Circulating human antibodies against dengue NS1 protein: potential of recombinant D2V-NS1 proteins in diagnostic tests

Production of Properly Folded NS1 Protein in Bacterial Cells

Dengue virus (DENV) NS1 protein is a multifunctional protein involved in several pathogenic processes but also has been described as a protective antigen suitable for eliciting humoral response against DENV. NS1 is essential for virus replication and can be found in different cell compartments and at different oligomeric states. It is secreted to the extracellular medium and can also be found circulating in the blood of infected patients, being routinely used as the serum biomarker for early dengue diagnosis. High-yield production of the recombinant NS1 protein in a native-like conformation is essential for studies regarding its function during DENV infection as well as to those interested in the development of new diagnostic approaches based on this protein. In this chapter, we describe an optimized protocol for high-yield expression of native-like NS1 in Escherichia coli bacterial cells.

Finding small molecules with pan-serotype activity to target Dengue non-structural protein 1

Dengue virus (DENV) is a mosquito-borne flavivirus which causes Dengue fever and severe Dengue. It exists as four antigenically different serotypes that are further classified into genotypes with varying degrees of pathogenicity. The non-structural protein 1 (NS1) of DENV has an important role in viral replication and its pathogenesis. NS1 is also considered as an important diagnostic marker for Dengue pathogenesis. To the best of our knowledge, there are no attempts to explore small molecule drugs to target the NS1 of all the serotypes. Here, we have taken the DENV 2 NS1 crystal structure as a reference to model the NS1 structure of the other three serotypes. Once the active site of the NS1 is identified, virtual screening of plant flavonoids is carried out against the NS1 of all the four serotypes. The top 200 molecules in the library with high binding affinities are further analysed to find the common ones having comparable affinities to all the four serotypes. The predicted common flavonoids are subjected to ADMET profiling to further select the most potential molecules that can be used to target NS1 of all the four serotypes.

Antigen production using heterologous expression of dengue virus-2 non-structural protein 1 (NS1) in Nicotiana tabacum (Havana) for immunodiagnostic purposes

KEY MESSAGE

Expression of dengue-2 virus NS1 protein in Nicotiana tabacum plants for development of dengue immunodiagnostic kits. Dengue is one of the most important diseases caused by arboviruses in the world. A significant increase in its geographical distribution has been noticed over the last 20 years, with continuous transmission of several serotypes and emergence of the hemorrhagic fever in areas where the disease was previously not prevalent. Although the methodological processes for dengue diagnosis are in deep development and improvement, a limitation for the realization of dengue diagnostic tests is the difficulty of large-scale production of the antigen to be used in diagnostic tests. Due to this demand, the purpose of this study was to obtain the non-structural protein 1 (NS1) from dengue-2 serotype by heterologous expression in Nicotiana tabacum (Havana). After confirmation of the NS1 protein gene integration in the plant genome, the heterologous protein was characterized using SDS-PAGE and immunoblotting. In an immunoenzymatic test, the recombinant NS1 protein presents an antigen potential for development of dengue immunodiagnostic kits.

Dengue NS1 and prM antibodies increase the sensitivity of acute dengue diagnosis test and differentiate from Japanese encephalitis infection

Accurate and early diagnosis of dengue infection is essential for dengue case management. In outbreak conditions, it is essential to include two different tests to diagnose dengue and the choice depends on the number of days after the onset of illness in which the sample is collected. During the laboratory diagnosis of dengue in late acute and convalescent phase by MAC-ELISA, it is necessary to rule out possible cross reactions of closely related flavivirus, such as Japanese encephalitis virus which is commonly co-circulating. In the present investigation, the usefulness of dengue virus NS1 and prM antibodies in diagnosing and differentiating dengue from Japanese encephalitis infection was assessed using samples collected during out-breaks. It was shown here that, detection of antibodies against dengue NS1 and prM proteins increases the sensitivity of dengue diagnosis until 15days. Moreover, detection of antibodies against both proteins was able to differentiate dengue from Japanese encephalitis infection.

The flavivirus NS1 protein: molecular and structural biology, immunology, role in pathogenesis and application as a diagnostic biomarker

The flavivirus nonstructural glycoprotein NS1 is an enigmatic protein whose structure and mechanistic function have remained somewhat elusive ever since it was first reported in 1970 as a viral antigen circulating in the sera of dengue-infected patients. All flavivirus NS1 genes share a high degree of homology, encoding a 352-amino-acid polypeptide that has a molecular weight of 46-55 kDa, depending on its glycosylation status. NS1 exists in multiple oligomeric forms and is found in different cellular locations: a cell membrane-bound form in association with virus-induced intracellular vesicular compartments, on the cell surface and as a soluble secreted hexameric lipoparticle. Intracellular NS1 co-localizes with dsRNA and other components of the viral replication complex and plays an essential cofactor role in replication. Although this makes NS1 an ideal target for inhibitor design, the precise nature of its cofactor function has yet to be elucidated. A plethora of potential interacting partners have been identified, particularly for the secreted form of NS1, with many being implicated in immune evasion strategies. Secreted and cell-surface-associated NS1 are highly immunogenic and both the proteins themselves and the antibodies they elicit have been implicated in the seemingly contradictory roles of protection and pathogenesis in the infected host. Finally, NS1 is also an important biomarker for early diagnosis of disease. In this article, we provide an overview of these somewhat disparate areas of research, drawing together the wealth of data generated over more than 40 years of study of this fascinating protein.

Polyclonal antibodies against properly folded Dengue virus NS1 protein expressed in E. coli enable sensitive and early dengue diagnosis

The non-structural 1 (NS1) protein plays an important role in dengue diagnosis because it has been detected as a soluble serum antigen in both primary and secondary infections. The NS1 protein was expressed in Escherichia coli cells, and the efficiency of four different refolding protocols was tested. All of the protocols generated dimeric NS1 in a conformation similar to that of the protein expressed by eukaryotic cells. A polyclonal antibody produced from the properly folded E. coli recombinant NS1 (rNS1) protein proved to be a useful tool for the diagnosis of Dengue virus because it detected 100% of the Dengue virus 2 (DENV2) in infected patients' sera and 60% of the DENV IgM-positive sera not detected by commercial NS1-based diagnostic kits. These data suggest a high-efficiency method for correctly folding rNS1 that maintains its structural and immunogenic properties. In addition, a detection method using the polyclonal antibody against correctly folded rNS1 seemed to be more sensitive and efficient for NS1 detection in serum, highlighting its usefulness for developing a high-sensitivity diagnostic kit.

Concanavalin A and polyvinyl butyral use as a potential dengue electrochemical biosensor

Immobilization of concanavalin A on gold electrode by means of gold nanoparticles and polyvinyl butyral was carried out and investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The system was tested with sera from patients infected by dengue fever (DF) and dengue hemorrhagic fever (DHF). Electrochemical impedance spectroscopy (in the frequency range from 100mHz to 100KHz), and cyclic voltammetry (from -0.2 to 0.7V vs. Ag/AgCl), was performed in phosphate buffer solution containing 10mM K(3)[Fe(CN)(6)]/K(4)[Fe(CN)(6)] (1:1) mixture as a redox probe. As biomolecules accumulated on the electrode surface the voltammetric response changed from a clear diffusional to an irreversible behavior. Impedance spectroscopy showed a clear increase of the electron-transfer resistance when the sensor is exposed to contaminated sera (DF or DHF) as compared to exposure to uncontaminated serum (NDF). The results were analyzed through an equivalent circuit and values of charge transfer resistance and capacitance were obtained. Variations in charge transfer resistance were used to distinguish the sensor response for the different sera investigated (DF, DHF and NDF). Alternatively, a three-dimensional graph gave the best response for differentiation of all three blood sera. The distinctive patterns of impedimetric responses observed were ascribed to different glycoprotein patterns in the sera investigated. Therefore, the lectin immobilization on electrode surface with gold nanoparticles and polyvinyl butyral, combined with the three-dimensional impedance analysis introduced herein are valuable tools in the development of a biosensor for immunological response to diseases.

Evaluation of an NS1 antigen detection for diagnosis of acute dengue infection in patients with acute febrile illness

Diagnosis of dengue infection during the febrile stage has been challenging. We evaluated the accuracy of NS1 protein detection in diagnosing dengue infection in patients presenting with acute febrile illness in Bangkok, Thailand. Of the 235 subjects presented with fever of unknown source within 5 days, 132 (56.2%) were male with the median age of 17.8 (range, 3-52) years. The median duration of fever was 4 (range, 1-5) days. One hundred seventy-one (72.8%) patients had dengue infection, of which 158 (92.4%) were secondary infections. The sensitivity of NS1 Ag test was 63.2% (95% confidence interval [CI], 55.7-70.0), and the specificity was 98.4% (95% CI, 91.7-99.7). The positive and negative predictive values were 99.0% and 52.5%, respectively. The immune complex dissociation by acid treatment increase sensitivity from 63.2% to 72%. In an endemic area, Plateliatrade mark NS1 Ag test has limited sensitivity but very high specificity for diagnosis of dengue infection in patients with acute febrile illness.

Protection against dengue type 2 virus induced in mice immunized with a DNA plasmid encoding the non-structural 1 (NS1) gene fused to the tissue plasminogen activator signal sequence

Dengue is one of the most important arboviral diseases in humans, and although efforts over the last decades have dealt with the development of a vaccine, this vaccine is not available yet. In order to evaluate the potential of a DNA vaccine based on the non-structural 1 (NS1) protein against dengue virus (DENV), we constructed the pcTPANS1 plasmid which contains the secretory signal sequence derived from human tissue plasminogen activator (t-PA) fused to the full length of the DENV-2 NS1 gene. Results indicate that pcTPANS1 promotes correct expression of NS1 in eukaryotic cells and drives secretion of the recombinant protein to the surrounding medium in a dimeric form. Balb/c mice, intramuscularly inoculated with this plasmid, presented high levels of antibodies, recognizing mainly surface-exposed conformational epitopes present in the NS1 protein expressed by insect cells. Long-term antibody response was observed in animals 56 weeks after the first plasmid inoculation, and a rapid, efficient secondary response was observed after a DNA boost. Vaccinated animals were challenged against DENV-2 in two murine models, based on intracerebral (i.c.) and intraperitoneal (i.p.) virus inoculations, and in both cases, pcTPANS1-immunized mice were protected. Overall, these results provide further support for the use of such a plasmid in a possible approach for the development of a vaccine against DENV.