Development of dengue IgM-capture enzyme-linked immunosorbent assay with higher sensitivity using monoclonal detection antibody

Immunization with different recombinant West Nile virus envelope proteins induces varying levels of serological cross-reactivity and protection from infection

Introduction

West Nile Virus (WNV) is a zoonotic flavivirus transmitted by mosquitoes. Especially in the elderly or in immunocompromised individuals an infection with WNV can lead to severe neurological symptoms. To date, no human vaccine against WNV is available. The Envelope (E) protein, located at the surface of flaviviruses, is involved in the invasion into host cells and is the major target for neutralizing antibodies and therefore central to vaccine development. Due to their close genetic and structural relationship, flaviviruses share highly conserved epitopes, such as the fusion loop domain (FL) in the E protein, that are recognized by cross-reactive antibodies. These antibodies can lead to enhancement of infection with heterologous flaviviruses, which is a major concern for potential vaccines in areas with co-circulation of different flaviviruses, e.g. Dengue or Zika viruses.

Material

To reduce the potential of inducing cross-reactive antibodies, we performed an immunization study in mice using WNV E proteins with either wild type sequence or a mutated FL, and WNV E domain III which does not contain the FL at all.

Results and discussion

Our data show that all antigens induce high levels of WNV-binding antibodies. However, the level of protection against WNV varied, with the wildtype E protein inducing full, the other antigens only partial protection. On the other hand, serological cross-reactivity to heterologous flaviviruses was significantly reduced after immunization with the mutated E protein or domain III as compared to the wild type version. These results have indications for choosing antigens with the optimal specificity and efficacy in WNV vaccine development.

A novel colorimetric biosensor for rapid detection of dengue virus upon acid-induced aggregation of colloidal gold

The dengue virus, once transmitted to people through a mosquito bite, causes an infectious disease called dengue fever. Dengue fever can develop into two fatal syndromes, namely dengue shock syndrome and dengue hemorrhagic fever. The existing strategies for detecting dengue infection mainly employ serological immunoassays and a real time PCR technique. Along with the positive features of efficiency, accuracy, and reproducibility, these procedures are limited by being time-consuming, costly, requiring special equipment for analysis, and unable to be carried out at the point-of-care level. Herein, we developed a colorimetric nanosensor for detecting dengue virus in clinical samples that is rapid, accurate, sensitive, and less expensive. The sensing platform relies on the specific binding between the DNA-conjugated AuNPs and genomic RNA of dengue, which results in the DNA-RNA heteroduplex structure formation that turns the gold colloid's ruby red color to blue due to the nano-aggregation in an acidic environment, which can be detected by the naked eye or measuring the absorbance. The DNA probe was designed to bind to a genomic RNA conserved region recognized in all four dengue serotypes. Dengue virus serotype 1 was utilized as a framework for virus detection; the designed nanosensor exhibited great specificity and selectivity, with the detection limit of ∼1 pg μL-1 (∼1.66 × 106 RNA copies per reaction) and time of analysis of about 1 h including the RNA extraction step. The proposed colorimetric nanosensor offers an alternative tool for specific and highly sensitive detection of dengue that eliminates the requirement for thermal cycling and primer sets in PCR-based assays.

Development of a Rapid Gold Nanoparticle-Based Lateral Flow Immunoassay for the Detection of Dengue Virus

Flavivirus detection in humans and mosquito reservoirs has been an important issue since it can cause a variety of illnesses and could represent a health problem in geographical zones where the vector is endemic. In this work, we designed and characterized a biosensor based on gold nanoparticles (AuNPs) and antibody 4G2 for the detection of dengue virus (DENV) in vitro, obtaining different conjugates (with different antibody concentrations). The AuNP–4G2 conjugates at concentrations of 1, 3, and 6 µg/mL presented an increase in the average hydrodynamic diameter compared to the naked AuNPs. Also, as part of the characterization, differences in the UV-Vis absorbance spectrum and electrophoretic migration were observed between the conjugated AuNPs (with BSA or antibody) and naked AuNPs. Additionally, we used this biosensor (AuNP–4G2 conjugate with 3 µg/mL antibody) in the assembly of a competitive lateral flow assay (LFA) for the development of an alternative test to detect the flavivirus envelope protein in isolated DENV samples as a future tool for dengue detection (and other flaviviruses) in the mosquito vector (Aedesaegypti) for the identification of epidemic risk regions. Functionality tests were performed using Dengue virus 2 isolated solution (TCID₅₀/mL = 4.58 × 10³) as a positive sample and PBS buffer as a negative control. The results showed that it is possible to detect Dengue virus in vitro with this gold nanoparticle-based lateral flow assay with an estimated detection limit of 5.12 × 10² PFU. We suggest that this biosensor could be used as an additional detection tool by coupling it to different point-of-care tests (POCT) for the easy detection of other flaviviruses.

A summary of the imported cases of Chikungunya fever in Japan from 2006 to June 2016

BACKGROUND

Due to the huge 2-way human traffic between Japan and Chikungunya (CHIK) fever-endemic regions, 89 imported cases of CHIK fever were confirmed in Japan from January 2006 to June 2016. Fifty-four of 89 cases were confirmed virologically and serologically at the National Institute of Infectious Diseases, Japan and we present the demographic profiles of the patients and the phylogenetic features of 14 CHIK virus (CHIKV) isolates.

METHODS

Patients were diagnosed with CHIK fever by a combination of virus isolation, viral RNA amplification, IgM antibody-, IgG antibody-, and/or neutralizing antibody detection. The whole-genome sequences of the CHIKV isolates were determined by next-generation sequencing.

RESULTS

Prior to 2014, the source countries of the imported CHIK fever cases were limited to South and Southeast Asian countries. After 2014, when outbreaks occurred in the Pacific and Caribbean Islands and Latin American countries, there was an increase in the number of imported cases from these regions. A phylogenetic analysis of 14 isolates revealed that four isolates recovered from three patients who returned from Sri Lanka, Malaysia and Angola, belonged to the East/Central/South African genotype, while 10 isolates from 10 patients who returned from Indonesia, the Philippines, Tonga, the Commonwealth of Dominica, Colombia and Cuba, belonged to the Asian genotype.

CONCLUSION

Through the phylogenetic analysis of the isolates, we could predict the situations of the CHIK fever epidemics in Indonesia, Angola and Cuba. Although Japan has not yet experienced an autochthonous outbreak of CHIK fever, the possibility of the future introduction of CHIKV through an imported case and subsequent local transmission should be considered, especially during the mosquito-active season. The monitoring and reporting of imported cases will be useful to understand the situation of the global epidemic, to increase awareness of and facilitate the diagnosis of CHIK fever, and to identify a future CHIK fever outbreak in Japan.

Zika virus infection of cellular components of the blood-retinal barriers: implications for viral associated congenital ocular disease

BACKGROUND

Ocular abnormalities present in microcephalic infants with presumed Zika virus (ZIKV) congenital disease includes focal pigment mottling of the retina, chorioretinal atrophy, optic nerve abnormalities, and lens dislocation. Target cells in the ocular compartment for ZIKV infectivity are unknown. The cellular response of ocular cells to ZIKV infection has not been described. Mechanisms for viral dissemination in the ocular compartment of ZIKV-infected infants and adults have not been reported. Here, we identify target cells for ZIKV infectivity in both the inner and outer blood-retinal barriers (IBRB and OBRB), describe the cytokine expression profile in the IBRB after ZIKV exposure, and propose a mechanism for viral dissemination in the retina.

METHODS

We expose primary cellular components of the IBRB including human retinal microvascular endothelial cells, retinal pericytes, and Müller cells as well as retinal pigmented epithelial cells of the OBRB to the PRVABC56 strain of ZIKV. Viral infectivity was analyzed by microscopy, immunofluorescence, and reverse transcription polymerase chain reaction (RT-PCR and qRT-PCR). Angiogenic and proinflammatory cytokines were measured by Luminex assays.

RESULTS

We find by immunofluorescent staining using the Flavivirus 4G2 monoclonal antibody that retinal endothelial cells and pericytes of the IBRB and retinal pigmented epithelial cells of the OBRB are fully permissive for ZIKV infection but not Müller cells when compared to mock-infected controls. We confirmed ZIKV infectivity in retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells by RT-PCR and qRT-PCR using ZIKV-specific oligonucleotide primers. Expression profiles by Luminex assays in retinal endothelial cells infected with ZIKV revealed a marginal increase in levels of beta-2 microglobulin (β2-m), granulocyte macrophage colony-stimulating factor (GMCSF), intercellular adhesion molecule 1 (ICAM-1), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP1), and vascular cell adhesion molecule 1 (VCAM-1) and higher levels of regulated upon activation, normal T cell expressed and presumably secreted (RANTES) but lower levels of interleukin-4 (IL-4) compared to controls.

CONCLUSIONS

Retinal endothelial cells, retinal pericytes, and retinal pigmented epithelial cells are fully permissive for ZIKV lytic replication and are primary target cells in the retinal barriers for infection. ZIKV infection of retinal endothelial cells and retinal pericytes induces significantly higher levels of RANTES that likely contributes to ocular inflammation.

Development of a high-throughput colorimetric Zika virus infection assay

Zika virus (ZIKV) is an emerging pathogen that causes congenital infections which may result in birth defects, such as microcephaly. Currently, no approved treatment or vaccination is available. ZIKV can be readily detected in cell culture where virally infected cells are normally stained by specific antibodies. As ZIKV regularly causes a cytopathic effect, we were wondering whether this viral property can be used to quantitatively determine viral infectivity. We here describe the use of an 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide-(MTT)-based cell viability assay that allows to determine ZIKV-induced cell death. We show that this colorimetric assay quantifies ZIKV infection over a broad range of viral dilutions in both monkey and human cells. It allows to determine inhibitory activities of antivirals that block ZIKV or to define the neutralizing antibody titers of ZIKV antisera. This MTT-based ZIKV detection assay can be evaluated by naked eye or computational tools, has a broad linear range, does not require large equipment or costly reagents, and thus represents a promising alternative to antibody-based assays, in particular in resource-poor settings. We propose to use this simple, fast, and cheap method for quantification of ZIKV neutralizing antibodies and testing of antiviral compounds.

Engineered Aedes aegypti JAK/STAT Pathway-Mediated Immunity to Dengue Virus

We have developed genetically modified Ae. aegypti mosquitoes that activate the conserved antiviral JAK/STAT pathway in the fat body tissue, by overexpressing either the receptor Dome or the Janus kinase Hop by the blood feeding-induced vitellogenin (Vg) promoter. Transgene expression inhibits infection with several dengue virus (DENV) serotypes in the midgut as well as systemically and in the salivary glands. The impact of the transgenes Dome and Hop on mosquito longevity was minimal, but it resulted in a compromised fecundity when compared to wild-type mosquitoes. Overexpression of Dome and Hop resulted in profound transcriptome regulation in the fat body tissue as well as the midgut tissue, pinpointing several expression signatures that reflect mechanisms of DENV restriction. Our transcriptome studies and reverse genetic analyses suggested that enrichment of DENV restriction factor and depletion of DENV host factor transcripts likely accounts for the DENV inhibition, and they allowed us to identify novel factors that modulate infection. Interestingly, the fat body-specific activation of the JAK/STAT pathway did not result in any enhanced resistance to Zika virus (ZIKV) or chikungunya virus (CHIKV) infection, thereby indicating a possible specialization of the pathway’s antiviral role.

Dengue has represented a significant public health burden for a number of decades, and given the lack of dengue-specific drugs and limited availability of licensed vaccine, new methods for prevention and control are urgently needed. Here, we investigated whether genetic manipulation of the mosquitoes’ native JAK/STAT pathway-mediated anti-DENV defense system could be used to render mosquitoes more resistant to infection. We generated Ae. aegypti mosquitoes overexpressing the JAK/STAT pathway components Dome and Hop under the control of a bloodmeal-inducible, fat body-specific vitellogenin (Vg) promoter. These genetically modified mosquitoes showed an increased resistance to DENV infection, likely because of higher expression of DENV restriction factors and lower expression of DENV host factors, as indicated by transcriptome analyses. Expression of the transgenes had a minimal impact on mosquito longevity; however, it significantly impaired the mosquitoes’ fecundity. Interestingly, bloodmeal-inducible fat body-specific overexpression of either Hop or Dome did not affect mosquito permissiveness to either ZIKV or CHIKV infection, suggesting a possible specialization of JAK/STAT pathway antiviral defenses. Thus, our study is the first to provide a proof-of-concept that genetic engineering of the mosquitoes’ JAK/STAT immune pathway can be used to render this host more resistant to DENV infection.

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.

Clinical profile of dengue infection in patients with hematological diseases

Managing hematological disorders in a tropical country presents several unique diagnostic and management problems. Apart from the disease process, we need to be aware of infections that can exacerbate or mimic serious hematological problems. We present here a series of five patients with pre-existing hematological diseases who were infected by dengue virus. These cases highlight the need to keep a strong suspicion of common endemic diseases in tropical countries before considering extensive workup for the basic hematological disease. There was no mortality and all patients recovered without any significant impact on their pre-existing hematological condition inspite of their low baseline blood counts. There was no excessive bleeding, prolonged stay in the hospital or relapse of underlying hematological disease in these patients and the only major concern was the increased anxiety among both the patient and treating physician regarding the relapse/progression of pre-existing hematological disease.

The laboratorial diagnosis of dengue: applications and implications

The diagnosis of infection by the dengue virus relies, in most cases, on the clinical judgment of the patient, since only a few major centers have clinical laboratories that offer diagnostic tests to confirm the clinical impressions of an infection. At present, routine laboratory diagnosis is done by different kinds of testing. Among them are the methods of serological research, virus isolation, detection of viral antigens, and detection of viral genomes. The continued development of diagnostic tests, which are cheap, sensitive, specific, easy to perform, and capable of giving early diagnosis of the dengue virus infection is still a need. There are also other obstacles that are not specifically related to the technological development of diagnostic methods. For instance, infrastructure of the laboratories, the training of personnel, and the capacity of research of these laboratories are still limited in many parts of Brazil and the world, where dengue is endemic. Clinical laboratories, especially the ones that serve regions with a high incidence of dengue, should be aware of all the diagnostic methods available for routine these days, and choose the one that best suit their working conditions and populations served, in order to save lives.

Production and characterization of monoclonal antibody specific to recombinant dengue multi-epitope protein

Monoclonal antibodies against novel dengue recombinant protein were produced following immunization of Balb/c mice with recombinant dengue multi-epitope protein (r-DMEP) expressed in Escherichia coli vector and purified in a single-step chromatography system. Antigenicity of r-DMEP was evaluated by dot enzyme immunoassay. Mice were immunized intraperitoneally with five doses each of 100 microg of this novel antigen at 1-week intervals and a final intravenous booster dose prior to the fusion. Hybridomas resulted from fusion of myeloma cells and splenocytes using PEG-1500 as an additive. Selection of the hybrids was done using HAT medium, and the hybrids thus selected were finally screened qualitatively and quantitatively by dot and plate immunoassays, respectively. Five antibody secretory hybrid clones exhibited specific reactivity against r-DMEP by dot-ELISA, whereas a lone clone was found to be cross-reactive with Japanese encephalitis virus (JEV). Monoclonal antibodies (MAbs) specific to r-DME protein recognized the envelope and non-structural epitopes by Western blot analysis. These MAbs were further checked for their diagnostic efficacy using dengue suspected clinical samples and found overall sensitivity and specificity for DRDE dipstick ELISA. MAb-based dipstick ELISA results were 85%, 75% and 85%, 90%, respectively.

Confirmation of dengue virus infection by detection of dengue virus type 1 genome in urine and saliva but not in plasma

We successfully detected dengue virus (DENV) genome in urine and saliva but not in plasma samples from a Japanese dengue fever patient. The results of the present study suggest that detection of DENV genome in urine and saliva can be an effective diagnostic method, particularly for children with viral hemorrhage.

Detection of antibodies to Japanese encephalitis virus in the wild boars in Hiroshima prefecture, Japan

Serum specimens were collected from 25 wild boars in Hiroshima prefecture located in the western region of Japan from November 2004 to February 2005. The sera were tested for antibodies to Japanese encephalitis virus (JEV) by IgM capture and IgG enzyme-linked immunosorbent assays (ELISA), and plaque reduction neutralization test. Seventeen samples (68%) were positive for neutralizing antibody to JEV. All the neutralizing antibody-positive samples were positive for IgG-ELISA. One was also positive for IgM. The results indicate that approximately 70% of the wild boars were positive for anti-JEV antibody, and raises the possibility that wild boars may play a role in the infectious cycle of JEV in this region.

Immunoglobulin A antibody responses in dengue patients: a useful marker for serodiagnosis of dengue virus infection

We determined the usefulness of an immunoglobulin A (IgA) antibody-capture enzyme-linked immunosorbent assay for serodiagnosis of dengue virus infections. The results indicate that the presence of IgA and IgM in serum samples assures recent primary dengue virus infection even with a single serum sample.

Dengue diagnosis, advances and challenges

Dengue diagnosis was one of the topics discussed at the symposium 'The Global Threat of Dengue - Desperately Seeking Solutions' organized during the 10th International Congress of Infectious Diseases held in Singapore in 2002. In this paper, a review is presented focusing on the main advances, problems and challenges of dengue diagnosis.IgM capture ELISA, virus isolation in mosquito cell lines and live mosquitoes, dengue specific monoclonal antibodies and PCR have all represented major advances in dengue diagnosis. However, an appropriate rapid, early and accessible diagnostic method useful both for epidemiological surveillance and clinical diagnosis is still needed. Also, tools that suggest a prognosis allowing for better management are also needed. Finally, laboratory infrastructure, technical expertise and research capacity must be improved in endemic countries in order to positively influence dengue surveillance, clinical case management and the development of new approaches to dengue control.

Evaluation of an immunoglobulin M capture enzyme-linked immunosorbent assay for diagnosis of Orientia tsutsugamushi infection

To differentiate scrub typhus from other acute febrile diseases, a rapid and reliable serological diagnosis is important. We developed an immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA) for diagnosis of recent Orientia tsutsugamushi infections in humans. The 56-kDa major outer membrane protein of O. tsutsugamushi is well known as the most immunodominant antigen in scrub typhus. The test is based on the use of the biotinylated recombinant 56-kDa protein of O. tsutsugamushi Boryong, Bor56, which was expressed as a fusion protein with a maltose-binding protein in Escherichia coli. In the test, the serum IgM antibodies were captured by anti-human IgM antibodies coated onto a microtiter plate. The captured IgM antibodies were revealed through sequential addition of biotinylated Bor56 antigen and peroxidase-conjugated streptavidin to the plate. The IgM capture ELISA was compared with the immunofluorescence antibody assay (IFA) by testing 176 serum samples from patients with diagnosed cases of rickettsial disease and patients with other acute febrile diseases. Of the 81 IgG IFA-positive samples, 78 tested positive (sensitivity, 96.3%) and all 31 IgM IFA-positive samples tested positive (sensitivity, 100%) by the IgM capture ELISA. The specificity of the IgM capture ELISA was 99%, and 1 of the 95 IFA-negative samples was positive in the assay. These results strongly suggest that IgM capture ELISA using the recombinant Bor56 antigen is a reliable and detailed method for the detection of early O. tsutsugamushi infection.

Dengue

PURPOSE OF REVIEW

Because efforts to control dengue are flagging, this review focuses on the mechanisms underlying severe disease and on treatment options, good and bad.

RECENT FINDINGS

The year 2001 witnessed unprecedented global dengue epidemic activity in the American hemisphere, the Pacific islands and continental Asia. Early diagnosis of dengue is important but what is the value and appropriate use of the tourniquet test? A negative test does not rule out dengue infection, a positive test should be followed by close surveillance for early signs of dengue hemorrhagic fever. Low platelet counts do not predict clinically significant bleeding in dengue. It follows that platelet or blood transfusions should not be administered based upon platelet count alone. Dengue hemorrhagic fever or dengue shock syndrome cases frequently have compensated consumptive coagulopathy that seldom requires treatment. Bleeding is most likely caused by activated platelets resulting from damaged capillary endothelium. Dengue hemorrhagic fever and dengue shock syndrome can be safely treated with just normal saline. Colloids should be immediately given to children presenting with a pulse pressure at or below 10 mmHg. Human leukocyte antigen alleles correlate with both protection and susceptibility to dengue hemorrhagic fever and dengue shock syndrome; studies in Haiti suggest that blacks have a gene providing nearly complete protection against severe dengue illness.

SUMMARY

The role that antibodies play in protecting and enhancing dengue infections has been largely ignored. Such studies require definitive knowledge of what cells are infected in human dengue and an understanding of all the early antibody-accessible steps of infection of these target cells.

Evaluation of dengue IgM detection tests using sera from patients with autoimmune diseases

Three commercial dengue IgM test kits and 'in-house' IgM-capture enzyme-linked immunosorbent assay (ELISA) were examined for false positive reactions, using 49 serum samples from patients with autoimmune diseases. All the samples were found to be negative by the 'in-house' IgM-capture ELISA. Five samples were determined to be positive by the immunochromatographic test and three of the five samples were also found positive by one commercial IgM-capture ELISA kit. These results suggest that a possibility of false positive reaction should be considered when serum samples from autoimmune disease patients are tested for dengue IgM by some commercial dengue IgM test kits.

Dengue: an update

This review is an update of dengue and dengue haemorrhagic fever (DHF) based on international and Cuban experience. We describe the virus characteristics and risk factors for dengue and DHF, and compare incidence and the case fatality rates in endemic regions (southeast Asia, western Pacific, and the Americas). The clinical picture and the pathogenesis of the severe disease are explained. We also discuss the viral, individual, and environmental factors that determine severe disease. Much more research is necessary to clarify these mechanisms. Also reviewed are methods for viral isolation and the serological, immunohistochemical, and molecular methods applied in the diagnosis of the disease. We describe the status of vaccine development and emphasise that the only alternative that we have today to control the disease is through control of its vector Aedes aegypti.