Identification of three novel linear B-cell epitopes on the VP5 protein of BTV16

Development of a monoclonal antibody specifically recognizing a linear epitope on the capsid protein of the emerging Group III Getah virus

Getah virus (GETV) is an emerging mosquito-borne alphavirus that can infect horses, pigs and other animals. Given the public health threat posed by GETV, research on its pathogenesis, diagnosis and prevention is urgently needed. In the current study, prokaryotic expression systems were used to express the capsid protein of GETV. This protein was then used to immunize BALB/c mice in order to generate monoclonal antibodies (mAbs). Subsequently, hybridoma cells secreting a mAb (2B11-4) against the capsid protein were obtained using the hybridoma technique. A B cell linear epitope, 18-PAYRPWR-24, located at the capsid protein's N-terminal region was identified using western blotting analysis with the produced mAb, 2B11-4. Sequence alignment indicated that this epitope was highly conserved in group III (GIII) strains of GETV, but varied among the other genotypes. Western blotting showed that mAb 2B11-4 could discriminate Group III GETVs from other genotypes. This study describes the preparation of a mAb against the GETV capsid protein and the identification of the specific localization of B-cell epitopes, and will contribute towards a better understanding of the biological importance of the GETV capsid protein. It will also pave the way for developing immunological detection methods and genotype diagnosis for GETVs.

Identification of novel B-cell epitopes on the capsid protein of type 1 porcine astrovirus, using monoclonal antibodies

Porcine astrovirus (PAstV) is prevalent in pigs worldwide and could cause clinical symptoms such as diarrhea and encephalitis. The capsid protein (Cap) of PAstV plays a determinant role for virus immunological characteristics. In this study, the major antigenic regions of PAstV1 Cap were expressed through prokaryotic expression systems and immunized to BALB/c mice. Finally, two anti-Cap monoclonal antibodies (named mAb F4-4 and D3F10) were screened by indirect immune-fluorescence assay (IFA). A series of truncated GST-fused or artificially synthesized peptides were used to detect their reactivity with the mAbs and PAstV positive serum. Two novel B cell epitopes (120-GNNTFG-125, 485-RISDPTWFSA-494) were identified by using these two mAbs. Moreover, sequence alignment result showed that epitope 120-GNNTFG-125 was highly conserved in type 1 PAstV capsid protein. Cross-reactivity analysis further confirmed the genotype-specificity of mAb F4-4. The results of this study demonstrated to be the first description of monoclonal antibody preparation and B-cell epitope mapping on PAstV capsid protein, which may provide new information on the biological significance of PAstV capsid protein and lay a foundation for the development of PAstV immunological tests and genotype diagnostic methods.

Analysis of Conserved, Computationally Predicted Epitope Regions for VP5 and VP7 Across three Orbiviruses

Orbiviruses are double-stranded RNA viruses that have profound economic and veterinary significance, 3 of the most important being African horse sickness virus (AHSV), bluetongue virus (BTV), and epizootic hemorrhagic disease virus (EHDV). Currently, vaccination and vector control are used as preventative measures; however, there are several problems with the current vaccines. Comparing viral amino acid sequences, we obtained an AHSV-BTV-EHDV consensus sequence for VP5 (viral protein 5) and for VP7 (viral protein 7) and generated homology models for these proteins. The structures and sequences were analyzed for amino acid sequence conservation, entropy, surface accessibility, and epitope propensity, to computationally determine whether consensus sequences still possess potential epitope regions. In total, 5 potential linear epitope regions on VP5 and 11 on VP7, as well as potential discontinuous B-cell epitopes, were identified and mapped onto the homology models created. Regions identified for VP5 and VP7 could be important in vaccine design against orbiviruses.

Identification of four novel group-specific bluetongue virus NS3 protein B-cell epitopes

BACKGROUND

The non-structural protein 3 (NS3) of bluetongue virus (BTV) is the second smaller non-structural protein produced in host cells, playing an important role in BTV trafficking and release.

RESULTS

In this study, we generated five BTV NS3-reactive monoclonal antibodies (mAbs), named 3D8, 2G9, 1B5, 4H8, and 2B12. A panel of overlapping NS3-derived peptides representing the entirety of the BTV15 NS3 protein was screened to identify linear peptide epitopes recognized by each mAb. Based on the initial screen, a series of progressively truncated peptides were produced to identify the minimal linear peptide sequence required to maintain mAb binding. We found that mAb 3D8 reacted with the motif (36)PPRYA(40), 2G9 reacted with the motif (82)AEAFRDDVRLRQIK(95), 1B5 reacted with the motif (205)YNDAVRMSF(213), 2B12 and 4H8 reacted with the motif (204)SYNDAVRMSF(213). Sequence alignments demonstrated that these linear epitopes are highly conserved among all BTV serotypes, consistent with the observation that each mAb was able to recognize cells infected with BTV1-24 serotypes tested and each identified B cell epitope was able to be recognized by BTV-infect sheep serum.

CONCLUSION

This collection of mAbs along with defined linear epitopes may provide useful reagents for investigations of NS3 protein function and the development of BTV group-specific diagnostics.

Analysis of murine B-cell epitopes on bluetongue virus 12 nonstructural protein 1

The bluetongue virus (BTV) NS1 protein is one of the major proteins synthesized during BTV infection and is responsible for the generation of virus-specific tubules. Although some functional and structural studies on the BTV NS1 protein have been reported, there have been no reports describing the linear B-cell epitopes recognized by humoral immune responses published to date. In this study, 25 BTV12 NS1-reactive monoclonal antibodies (MAbs) and polyclonal antisera (polyclonal antibodies, PAbs) were generated and analyzed. We identified 14 linear NS1 epitopes recognized by the PAbs and MAbs using NS1-derived peptides in an enzyme-linked immunosorbent assay. Moreover, we predicted 23 linear B-cell epitopes using the ABCpred online server which employs an artificial neural network. Analysis of the predicted and identified epitopes of NS1 demonstrated the feasibility of B-cell epitope prediction. Sequence alignments indicated that the epitopes recognized by MAbs are highly conserved among BTV serotypes, but not among the other members of the genus Orbivirus, such as the African horse sickness virus (AHSV), epizootic hemorrhagic disease virus (EHDV), and Chuzan disease virus (CV). Importantly, we identified specific MAbs that recognized all BTV serotypes tested as well as MAbs that recognized only BTV12, suggesting that these NS1-specific MAbs could serve as a basis for BTV diagnostic approaches. The generation and identification of NS1 protein epitopes will provide the foundation for further studies about the function and structure of NS1 and novel epitope-based vaccines.

Purification, stability, and immunogenicity analyses of five bluetongue virus proteins for use in development of a subunit vaccine that allows differentiation of infected from vaccinated animals

Bluetongue virus (BTV) causes bluetongue disease, a vector-borne disease of ruminants. The recent northerly spread of BTV serotype 8 in Europe resulted in outbreaks characterized by clinical signs in cattle, including unusual teratogenic effects. Vaccination has been shown to be crucial for controlling the spread of vector-borne diseases such as BTV. With the aim of developing a novel subunit vaccine targeting BTV-8 that allows differentiation of infected from vaccinated animals, five His-tagged recombinant proteins, VP2 and VP5 of BTV-8 and NS1, NS2, and NS3 of BTV-2, were expressed in baculovirus or Escherichia coli expression systems for further study. Optimized purification protocols were determined for VP2, NS1, NS2, and NS3, which remained stable for detection for at least 560 to 610 days of storage at +4°C or -80°C, and Western blotting using sera from vaccinated or experimentally infected cattle indicated that VP2 and NS2 were recognized by BTV-specific antibodies. To characterize murine immune responses to the four proteins, mice were subcutaneously immunized twice at a 4-week interval with one of three protein combinations plus immunostimulating complex ISCOM-Matrix adjuvant or with ISCOM-Matrix alone (n = 6 per group). Significantly higher serum IgG antibody titers specific for VP2 and NS2 were detected in immunized mice than were detected in controls. VP2, NS1, and NS2 but not NS3 induced specific lymphocyte proliferative responses upon restimulation of spleen cells from immunized mice. The data suggest that these recombinant purified proteins, VP2, NS1, and NS2, could be an important part of a novel vaccine design against BTV-8.