Protective immune response in mice vaccinated with a recombinant adenovirus containing capsid precursor polypeptide P1, nonstructural protein 2A and 3C protease genes (P12A3C) of encephalomyocarditis virus

Structures and Corresponding Functions of Five Types of Picornaviral 2A Proteins

Among the few non-structural proteins encoded by the picornaviral genome, the 2A protein is particularly special, irrespective of structure or function. During the evolution of the Picornaviridae family, the 2A protein has been highly non-conserved. We believe that the 2A protein in this family can be classified into at least five distinct types according to previous studies. These five types are (A) chymotrypsin-like 2A, (B) Parechovirus-like 2A, (C) hepatitis-A-virus-like 2A, (D) Aphthovirus-like 2A, and (E) 2A sequence of the genus Cardiovirus. We carried out a phylogenetic analysis and found that there was almost no homology between each type. Subsequently, we aligned the sequences within each type and found that the functional motifs in each type are highly conserved. These different motifs perform different functions. Therefore, in this review, we introduce the structures and functions of these five types of 2As separately. Based on the structures and functions, we provide suggestions to combat picornaviruses. The complexity and diversity of the 2A protein has caused great difficulties in functional and antiviral research. In this review, researchers can find useful information on the 2A protein and thus conduct improved antiviral research.

Inactivation of non-enveloped virus by 1,5 iodonaphthyl azide

Background

A photoactive hydrophobic agent 1,5-iodonaphthyl-azide (INA), has been previously shown to completely inactivate the enveloped viruses. INA sequesters into the lipid bilayer of the virus envelope and upon UV-irradiation bind to the hydrophobic domains of the envelope glycoproteins. In our earlier study, we have shown that the Venezuelan equine encephalitis virus (VEEV) genomic RNA was also inactivated during the inactivation of the virus with INA.

Findings

In the present study, we evaluated if the RNA inactivation property of INA can be used to inactivate non-enveloped RNA viruses. Encephalomyocarditis virus (EMCV) was used as a model non-enveloped virus. Treatment with INA followed by UV-irradiation resulted in complete inactivation of EMCV. RNA isolated from INA-inactivated EMCV was non-infectious and INA was found to be associated with the viral RNA genome. INA-inactivated EMCV induced robust total antibody response. However binding capacity of INA-inactivated EMCV to neutralizing antibody was inhibited.

Conclusion

This is the first study to show that INA can completely inactivate non-enveloped virus. Our results suggest that the amino acid composition of the neutralizing epitope may interfere with the protective antibody response generated by the INA-inactivated non-enveloped virus.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1006-2) contains supplementary material, which is available to authorized users.

A virus-like particle vaccine platform elicits heightened and hastened local lung mucosal antibody production after a single dose

We show that a model antigen, ovalbumin (OVA), can be chemically conjugated to the exterior of a small heat shock protein (sHsp) cage that has structural similarities to virus-like particles (VLPs). OVA–sHsp conjugation efficiency was dependent upon the stoichiometry and the length of the small molecule linker utilized, and the attachment position on the sHsp cage. When conjugated OVA–sHsp was delivered intranasally to naïve mice, the resulting immune response to OVA was accelerated and intensified, and OVA-specific IgG1 responses were apparent within 5 days after a single immunizing dose, illustrating its utility for vaccine development. If animals were pretreated with a disparate VLP, P22 (a non-replicative bacteriophage capsid), before OVA–sHsp conjugate immunization, OVA-specific IgG1 responses were apparent already by 4 days after a single immunizing dose of conjugate in OVA-naïve mice. Additionally, the mice pretreated with P22 produced high titer mucosal IgA, and isotype-switched OVA-specific serum IgG. Similarly, sHsp pretreatment enhanced the accumulation of lung germinal center B cells, T follicular helper cells, and increased polymeric Ig receptor expression, priming the lungs for subsequent IgG and IgA responses to influenza virus challenge. Thus, sHsp nanoparticles elicited quick and intense antibody responses and these accelerated responses could similarly be induced to antigen chemically conjugated to the sHsp. Pretreatment of mice with P22 further accelerated the onset of the antibody response to OVA–sHsp, demonstrating the utility of conjugating antigens to VLPs for pre-, or possibly post-exposure prophylaxis of lung, all without the need for adjuvant.

Recombinant pseudorabies virus expressing P12A and 3C of FMDV can partially protect piglets against FMDV challenge

One of the crucial factors for evaluation of an effective genetically engineered vaccine is whether susceptible animals are protected from virus challenge after vaccination. In this study, a recombinant pseudorabies virus (PRV-P12A3C) that expressed capsid precursor polypeptide P12A and nonstructural protein 3C of foot-and-mouth disease virus (FMDV) was used as a vaccine. The expression of P12A3C and its immunogenicity and protective efficacy against FMDV challenge were measured. Humoral and cellular immune responses were evaluated after each immunization. Subsequently, each piglet was challenged with 1000 ID(50) (50% infection dose) FMDV serotype O, named OR/80, which is used to produce vaccine in China. PRV-P12A3C induced a high level of neutralizing antibody and FMDV-specific lymphocytes. Inactivated vaccine provided 100% protection, and the vector strain (TK(-)/gE(-)/gI(-)) showed no protection. PRV-P12A3C induced 60% protection, compared with piglets that were vaccinated with TK(-)/gE(-)/gI(-). The severity of clinical signs for the remaining two piglets was lighter and the appearance of vesicles was delayed.

Immunogenicity and safety of virus-like particle of the porcine encephalomyocarditis virus in pig

Background

In this study, porcine encephalomyocarditis virus (EMCV) virus-like particles (VLPs) were generated using a baculovirus expression system and were tested for immunogenicity and protective efficacy in vivo.

Results

VLPs were successfully generated from Sf9 cells infected with recombinant baculovirus and were confirmed to be approximately 30-40 nm by transmission electron microscopy (TEM). Immunization of mice with 0.5 μg crude protein containing the VLPs resulted in significant protection from EMCV infection (90%). In swine, increased neutralizing antibody titers were observed following twice immunization with 2.0 μg crude protein containing VLPs. In addition, high levels of neutralizing antibodies (from 64 to 512 fold) were maintained during a test period following the second immunization. No severe injection site reactions were observed after immunization and all swine were healthy during the immunization period

Conclusion

Recombinant EMCV VLPs could represent a new vaccine candidate to protect against EMCV infection in pig farms.

Immune responses and expression of the virus-like particle antigen of the porcine encephalomyocarditis virus

Virus-like particles (VLPs) are particles that consist of viral capsid proteins and are structurally similar to authentic virus. To express VLPs of the porcine encephalomyocarditis virus (EMCV) and investigate their efficacy and immuno response in vivo, a plasmid (P12A3C-pCI) containing the P12A and 3C genes of the EMCV-K3 viral strain was constructed. The VLPs of EMCV-K3 were successfully assembled in 293FT cells on 3 days after transfection with P12A3C-pCI and were identified as particles of about 30-40 nm using transmission electron microscopy (TEM). In an in vivo experiment, the murine cytokines induced by VLPs of naked DNA vaccine showed that the Th1 indicators IL-2, TNF-alpha and GM-CSF, and the Th2 indicators IL-4 and IL-10 were increased. The immunization of mice with the P12A3C-pCI plasmid induced high levels of neutralizing antibody from 128- to 256-fold and led to a significant protection ratio (90%) after challenge with EMCV-K3 (wild-type strain). These VLPs may represent a novel vaccine strategy for the control of EMCV infection on pig farms.