Comparison of immune responses induced by porcine parvovirus virus-like particles and inactivated vaccine.
Laboratory-prepared inactivated porcine parvovirus (PPV) vaccines and VP2 virus-like particles (VLPs) were utilized to immunize gilts. PPV BQ strain and SP2/0 cells were used. Hemagglutination-inhibiting (HI) antibody titers were measured in the immunized gilts and the differences in cytokine production of interferon gamma (IFN-γ, IL-2 and IL-4) were compared. CD4+ and CD8+ T cells proliferation were compared by flow cytometry. The variation between the immune response level induced by inactivated PPV vaccine and VP2 VLPs were determined. The results showed that all vaccinated gilts had HI antibody titers reaching 1:256 for at least one month post immunization and the peak level of antibody could be sustained for one month; further, PPV antibodies could be detected in the second week post immunization with VP2 VLPs. We also found that the level of cytokines (IFN-γ, IL-2 and IL-4) were all increased post immunization and continued to rise after the booster immunization; the level of increase in IFN-γ and IL-2 were significantly higher than IL-4. The flow cytometry results showed that the numbers of the CD4+ and CD8+ T cells subsets were significantly higher in the groups immunized with inactivated PPV vaccine or VP2 VLPs than those of negative control group (p<0.01); additionally, the number of CD4+ cells in the gilts that received VP2 VLP immunization was significantly higher than the inactivated vaccine group (p<0.01). In summary, the inactivated PPV vaccine and PPV VP2 VLPs were both able to induce humoral and cellular immunity, but the VP2 VLPs lead to better cellular immune responses in gilts compared to those of the inactivated vaccine..