DR haplotype diversity of the cynomolgus macaque as defined by its transcriptome

The DR region of particular primate species may display allelic polymorphism and gene copy number variation (region configuration polymorphism). The sum of these distinct types of polymorphism is defined as complexity. To date, however, the DR region of cynomolgus macaques (Macaca fascicularis) has been poorly defined. Transcriptome analysis of a pedigreed colony, comprising animals from Indonesia and Indochina, revealed a total of 15 Mafa-DRA and 57 DRB alleles, specifying 28 different region configurations. The DRA alleles can be divided into two distinct lineages. One lineage is polymorphic, but the majority of the amino acid replacements map to the leader peptide. The second lineage is at best oligomorphic, and segregates with one specific Mafa-DRB allele. The number of Mafa-DRB genes ranges from two to five per haplotype. Due to the presence of pseudogenes, however, each haplotype encodes only one to three bona fide DRB transcripts. Depending on the region configuration in which the Mafa-DRB gene is embedded, identical alleles may display differential transcription levels. Region configurations appear to have been generated by recombination-like events. When genes or gene segments are relocated, it seems plausible that they may be placed in the context of distinct transcription control elements. As such, DRB region-related transcription level differences may add an extra layer of polymorphism to this section of the adaptive immune system

Structure of the St. Louis encephalitis virus postfusion envelope trimer

St. Louis encephalitis virus (SLEV) is a mosquito-borne flavivirus responsible for several human encephalitis outbreaks over the last 80 years. Mature flavivirus virions are coated with dimeric envelope (E) proteins that mediate attachment and fusion with host cells. E is a class II fusion protein, the hallmark of which is a distinct dimer-to-trimer rearrangement that occurs upon endosomal acidification and insertion of hydrophobic fusion peptides into the endosomal membrane. Herein, we report the crystal structure of SLEV E in the posfusion trimer conformation. The structure revealed specific features that differentiate SLEV E from trimers of related flavi- and alphaviruses. SLEV E fusion loops have distinct intermediate spacing such that they are positioned further apart than previously observed in flaviviruses but closer together than Semliki Forest virus, an alphavirus. Domains II and III (DII and DIII) of SLEV E also adopt different angles relative to DI, which suggests that the DI-DII joint may accommodate spheroidal motions. However, trimer interfaces are well conserved among flaviviruses, so it is likely the differences observed represent structural features specific to SLEV function. Analysis of surface potentials revealed a basic platform underneath flavivirus fusion loops that may interact with the anionic lipid head groups found in membranes. Taken together, these results highlight variations in E structure and assembly that may direct virus-specific interactions with host determinants to influence pathogenesis

Vaccine candidates derived from a novel infectious cDNA clone of an American genotype dengue virus type 2

BACKGROUND: A dengue virus type 2 (DEN-2 Tonga/74) isolated from a 1974 epidemic was characterized by mild illness and belongs to the American genotype of DEN-2 viruses. To prepare a vaccine candidate, a previously described 30 nucleotide deletion (Δ30) in the 3' untranslated region of DEN-4 has been engineered into the DEN-2 isolate. METHODS: A full-length cDNA clone was generated from the DEN-2 virus and used to produce recombinant DEN-2 (rDEN-2) and rDEN2Δ30. Viruses were evaluated for replication in SCID mice transplanted with human hepatoma cells (SCID-HuH-7 mice), in mosquitoes, and in rhesus monkeys. Neutralizing antibody induction and protective efficacy were also assessed in rhesus monkeys. RESULTS: The rDEN2Δ30 virus was ten-fold reduced in replication in SCID-HuH-7 mice when compared to the parent virus. The rDEN-2 viruses were not infectious for Aedes mosquitoes, but both readily infected Toxorynchites mosquitoes. In rhesus monkeys, rDEN2Δ30 appeared to be slightly attenuated when compared to the parent virus as measured by duration and peak of viremia and neutralizing antibody induction. A derivative of rDEN2Δ30, designated rDEN2Δ30-4995, was generated by incorporation of a point mutation previously identified in the NS3 gene of DEN-4 and was found to be more attenuated than rDEN2Δ30 in SCID-HuH-7 mice. CONCLUSIONS: The rDEN2Δ30 and rDEN2Δ30-4995 viruses can be considered for evaluation in humans and for inclusion in a tetravalent dengue vaccine

Combinatorial Computational Approaches to Identify Tetracycline Derivatives as Flavivirus Inhibitors

Limited structural information of drug targets, cellular toxicity possessed by lead compounds, and large amounts of potential leads are the major issues facing the design-oriented approach of discovering new leads. In an attempt to tackle these issues, we have developed a process of virtual screening based on the observation that conformational rearrangements of the dengue virus envelope protein are essential for the mediation of viral entry into host cells via membrane fusion. Screening was based solely on the structural information of the Dengue virus envelope protein and was focused on a target site that is presumably important for the conformational rearrangements necessary for viral entry. To circumvent the issue of lead compound toxicity, we performed screening based on molecular docking using structural databases of medical compounds. To enhance the identification of hits, we further categorized and selected candidates according to their novel structural characteristics. Finally, the selected candidates were subjected to a biological validation assay to assess inhibition of Dengue virus propagation in mammalian host cells using a plaque formation assay. Among the 10 compounds examined, rolitetracycline and doxycycline significantly inhibited plaque formation, demonstrating their inhibitory effect on dengue virus propagation. Both compounds were tetracycline derivatives with IC(50)s estimated to be 67.1 µM and 55.6 µM, respectively. Their docked conformations displayed common hydrophobic interactions with critical residues that affected membrane fusion during viral entry. These interactions will therefore position the tetracyclic ring moieties of both inhibitors to bind firmly to the target and, subsequently, disrupt conformational rearrangement and block viral entry. This process can be applied to other drug targets in which conformational rearrangement is critical to function

Immature Dengue Virus: A Veiled Pathogen?

Cells infected with dengue virus release a high proportion of immature prM-containing virions. In accordance, substantial levels of prM antibodies are found in sera of infected humans. Furthermore, it has been recently described that the rates of prM antibody responses are significantly higher in patients with secondary infection compared to those with primary infection. This suggests that immature dengue virus may play a role in disease pathogenesis. Interestingly, however, numerous functional studies have revealed that immature particles lack the ability to infect cells. In this report, we show that fully immature dengue particles become highly infectious upon interaction with prM antibodies. We demonstrate that prM antibodies facilitate efficient binding and cell entry of immature particles into Fc-receptor-expressing cells. In addition, enzymatic activity of furin is critical to render the internalized immature virus infectious. Together, these data suggest that during a secondary infection or primary infection of infants born to dengue-immune mothers, immature particles have the potential to be highly infectious and hence may contribute to the development of severe disease

Identification of Continuous Human B-Cell Epitopes in the Envelope Glycoprotein of Dengue Virus Type 3 (DENV-3)

BACKGROUND:Dengue virus infection is a growing global public health concern in tropical and subtropical regions of the world. Dengue vaccine development has been hampered by concerns that cross-reactive immunological memory elicited by a candidate vaccine could increase the risk of development of more severe clinical forms. One possible strategy to reduce risks associated with a dengue vaccine is the development of a vaccine composed of selected critical epitopes of each of the serotypes. METHODOLOGY/PRINCIPAL FINDINGS:Synthetic peptides were used to identify B-cell epitopes in the envelope (E) glycoprotein of dengue virus type 3 (DENV-3). Eleven linear, immunodominant epitopes distributed in five regions at amino acid (aa) positions: 51-65, 71-90, 131-170, 196-210 and 246-260 were identified by employing an enzyme- linked immunosorbent assay (ELISA), using a pool of human sera from dengue type 3 infected individuals. Peptides 11 (aa51-65), 27 and 28 (aa131-150) also reacted with dengue 1 (DENV-1) and dengue 2 (DENV-2) patient sera as analyzed through the ROC curves generated for each peptide by ELISA and might have serotype specific diagnostic potential. Mice immunized against each one of the five immunogenic regions showed epitopes 51-65, 131-170, 196-210 and 246-260 elicited the highest antibody response and epitopes131-170, 196-210 and 246-260, elicited IFN-gamma production and T CD4+ cell response, as evaluated by ELISA and ELISPOT assays respectively. CONCLUSIONS/SIGNIFICANCE:Our study identified several useful immunodominant IgG-specific epitopes on the envelope of DENV-3. They are important tools for understanding the mechanisms involved in antibody dependent enhancement and immunity. If proven protective and safe, in conjunction with others well-documented epitopes, they might be included into a candidate epitope-based vaccine

Attenuation of Vaccinia Tian Tan Strain by Removal of Viral TC7L-TK2L and TA35R Genes

Vaccinia Tian Tan (VTT) was attenuated by deletion of the TC7L-TK2L and TA35R genes to generate MVTT3. The mutant was generated by replacing the open reading frames by a gene encoding enhanced green fluorescent protein (EGFP) flanked by loxP sites. Viruses expressing EGFP were then screened for and purified by serial plaque formation. In a second step the marker EGFP gene was removed by transfecting cells with a plasmid encoding cre recombinase and selecting for viruses that had lost the EGFP phenotype. The MVTT3 mutant was shown to be avirulent and immunogenic. These results support the conclusion that TC7L-TK2L and TA35R deletion mutants can be used as safe viral vectors or as platform for vaccines

Antibodies against the Envelope Glycoprotein Promote Infectivity of Immature Dengue Virus Serotype 2

Cross-reactive dengue virus (DENV) antibodies directed against the envelope (E) and precursor membrane (prM) proteins are believed to contribute to the development of severe dengue disease by facilitating antibody-dependent enhancement of infection. We and others recently demonstrated that anti-prM antibodies render essentially non-infectious immature DENV infectious in Fcγ-receptor-expressing cells. Immature DENV particles are abundantly present in standard (st) virus preparations due to inefficient processing of prM to M during virus maturation. Structural analysis has revealed that the E protein is exposed in immature particles and this prompted us to investigate whether antibodies to E render immature particles infectious. To this end, we analyzed the enhancing properties of 27 anti-E antibodies directed against distinct structural domains. Of these, 23 bound to immature particles, and 15 enhanced infectivity of immature DENV in a furin-dependent manner. The significance of these findings was subsequently tested in vivo using the well-established West Nile virus (WNV) mouse model. Remarkably, mice injected with immature WNV opsonized with anti-E mAbs or immune serum produced a lethal infection in a dose-dependent manner, whereas in the absence of antibody immature WNV virions caused no morbidity or mortality. Furthermore, enhancement infection studies with standard (st) DENV preparations opsonized with anti-E mAbs in the presence or absence of furin inhibitor revealed that prM-containing particles present within st virus preparations contribute to antibody-dependent enhancement of infection. Taken together, our results support the notion that antibodies against the structural proteins prM and E both can promote pathogenesis by enhancing infectivity of prM-containing immature and partially mature flavivirus particles

Dengue Virus Ensures Its Fusion in Late Endosomes Using Compartment-Specific Lipids

Many enveloped viruses invade cells via endocytosis and use different environmental factors as triggers for virus-endosome fusion that delivers viral genome into cytosol. Intriguingly, dengue virus (DEN), the most prevalent mosquito-borne virus that infects up to 100 million people each year, fuses only in late endosomes, while activation of DEN protein fusogen glycoprotein E is triggered already at pH characteristic for early endosomes. Are there any cofactors that time DEN fusion to virion entry into late endosomes? Here we show that DEN utilizes bis(monoacylglycero)phosphate, a lipid specific to late endosomes, as a co-factor for its endosomal acidification-dependent fusion machinery. Effective virus fusion to plasma- and intracellular- membranes, as well as to protein-free liposomes, requires the target membrane to contain anionic lipids such as bis(monoacylglycero)phosphate and phosphatidylserine. Anionic lipids act downstream of low-pH-dependent fusion stages and promote the advance from the earliest hemifusion intermediates to the fusion pore opening. To reach anionic lipid-enriched late endosomes, DEN travels through acidified early endosomes, but we found that low pH-dependent loss of fusogenic properties of DEN is relatively slow in the presence of anionic lipid-free target membranes. We propose that anionic lipid-dependence of DEN fusion machinery protects it against premature irreversible restructuring and inactivation and ensures viral fusion in late endosomes, where the virus encounters anionic lipids for the first time during entry. Currently there are neither vaccines nor effective therapies for DEN, and the essential role of the newly identified DEN-bis(monoacylglycero)phosphate interactions in viral genome escape from the endosome suggests a novel target for drug design