Antibodies to foot-and-mouth disease virus infection associated (VIA) antigen: use of a bioengineered VIA protein as antigen in an ELISA

An overview on ELISA techniques for FMD

Background

FMD is one of the major causes of economic loss of cloven-hoofed animals in the world today. The assessment of dominant genotype/lineage and prevalent trends and confirmation the presence of infection or vaccination not only provides scientific basis and first-hand information for appropriate control measure but also for disease eradication and regaining FMD free status following an outbreak. Although different biological and serological approaches are still applied to study this disease, ELISA test based on the distinct format, antigen type and specific antibody reinforce its predominance in different research areas of FMD, and this may replace the traditional methods in the near future. This review gives comprehensive insight on ELISA currently available for typing, antigenic analysis, vaccination status differentiation and surveillance vaccine purity and content at all stages of manufacture in FMDV. Besides, some viewpoint about the recent advances and trends of ELISA reagent for FMD are described here.

Methods

More than 100 studies regarding ELISA method available for FMD diagnosis, antigenic analysis and monitor were thoroughly reviewed. We investigated previous sagacious results of these tests on their sensitivity, specificity.

Results

We found that in all ELISA formats for FMD, antibody-trapping and competitive ELISAs have high specificity and RT-PCR (oligoprobing) ELISA has extra sensitivity. A panel of monoclonal antibodies to different sites or monoclonal antibody in combination of antiserum is the most suitable combination of antibodies in ELISA for FMD. Even though from its beginning, 3ABC is proven to be best performance in many studies, no single NSP can differentiate infected from vaccinated animals with complete confidence. Meanwhile, recombinant antigens and peptide derived from FMDV NPs, and NSPs have been developed for use as an alternative to the inactivated virus antigen for security.

Conclusions

There is a need of target protein, which accurately determines the susceptible animal status based on the simple, fast and reliable routine laboratory test. A further alternative based on virus-like particle (VLP, also called empty capsids) in combination of high throughput antibody technique (Phage antibody library/antibody microarray) may be the powerful ELISA diagnostic reagents in future.

A Brief Review on Diagnosis of Foot-and-Mouth Disease of Livestock: Conventional to Molecular Tools

Foot-and-mouth disease (FMD) is one of the highly contagious diseases of domestic animals. Effective control of this disease needs sensitive, specific, and quick diagnostic tools at each tier of control strategy. In this paper we have outlined various diagnostic approaches from old to new generation in a nutshell. Presently FMD diagnosis is being carried out using techniques such as Virus Isolation (VI), Sandwich-ELISA (S-ELISA), Liquid-Phase Blocking ELISA (LPBE), Multiplex-PCR (m-PCR), and indirect ELISA (DIVA), and real time-PCR can be used for detection of antibody against nonstructural proteins. Nucleotide sequencing for serotyping, microarray as well as recombinant antigen-based detection, biosensor, phage display, and nucleic-acid-based diagnostic are on the way for rapid and specific detection of FMDV. Various pen side tests, namely, lateral flow, RT-LAMP, Immunostrip tests, and so forth. are also developed for detection of the virus in field condition.

Discriminating foot-and-mouth disease virus-infected and vaccinated animals by use of beta-galactosidase allosteric biosensors

Recombinant beta-galactosidases accommodating one or two different peptides from the foot-and-mouth disease virus (FMDV) nonstructural protein 3B per enzyme monomer showed a drastic enzymatic activity reduction, which mainly affected proteins with double insertions. Recombinant beta-galactosidases were enzymatically reactivated by 3B-specific murine monoclonal and rabbit polyclonal antibodies. Interestingly, these recombinant beta-galactosidases, particularly those including one copy of each of the two 3B sequences, were efficiently reactivated by sera from infected pigs. We found reaction conditions that allowed differentiation between sera of FMDV-infected pigs, cattle, and sheep and those of naïve and conventionally vaccinated animals. These FMDV infection-specific biosensors can provide an effective and versatile alternative for the serological distinction of FMDV-infected animals.

Anti-3AB antibodies in the Chinese yellow cattle infected by the O/Taiwan/99 foot-and-mouth disease virus

The O/Taiwan/99 foot-and-mouth disease virus (FMDV), a South Asian topotype of serotype O, was introduced into Taiwan in 1999. The Chinese yellow cattle infected by the virus did not develop clinical lesions under experimental and field conditions. A blocking enzyme-linked immunosorbent assay (ELISA) kit with the 3AB antigen, a polypeptide of FMDV non-structural (NS) proteins, was used to evaluate the development and duration of anti-3AB antibodies, proving active viral replication, in the Chinese yellow cattle. The specificity of the assay was 99%, as was established with negative sera from regularly vaccinated and from naïve cattle. The sensitivity tested with sera from naturally infected animals was approximately 64% and it was lower than that obtained by serum neutralization (SN) test. Under experimental infection, the Chinese yellow cattle developed lower anti-3AB antibodies than that developed in other species. Duration of anti-3AB antibodies was traced in two herds of naturally infected animals, indicating that anti-3AB antibodies persisted for approximately 6 months after outbreaks. On the basis of this study, we propose that the Chinese yellow cattle may have natural resistance, which limits viral replication and reduces the development of anti-3AB antibodies.

Baculovirus expressed 2C of foot-and-mouth disease virus has the potential for differentiating convalescent from vaccinated animals

Determining whether animals have been infected with foot-and-mouth disease virus or vaccinated is important because infected animals frequently become carriers of the virus, shed it intermittently and thus may be the source of new outbreaks of the disease. We had shown previously that the sera of convalescent animals contain antibodies to 2C, a highly conserved non-structural protein, whereas the sera of vaccinated animals do not. This is explained by observation that 2C is retained on the membranes of cells used for growing the virus for vaccine production. In contrast, the non-structural protein 3D, which is released into the medium, is not removed by centrifugation or filtration during vaccine production and therefore stimulates an immune response in both vaccinated and convalescent cattle. In this study we produced 2C and 3D in insect cells infected with recombinant baculoviruses. As demonstrated by serology and electron microscopy, 2C is also retained on the membranes of the insect cells. Both expressed proteins react with sera of convalescent animals, indicating that they are conformationally similar, but the 2C does not react with sera from vaccinated animals. The baculovirus expressed 2C appears to be a suitable antigen for the development of a reliable diagnostic test.

Detection of antibodies against foot-and-mouth disease virus using a liquid-phase blocking sandwich ELISA (LPBE) with a bioengineered 3D protein

A liquid-phase blocking sandwich enzyme-linked immunosorbent assay (ELISA-3D) was developed to detect specific antibodies to the 3D protein in sera from foot-and-mouth disease (FMD) virus (FMDV)-infected animals. The assay uses a nonstructural 3D recombinant protein and two polyclonal antisera, one for capture (bovine) and the other for detector (guinea pig). The specificity of the assay was demonstrated by negative results with 101 sera of cattle from the FMD-free zone in Argentina and with bovine and porcine sera raised against various RNA and DNA viruses. The ELISA-3D was able to detect antibodies in cattle after natural or experimental infection with FMDV of A, O, or C types as early as 5 days postinfection and at later stages in persistently infected animals. Comparison of the results with those obtained with the routinely used agar gel immunodiffusion test and a previously described ELISA, both employing a partially purified virus-infection-associated antigen, shows that the ELISA-3D is highly sensitive and specific and gives reproducible results. Its use as a tool for monitoring viral activity and for certification of FMDV-free animals is recommended.

Identification of native foot-and-mouth disease virus non-structural protein 2C as a serological indicator to differentiate infected from vaccinated livestock

Cattle and pigs which have been vaccinated against foot-and-mouth disease can be distinguished from convalescent animals by radio-immunoprecipitation and sodium dodecyl sulphate polyacrylamide gel electrophoresis of the virus-induced proteins reacting with the respective sera. Baby hamster kidney cells infected with foot-and-mouth disease virus (FMDV) (serotype A24) were labelled with 35S-methionine and the virus-induced proteins were precipitated with sera from vaccinated and subsequently challenged animals, convalescent animals retained for over 300 days, animals vaccinated or infected with viruses belonging to all serotypes of FMDV, and animals infected with encephalomyocarditis (EMC) or porcine or bovine enteroviruses. In addition to the structural proteins of the virus, the non-structural proteins 2C, 3ABC, 3C, 3CD and 3D were precipitated by convalescent sera, but only 3D was precipitated by serum from vaccinated animals. Proteins L, 2C and 3C were precipitated only after challenge with a heterotypic virus (serotype O1 Tunisia), indicating that virus replication of the challenge virus had taken place. No precipitation was detected with sera from EMC or enterovirus-infected animals. The results indicate that protein 2C, and to a lesser extent the polypeptide 3ABC, could be used to differentiate potential carrier convalescent animals from vaccinated livestock.

Immunogenicity of non-structural proteins of foot-and-mouth disease virus: differences between infected and vaccinated swine

Non-structural as well as VP1 recombinant proteins of foot-and-mouth disease virus (FMDV) produced in E. coli, have been used to study the specific antibody response of infected or vaccinated swine. An analysis of sera from infected pigs, using a direct ELISA, showed that polypeptide 3ABC (spanning non-structural proteins 3A, 3B and 3C) was the most antigenic among the recombinant proteins studied and allowed specific detection of FMDV infected swine from the second week after the infection. The sensitivity of this assay was comparable to that obtained when the whole FMDV was used as ELISA antigen. Conversely, use of polypeptide 3ABC did not allow detection of significant levels of antibodies in sera from vaccinated animals. This differential pattern of ELISA reactivities offers a promising approach for the distinction of infected from vaccinated pigs. In addition, a highly specific and sensitive method of diagnosis for FMDV replication was achieved using an immunoblotting assay which detected antibodies against the 3ABC polypeptide.

Expression of the aphthovirus RNA polymerase gene in Escherichia coli and its use together with other bioengineered nonstructural antigens in detection of late persistent infections

A plasmid has been constructed containing the DNA sequences that direct the expression of the aphthovirus RNA-dependent RNA polymerase (virus infection-associated antigen, VIAA) in its native form. The aphthovirus polypeptide was designed to contain only a single additional amino acid, the N-terminal methionine. The recombinant protein has been purified and used in enzyme-linked immunoelectrotransfer blots to detect aphthovirus-specific antibodies in the sera of persistently infected animals. Furthermore, studies were carried out to test the hypothesis that antibodies against other nonstructural antigens appear in the sera of these animals. It was established that antibodies against polypeptides 3A and 3B can serve as complementary markers for late aphthovirus-carrier state detection. The considerable potential of this approach to detect aphthovirus-specific antibodies, when the isolation of infectious virus is not possible, was demonstrated. Negative results were obtained in animals from virus-free areas and in vaccinated cattle. This assay has the added advantage that no infectious or noninfectious virus is involved during antigen production.

Rapid and sensitive detection of foot-and-mouth disease virus in tissues by enzymatic RNA amplification of the polymerase gene

Direct detection of foot-and-mouth disease (FMD) virus from infected bovine and porcine tissue was investigated using a modified polymerase chain reaction (PCR) technique. A high degree of conservation was found in the genomic region coding for the viral RNA polymerase among the seven FMD viral (FMDV) serotypes. An oligomeric primer pair and probe were constructed from consensus sequence data within this area. First strand cDNA was synthesized using random hexamers and Moloney MuLV reverse transcriptase. The oligomeric primers used for PCR of the random primed cDNA yielded a 454-base-pair target amplification product. The PCR product was sized by agarose gel electrophoresis and hybridized strongly with the consensus sequence oligomeric probe. The PCR product was further examined by digestion with NcoI, confirming the predicted internal restriction enzyme site. All seven serotypes of FMDV RNA were amplified in a few hours and the PCR product tested positive. The sensitivity of the enzymatic amplification for detection of FMDV was 10 TCID50 by gel electrophoresis and less than 1 TCID50 when combined with hybridization to a labeled probe. The technique was specific, as determined by examination of at least 12 other viruses, including enteroviruses and other agents of vesicular disease. In vitro enzymatic amplification of cDNA from FMDV RNA using the modified PCR technique is highly specific, rapid and at least as sensitive as presently used procedures for FMDV laboratory diagnosis.

Detection of foot-and-mouth disease virus infection-associated antigen antibodies: comparison of the enzyme-linked immunosorbent assay and agar gel immunodiffusion tests

A liquid-phase enzyme-linked immunosorbent assay (ELISA) was compared with the standard agar gel immunodiffusion test (AGID) to identify and quantify antibodies against foot-and-mouth disease (FMD) virus infection-associated (VIA) antigen. A total of 3181 cattle sera were tested. Of these sera, 1885 were from cattle which had not been exposed to FMD. A total of 1296 sera were either from cattle which were experimentally exposed to FMD virus or from cattle involved in field outbreaks. The results indicate that the ELISA has the same specificity as the AGID test, but is more efficient in detecting cattle exposed to FMD virus. The ELISA technique will probably prove to be a more satisfactory test in support of the prevention, control and eradication programs for the disease.