Comparison of capture immunoglobulin M (IgM) and IgG enzyme-linked immunosorbent assay (ELISA) and nonstructural protein NS1 serotype-specific IgG ELISA for differentiation of primary and secondary dengue virus infections

We have found that NS1 serotype-specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) can be used to differentiate primary and secondary dengue virus infections. This is due to the fact that the NS1-specific IgG antibody cannot be detected before day 9 of illness for primary infection, so the NS1-specific IgG antibodies measured in acute-phase sera must come from previous infection. Comparison of NS1 serotype-specific IgG ELISA with envelope- and membrane-specific capture IgM and IgG ELISA in the differentiation of primary and secondary dengue virus infections showed good correlation (95.90% agreement). Most important, we have found that the serotype of the dengue virus from the majority of patients with primary infection could be correctly identified when convalescent-phase or postinfection sera were analyzed by NS1 serotype-specific IgG ELISA. These findings suggested that NS1 serotype-specific IgG ELISA could be reliably applied for serodiagnosis and seroepidemiological study of dengue virus infection.     

Comparison of Capture Immunoglobulin M (IgM) and IgG Enzyme-Linked Immunosorbent Assay (ELISA) and Nonstructural Protein NS1 Serotype-Specific IgG ELISA for Differentiation of Primary and Secondary Dengue Virus Infections

We have found that NS1 serotype-specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) can be used to differentiate primary and secondary dengue virus infections. This is due to the fact that the NS1-specific IgG antibody cannot be detected before day 9 of illness for primary infection, so the NS1-specific IgG antibodies measured in acute-phase sera must come from previous infection. Comparison of NS1 serotype-specific IgG ELISA with envelope- and membrane-specific capture IgM and IgG ELISA in the differentiation of primary and secondary dengue virus infections showed good correlation (95.90% agreement). Most important, we have found that the serotype of the dengue virus from the majority of patients with primary infection could be correctly identified when convalescent-phase or postinfection sera were analyzed by NS1 serotype-specific IgG ELISA. These findings suggested that NS1 serotype-specific IgG ELISA could be reliably applied for serodiagnosis and seroepidemiological study of dengue virus infection.     

Dengue NS1-specific antibody responses: isotype distribution and serotyping in patients with Dengue fever and Dengue hemorrhagic fever

To understand the antibody responses to dengue (DEN) nonstructural 1 (NS1) glycoprotein and their roles in protective immunity or pathogenesis of dengue fever (DF) and dengue hemorrhagic fever (DHF), we have analyzed the NS1-speccific IgM, IgA and IgG antibodies from patients with DF and DHF. An isotype-specific, indirect enzyme-linked immunosorbent assay (ELISA) was established by coating a NS1-specific monoclonal antibody (MAb), D2/8-1, to capture soluble NS1 antigens secreted in the culture supernatants of Vero cells infected with DEN virus. We observed strong anti-NS1 antibody responses in all of the convalescent sera of patients with DF and DHF. Similar NS1-specific isotypic and serotypic antibody responses were found in the sera from DF and DHF patients. The results showed that all DEN infections induced significant NS1-specific IgG, whereas 75% and 60% of primary DF patients vs. 40% and 90% of secondary DF patients produced IgM and IgA antibodies, respectively. Specificity analysis showed that DEN NS1-specific IgG and IgA antibodies cross-react strongly to Japanese encephalitis (JE) virus NS1 glycoprotein, whereas DEN NS1-specific IgM antibodies do not cross-react to JE virus NS1 glycoprotein at all. The serotype specificity of NS1-specific IgM, IgA and IgG were found to be 80%, 67% and 75% for primary infections, and 50%, 22% and 30% for secondary infections in positive samples of DF patients. Similar pattern was found in DHF patients. The results showed that all of the DF and DHF patients produced significant NS1-specific antibodies. We did not observe direct correlation between the anti-NS1 antibody responses and DHF because sera from patients with DF and DHF showed similar anti-NS1 antibody responses.     

Ⅰ型登革病毒NS1抗原捕获ELISA的建立和初步临床诊断应用

目的以登革病毒特异性非结构蛋白1（NS1）单克隆抗体为基础建立Ⅰ型登革病毒（DEN1）抗原检测的酶联免疫吸附（ELISA）法，并探索从病人早期血清样品中检测DEN1-NS1的可行性。方法利用已制备的抗DEN1-NS1单克隆抗体（单抗），进行多种抗体组合配对优化模式的分析，建立双抗体夹心抗原捕获ELISA，以469份健康人血清样品确定cut off值，检测DEN1感染患者急性期血清样品。结果对多种抗体组合反复筛选，最终确立了最佳的包被单抗和酶标测定单抗，建立了抗体夹心捕获DEN1-NS1抗原的酶联免疫测定方法，能特异检测DEN1，与其他血清型登革病毒不发生交叉反应。检测16例临床确诊DEN1感染病人急性期血清样品，15例呈特异的抗原反应阳性。结论成功建立了DEN1-NS1抗原捕获ELISA并应用于临床血清样品的检测，为登革热的早期实验室诊断提供技术方法。     

Dengue NS1 antigen detection: A useful tool in early diagnosis of dengue virus infection

Purpose: This study was undertaken to evaluate the efficacy of NS1 antigen (Ag) assay as an early marker for dengue virus (DV) infection. Materials and Methods: Group I evaluated the performance of NS1 antigen (Ag) assay in comparison to MAC-ELISA and their detection rate when performed together in a single sample. Six hundred acute/early convalescent sera were screened by both the assays. Group II evaluated the efficacy of a single assay in 30 acute phase sera of paediatric OPD patients screened only by NS1 Ag assay. Group III evaluated the specificity of NS1 assay in comparison to MAC-ELISA on 40 samples included as controls. Results: In Group I, 140 (23.3%) and 235 (39.1%) samples were positive by NS1 assay and MAC-ELISA respectively. The detection rate increased to 320 (53.3%) when both the assays were used together on a single sample. NS1 Ag positivity varied from 71.42% to 28.4% in acute and early convalescent sera, conversely IgM detection rate was 93.61% and 6.38% in early convalescent and acute phase sera respectively (P < 0.0001). In Group II, 66.66% (20) samples were positive by NS1 assay. All the samples in Group III were negative showing 100% specificity of both the assays. Conclusion: NS1 Ag assay holds promise in early diagnosis of dengue infection. When used in combination with MAC-ELISA on a single sample it significantly improves the diagnostic algorithm without the requirement of paired sera.     

Retrospective study of Western blot profiles in immune sera of natural dengue virus infections

The Western blot (WB) assay was used to determine dengue virus antibodies present in human immune sera arising from recent primary and secondary dengue virus infections in Singapore. Cell lysates of dengue-2 virus-infected C6/36 and Vero cells were used. Antibodies directed against structural proteins of dengue-2 virus including envelope (E, gp60/50), capsid-premembrane (C-PrM, gp35), and premembrane (PrM, gp20) were detected, with antibody against envelope protein being most dominant. Similar WB profiles were detected in both primary and secondary dengue virus infections. The reactivity rate of antibodies to dengue-2 virus proteins was higher in infected Vero cell lysate than in infected C6/36 cell lysate, with the exception of antibodies to nonstructural proteins of NS1 and NS3, which were detected predominantly in infected C6/36 cell lysate. More than 75% of "normal" individuals (with no complaint of recent dengue virus infection) examined had low levels of dengue virus antibodies, but all presented with similar WB profiles as patients with recent dengue virus infections. This finding reflects a high seroprevalence of dengue virus infections and the long lasting nature of E, C-PrM, and PrM antibodies. Results from this study indicate that in natural dengue virus infections, native E, C-PrM, and PrM antigens of dengue virus are immunogenic and elicit long-lasting antibodies.     

Development of a dot enzyme immunoassay for dengue 3: a sensitive method for the detection of antidengue antibodies

Partially purified DEN3 virus was used as antigen in a sensitive dot enzyme immunoassay (DEIA) for the detection of antibodies to flavivirus antigens. We describe here the method used to prepare and optimise the antigen-bearing nitrocellulose membranes and present the results obtained from screening 20 acute phase sera from patients shown to have had recent dengue infections by the haemagglutination inhibition (HI) test. Sixteen pairs of acute and convalescent sera from dengue-negative patients had no detectable antibody to dengue virus by HI. These were shown to have no antibody detectable by DEIA. Sera positive for dengue antibodies by HI had DEIA titers ranging from 10 to several thousand times greater than the titers detected by HI.     

Nonstructural protein NS1 immunodominant epitope detected specifically in dengue virus infected material by a SELDI-TOF/MS based assay

Dengue virus (DV) infection is the most common mosquito-born viral disease of public health significance. Though most patients only suffer from flu-like symptoms, a small group of patients experiences more severe forms of the disease. The viral nonstructural protein 1 (NS1), a secreted protein correlating with viremia, is a key element used for dengue diagnosis with potential implications in severe dengue prognosis. Capture-ELISAs for the early detection of the NS1 protein in the sera during the acute febrile stage are commonly used in routine by diagnostic laboratories. In this study, the detection of NS1 protein in DV-infected material was assessed by an alternative method combining a single NS1-directed monoclonal antibody and the SELDI-TOF/MS technology. According to the epitope mapping, the antibodies used are mainly directed against an immuno-dominant peptide located on the C-terminal part of the protein. The NS1 SELDI-TOF assay is specific, has a sensitivity level close to capture-ELISAs and is potentially useful for a coupled serotyping/detection assay or for the detection of subtle post-translational modifications on the protein.     

Changes in levels of anti-dengue virus IgG subclasses in patients with disease of varying severity

Extensive complement activation precedes onset of shock in dengue patients and complement "split products" C3a and C5a could be responsible, directly or indirectly, for the increased vascular permeability and disseminated intravascular coagulation which characterises dengue haemorrhagic fever (DHF) dengue shock syndrome (DSS). As IgG subclasses vary in their capacity to activate the classical complement pathway after combining with antigen, we have used an indirect enzyme linked immunosorbent assay (ELISA) to assess levels of lgG1–4 against each dengue serotype in acute and convalescent sera from patients with disease of varying severity. Acute phase sera from patients with dengue haemorrhagic fever (DHF) or dengue shock syndrome (DSS) contained higher levels of anti-dengue antibodies of the IgG1, complement fixing, subclass than similar sera from dengue fever (DF) patients. Conversely, acute phase sera from DHF and DSS patients contained lower levels of anti-dengue antibodies of the poor complement activating lgG2 subclass than acute phase sera from DF patients. No significant differences were detected between the levels of anti-dengue lgG3 and lgG4 antibody in acute phase sera from DF, DHF, and DSS patients. With the exception of levels of antidengue lgG2 antibody from DHF patients which were lower than those from DF and DSS patients, levels of anti-dengue IgG1, lgG2, lgG3, and lgG4 were similar in convalescent sera from all patients. These results Provide a possible explanation for the activation of the serum complement system which precedes onset of shock in severe dengue infections. © 1993 Wiley-Liss, Inc.     

The identification of immunodominant linear epitopes of dengue type 2 virus capsid and NS4a proteins using pin-bound peptides

We have used multi-pin peptide synthesis strategy to identify B-cell epitopes on two small dengue virus proteins, capsid and NS4a. We have identified several linear, immunodominant epitopes on both these proteins. Almost all these epitopes mapped to regions predicted to be hydrophilic based on Kyte and Doolittle profiles. Of the capsid epitopes identified in this study, the most immunogenic ones mapped to the C-terminal alpha4 helix, which lies on the solvent-exposed surface of the capsid dimer. The capsid epitopes were dengue-specific in that they could recognize antibodies in dengue virus-, but not yellow fever virus (YFV)- or Japanese encephalitis virus (JEV)-immune sera. This study has demonstrated the presence of anti-NS4a antibodies in dengue-patient sera definitively, for the first time, using authentic NS4a-derived pin-bound peptides as capture antigens. All the NS4a epitopes mapped to the amino-terminal third of the NS4a molecule. Our study suggests that the immunodominant epitopes of these two dengue proteins might have the potential to be used as a part of a recombinant multi-epitope protein containing carefully chosen E and NS1 epitopes for the detection of dengue infections with a high degree of sensitivity and specificity.     

Clinical evaluation of the NS1 antigen‐capture ELISA for early diagnosis of dengue virus infection in Brazil

The fact that the diagnosis of infection with dengue virus is usually made by detecting IgM antibodies during the convalescent phase of the disease interferes with disease management and, consequently, with reducing mortality rates. This study evaluated the sensitivity and specificity of detection of NS1 in samples of patients suspected of acute dengue virus infection in Brazil. The results were used to institute treatment and the sensitivity and specificity of detection of NS1 were compared to the results of detection of IgM, virus isolation, and RT‐PCR. Detection of NS1 yielded better results than RT‐PCR and virus isolation. When considering IgM detection and RT‐PCR positive results as “gold standards,” the sensitivity and specificity of the NS1 assay were 95.9% and 81.1%, respectively. All patients enrolled in the study were treated promptly and had an uneventful course of the disease. The detection of NS1 provided better results than the diagnostic techniques used currently during the acute phase of disease (RT‐PCR and virus isolation). Detection of NS1 is an important tool for the diagnosis of acute dengue infection, particularly in highly endemic areas, allowing for rapid treatment of patients and reduction of disease burden. J. Med. Virol. 82:1400–1405, 2010. © 2010 Wiley‐Liss, Inc.     

Antibody responses to an immunodominant nonstructural 1 synthetic peptide in patients with dengue fever and dengue hemorrhagic fever

Two flaviviruses, dengue (DEN) virus and Japanese encephalitis (JE) virus, are important because of their global distribution and the frequency of epidemics in tropical and subtropical areas. To study the B-cell epitopes of nonstructural 1 (NS1) glycoprotein and anti-NS1 antibody response in DEN infection, a series of 15-mer synthetic peptides from the predicted B-cell linear epitopes of DEN-2 NS1 protein were prepared. Enzyme-linked immunosorbent assay (ELISA) was performed to analyze antibody responses to these peptides from sera of both DEN and JE patients. One peptide derived from DEN-2 NS1, D2 NS1-P1 (amino acids 1–15), was identified as the immunodominant epitope that reacted with sera from dengue fever (DF) patients but not JE patients. The isotype of D2 NS1-P1-specific antibodies was mainly immunoglobulin M (IgM) in all sera that tested positive. A specificity study demonstrated that sera from all four DEN types reacted with D2 NS1-P1. A dynamics study showed that specific antibodies to this peptide could be detected as early as 2 days after the onset of symptoms. We observed significant anti-D2 NS1-P1 antibody responses in 45% of patients with primary and secondary infections with DF or with dengue hemorrhagic fever. This is the first report demonstrating that significant anti-DEN NS1 antibodies can be induced in the sera of patients with primary DEN infection. J. Med. Virol. 57:1–8, 1999. © 1999 Wiley-Liss, Inc.     

Dengue virus serotyping based on envelope and membrane and nonstructural protein NS1 serotype-specific capture immunoglobulin M enzyme-linked immunosorbent assays

Envelope and membrane (E/M) and nonstructural protein NS1 serotype-specific capture Immunoglobulin M (IgM) enzyme-linked immunosorbent assays (ELISAs) were developed to differentiate four dengue virus serotypes. A total of 93 anti-dengue virus IgM-positive serum samples collected between days 5 and 45 of illness from 59 confirmed dengue patients were analyzed. The results showed that positive serotype specificity could be identified for 86.1 and 47.6% of serum samples tested for E/M-specific IgM antibodies versus 83.3 and 42.9% of serum samples tested for NS1-specific IgM antibodies from patients with primary and secondary dengue virus infections, respectively. Dual analyses with both E/M and NS1 serotype-specific capture IgM ELISAs showed that positive serotype specificity could be correctly identified for 98.6 and 61.9% of all of the primary and secondary serum samples tested, respectively. These findings suggested that E/M and NS1 serotype-specific capture IgM ELISAs have the potential to be of use in dengue virus serotyping.