Characterization of monoclonal antibodies to Marburg virus nucleoprotein (NP) that can be used for NP-capture enzyme-linked immunosorbent assay

The mortality, modes of infection, diagnostic tests, and treatments of Marburg virus disease: A systematic review

Background and Aims

Marburg virus (MARV) has regularly affected people since 1967 causing multiple outbreaks. There are presently no authorized therapies for the fatal Marburg virus disease (MVD), which poses an imminent risk to global public health. The MVD has so far claimed the lives of numerous people, with an increased number of cases being seen throughout the African continent. Hence, a review was carried out to analyze the geographical distribution of MVD, mortality, routes of transmission, and diagnostic and treatment modalities.

Methods

PubMed, Scopus, Web of Science, Google Scholar, and ProMED servers were used to conduct a systematic search in compliance with the PRISMA guidelines. The results were tabulated and analyzed.

Results

A total of 11 studies (7 case reports and 4 case series) were included in the final analysis, and 21 cases of MVD were analyzed. The most frequent symptoms were fever (66.67%), vomiting (57.14%), headache (52.38%), diarrhea (52.38%), and pain (47.62%). The most commonly used diagnostic test was RT-PCR (42.11%). Contact transmission (50%) and zoonotic transmission (37.5%) were the most prevalent routes of transmission. Antibiotics (61.5%) were the first line of treatment. The most common complications were hemorrhage (60%) and coagulopathies (33.3%). The mortality rate was 57.1%.

Conclusion

To avoid disastrous consequences, it is essential to reiterate the necessity of early diagnosis and treatment of MVD.

Unveiling a Drift Resistant Cryptotope within Marburgvirus Nucleoprotein Recognized by Llama Single-Domain Antibodies

Marburg virus (MARV) is a highly lethal hemorrhagic fever virus that is increasingly re-emerging in Africa, has been imported to both Europe and the US, and is also a Tier 1 bioterror threat. As a negative sense RNA virus, MARV has error prone replication which can yield progeny capable of evading countermeasures. To evaluate this vulnerability, we sought to determine the epitopes of 4 llama single-domain antibodies (sdAbs or VHH) specific for nucleoprotein (NP), each capable of forming MARV monoclonal affinity reagent sandwich assays. Here, we show that all sdAb bound the C-terminal region of NP, which was produced recombinantly to derive X-ray crystal structures of the three best performing antibody-antigen complexes. The common epitope is a trio of alpha helices that form a novel asymmetric basin-like depression that accommodates each sdAb paratope via substantial complementarity-determining region (CDR) restructuring. Shared core contacts were complemented by unique accessory contacts on the sides and overlooks of the basin yielding very different approach routes for each sdAb to bind the antigen. The C-terminal region of MARV NP was unable to be crystallized alone and required engagement with sdAb to form crystals suggesting the antibodies acted as crystallization chaperones. While gross structural homology is apparent between the two most conserved helices of MARV and Ebolavirus, the positions and morphologies of the resulting basins were markedly different. Naturally occurring amino acid variations occurring in bat and human Marburgvirus strains all mapped to surfaces distant from the predicted sdAb contacts suggesting a vital role for the NP interface in virus replication. As an essential internal structural component potentially interfacing with a partner protein it is likely the C-terminal epitope remains hidden or “cryptic” until virion disruption occurs. Conservation of this epitope over 50 years of Marburgvirus evolution should make these sdAb useful foundations for diagnostics and therapeutics resistant to drift.

Severe Fever with Thrombocytopenia Syndrome Virus Antigen Detection Using Monoclonal Antibodies to the Nucleocapsid Protein

Background

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infectious disease with a high case fatality rate, and is caused by the SFTS virus (SFTSV). SFTS is endemic to China, South Korea, and Japan. The viral RNA level in sera of patients with SFTS is known to be strongly associated with outcomes. Virological SFTS diagnosis with high sensitivity and specificity are required in disease endemic areas.

Methodology/Principal Findings

We generated novel monoclonal antibodies (MAbs) against the SFTSV nucleocapsid (N) protein and developed a sandwich antigen (Ag)-capture enzyme-linked immunosorbent assay (ELISA) for the detection of N protein of SFTSV using MAb and polyclonal antibody as capture and detection antibodies, respectively. The Ag-capture system was capable of detecting at least 350–1220 TCID₅₀/100 μl/well from the culture supernatants of various SFTSV strains. The efficacy of the Ag-capture ELISA in SFTS diagnosis was evaluated using serum samples collected from patients suspected of having SFTS in Japan. All 24 serum samples (100%) containing high copy numbers of viral RNA (>10⁵ copies/ml) showed a positive reaction in the Ag-capture ELISA, whereas 12 out of 15 serum samples (80%) containing low copy numbers of viral RNA (<10⁵ copies/ml) showed a negative reaction in the Ag-capture ELISA. Among these Ag-capture ELISA-negative 12 samples, 9 (75%) were positive for IgG antibodies against SFTSV.

Conclusions

The newly developed Ag-capture ELISA is useful for SFTS diagnosis in acute phase patients with high levels of viremia.

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne emerging infectious disease caused by a novel bunyavirus, SFTS virus (SFTSV). Since first discovered in China in 2011, SFTSV has been detected from SFTS patients and ticks with expanding geographic ranges from China to Japan and South Korea. The potential for SFTS spread to other warm or sub-tropical regions makes it a serious concern to the public health. It is of great importance to detect SFTSV rapidly and specifically for the effective control of the disease. For the diagnosis of viral infections, a sandwich antigen (Ag)-capture ELISA detecting viral nucleoprotein (N) in viremic serum samples has been widely applied to detect the agents, since it is the most abundant viral antigen and has highly conserved amino acid sequence. In this study, using the novel monoclonal antibodies raised against SFSTV-N, an Ag-capture ELISA system was developed, and the validation of this system was performed using sera collected from SFTS-suspected patients. Our data show that the Ag-capture ELISA was useful for the diagnosis of SFTS patients in the acute phase of the disease. This study shows a novel methodology for the diagnosis of SFTS, which may provide helpful information for the effective control of the disease.

Ebolavirus nucleoprotein C-termini potently attract single domain antibodies enabling monoclonal affinity reagent sandwich assay (MARSA) formulation

BACKGROUND

Antigen detection assays can play an important part in environmental surveillance and diagnostics for emerging threats. We are interested in accelerating assay formulation; targeting the agents themselves to bypass requirements for a priori genome information or surrogates. Previously, using in vitro affinity reagent selection on Marburg virus we rapidly established monoclonal affinity reagent sandwich assay (MARSA) where one recombinant antibody clone was both captor and tracer for polyvalent nucleoprotein (NP). Hypothesizing that the closely related Ebolavirus genus may share the same Achilles' heel, we redirected the scheme to see whether similar assays could be delivered and began to explore their mechanism.

METHODS AND FINDINGS

In parallel we selected panels of llama single domain antibodies (sdAb) from a semi-synthetic library against Zaire, Sudan, Ivory Coast, and Reston Ebola viruses. Each could perform as both captor and tracer in the same antigen sandwich capture assay thereby forming MARSAs. All sdAb were specific for NP and those tested required the C-terminal domain for recognition. Several clones were cross-reactive, indicating epitope conservation across the Ebolavirus genus. Analysis of two immune shark sdAb revealed they also targeted the C-terminal domain, and could be similarly employed, yet were less sensitive than a comparable llama sdAb despite stemming from immune selections.

CONCLUSIONS

The C-terminal domain of Ebolavirus NP is a strong attractant for antibodies and enables sensitive sandwich immunoassays to be rapidly generated using a single antibody clone. The polyvalent nature of nucleocapsid borne NP and display of the C-terminal region likely serves as a bountiful affinity sink during selections, and a highly avid target for subsequent immunoassay capture. Combined with the high degree of amino acid conservation through 37 years and across wide geographies, this domain makes an ideal handle for monoclonal affinity reagent driven antigen sandwich assays for the Ebolavirus genus.

Laboratory detection and diagnosis of filoviruses

Ebola virus (EBOV) and Marburg virus (MARV), belonging to the Filoviridae family, emerged four decades ago and caused severe viral hemorrhagic fever in human and other primates. As high as 50-90% mortality, filoviruses can cause significant threats to public health. However, so far no specific and efficient vaccine has been available, nor have other treatment methods proved to be effective. It is of great importance to detect these pathogens specific, rapidly and sensitively in order to control future filovirus outbreaks. Here, recent progresses in the development of detection and diagnosis methods for EBOV and MARV are summarized.

Monoclonal antibody to dengue capsid protein: its application in dengue studies

Dengue fever (DF) and dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) are considered the most important arthropod-borne viral diseases in terms of morbidity and mortality. The emergency and severity of dengue (Den) infections increase the necessity of an early, quick and effective dengue laboratory diagnostic. Viral isolation is considered a gold standard for diagnosis of dengue infection using monoclonal antibodies (mAbs) as a tool for determining serotype specificity. Alternatives have been used to improve sensitivity and time to dengue diagnosis. Based on the early expression of dengue C protein in the life cycle, we focused our study on the application of an anti-dengue 2 virus capsid protein mAb in dengue diagnosis. The kinetic expression of dengue-2 capsid in mosquito cells and its immuno-localization in experimentally infected suckling albin Swiss (OF-1) mice brain tissues was established. The results demonstrate the possible utility of this mAb in early dengue diagnosis versus traditional isolation. In addition, a preliminary study of an enzyme immunoassay method using 8H8 mAb for specific detection of dengue C protein antigen was performed, making possible recombinant C protein quantification. The results suggest that detection of dengue capsid protein could be useful in the diagnosis of early dengue infection.

Production and characterization of monoclonal antibodies to nucleoprotein of Marburg virus

Monoclonal antibodies (MAbs) against the nucleoprotein of Marburg virus (MARV-NP) with high specificity and activity would be useful for the diagnosis of MARV. In this report, a recombinant MARV-NP was successfully expressed by an Escherichia coli expression system. After immunization and cell fusion, three mouse hybridomas (1H4, 2G1, and 3B5) producing MAbs to MARV-NP were established. The MAbs obtained were fully characterized using indirect ELISA and Western blot analysis. The ELISA results showed that the MAbs' titers were in the range of 1:6.400 x 10(3) - 1:1.280 x 10(4) in culture fluids, and 1:1.024 x 10(6) - 1:8.192 x 106 in ascitic fluids. The isotypes of the three MAbs were tested to be IgG1(kappa) and all the MAbs recognized the same antigenic epitope. Western blot analyses demonstrated that all the MAbs were directed against MARV-NP with the affinity constants (Kaff) of about 1.100 x 10(9) M(-1), 1.235 x 10(9) M(-1), and 1.408 x 10(9) M(-1) for the MAbs 1H4, 2G1, and 3B5, respectively.

Development of recombinant nucleoprotein-based diagnostic systems for Lassa fever

Diagnostic systems for Lassa fever (LF), a viral hemorrhagic fever caused by Lassa virus (LASV), such as enzyme immunoassays for the detection of LASV antibodies and LASV antigens, were developed using the recombinant nucleoprotein (rNP) of LASV (LASV-rNP). The LASV-rNP was expressed in a recombinant baculovirus system. LASV-rNP was used as an antigen in the detection of LASV-antibodies and as an immunogen for the production of monoclonal antibodies. The LASV-rNP was also expressed in HeLa cells by transfection with the expression vector encoding cDNA of the LASV-NP gene. An immunoglobulin G enzyme-linked immunosorbent assay (ELISA) using LASV-rNP and an indirect immunofluorescence assay using LASV-rNP-expressing HeLa cells were confirmed to have high sensitivity and specificity in the detection of LASV-antibodies. A novel monoclonal antibody to LASV-rNP, monoclonal antibody 4A5, was established. A sandwich antigen capture (Ag-capture) ELISA using the monoclonal antibody and an anti-LASV-rNP rabbit serum as capture and detection antibodies, respectively, was then developed. Authentic LASV nucleoprotein in serum samples collected from hamsters experimentally infected with LASV was detected by the Ag-capture ELISA. The Ag-capture ELISA specifically detected LASV-rNP but not the rNPs of lymphocytic choriomeningitis virus or Junin virus. The sensitivity of the Ag-capture ELISA in detecting LASV antigens was comparable to that of reverse transcription-PCR in detecting LASV RNA. These LASV rNP-based diagnostics were confirmed to be useful in the diagnosis of LF even in institutes without a high containment laboratory, since the antigens can be prepared without manipulation of the infectious viruses.

Interaction of Tsg101 with Marburg virus VP40 depends on the PPPY motif, but not the PT/SAP motif as in the case of Ebola virus, and Tsg101 plays a critical role in the budding of Marburg virus-like particles induced by VP40, NP, and GP

Marburg virus (MARV) VP40 is a matrix protein that can be released from mammalian cells in the form of virus-like particles (VLPs) and contains the PPPY sequence, which is an L-domain motif. Here, we demonstrate that the PPPY motif is important for VP40-induced VLP budding and that VLP production is significantly enhanced by coexpression of NP and GP. We show that Tsg101 interacts with VP40 depending on the presence of the PPPY motif, but not the PT/SAP motif as in the case of Ebola virus, and plays an important role in VLP budding. These findings provide new insights into the mechanism of MARV budding.