Cloning and application of recombinant dengue virus prM-M protein for serodiagnosis of dengue virus infection.

We studied the use of the precursor to the M structural protein (prM) found only on the surface of mature dengue virus as a target protein to detect dengue virus infection. Recombinant D2-16681 prM-M protein was constructed and tested for immunogenicity with dengue and Japanese encephalitis patient sera by Western blot analysis and indirect ELISA. The sensitivity and specificity of indirect ELISA were 48.1 and 85.5%, respectively, and Western blot assay were 23.1 and 98.7%, respectively, for detection of dengue virus. Although the sensitivity of the indirect ELISA is low, the indirect ELISA using recombinant D2-16681 prM-M proteins as antigen may be used for early detection of dengue virus infection.

The serotype-independent but concentration-dependent enhancing antibodies among Thai dengue patients.

Antibody-dependent enhancement of infection (ADE) is central to explaining the development of severe disease at the end of post-dengue virus infection. Non-neutralizing anti-dengue antibodies bound to the dengue virion enhances the virus entrance into the target cells via the Fc receptor. The titer of enhancing antibodies in dengue patients is not determined during dengue virus infection. Sensitive flow cytometry detecting dengue virus-infected K562 cells was used to quantitate enhancing activity among Thai DF and DHF patients against four serotypes and the patient's dengue isolate. The titer was defined as the reciprocal of the final dilution that loses enhancing activity. The serum of Thai patients confirmed to have dengue infection were found to have high titers of enhancing antibodies and increased gradually through the convalescent phase of infection. The enhancing antibody titers were not different among the four serotypes or from the infecting isolate. The anti-dengue antibodies from dengue patients can enhance dengue virus infections in a concentration-dependent, serotype-independent manner.

Identification of dengue virus in Aedes mosquitoes and patients' sera from Si Sa Ket Province, Thailand.

Dengue fever (DF), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) are the re-emerging infectious diseases caused by dengue (DEN) virus, transmitted by Aedes mosquito. There are more than 100,000 cases of dengue infection and more than 100 deaths annually in Thailand. Virological surveillance for DEN viruses is used as an early warning system to predict outbreaks. The seroprevalence of infection and serotypes of DEN virus in 116 pediatric patients at Si Sa Ket Province, Thailand were analyzed during June to September 2004. At the same period, Aedes mosquitoes were caught from patients' and their neighbors' houses, from control houses, located in villages with no report of dengue infection during the previous 3 years. The majority of DHF cases were secondary infections of DEN-2 and DEN-4 serotypes. Of the 1,652 Aedes mosquitoes collected 1,583 were Ae. aegypti and 69 Ae. albopictus. Ten mosquitoes from each house were pooled and dengue viruses were determined using RT-PCR assay; only 1 positive pooled was found. Although the dengue infection rate in the field caught mosquitoes was low, the existing dengue virus control program in transmission areas by aerial spraying to destroy the larva breeding sites should be continued.

Neutralization titers against influenza A (H3N2) and influenza B viruses among a non-vaccinated population from Thailand.

Influenza A and B viruses are viral respiratory pathogens that can cause severe infections among birds and mammals. Neutralization assays using human sera are useful to evaluate the risk of circulating viruses to humans. In this study, 359 serum samples from healthy Thai volunteers, who had not been vaccinated against influenza for at least five years, were investigated by microneutralization (MN) assays against influenza A H3N2 and influenza B viruses in 2009. There was no significant difference in neutralization activities against 2006 and 2008 isolates of influenza A H3N2 viruses. However, neutralization titers to influenza B viruses among 2008 isolates were quite low. The results indicate the non-vaccinated study population had some neutralizing antibodies against influenza A H3N2 but not against influenza B viruses.

Dengue virus type 2 recognizes the carbohydrate moiety of neutral glycosphingolipids in mammalian and mosquito cells.

Dengue viruses infect cells by attaching to a surface receptor which remains unknown. The putative receptor molecules of dengue virus type 2 on the surface of mosquito (AP-61) and mammalian (LLC-MK2) cell lines were investigated. The immunochemical detection and structural analysis of carbohydrates demonstrated that the neutral glycosphingolipids, L-3 (GlcNAcß1-3Manß1-4Glcß1-1'Cer) in AP-61 cells, and nLc(4) Cer (Galß1-4GlcNAcß1-3Galß1-4Glcß1-1'Cer) in LLC-MK2 cells were recognized by the virus. These findings strongly suggest that neutral glycosphingolipids share the key determinant for virus binding and that the ß-GlcNAc residue may play an important role in dengue virus binding to the host cell surface.

The impact of antigenic drift of influenza A virus on human herd immunity: Sero-epidemiological study of H1N1 in healthy Thai population in 2009.

To examine the effect of the antigenic drift of H1N1 influenza viruses on herd immunity, neutralization antibodies from 744 sera from Thai healthy volunteers in 2008-2009, who had not been vaccinated for at least the last 5 years, were investigated by microneutralization (MN) and hemagglutination inhibition (HI) assays. Significantly higher MN titers were observed for the H1N1 Thai isolate in 2006 than in 2008. The results indicate that the antigenically drifted virus effectively escaped herd immunity. Since the low neutralization activity of herd immunity against drifted viruses is an important factor for viruses to spread efficiently, continuous sero-epidemiological study is required for public health.

Systematic syntheses of influenza neuraminidase inhibitors: a series of carbosilane dendrimers uniformly functionalized with thioglycoside-type sialic acid moieties.

In order to develop novel influenza sialidase inhibitors, we constructed a library of glycoclusters composed of twelve types of sialylated dendrimers with thioglycosidic linkage that are resistant to hydrolysis by the sialidases. These sialodendrimers were synthesized by condensation reaction between a thiosialoside modified on the aglycon terminal end by a thioacetyl group and twelve types of carbosilane dendrimers having brominated terminal ends under deacetylation conditions, and temporal re-protection was performed for purification. Removal of all protection of the glycodendrimers was accomplished by transesterification and subsequent saponification to provide corresponding water-soluble glycodendrimers in good yields. For investigation of the structure-activity relationship, dendrimer scaffolds having differences in number of the sugar moieties, such as 3-, 4-, 6- and 12-functionalized dendrimers, and in linkage patterns, such as normal aliphatic linkage, ether- and amide-linkages. Biological evaluations of these glycodendrimers showed that all of the ether- and amide-elongated compounds had inhibitory potencies for the influenza sialidases in the mM range, while compounds having normal aliphatic linkage did not have any activities except for a 12-functionalized compound.

In vitro inhibition of human influenza A virus infection by fruit-juice concentrate of Japanese plum (Prunus mume SIEB. et ZUCC).

Using a plaque reduction assay, treatment of human influenza A viruses with the fruit-juice concentrate of Japanese plum (Prunus mume SIEB. et ZUCC) showed strong in vitro anti-influenza activity against human influenza A viruses before viral adsorption, but not after viral adsorption, with 50% inhibitory concentration (IC50) values against A/PR/8/34 (H1N1) virus, A/Aichi/2/68 (H3N2) virus and A/Memphis/1/71 (H3N2) virus of 6.35+/-0.17, 2.84+/-1.98 and 0.53+/-0.10 microg/ml, respectively. The plum-juice concentrate exhibited hemagglutination activity toward guinea pig erythrocytes. Its hemagglutination activity was inhibited by the monosaccharide N-acetylneuraminic acid and a sialoglycoprotein (fetuin), but not by the other tested monosaccharides (mannose, galactose, glucose and N-acetylglucosamine), suggesting the presence of a lectin-like molecule(s) in the Japanese plum-juice concentrate. Our findings suggest that the fruit-juice concentrate of Japanese plum may prevent and reduce infection with human influenza A virus, possibly via inhibition of viral hemagglutinin attachment to host cell surfaces by its lectin-like activity.

Characterization of atypical lymphocytes and immunophenotypes of lymphocytes in patients with dengue virus infection.

To characterize the immunophenotypes of lymphocytes in patients with dengue infection, we performed flow cytometric analysis of peripheral blood mononuclear cells collected from 49 dengue hemorrhagic fever (DHF), 25 dengue fever (DF), and 26 dengue-like syndrome (DLS) cases. The mean total atypical lymphocytes in DHF (916.1 +/- 685.6 cells/microl) and DF (876.2 +/- 801.9 cells/microl) were higher than those of DLS (310.5 +/- 181.4 cells/microl). An atypical lymphocyte count of 10% or higher was a good indicator of dengue infection (sensitivity 50% and specificity 86%). Flow cytometric studies showed that the percentages of atypical lymphocytes correlated with those of CD19+ B lymphocytes and inversely correlated with the percentages of CD69+ lymphocytes. The mean absolute counts of atypical lymphocytes and CD19+ cells on the discharge day were significantly higher than those on the admission day. Low percentages of TdT+ cells were found in all groups of patients. We concluded that atypical lymphocyte and CD19+ cell counts may be a useful diagnostic tool for dengue infection and the recovery from the disease could be judged when numbers of both cell types are significantly elevated.

An avian influenza H5N1 virus that binds to a human-type receptor.

Avian influenza viruses preferentially recognize sialosugar chains terminating in sialic acid-alpha2,3-galactose (SAalpha2,3Gal), whereas human influenza viruses preferentially recognize SAalpha2,6Gal. A conversion to SAalpha2,6Gal specificity is believed to be one of the changes required for the introduction of new hemagglutinin (HA) subtypes to the human population, which can lead to pandemics. Avian influenza H5N1 virus is a major threat for the emergence of a pandemic virus. As of 12 June 2007, the virus has been reported in 45 countries, and 312 human cases with 190 deaths have been confirmed. We describe here substitutions at position 129 and 134 identified in a virus isolated from a fatal human case that could change the receptor-binding preference of HA of H5N1 virus from SAalpha2,3Gal to both SAalpha2,3Gal and SAalpha2,6Gal. Molecular modeling demonstrated that the mutation may stabilize SAalpha2,6Gal in its optimal cis conformation in the binding pocket. The mutation was found in approximately half of the viral sequences directly amplified from a respiratory specimen of the patient. Our data confirm the presence of H5N1 virus with the ability to bind to a human-type receptor in this patient and suggest the selection and expansion of the mutant with human-type receptor specificity in the human host environment.

Novel linear polymers bearing thiosialosides as pendant-type epitopes for influenza neuraminidase inhibitors.

A conventional synthesis of alpha-thioglycoside of sialic acid as a glycomonomer was accomplished. Radical copolymerization of the glycomonomer with vinyl acetate proceeded smoothly to afford a new class of glycopolymers having thiosialoside residues, in which all protection was removed by a combination of transesterification and saponification to provide a water-soluble thiosialoside cluster. The results of a preliminary study on biological responses against influenza virus neuraminidases using the thiosialoside polymer as a candidate for a neuraminidase inhibitor showed that the glycopolymer has potent inhibitory activity against the neuraminidases.

Thiosialoside clusters using carbosilane dendrimer core scaffolds as a new class of influenza neuraminidase inhibitors.

An efficient synthesis of a series of carbosilane dendrimers uniformly functionalized with alpha-thioglycoside of sialic acid was accomplished. The results of a preliminary study on biological responses against influenza virus sialidases using thiosialoside clusters showed that some of the glycodendrimers have inhibitory potencies against the sialidases.

Rapid detection of dengue viral RNA in mosquitoes by nucleic acid-sequence based amplification (NASBA).

RNA amplification by nucleic acid sequence-based amplification (NASBA) was used to detect serotype specific dengue viruses in artificially-infected female Aedes mosquitoes, in comparison with RT-PCR technique. NASBA could detect dengue virus serotype 2 and 4 below 0.1 PFU, which was more sensitive than RT-PCR, but this technique was as sensitive as RT-PCR when detecting dengue virus serotype 1 and 3. Dengue viruses could be detected at the thorax of mosquitoes at 0, 7, and 14 days after inoculation with dengue virus serotype 2. This method should be useful for virological surveillance of dengue infected Aedes mosquitoes, as an early warning system to predict outbreaks of dengue viruses.

Clinical differences among PCR-proven dengue serotype infections.

The objective of this study was to compare the clinical spectra of the dengue serotypes proven by the PCR technique. This retrospective study reviewed the clinical information of dengue-infected patients who were admitted to northeastern provincial hospitals in Thailand from June to September 2002. Dengue infection and viral serotypes were confirmed by polymerase chain reaction (PCR). Paired anti-dengue immunoglobulin G (IgG) and IgM from paired sera were analyzed by enzyme-linked immunosorbent assay (ELISA). Ninety-nine PCR-proven dengue-infected Thai patients were studied. Their ages ranged from 3-30 years. They were infected with DEN1, DEN2, DEN3 and DEN4 in 21, 55, 12, and 12%, respectively. Twenty-two percent had primary and 78% had secondary infections. Dengue fever was the most common presentation for both primary (77.2%) and secondary infections (46.7%). The ratios of dengue fever:dengue hemorrhagic fever (DF:DHF) and non-dengue shock syndrome:dengue shock syndrome (non-DSS:DSS) for DEN2 was the lowest of the dengue serotypes. There was no difference in the duration of fever, percentage of hepatomegaly and bleeding among the serotypes in both DF and DHF. The trends in the white blood cells, lymphocyte and atypical lymphocyte counts in DEN3 were the highest, while those of DEN1 were the lowest of the dengue serotypes.