| Porcine parvovirus (PPV) is one of the main pathogens which can cause reproductive failurein sows. PPV infection is distributed worldwide, and has become endemic disease in manyplaces, causes severe economic losses to the pig industry. PPV belonging to Parvoviridaeparvovirus genus, is a single negative stranded DNA virus without envelope. Capsid proteinsinclude VP1, VP2and VP3, of the three proteins VP2is the main structural protein anddetermines tissue tropism of the virus, the virulence and hemagglutination activity and canstimulate body to produce neutralizing antibodies. VP2could self-assemble into virus likeparticles (VLPs) in baculovirus expression vector system (BEVS) and is the preferred protein insubunit vaccine research. To estimate the potency as subunit vaccine, VP2proteins wererespectively expressed using BEVS and pET expression system and used to compare thereactogenicity and immunogenicity.Electron microscopy was used to observe two kinds of VP2. VP2expressed in BEVS couldself-assemble into VLPs, and VP2expressed in pET expression system could not assemble intoVLPs. Western blot showed that both of these two proteins were able to react to PPV positiveserum. Hemagglutination (HA) showed that VP2expressed in BEVS could produce ahemagglutination activity with the hemagglutination titer of210, while VP2expressed in pETexpression system had no hemagglutination activity. Two kinds of VP2proteins were used asimmunoreagents to immunize guinea pigs. Guinea pigs were randomly distributed into sevengroups:Ⅰ group (inactivated vaccine1.5mL/guinea pig), Ⅱ group (inactivated vaccine0.5mL/guinea pig), Ⅲ group (VLPs300μg/guinea pig), Ⅳ group (VLPs100μg/guinea pig), Ⅴgroup (VP2300μg/guinea pig), Ⅵ group (VP2100μg/guinea pig) and Ⅶ group(non-immunized). Serums were taken once a week and tested by hemagglutination inhibition (HI)to measure the PPV antibody titer. The antibody levels of group Ⅲ and group Ⅳ were similar,and higher than that of group Ⅱ, but lower than that of group Ⅰ. The antibody levels of groupⅤ and groupⅥ were the lowest. Group Ⅰ, group Ⅲ and group Ⅴcould stimulate betterhumoral immune responses than group Ⅱ, group Ⅳ and group Ⅵ, respectively. After challenge,results of MTT lymphocyte proliferation test showed that immunoreagents all could inducecellular immune responses with different levels. Results of nanoPCR showed that only the guinea pigs organs of non-immunized group were detected to be PPV positive. In conclusion,VP2expressed in BEVS had better reactogenicity and immunogenicity, and was applicable fordevelopment of subunit vaccine. |
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