Virus-like particles of recombinant PCV2b carrying FMDV-VP1 epitopes induce both anti-PCV and anti-FMDV antibody responses.

Mixed infection of porcine circovirus type 2 (PCV2) and foot-and-mouth disease virus (FMDV) is devastating to swine populations. To develop an effective vaccine that can protect the pigs from the infection of PCV2 and FMDV, we used the neutralizing B cell epitope region (aa 135-160) of FMDV to replace the regions aa 123-151 and aa 169-194 of the PCV2b Cap protein to generate a recombinant protein designated as Capfb. The Capfb protein was expressed in Escherichia coli system and the purified Capfb protein assembled into virus-like particles (VLPs) through dialysis. The ability of the Capfb protein to induce effective immune response against FMDV and PCV2b was tested in mice and guinea pigs. The results showed that the Capfb-VLPs could elicit anti-PCV2b and anti-FMDV antibody response in mice and guinea pigs without inducing antibodies against decoy epitope. Moreover, the Capfb-VLPs could enhance the percentage and activation of B cells in lymph nodes when the mice were stimulated with inactivated FMDV or PCV2b. These data suggested that the Capfb-VLPs could be an efficacious candidate antigen for developing a novel PCV2b-FMDV bivalent vaccine.

A simple method of extracting Cap antigen of PCV2b from emulsified vaccines for testing its stability and antigenicity.

Oil-based emulsions are commonly used adjuvants for veterinary vaccines. After formulation, it is required to extract protein antigens from emulsified vaccines for testing their stability and antigenicity. To establish a simple method to extract the protein antigens, two emulsified vaccines, designated as Cap-206 and Cap-35, were prepared by formulating a 28-kDa capsid protein (Cap) of PCV2b with ISA 206, a water-in-oil-in-water emulsion, or ISA 35, an oil-in-water emulsion. We found that the freeze-thaw-centrifugation method with steps of freezing at -20 °C for 12 h, thawing at room temperature and centrifuging at 9000×g for 10 min could separate the aqueous phase from Cap-206, and a centrifugation method by centrifuging at 9000×g for 10 min could isolate the aqueous portion from Cap-35. The Cap proteins were recovered from the aqueous phase and could be evaluated for their stability and antigenicity by SDS-PAGE, Western blot and ELISA. The freeze-thaw-centrifugation or the centrifugation method could also be used to recover recombinant mycobacterial heat-shock protein 65, a larger protein with molecular weight of 57-kDa, from ISA 206 or ISA 35 emulsions. The methods could be used to recover protein antigens from oil-based emulsion formulated vaccines for monitoring their stability and antigenicity during vaccine manufacture and storage.

Replacing the decoy epitope of PCV2b capsid protein with a protective epitope enhances efficacy of PCV2b vaccine.

Microbial pathogens may evolve decoy epitopes to evade host immune responses. In recent years, a decoy epitope has been identified in the capsid protein (CP) of porcine circovirus type 2b (PCV2b) to divert the immune response away from protective epitopes in pigs. To avoid the decoy effect, we designed and produced a recombinant PCV2b CP (ΔCP) by replacing the decoy epitope with a neutralizing B cell epitope derived from CP and tested the ability of ΔCP to induce protective antibody responses in mice and pigs. As expected, the ΔCP, unlike inactivated PCV2b vaccines, recombinant PCV2b CP, and natural PCV2b infection, did not induce anti-decoy epitope antibodies. Although unable to form typical virus-like particles (VLPs), the ΔCP could increase the production of the anti-PCV2b antibodies among which no antibody against the decoy epitopes, and therefore induces improved protective immune responses in pigs challenged with PCV2b. These results provide an alternative strategy for development of recombinant subunit vaccines against PCV2b, and possibly other viruses, by replacing the decoy epitope with a protective epitope.

Impact of Fighting on Antibody Response to Hepatitis B Virus Vaccine in Mice.

Antibody responses to vaccines can be influenced by various behavioral and psychosocial factors. Few reports exist on the impact of fighting on antibody response to vaccines. This study unexpectedly found that fighting could significantly enhance antibody production in male mice immunized with hepatitis B virus (HBV) vaccines. To confirm the finding, a mouse-fighting model was established in which it was observed that only intense fighting, not mild fighting, enhanced the antibody response to HBV surface antigen in male mice, and that the frequency of fighting and active attacks during fighting showed no obvious relationship with the antibody levels in the male mice that experienced fighting. In addition, fighting can cause significant upregulation of CD80 in CD11c(+) cells in the spleen of male mice. These data suggest that fighting could influence the humoral immune response in individuals immunized with vaccines or infected with microbes.

Detection of the Assembly and Disassembly of PCV2b Virus-Like Particles Using Fluorescence Spectroscopy Analysis.

Monitoring the assembly and disassembly of virus-like particles (VLPs) is important in developing effective VLP-based vaccines. We tried to establish a simple and rapid method to evaluate the status of VLP assembly using fluorescence spectroscopic analysis (FSA) while developing a VLP-based vaccine against porcine circovirus type 2b (PCV2b). We synthesized the gene coding for PCV2b capsid protein (CP). The CP was expressed in Escherichia coli in a soluble form, dialyzed into three different buffers, and assembled into VLPs. The immunogenicity of the VLPs was evaluated by an enzyme-linked immunosorbent assay using the sera of mice immunized with inactivated PCV2b. The VLP assembly was detected using transmission electron microscopy and FSA. The assembled VLPs showed a distinct FSA curve with a peak at 320 nm. We found that the assembly status was related to the immunogenicity, fluorescence intensity, and morphology of the VLP. The FSA assay was able to monitor the various denatured statuses of PCV2b VLPs treated with ß-mercaptoethanol or ß-mercaptoethanol plus urea. We have demonstrated that FSA can be used to detect the assembly of PCV2b VLPs produced in E. coli. This provides a simple solution for monitoring VLP assembly during the production of VLP-based vaccines.

Influence of hydrophilic amino acids and GC-content on expression of recombinant proteins used in vaccines against foot-and-mouth disease virus in Escherichia coli.

Epitope-based protein expression in Escherichia coli can be improved by adjusting its amino acid composition and encoding genes. To that end, we analyzed 24 recombinant epitope proteins (rEPs) that carry multiple epitopes derived from VP1 protein of foot-and-mouth disease virus. High level expression of the rEPs was attributed to a high content of Arg, Asn, Asp and Thr, a low content of Gln, Pro and Lys, a high content of hydrophilic amino acids and a higher isoelectric point value resulting from abundant Arg. It is also attributed to the appropriate guanine and cytosine content in the encoding genes. The data provide a reference for adjusting the amino acid composition in designing epitope-based proteins used in vaccines and for adjusting the synonymous codons to improve their expressions in E. coli.