Highly sensitive immunoassay for direct diagnosis of viral hemorrhagic septicemia which uses antinucleocapsid monoclonal antibodies

Variable domain antibodies specific for viral hemorrhagic septicemia virus (VHSV) selected from a randomized IgNAR phage display library

Phage display libraries are used to screen for nucleotide sequences that encode immunoglobulin variable (V) regions that are specific for a target antigen. We previously constructed an immunoglobulin new antigen receptor (IgNAR) phage display library. Here we used this library to obtain an IgNAR V region that is specific for viral hemorrhagic septicemia virus (VHSV). A phage clone (clone 653) was found to be specific for VHSV by the biopanning method. The V region of clone 653 was used to construct a 6 × His tagged recombinant IgNAR-653 V protein (rIgNAR-653) using the Escherichia coli pET system. The rIgNAR-653 protein bound specifically to VHSV, confirming its activity.

RNA aptamers inhibit the growth of the fish pathogen viral hemorrhagic septicemia virus (VHSV)

Viral hemorrhagic septicemia virus (VHSV) is a serious disease impacting wild and cultured fish worldwide. Hence, an effective therapeutic method against VHSV infection needs to be developed. Aptamer technology is a new and promising method for diagnostics and therapeutics. It revolves around the use of an aptamer molecule, an artificial ligand (nucleic acid or protein), which has the capacity to recognize target molecules with high affinity and specificity. Here, we aimed at selecting RNA aptamers that can specifically bind to and inhibit the growth of a strain of fish VHSV both in vitro and in vivo. Three VHSV-specific RNA aptamers (F1, F2, and C6) were selected from a pool of artificially and randomly produced oligonucleotides using systematic evolution of ligands by exponential enrichment. The three RNA aptamers showed obvious binding to VHSV in an electrophoretic mobility shift assay but not to other tested viruses. The RNA aptamers were tested for their ability to inhibit VHSV in vitro using hirame natural embryo (HINAE) cells. Cytopathic effect and plaque assays showed that all aptamers inhibited the growth of VHSV in HINAE cells. In vivo tests using RNA aptamers produced by Rhodovulum sulfidophilum showed that extracellular RNA aptamers inhibited VHSV infection in Japanese flounder. These results suggest that the RNA aptamers are a useful tool for protection against VHSV infection in Japanese flounder.

Typing of viral hemorrhagic septicemia virus by monoclonal antibodies

Seven mAbs with specific reaction patterns against each of the four genotypes and eight subtypes of viral hemorrhagic septicemia virus (VHSV) were produced, aiming to establish an immunoassay for typing VHSV isolates according to their genotype. Among the mAbs, VHS-1.24 reacted with all genotypes except genotype Ie, whilst mAb VHS-9.23 reacted with all genotypes except genotype III. mAb VHS-3.80 reacted with genotypes Ib, Ic, Id and II. mAb VHS-7.57 reacted with genotypes II and IVa, and mAb VHS-5.18 with genotype Ib only. Interestingly, mAb VHS-3.75 reacted with all of the genotype III isolates except a rainbow trout-pathogenic isolate from the west coast of Norway, and reacted in addition with the IVb isolate, CA-NB00-01, from the east coast of the USA. Finally, mAb VHS-1.88 reacted with all genotype IVb isolates from the Great Lakes, but not with CA-NB00-01. In conclusion, we can distinguish between all four genotypes and between five of eight subtypes of VHSV by testing isolates in immunoassay using a panel of nine mAbs. By Western blotting and transfection of cell cultures, it was shown that mAb VHS-1.24 recognized an epitope on the viral phosphoprotein (P), whilst all others recognized antigenic determinants on the nucleoprotein (N). From amino acid alignments of the various genotypes and subtypes of VHSV isolates, it was possible to determine the epitope specificity of mAb VHS-1.24 to be aa 32-34 in the P-protein; the specificities of mAbs VHS-3.80, VHS-7.57 and VHS-3.75 were found to be aa 43 and 45-48, aa 117 and 121, and aa 103, 118 and 121 of the N-protein, respectively.

Molecular targets for diagnostics and therapeutics of severe acute respiratory syndrome (SARS-CoV)

PURPOSE

The large number of deaths in a short period of time due to the spread of severe acute respiratory syndrome (SARS) infection led to the unparalleled collaborative efforts world wide to determine and characterize the new coronavirus (SARS-CoV). The full genome sequence was determined within weeks of the first outbreak by the Canadian group with international collaboration. As per the World Health Organization (WHO), the continual lack of a rapid laboratory test to aid the early diagnosis of suspected cases of SARS makes this area a priority for future research. To prevent deaths in the future, early diagnosis and therapy of this infectious disease is of paramount importance.

METHODS

This review describes the specific molecular targets for diagnostics and therapeutics of viral infection.

RESULTS

The three major diagnostic methods available for SARS includes viral RNA detection by reverse transcription polymerase chain reaction (RT-PCR), virus induced antibodies by immunofluorescence assay (IFA) or by enzyme linked immunosorbant assay (ELISA) of nucleocapsid protein (NP). The spike glycoprotein of SARS-CoV is the major inducer of neutralizing antibodies. The receptor binding domain (RBD) in the S1 region of the spike glycoprotein contains multiple conformational epitopes that induces highly potent neutralizing antibodies. The genetically engineered attenuated form of the virus or viral vector vaccine encoding for the SARS-CoV spike glycoprotein has been shown to elicit protective immunity in vaccinated animals.

CONCLUSION

NP is the preferred target for routine detection of SARS-CoV infection by ELISA which is an economical method compared to other methods. The RBD of the spike glycoprotein is both a functional domain for cell receptor binding and also a major neutralizing determinant of SARS-CoV. The progress in evaluating a therapeutic or vaccine would depend on the avail ability of clinically relevant animal model.

Rapid detection and quantitation of viral hemorrhagic septicemia virus in experimentally challenged rainbow trout by real-time RT-PCR

A quantitative real-time RT-PCR (Q-RT-PCR) was developed to detect and determine the amount of viral hemorrhagic septicemia virus (VHSV) in organs of experimentally infected rainbow trout. Primers and TaqMan probes targeting the glycoprotein (G) and the nucleoprotein (N) genes of the virus were designed. The efficiency, linear range and detection limit of the Q-RT-PCR were assessed on cell cultured virus samples. VHSV N gene amplification was more efficient and more sensitive than the VHSV G amplicon. On cell culture grown virus, samples could be accurately assayed over a range of seven logs of infectious particles per reaction. To demonstrate the utility of Q-RT-PCR in vivo, bath infection trials were carried out and samples from fish spleen, kidney, liver and blood were harvested and tested for VHSV. Q-RT-PCR was a more reliable method than either conventional RT-PCR or the cell culture assay for virus diagnosis. Results of VHSV RNA detection in fish shortly after infection as well as on asymptomatic fish several weeks after experimental challenge are presented here. This is the first report showing the utility of Q-RT-PCR for VHSV detection and quantitation both in vitro and in vivo. The suitability of this method to test the efficacy of antiviral treatments is also discussed.

Validation of Accuracy of Enzyme-Linked Immunosorbent Assay in Hybridoma Screening and Proposal of an Improved Screening Method

The 96-well plate format of enzyme-linked immunosorbent assay (ELISA) is the de facto standard in screening hybridomas for active antibody. Despite its widespread use, there have been few or no systematic attempts to validate its accuracy and answer the fundamental question, is it finding all the positives? We report here on a comparison between ELISA and a semiautomated flow-based kinetic exclusion assay (KinExA), both used in screening the same hybridoma cell line. Our finding is that ELISA is both overreporting (false positives) and underreporting (false negatives) compared to the KinExA system. The large number of hybridoma cells (e.g., cultured in six 96-well plates) that must be checked is daunting in considering any method other than ELISA for routine screening. To overcome this, we devised a sampling strategy in which wells are combined in a specified pattern, allowing a significant reduction in the total number of measurements required.

Sensitive and specific monoclonal antibody-based capture enzyme immunoassay for detection of nucleocapsid antigen in sera from patients with severe acute respiratory syndrome

A rapid antigen test for the diagnosis of severe acute respiratory syndrome (SARS) is essential for control of this disease at the point of management. The nucleocapsid (N) protein of SARS-associated coronavirus (SARS-CoV) is abundantly expressed in infected-cell culture filtrate as demonstrable by Western blotting using convalescent-phase sera from patients with SARS. We used monoclonal antibodies specifically directed against N protein to establish a sensitive antigen capture sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of SARS-CoV. The assay employed a mixture of three monoclonal antibodies for capture and rabbit polyclonal antibodies for detection of serum antigen in 32 cases of clinically probable SARS as defined by the World Health Organization during the epidemic in Guangzhou, China. Recombinant N protein was used as a standard to establish a detection sensitivity of approximated 50 pg/ml. The linear range of detection in clinical specimens was from 100 pg/ml to 3.2 ng/ml. Using a panel of sera collected at different points in time, the amount of circulating N antigen was found to peak 6 to 10 days after the onset of symptoms. The sensitivity of the assay was 84.6% in 13 serologically confirmed SARS patients with blood taken during the first 10 days after the onset of symptoms (11 of 13). The specificity of the assay was 98.5% in 1,272 healthy individuals (1,253 of 1,272). There was no cross-reaction with other human and animal coronaviruses in this assay. In conclusion, a sensitive and quantitative antigen capture ELISA was established for the early diagnosis and disease monitoring of SARS-CoV infection.

Enhanced detection of viral hemorrhagic septicemia virus (a salmonid rhabdovirus) by pretreatment of the virus with a combinatorial library-selected peptide

A 17-mer peptide (SAAEASAKATAEATAKG, p5) was selected by screening a combinatorial library for its ability to enhance in vitro the infectivity of viral hemorrhagic septicemia virus (VHSV), a salmonid rhabdovirus. Preincubation of VHSV samples with p5 at micromolar concentrations led to up to 5-fold increase of viral titers compared to untreated samples, as measured by a 1-day post-infection immunochemical focus assay. Treatment with p5 also increased VHSV titers when using the more traditional plaque and end-point dilution assays. Preincubation of p5 with infectious hematopoietic necrosis virus (another rhabdovirus of salmonids), but not with infectious pancreatic necrosis virus (birnavirus) also led to a similar increase in sensitivity. These results indicate that the addition of p5 may be used to improve the sensitivity of diagnostic tests for salmonid rhabdoviruses.

Development, characterization and future prospects of monoclonal antibodies against spores of Glugea atherinae (protozoa-microsporidia-fish parasites)

Monoclonal antibodies against spores of Glugea atherinae were obtained after lymphocytic hybridization made from immunized mouse splenocytes. Screening using an indirect enzyme linked immunosorbent assay (ELISA), revealed seven monoclonal antibodies with an intense but variable reaction with the spores of fish microsporidia, and a moderate reaction with those of an insect microsporidium (Nosema sp.). The reaction was weaker with spores of Encephalitozoon intestinalis found in HIV+ patients. FITC and Dot Blot confirmed the majority of these results. After biotinylation of the seven antibodies, inhibition tests allowed the localization of two different recognition domains on the spores of Glugea atherinae. The multiple antigenic determinants and their probable polysaccharide nature seem to be in accord with the class IgM of the antibodies produced. This work confirms the potential of these antibodies for microsporidian taxonomy and diagnosis, especially the use of Mabs 12F9 and 12H5 for detection of spores in stools of HIV+ patients.

Fast neutralization/immunoperoxidase assay for viral haemorrhagic septicaemia with anti-nucleoprotein monoclonal antibody

An enzyme-immunohistochemical procedure was employed to facilitate neutralization/diagnostic tests for viral haemorrhagic septicaemia virus (VHSV), a significant pathogen in trout farms throughout Europe. The method described can be used for trout or mice antibodies; increases speed (1 day), simplicity, and minimizes the use of reagents compared to other neutralization assays. Furthermore, the test requires a minimum handling of the cell cultures under sterile conditions, decreasing frequent contamination due to the non-sterile conditions of the fish pathological samples. Foci of 5-20 infected epithelioma papillosum carp (EPC) cells are detected and counted with an inverted microscope in under 16 h after infection of EPC monolayers using a high titre anti-N VHSV monoclonal antibody (MAb) 2C9. MAb 2C9 recognizes different viral haemorrhagic septicaemia virus serotypes and VHSV isolates from different host species (trout, salmon and barbel) and Spanish geographical locations. The high titre and specificity of MAb 2C9 favour its conjugation to peroxidase and also make it possible to use in direct immunoperoxidase staining of the VHSV infected EPC monolayers. This neutralization/immunoperoxidase assay should improve diagnostics that use currently agarose or methylcellulose plaque reduction neutralization assays.

Applications of monoclonal antibodies in aquaculture

Monoclonal antibodies (MAbs) currently are being applied to the study of fish immunology and fish infectious diseases. MAbs to fish immunoglobulins (Igs) have helped isolate fish Igs, identify heavy and light chain variants in fish Ig, study the ontogeny of B lymphocytes, and improve techniques for the measurement of fish Ig and specific antibodies (Abs). MAbs have been obtained against several leucocyte surface antigens and are being used as markers for different subsets of fish leukocytes: neutrophils, non-specific cytotoxic cells and cells responsible for the mixed leucocyte reaction. The sensitivity and specificity of many immunoassays for identifying fish pathogens have been improved by the use of MAbs. Further improvement of these tests is currently being attempted by the use of MAbs together with the polymerase chain reaction (PCR). Epizootiological studies of fish diseases are beginning to emerge from the use of these reagents and techniques. In the near future these new methods should detect low levels of pathogens in adult carriers and perhaps in eggs, thus helping to prevent the dissemination of fish diseases. MAbs to fish pathogens are also being used for passive immunization studies as well as for conformational probes in the development of genetically engineered vaccines.

Comparison of monoclonal antibody-based sandwich enzyme-linked immunosorbent assay and virus isolation for detection of peste des petits ruminants virus in goat tissues and secretions

A monoclonal antibody-based sandwich enzyme-linked immunosorbent assay (S-ELISA) was developed for specific detection of peste des petits ruminants virus. Compared with virus isolation in Vero cell cultures using 89 paired tissue and secretion samples from six experimentally infected goats, S-ELISA was significantly more sensitive (71.9% versus 65.2%; P < 0.05). The S-ELISA is a suitable alternative to virus isolation.