Displaying epitope B and epitope 7 of porcine reproductive and respiratory syndrome virus on virus like particles of porcine circovirus type 2 provides partial protection to pigs.

The Cap of porcine circovirus type 2 (PCV2) can be assembled into virus like particles (VLPs) in vitro that have multiple loops located on the particle surface. This would make it a good vehicle for displaying exogenous proteins or epitopes. We derived two epitopes, epitope B (EpB, S37HIQLIYNL45) and epitope 7 (Ep7, Q196WGRL200) from Gp5 of the highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV). We replaced the core region of Loop CD (L75PPGGGSN82) and the carboxyl terminus (K222DPPL226) of PCV2 Cap, respectively, to construct a bi-epitope chimeric PCV2 Cap. Its immunogenicity and protective effects were evaluated as one PRRSV subunit vaccine. The chimeric PCV2 Cap was soluble, efficiently expressed in an Escherichia coli expression system, and could be self-assembled into chimeric virus like particles (cVLPs) with a diameter of 12-15 nm. Western blotting confirmed that the cVLPs could be specifically recognized by anti-PCV2, anti-EpB and anti-Ep7 antibodies. The cVLPs vaccine could alleviate the clinical symptoms and reduce the viral loads after HP-PRRSV challenge in 100-120 days old pigs. These data suggest that the cVLPs vaccine could provide pigs with partial protection against homologous PRRSV strains, and it provides a new design for additional PRRSV subunit vaccines.

Establishment of a Rep' protein antibody detection method to distinguish natural infection with PCV2 from subunit vaccine immunization.

Introduction. PCV2 is a DNA virus that exists widely in pigs and has caused great economic losses to the pig industry worldwide. In the existing commercial PCV2 enzyme-linked immunosorbent assay (ELISA) kits both natural infection with PCV2 and vaccine immunization produce results that are positive for PCV2 Cap antibodies and therefore they cannot diagnose PCV2 infection in immunized pig farms.Aim. To establish a PCV2 non-structural protein antibody detection method that distinguishes between antibodies resulting from natural prior exposure (infection) and those induced by subunit vaccine immunization.Methodology. Based on the non-structural Rep' protein, we established an indirect ELISA (iELISA) using sera from guinea pigs and piglets.Results. The results for iELISA for guinea pig serum showed that animals vaccinated with a whole-virus inactivated PCV2 vaccine had 100 % (10/10) Cap antibody positivity and 100 % (10/10) Rep' antibody positivity. Guinea pigs vaccinated with a recombinant subunit PCV2 vaccine had 100 % (10/10) Cap antibody positivity, while no (0/10) guinea pigs were Rep' antibody-positive. The combined detection results for the Rep' iELISA and a PCV2 Antibody Test kit (Commercial) showed that pigs vaccinated with a whole-virus inactivated PCV2 vaccine or PCV2 SD/2017 had 100 % (5/5) Cap antibody positivity and 100 % (5/5) Rep' antibody positivity. Pigs vaccinated with a recombinant subunit PCV2 vaccine had 100 % (5/5) Cap antibody positivity, while no (0/10) pigs were Rep' antibody-positive.Conclusion. This paper describes an effective iELISA method that can distinguish natural infection with PCV2 (Cap and Rep positive) or inoculation with a whole-virus inactivated vaccine (Cap and Rep positive) from subunit vaccine immunization (Cap-positive, Rep-negative). These comparative assays could be very useful in the control of PCV2 in pig herds.

Large-scale manufacture and use of recombinant VP2 vaccine against infectious bursal disease in chickens.

A new subunit vaccine against infectious bursal disease (IBD) was developed; the antigen used in the vaccine was expressed by a new engineering strain, E. coli BL21/pBV220-VP2. The study on the production and use of the vaccine was performed. The results showed that the recombinant VP2 was water-soluble and demonstrated natural antigen activity in vitro. The antibody induced by rVP2 subunit vaccine could protect chickens from challenges of IBDV strains, both BC 6/85 and JZ 3/02. The vaccine, in which the VP2 AGP titre is 1:4, would be enough to protect SPF chickens of 19-day-old, but seemed to be relatively lower to protect commercial Avian Broilers under 10-day-age. In field study, Avian Broilers were vaccinated with rVP2 subunit vaccine of 1:16 AGP titre at the age of 7 days. The protection rate was varied from 72% to 95% in different chicken farms. To study the method of serological evaluation, antibody respond to vaccination had been detected with three kinds of tests. The correct ratio of detection decreased in the order of VP2-based ELISA, AGP test, and virions-based ELISA, if the result of IBDV detection was used as standard of judging. Correlation coefficient between the OD values of VP2-based ELISA and the virions-based ELISA was 0.782. The results will make it possible for the vaccine to be produced commercially and used in poultry industry in large scale.