in students in China. Urinary fluoride content was found to be a primary health indicator of the prevalence of dental fluorosis in the community. In the fluorosis areas, osteosclerosis in skeletal fluorosis patients was observed with a high prevalence. A biochemical marker of bone resorption, urinary deoxypyridinoline content was much higher in residents in China than in residents in Japan. It was suggested that bone resorption was stimulated to a greater extent in residents in China and fluoride may stimulate both bone resorption and bone formation. Renal function especially glomerular filtration rate was very sensitive to fluoride exposure. Inorganic phosphate concentrations in urine were significantly lower in the residents in fluorosis areas in China than in non-fluorosis area in China and Japan. Since airborne fluoride from the combustion of coal pollutes extensively both the living environment and food, it is necessary to reduce fluoride pollution caused by coal burning.

Pur alpha protein implicated in dendritic RNA transport interacts with ribosomes in neuronal cytoplasm

We have previously reported that pur alpha, known to be a regulator of DNA replication and transcription, links neural BC1 RNA to microtubules via dendrite-targeting RNA motifs. Here we demonstrate the subcellular localization of pur proteins within the brain. Pur proteins were detected in neurons but not in glia. Immunohistochemical staining was prominent in perikarya and proximal dendrites and also extended into primary dendritic processes, but no significant signals were detected in the distal regions of dendrite. When homogenates of mouse brain were fractionated, pur alpha was most concentrated in the microsomal pellet. Consistently, pur alpha co-fractionated with free polysomes as well as with membrane-bound polysomes and the association with polysomes was mediated by binding ribosomal subunits. Levels of ribosomes with pur alpha progressively increased during postnatal development of the brain.

[A case of multiple intracranial cavernous angiomas presented with dementia and parkinsonism--clinical and MRI study for 10 years]

We report a case of multiple intracranial cavernous angiomas with serial clinical examination and with MRI imaging for 10 years. The patient, 72 years old woman, had slowly progressive postural tremor and Parkinsonism followed by dementia. Pathological confirmation of cavernous angioma was obtained. At the age of 62, brain MRI study demonstrated hydrocephalus, multiple small hypointensity dots in cerebellum and cerebral white matter, and reticulated cores predominantly adjacent to the ventricles on T2-weighted images. Serial MRI imaging shows that the number of small dots has markedly increased and that hypointense lesions surrounding reticulated core, corresponding to hemosidern deposit, have extended. This case indicates that probably due to chronic compression and continuous hemorrhage' multiple and long-standing intracranial lesions could cause dementia and Parkinsonism, which are uncommon symptoms of cavernous angioma.

[A case of chorea-acanthocytosis with dilated cardiomyopathy and myopathy]

We report a patient of chorea-acanthocytosis (CA), presenting with dilated cardiomyopathy and myopathy. The patient, 40-year-old male, was seen in our clinic because of progressive gait disturbance. Neurologically, he had chorea, tic, dystonia, diminished tendon reflexes and mild muscular atrophy and weakness. Serum creatine kinase level was elevated to 5.514 IU/l, MRI study showed atrophy of the putamen and caudate nucleus. Peripheral nerve involvement was confirmed pathologically and electrophysiologically. Acanthocytosis was found after repeated blood examinations. Furthermore, he had dilated cardiomyopathy on echocardiogram and cardiac muscle biopsy, and his muscle biopsy taken from gastrocnemius indicated myopathic changes with fiber necrosis. From these clinical and laboratory data, he was suspected to have McLeod syndrome (McS). However, he had normal expression of Kell antigens, and direct sequence of XK gene from genomic DNA sample showed no mutations. Accordingly, he was diagnosed as having CA. As CA shares the similar clinical and laboratory features with McS except Kell antigens, the evaluation of Kell blood system is crucial for differential diagnosis. As seen in our patient, blood sampling should be repeated for identification of acanthocytosis, because the finding is not always clearly present.

Three Japanese encephalitis cases in Okinawa, Japan, 1991

Since 1974, no Japanese encephalitis (JE) case had been reported on Okinawa island in either Okinawan people or US servicemen. In 1991, three US marines stationed on Okinawa island developed encephalitis symptoms. Neutralization (N) test and IgM-capture ELISA were carried out on the serial samples of serum and cerebrospinal fluid (CSF) taken from the patients. In each patient N test on both serum and CSF samples gave a significant rise in JE antibody titer in the comparison between the acute and convalescent phases, indicating that all the cases were infected with JE virus. The IgM-capture ELISA also showed a significant rise of antibody titer of the serum and CSF samples in the convalescent phase in patients 2 and 3, while in patient 1 a significant rise in IgM antibody was observed in the serum sample, but not in the CSF sample. None of the patients had been administered JE vaccine. This report underscores the importance of JE vaccination.

Low bone mineral density in a case of mosaicism Klinefelter syndrome: rapid response to testosterone therapy

Male hypogonadism has been recognized as one of the major causes of secondary osteoporosis, but most cases seem to be left undiagnosed. We report a 54-year-old case of mosaicism Klinefelter syndrome lacking typical clinical features such as tall stature or low intelligence, who was found to have marked decrease in lumbar bone mineral density (BMD: 0.686 g/cm2) during treatment of diabetes mellitus. In investigation for etiologies of secondary osteoporosis, he was diagnosed as having mosaicism Klinefelter syndrome (XXY/XY/XX). Although he was infertile, he lacked typical clinical features of Klinefelter syndrome. Testosterone replacement was started, which resulted in an increase in BMD up to 0.712 g/cm2 two months after the initiation of therapy. The fact that BMD increased shortly after the initiation of testosterone replacement therapy in the present case supported a beneficial effect of testosterone on BMD, as recently suggested in idiopathic hypogonadotropic hypogonadism. Although the present case was diagnosed as having mosaicism Klinefelter syndrome by investigating etiologies for osteoporosis, it may be stressed that male hypogonadism, in general, should be adequately suspected in the presence of infertility and from the findings of physical examination.

Evaluation of molecular strategies to develop a live dengue vaccine

BACKGROUND

Millions of individuals are estimated to become infected with dengue virus each year, particularly in tropical and subtropical regions. Mortality is low but infection can lead to a severe form of dengue, characterised by haemorrhage and shock. A safe and effective vaccine against dengue is still not available.

OBJECTIVE

To use the successful construction of dengue type 4 virus (DEN4) cDNA, which yields infectious RNA transcripts, to provide a new approach to the development of safe and effective dengue vaccines.

STUDY DESIGN

The 3' and 5' noncoding (NC) regions of the genome were targeted to construct DEN4 deletion mutants, because the sequences in these regions are thought to play an important role in the regulation of viral replication. DEN4 cDNA was also employed to construct a viable chimeric virus with dengue type 1, 2 or 3 antigenicity, by substitution of heterotypic structural protein genes.

RESULTS

Most viable mutants, recovered from the cDNA constructs, were partially restricted for growth in simian cells as analysed by plaque morphology assay and viral yield analysis. Several 3' NC deletion mutants which exhibited a range of growth restriction in cell culture were further evaluated for infectivity and immunogenicity in rhesus monkeys. Occurrence and duration of viraemia were reduced for these deletion mutants, compared to the wild type DEN4. Analysis of antibody response to infection in rhesus monkeys also indicated that some of these mutants were attenuated. These DEN4 deletion mutants represent promising live dengue vaccine candidates that merit further clinical evaluation. Chimera DEN1/DEN4 or DEN2/DEN4 which expresses DEN1 or DEN2 antigenicity were also used to infect monkeys. Most monkeys immunised with these chimeric viruses, singly or in combination, developed high titres of neutralising antibodies and were protected against homotypic wild type DEN1 or DEN2 challenge.

CONCLUSIONS

DEN4 and its derived chimeric viruses of other three dengue serotype specificity, that contain appropriate attenuating mutations, have a potential use in a tetravalent live vaccine against dengue.

Reconstruction for the brilliance-upgrading project of the Photon Factory storage ring

Reconstruction of the Photon Factory storage ring (PF ring; 2.5 GeV) is now in progress to provide very brilliant synchrotron radiation to users, i.e. the emittance is being reduced by a factor of five. Components, such as the quadrupole and sextupole magnets, vacuum chambers, beamlines and beam-position monitors, are being replaced by new ones in 16 normal-cell sections of the PF ring. The accelerating cavities, injection systems and control systems are also being replaced. Operation will commence when the improvements are completed on 1 October 1997.

New beam-position monitor system for upgraded Photon Factory storage ring

Accompanying the brilliance-upgrading project at the Photon Factory storage ring, the beam-position monitor (BPM) system has been renovated. The new system was designed to enable precise and fast measurements to correct the closed-orbit distortion (COD), as well as to feed back the orbit position during user runs. There are 42 BPMs newly installed, amounting to a total of 65 BPMs. All of the BPMs are calibrated on the test bench using a coaxially strung metallic wire. The measured electrical offsets are typically 200 micro m in both directions, which is 1/2-1/3 of those of the old-type BPMs. In the signal-processing system, PIN diode switches are employed in order to improve reliability. In the fastest mode, this system is capable of measuring COD within about 10 ms; this fast acquisition will allow fast suppression of the beam movement for frequencies up to 50 Hz using a global feedback system.

Health effects of indoor fluoride pollution from coal burning in China

The combustion of high fluoride-content coal as an energy resource for heating, cooking, and food drying is a major exhaust emission source of suspended particulate matter and fluoride. High concentrations of these pollutants have been observed in indoor air of coal-burning families in some rural areas in China. Because airborne fluoride has serious toxicological properties, fluoride pollution in indoor air and the prevalence of fluorosis have been analyzed in a fluorosis area and a healthy nonfluorosis area in China and in a rural area in Japan. For human health, fluoride in indoor air has not only been directly inhaled by residents but also has been absorbed in stored food such as corn, chilies, and potatoes. In the fluorosis area in China, concentrations of urinary fluoride in the residents have been much higher than in the nonfluorosis area in China and in the rural area in Japan. In the fluorosis area, almost all elementary and junior high school students 10-15 years of age had dental fluorosis. Osteosclerosis in the skeletal fluorosis patients was very serious. Urinary deoxypyridinoline in rural residents in China was much higher than in rural residents in Japan. Data suggest that bone resorption was extremely stimulated in the residents in China and that fluoride may stimulate both bone resorption and bone formation. Because indoor fluoride from combustion of coal is easily absorbed in stored food and because food consumption is a main source of fluoride exposure, it is necessary to reduce airborne fluoride and food contamination to prevent serious fluorosis in China.

Single-pass BPM system of the Photon Factory storage ring

At the 2.5 GeV ring of the Photon Factory, a single-pass beam-position monitor (BPM) system is being prepared for the storage ring and the beam transport line. In the storage ring, the injected beam position during the first several turns can be measured with a single injection pulse. The BPM system has an adequate performance, useful for the commissioning of the new low-emittance lattice. Several stripline BPMs are being installed in the beam transport line. The continuous monitoring of the orbit in the beam transport line will be useful for the stabilization of the injection energy as well as the injection beam orbit.

Mutational analysis of a neutralization epitope on the dengue type 2 virus (DEN2) envelope protein: monoclonal antibody resistant DEN2/DEN4 chimeras exhibit reduced mouse neurovirulence

The antigenic site of dengue type 2 virus (DEN2)-neutralizing monoclonal antibody (mab) 3H5 was investigated by mutational analysis. Sequence comparisons indicated that much of the 12-amino-acid sequence extending from position 386 to 397 of the DEN2 envelope glycoprotein (E) previously thought to represent the DEN2-specific mab 3H5 binding site was also present in some dengue type 1, 3, or 4 virus strains. However, the region occupied by the Glu-Pro-Gly sequence at upstream positions 383 to 385 was completely conserved among DEN2 strains, but divergent in other serotype viruses, suggesting that this sequence might be part of the antigenic site of mab 3H5. We investigated this possibility by employing the previously constructed chimeric DEN2(PreM-E)/DEN4 cDNA clone to produce viable mutants bearing DEN2 PreM and E sequences that could be analyzed for binding to and neutralization by mab 3H5. We constructed 13 such DEN2 mutants that contained a single amino acid substitution in the region between positions 383 and 393 of DEN2 E. Each single substitution in the region spanning positions 386 through 393 of DEN2 yielded a virus that was as reactive with mab 3H5 as the parental chimeric virus. These results are consistent with the extent of sequence conservation in the region. In contrast, 5 of 6 mutants that sustained an amino acid substitution at position 383, 384, or 385 failed to react with mab 3H5 as detected by immunofluorescence assay and failed to be neutralized by the mab. Interestingly, each of the 5 mab-resistant DEN2 mutants also exhibited reduced mouse neurovirulence compared to parental chimeric DEN2 when inoculated intracerebrally. These observations suggest that the Glu-Pro-Gly sequence at positions 383-386 of the DEN2 E is a component of the site against which mab 3H5 is directed. In the recently determined three-dimensional structure of the related tick-borne encephalitis virus E, the Glu-Pro-Gly sequence would be located on the lateral surface of the immunoglobulin-like domain that is proposed to bind to the host cell receptor.

Studies on serological cross-reaction in sequential flavivirus infections

Acute- and convalescent-phase sera from patients with dengue (DEN) hemorrhagic fever (DHF) and Japanese encephalitis (JE) that contained pre-existing flavivirus antibodies were tested for cross-reacting antibodies to DEN, JE and yellow fever (YF) viruses by a neutralization (N) test. A fourfold or greater rise in N antibody titer in the convalescent-phase was considered significant. Of 39 DHF cases, obtained at Chiang Mai University Hospital, Thailand, 15 (38.5%) showed a rise in DEN antibody titer, while another 15 (38.5%) showed a significant rise in both DEN and JE N antibody titers. On the other hand, eight (61.5%) of 13 JE cases obtained at the same Hospital, showed a significant rise in JE antibody titer, while two (15.4%) showed a significant rise in both DEN and JE antibody titers. Sucrose gradient centrifugation and fractionation of these two cross-reactive JE sera revealed that IgM class antibody was specific for JE, while IgG class antibody was cross-reactive. Of three JE cases with pre-existing YF antibody obtained in Okinawa, Japan, two showed a significant rise in YF and JE antibodies. Both IgM and IgG class antibodies to YF virus were elevated. These results indicate that the cross-reactivity among flaviviruses in different subgroups (complexes), was observed quite often, even by the N test, in sequential flavivirus infection.

Epidemiological and ecological studies of Japanese encephalitis in Okinawa, subtropical area in Japan. II. Prevalence of Japanese encephalitis antibody in residents in Okinawa, Miyako and Ishigaki islands

During 1989 to 1990, human sera were collected by age groups in Okinawa (the northern, central and southern areas), Miyako and Ishigaki islands and examined for the neutralization (N) antibodies to two strains, Nakayama (vaccine strain) and C307 (Okinawan strain), of Japanese encephalitis (JE) virus. In Okinawa island, the N antibody positive rate to C307 was higher than that to Nakayama, while in Miyako and Ishigaki islands, the positive rate to Nakayama was higher than that to C307, suggesting that JE virus transmission rate was higher in Okinawa than in Miyako and Ishigaki islands. In Okinawa Prefecture, JE vaccine had not been administered to most of residents over 31 years of age at the time of serum collection. In residents over 31 years old, the positive rate to C307 was highest in the north of Okinawa (83.3%) and was lowest in Miyako (26.3%), with the second lowest in Ishigaki (33.3%). The distribution of N antibody titers to C307 gave hyperbolic patterns in the 0-5 age groups in Miyako and Ishigaki, and also in the 31-40, 41-50 age groups in Miyako and the 41-50 age group in Ishigaki, suggesting low rates of natural infection in these 4-5 decades in both islands. In residents of ages subjected to JE vaccine, a characteristic pattern was obtained, in which the curves to Nakayama shifted to higher titers than those to C307, suggesting that the first antigenic stimulation was caused by vaccine, not by natural infection of JE virus.

Epidemiological and ecological studies of Japanese encephalitis in Okinawa, subtropical area in Japan. I. Investigations on antibody levels to Japanese encephalitis virus in swine sera and vector mosquito in Okinawa, Miyako and Ishigaki islands

From 1985 to 1989, serum specimens of swine raised in the northern, central and southern areas in Okinawa island were examined for Japanese encephalitis (JE) virus antibody by ELISA and hemagglutination-inhibition test. The antibody positive rate was found to be higher in the north and central than in the south. The 2-mercaptoethanol sensitive antibody to JE was detected mostly in June and July, and occasionally in other months except February and March. There was no month when all specimens from three areas turned antibody-negative simultaneously, indicating that JE virus transmission to swine lasted longer in Okinawa island than in other temperature areas in Japan. From 1986 to 1991, the vector mosquitoes (Culex tritaeniorhynchus) were collected in a pig farm in the south of Okinawa island. A total of 153 strains of JE virus was isolated from the vector mosquitoes mainly in June. In Miyako and Ishigaki islands, the antibody positive rate in swine sera was found to be extremely low, compared with that in Okinawa island. In Miyako island, where no paddy rice field is cultivated, a few adults as well as larvae of the vector mosquito were collected, while in Ishigaki island, where there are many watered rice fields, a lot of adults as well as larvae were collected. Although the environmental situation is quite different between the two islands, JE virus transmission appeared to be very low in both islands.

Potential use of a baculovirus-expressed dengue-4 E protein as a diagnostic antigen in regions endemic for dengue and Japanese encephalitis

Truncated dengue-4 E protein was produced as a fusion protein in insect cells using a baculovirus expression vector to examine its usefulness as a diagnostic antigen. A peroxidase-anti-peroxidase (PAP) staining method was used to examine the immunoreactivity of the antigenic determinants in recombinant virus-infected Sf-9 cells with human sera obtained from dengue (DEN) and Japanese encephalitis (JE) endemic areas (41 sera from DEN patients and 39 sera from JE patients or individuals with high JE-antibody titers). The expressed E protein, in which one-third of the carboxy-terminal end was deleted, reacted with sera from DEN patients, but it failed to react or responded only faintly with sera from JE patients. The antibody titers obtained by the staining method correlated with those obtained by enzyme-linked immunosorbent assay (ELISA) (r = 0.64, P less than 0.01). Calculation of the ratio (R) of the titer obtained by the PAP staining method to the ELISA titer can clearly differentiate DEN antibody from JE antibody (high R values in DEN sera and low R values in JE sera). The recombinant protein would be especially useful for diagnostic purposes in regions where DEN and JE viruses co-circulate.

Detection of dengue 4 virus core protein in the nucleus. I. A monoclonal antibody to dengue 4 virus reacts with the antigen in the nucleus and cytoplasm

A mouse monoclonal antibody (MAb) to dengue 4 (DEN-4) virus reacted with the antigen in the nucleus as well as in the cytoplasm of DEN-4-infected mammalian and mosquito cells, as demonstrated by the peroxidase-antiperoxidase staining method. The intranuclear antigen appeared to accumulate at the nucleoli, forming spots, whereas the cytoplasmic antigen appeared to be localized mainly in large perinuclear foci in the infected cells. The MAb-reactive antigen was produced in the presence of actinomycin D, which caused the accumulation in the nucleus to be altered to a dispersed pattern. Radioimmunoprecipitation analysis of [35S]methionine-labelled purified virions and Western blot analysis of the antigens prepared from the infected mammalian and mosquito cells showed that the MAb was directed against the DEN-4 virus core protein (Mr 15.5K). These results indicated that the DEN-4 virus core protein was partially transported, soon after its synthesis in the cytoplasm, into the nucleus and accumulated at the nucleoli.

Detection of dengue 4 virus core protein in the nucleus. II. Antibody against dengue 4 core protein produced by a recombinant baculovirus reacts with the antigen in the nucleus

The dengue 4 virus (DEN-4) core gene and part of the PreM genes were inserted into the baculovirus polyhedrin gene region. The recombinant baculovirus directed the synthesis of the DEN-4 core protein fused to a part of the polyhedrin protein (Mr 25K), as determined by Western blot analysis using DEN-4 core monoclonal antibody. A mouse polyclonal antibody prepared against the DEN-4 core fusion protein showed antigenic reactivity with the authentic DEN-4 core protein (Mr 15.5K) present in the nucleus as well as in the cytoplasm of DEN-4-infected Vero cells as demonstrated by the peroxidase-antiperoxidase staining method. This antibody did not react with cells infected with DEN-1, -2, -3 or Japanese encephalitis virus, or mock-infected cells.

An improved micromethod for infectivity assays and neutralization tests of dengue viruses

An improved micromethod for infectivity assays and neutralization (N) tests of dengue (DEN) type 1-4 viruses was developed, using 96-well plates and the PAP (peroxidase-antiperoxidase) staining technique. The foci formed on BHK-21 cell monolayers in wells of the plate were readily countable under an ordinary stereomicroscope. This micromethod has the advantages over the micromethod of the Lab-Tek 8 chamber slide system of lower cost, requirement for smaller volumes of test sera and applicability to larger number of serum specimens for N tests of DEN viruses.

Trial of inactivated Japanese encephalitis vaccine in children with underlying diseases

Two shots of inactivated Japanese encephalitis (JE) vaccine were given to children, 139 with underlying diseases and 42 healthy, and their antibody responses were studied by the neutralization test. Before vaccination, most of the vaccinees did not have antibody against JE virus. One month after the second vaccination, they were all seroconverted and showed considerably high neutralizing titres. One healthy child developed fever on the day of vaccination without any severe symptoms afterwards, and no side reactions were observed in the handicapped children. These results suggest that the current JE vaccine is safe and can induce a strong immune response even in handicapped children.

Development of a micro-neutralization test for chikungunya virus

A rapid, micro-scale focus reduction neutralization test for chikungunya virus was developed. In the test, cell monolayers are prepared in a 96-well tissue culture plate and the PAP (peroxidase-antiperoxidase) staining technique is used for detection of foci of chikungunya virus infected cells. This test is suitable for rapid diagnosis and epidemiological studies of the virus.

Haemagglutination-inhibition test for haemorrhagic fever with renal syndrome using virus antigen prepared from infected tissue culture fluid

Haemagglutinating (HA) antigens of four strains of virus related to that causing haemorrhagic fever with renal syndrome (HFRS) were prepared from infected tissue culture fluids by ultracentrifugation. The titres of the precipitated antigens were increased considerably by acetone extraction and sonication. Acetone extraction completely inactivated infectious virus in the antigen preparations. The antigens were pH-dependent, with pH optima at 5.8. Good correlations were observed in human and rat sera between the titres obtained by the haemagglutination-inhibition (HI) test and an indirect fluorescent antibody test. Moreover, strong cross-reactions among these strains were demonstrated by the HI test. The HI test has not been used previously with HFRS viruses because of the danger involved in preparing HA antigen, but these results indicate that a safe method is available for serological identification of HFRS.

Rapid focus reduction neutralization test of Japanese encephalitis virus in microtiter system. Brief report

An improved rapid focus reduction neutralization test for Japanese encephalitis (JE) virus in microtiter system was developed. 96-well tissue culture plates were used for preparation of cell monolayers and PAP (peroxidase-antiperoxidase) staining technique was used for visualization of foci of infected cells. As the test has many advantages over other methods, it might be applied widely for rapid diagnosis and seroepidemiological studies.

Electron microscopic observation of a newly isolated flavivirus-like virus from field-caught mosquitoes

Of many unidentified virus strains which were isolated from field-caught mosquitoes by using C6/36 cells (a virus-sensitive clone of Aedes albopictus cells), three strains which formed small size plaques (SP virus) in C6/36 cells were investigated by electron microscopy. Although the SP virus strains did not react with antisera against known arboviruses in serological tests, they closely resembled flaviviruses in morphology. However, when they were compared to Japanese encephalitis (JE) virus, several differences in morphogenesis were observed. Proliferating membranous structures and electron-dense amorphous areas involving precursors of the virus were observed only in cells infected with the SP virus strains. Enlarged areas of endoplasmic reticulum containing mature virions were often observed adjacent to these structures. Since the SP virus strains were isolated from wild mosquitoes and multiplied only in mosquito cells, it seems appropriate to classify them as insect viruses which resemble togaviruses morphologically.

A seroepidemiological study of Japanese encephalitis and dengue virus infections in the Chiang Mai area, Thailand

As part of a virological and epidemiological survey of encephalitis in the Chiang Mai area, the neutralizing (N) antibody levels of healthy persons to Japanese encephalitis (JE) and dengue (DEN) type 1-4 viruses were examined. A total of 985 blood samples was collected by the filter paper method from subjects of nine age groups in five districts, four (Pasang, Sarapee, Doi Saket and Mae Taeng) in the Chiang Mai Valley and one (Fang) in another valley separated by several ranges of mountains from the Chiang Mai Valley. From analyses of the results of N tests on the specimens, the following conclusions were drawn about the prevalences of JE and DEN viruses in the Chiang Mai area: (1) In the Chiang Mai Valley, the percentage incidences of N antibodies to JE and DEN viruses increased with age and by the age of 15, two thirds or more of the residents had been infected with JE and all DEN viruses except DEN type 2 virus, which showed the lowest prevalence. (2) In the Fang district, the percentage incidence of N antibody to JE virus increased with age, but those to DEN viruses did not, indicating much lower prevalences in the past of all four serotypes of DEN viruses in this district than in the Chiang Mai Valley. (3) At present, most infants in the Chiang Mai area, including the Fang district, seem to be exposed to DEN viruses first and later to JE virus.

Retrospective serological studies on dengue epidemics in Osaka and Okinawa

In Japan, dengue epidemics were recorded once before the end of World War II (1942-1945) on the Main Islands and several times (1893-1955) on the Okinawa Islands. Blood samples were obtained from residents in Osaka and Okinawa, and their antibodies were examined by neutralization tests against dengue and Japanese encephalitis viruses. Of 60 serum samples each from Osaka and Okinawa, 11 and 15 sera, respectively, showed positive titers against one or more dengue serotypes. These results confirm that the epidemics had been very large. Moreover, the results showed that the epidemics had been due to dengue type 1 virus in Osaka and to dengue type 1 and 2 viruses in Okinawa.

Serological studies on volunteers inoculated experimentally with a dengue virus strain in 1943

In 1943, a large dengue epidemic occurred in the Osaka district and several samples of dengue virus were isolated from patients with dengue fever by workers in this Institute. These were inoculated into human volunteers to confirm that they were dengue virus. In the present study, serum samples were collected from the volunteers who had been inoculated with dengue virus and were examined serologically. In the neutralization test, all the sera showed a higher titer against dengue type 1 virus (DEN-1) than against the other three types of dengue virus, indicating that the virus strain isolated in 1943 was DEN-1.

A retrospective serological study of Japanese who contracted dengue fever in Thailand

Between September and November 1981, some members of a survey team from Japan suffered from a febrile illness diagnosed clinically as dengue fever during their stay in a village in Khon-Kaen Province, in the north-eastern part of Thailand. The morbidity rate in the team was as high as 69% (11/16). Blood samples were taken from 12 of the 16 members of the team in February, 1982 in Japan and the serum specimens were examined for antibodies to dengue (DEN), Japanese encephalitis (JE) and yellow fever (YF) viruses respectively. The results of the tests indicated that all 8 members who had had symptoms had been infected with DEN type 1 virus. No case of inapparent infection with dengue viruses was found. Of these 8 persons, seven had had neutralizing (N) antibody to JE virus before infection, but their clinical manifestations had been similar to those of an individual without N antibody to JE virus and were typical symptoms of dengue fever, such as leukopenia and "saddle-back" fever, without hemorrhagic manifestations, as seen from platelet counts and hematocrit values.

Neutralizing antibody responses to Japanese encephalitis vaccine in children

Two shots of the current Japanese encephalitis (JE) vaccine were given to children and their immune responses to the Nakayama strain (the vaccine strain) and two wild strains (JaGAr-01 and E-50) of JE virus were examined by neutralizing (N) antibody titrations. Seventy vaccinees had no N antibody to JE virus before the first vaccination and were bled one month after the second vaccination. The N antibody responses to the JaGAr-01 and E-50 strains were found to be similar and to be less than that to the Nakayama strain after the second vaccination: the geometric mean titers (GMT) of N antibodies to the JaGAr-01 and E-50 strains (as logarithms) were 1.87 and 1.75, respectively, while the GMT to the Nakayama strain was 2.89. The seroconversion rates to the Nakayama, JaGAr-01 and E-50 strains were 70/70 (100%), 69/70 (99%) and 68/70 (97%), respectively, after the second vaccination. Twenty-seven of the 70 vacciness were also bled before the second vaccination. Most of them showed a considerably high N antibody response against the Nakayama strain and only one vaccinee failed to show seroconversion after the first vaccination. However, the antibody response to the E-50 strain appeared to be rather low and 9 of 25 vaccinees did not show any seroconversion. Similarly 3 of 25 failed to show any seroconversion against the JaGAr-01 strain. These results indicate that at the initial immunization two shots, at least, of the current JE vaccine are necessary to stimulate effective immune responses to wild strains of JE virus.

Serological studies on a case of laboratory dengue infection

One of the authors (Y.O.), who had previously been immunized with Japanese encephalitis (JE) vaccine, showed symptoms of typical dengue fever 6 days after accidental infection with a newly isolated dengue type 4 virus strain from a patient with dengue hemorrhagic fever (DHF) in Thailand. His sera were examined by hemagglutination inhibition (HI), complement fixation (CF) and neutralization (N) tests. The JE N antibody titers of his sera were high even on the first day of the illness and remained almost constant during the next year. Antibodies that reacted with dengue viruses were detected from a very early stage of the illness by all three serological tests. In addition, his convalescent phase sera showed high titers against all 4 types of dengue virus. These data suggest that the dengue infection caused secondary stimulation of antigens of flavivirus. Sedimentation analysis of antibodies in Y.O.'s serum (day 9) was carried out and IgM antibody that reacted only with dengue type 4 virus and homologous infecting virus was separated. These findings clearly demonstrated that the laboratory infection of Y.O. was primary dengue infection with dengue type 4 virus.