VP1 B-C and D-E loops of bovine enterovirus cluster B can effectively display foot-and-mouth disease virus type O-conserved neutralizing epitope

Experimental immunization of mice with a recombinant bovine enterovirus vaccine expressing BVDV E0 protein elicits a long-lasting serologic response

Background

Bovine viral diarrhea virus (BVDV) is a cause of substantial economic loss to the cattle industry worldwide, and there are currently no effective treatment or preventive measures. Bovine enterovirus (BEV) has a broad host range with low virulence and is a good candidate as a viral vaccine vector. In this study, we explored new insertion sites for the expression of exogenous genes in BEV, and developed a recombinant infectious cDNA clone for BEV BJ101 strain expressing BVDV E0 protein.

Methods

A recognition site for the viral proteinase 3C^pro was inserted in the GpBSK-BEV plasmid at the 2C/3A junction by overlapping PCR. Subsequently, the optimized full-length BVDV E0 gene was inserted to obtain the recombinant infectious plasmid GpBSK-BEV-E0. The rescued recombinant virus was obtained by transfection with linearized plasmid. Expression of BVDV E0 in the recombinant virus was confirmed by PCR, western blotting, and immunofluorescence analysis, and the genetic stability was tested in MDBK cells over 10 passages. We further tested the ability of the recombinant virus to induce an antibody response in mice infected with BVDV and immunized them with the recombinant virus and parental strain.

Results

The rescued recombinant virus rBEV-E0 was identified and confirmed by western blot and indirect immunofluorescence. The sequencing results showed that the recombinant virus remained stable for 10 passages without genetic changes. There was also no significant difference in growth dynamics and plaque morphology between the recombinant virus and parental virus. Mice infected with both recombinant and parental viruses produced antibodies against BEV VP1, while the recombinant virus also induced antibodies against BVDV E0.

Conclusion

A new insertion site in the BEV vector can be used for the prevention and control of both BEV and BVDV, providing a useful tool for future research on the development of viral vector vaccines.

Heterogeneous Nuclear Ribonucleoprotein L Negatively Regulates Foot-and-Mouth Disease Virus Replication through Inhibition of Viral RNA Synthesis by Interacting with the Internal Ribosome Entry Site in the 5' Untranslated Region

Upon infection, the highly structured 5' untranslated region (5' UTR) of picornavirus is involved in viral protein translation and RNA synthesis. As a critical element in the 5' UTR, the internal ribosome entry site (IRES) binds to various cellular proteins to function in the processes of picornavirus replication. Foot-and-mouth disease virus (FMDV) is an important member in the family Picornaviridae, and its 5' UTR contains a functional IRES element. In this study, the cellular heterogeneous nuclear ribonucleoprotein L (hnRNP L) was identified as an IRES-binding protein for FMDV by biotinylated RNA pulldown assays, mass spectrometry (MS) analysis, and determination of hnRNP L-IRES interaction regions. Further, we found that hnRNP L inhibited the growth of FMDV through binding to the viral IRES and that the inhibitory effect of hnRNP L on FMDV growth was not due to FMDV IRES-mediated translation, but to influence on viral RNA synthesis. Finally, hnRNP L was demonstrated to coimmunoprecipitate with RNA-dependent RNA polymerase (3D^pol) in an FMDV RNA-dependent manner in the infected cells. Thus, our results suggest that hnRNP L, as a critical IRES-binding protein, negatively regulates FMDV replication by inhibiting viral RNA synthesis, possibly by remaining in the replication complex.IMPORTANCE Picornaviruses, as a large family of human and animal pathogens, cause a bewildering array of disease syndromes. Many host factors are implicated in the pathogenesis of these viruses, and some proteins interact with the viral IRES elements to affect function. Here, we report for the first time that cellular hnRNP L specifically interacts with the IRES of the picornavirus FMDV and negatively regulates FMDV replication through inhibiting viral RNA synthesis. Further, our results showed that hnRNP L coimmunoprecipitates with FMDV 3D^pol in a viral RNA-dependent manner, suggesting that it may remain in the replication complex to function. The data presented here would facilitate further understanding of virus-host interactions and the pathogenesis of picornavirus infections.

Identification of three linear B cell epitopes using monoclonal antibodies against bovine enterovirus VP2 protein

Bovine enterovirus (BEV) VP2 protein is a structural protein that plays an important role in inducing protective immunity in the host. The function of VP2 has been characterized, but there is little information on its B cell epitopes. Three monoclonal antibodies (mAbs) directed against BEV VP2 were generated and characterized from mice immunized with the recombinant VP2 protein. Three minimal linear epitopes ¹⁵²FQEAFWLEDG¹⁶¹, ¹⁶⁸LIYPHQ¹⁷³, and ⁴⁶DATSVD⁵¹ reactive to the three mAbs were identified using western blotting analysis. Three-dimensional model of the BEV-E virion and the VP2 monomer showed that epitope ¹⁵²FQEAFWLEDG¹⁶¹ is exposed on surface of the virion and epitopes ⁴⁶DATSVD⁵¹ and ¹⁶⁸LIYPHQ¹⁷³ are located inside the virion. Alignment of the amino acid sequences corresponding to the regions containing the three minimal linear epitopes in the VP2 proteins and their cross-reactivity with the three mAbs showed that epitope ¹⁶⁸LIYPHQ¹⁷³ is completely conserved in all BEV strains. Epitope ⁴⁶DATSVD⁵¹ is highly conserved among BEV-E strains and partly conserved among BEV-F strains. However, epitope ¹⁵²FQEAFWLEDG¹⁶¹ is not conserved among BEV-F strains. Using the mAbs of 3H4 and 1E10, we found that VP2 localized in the cytoplasm during viral replication and could be used to monitor the viral antigen in infected tissues using immunohistochemistry. A preliminary 3H4-epitope-based indirect ELISA allowed us to detect anti-BEV-strain-HY12 antibodies in mice. This study indicates that the three mAbs could be useful tools for investigating the structure and function of the viral VP2 protein and the development of serological diagnostic techniques for BEV infection.

Potent neutralization activity against type O foot-and-mouth disease virus elicited by a conserved type O neutralizing epitope displayed on bovine parvovirus virus-like particles

In this study, ten sites on the N terminus and different surface variable regions (VRs) of the bovine parvovirus (BPV) VP2 capsid protein were selected according to an alignment of its sequence with that of the BPV-1 strain HADEN for insertion of the type O foot-and-mouth disease virus (FMDV) conserved neutralizing epitope 8E8. Ten epitope-chimeric BPV VP2 capsid proteins carrying the 8E8 epitope were expressed in Sf9 cells, and electron micrographs demonstrated that these fusion proteins self-assembled into virus-like particles (VLPs) with properties similar to those of natural BPV virions. Immunofluorescence assay (IFA) and Western blot analysis demonstrated that each of the ten epitope-chimeric VLPs reacted with both anti-BPV serum and anti-type O FMDV mAb 8E8. These results indicated that insertions of the 8E8 epitope at these sites on the BPV VP2 protein did not interfere with the immunoreactivity of VP2 or VLP formation, and that the exogenous epitope 8E8 was correctly expressed in BPV VLPs. In addition, anti-BPV IgG antibodies were induced in mice by intramuscular inoculation with each of the ten chimeric VLPs, indicating that the immunogenicity of the chimeric VLPs was not disrupted. Importantly, potent anti-FMDV viral neutralizing (VN) antibodies, which exhibited the highest titre of 1 : 176, were induced by two chimeric VLPs, rBPV-VLP-8E8(391) and rBPV-VLP-8E8(395), in which the 8E8 epitope was inserted into positions 391/392 and 395/396, respectively, in the VR VIII of BPV VP2. Our results demonstrated that the 391/392 and 395/396 positions in the VR VIII of the BPV VP2 protein can effectively display a foreign epitope, making this an attractive approach for the design of nanoparticle-vectored and epitope-based vaccines.

Construction and evaluation of HA-epitope-tag introduction onto the VP1 structural protein of a novel HY12 enterovirus

In this study, we investigated the feasibility of using enterovirus HY12 as a vector to express an exogenous hemagglutinin (HA)-epitope tag onto the HY12-encoded VP1 protein via a reverse genetic system. Characteristics of recombinant (r) HY12-VP1-HA marker virus were determined by immunoperoxidase monolayer assay, western blot, electron microscopy, and serum-neutralisation assay. Sequence analysis demonstrated that the marker virus stably maintained the HA-epitope-tag in MDBK cells, with no changes in viral morphological features observed relative to those of the parental rHY12 virus. Furthermore, detection by immunofluorescence assay revealed the expression of HA-epitope tag and VP2 protein, which distinguish the marker virus from parental rHY12 virus. In addition, neonatal mice infected with the recombinant marker virus showed various microscopic pathological lesions and generated anti-HY12 virus and -HA-epitope-tag antibodies. These results indicated that the recombinant marker virus represented a valuable platform to promote the development of novel genetic vaccines.

Identification of a conformational neutralizing epitope on the VP1 protein of type A foot-and-mouth disease virus

Foot-and-mouth disease (FMD) caused by foot-and-mouth disease virus (FMDV), is a highly contagious infectious disease that affects domestic and wild cloven-hoofed animals worldwide. In recent years, outbreaks of serotype A FMD have occurred in many countries. High-affinity neutralizing antibodies against a conserved epitope could provide protective immunity against diverse subtypes of FMDV serotype A and protect against future pandemics. In this study, we generated a serotype A FMDV-specific potent neutralizing monoclonal antibody (MAb), 6C9, which recognizes a conformation-dependent epitope. MAb 6C9 potently neutralized FMDV A/XJBC/CHA/2010 with a 50% neutralization titer (NT₅₀) of 4096. Screening of a phage-displayed random 12-mer peptide library revealed that MAb 6C9 bound to phages displaying the consensus motif YxxPxGDLG, which is highly homologous to the ¹³⁵YxxPxxxxxGDLG¹⁴⁷ motif found in the serotype A FMDV virus-encoded structural protein VP1. To further verify the authentic epitope recognized by MAb 6C9, two FMDV A/XJBC/CHA/2010 mutant viruses, P138A and G144A, were generated using a reverse genetic system. Subsequent micro-neutralization assays and double-antibody sandwich (DAS) ELISA analyses revealed that the Pro¹³⁸ and Gly¹⁴⁴ residues of the conformational epitope that are recognized by 6C9 are important for MAb 6C9 binding. Importantly, the epitope ¹³⁵YxxPxxxxxGDLG¹⁴⁷ was highly conserved among different topotypes of serotype A FMDV strains in a sequence alignment analysis. Thus, the results of this study could have potential applications in the development of novel epitope-based vaccines and suitable a MAb-based diagnostic method for the detection of serotype A FMDV and the quantitation of antibodies against this serotype.

Identification of a conserved conformational epitope in the VP2 protein of foot-and-mouth disease virus

Foot-and-mouth disease (FMD), caused by foot-and-mouth disease virus (FMDV), is a highly contagious infectious disease that affects domestic and wild cloven-hoofed animals worldwide. VP2 is a structural protein of FMDV. In this study, a potent FMDV serotype-independent monoclonal antibody (MAb) 3D9 was generated. Screening of a phage-displayed random 12-peptide library revealed that MAb 3D9 bound to phages displaying a consensus motif GVYxxAYxW that is highly homologous to the ⁸⁹GVYxxxxxxxAYxxxxW¹⁰⁵ motif in the FMDV VP2 protein. Importantly, this conformational epitope was highly conserved among all seven serotypes of FMDV analyzed in sequence alignments. To further verify the authentic epitope recognized by MAb 3D9, a FMDV O/YS/CHA/05 mutant virus V90A was generated using a reverse genetics system. The results revealed that Val⁹⁰ was an important residue for MAb 3D9 binding within this conformational epitope. Thus, we finely mapped a conserved conformational epitope onto the FMDV VP2 protein. These results could be applied in the development of epitope-based vaccines and suitable MAb-based diagnostic methods for various FMDV serotype-independent tests.