Abstract: To obtain subunit antigens with good immune effect, in this study, six potentially protective subunit proteins of G. parasuis were expressed in prokaryotic cells. After immunizing mice with proteins, challenge experiments were performed to screen antigen candidates with better immune protection effects, thus laying the foundation for developing a subunit vaccine of G. parasuis with cross-protection effects. Sixty-three BALB/c mice were randomly divided into 9 groups, including HPSNAG-1330, CyaY, HPSNAG-0978, HPSNAG-0140, AfuA, Fe³⁺ABC-tbp, inactivated G. parasuis, challenge group and blank group. The mice were immunized the second time with an interval of 14 days. Among them, the 6 subunit vaccine groups were immunized with 50 μg of each protein per mouse, and the inactivated vaccine group was immunized with 4×10⁹ CFU per mouse. After 14 days of the secondary immunization, the mice were challenged with a dose of 1.26×10⁹ CFU. At the same time, the antibody levels, lymphocyte proliferation, IL-2, IL-6, IL-10, IFN-γ and TNF-α were detected. After the challenge, the clinical symptoms and survival rate of the mice were observed and recorded, and the pathological variations of the lung and spleen were also observed. Mice in all immunized groups can produce antibodies against the corresponding proteins. The lymphocyte proliferation experiment showed that recombinant proteins, except for the rAfuA, stimulated lymphocyte proliferation significantly in the inactivated vaccine group (P<0.05). At the same time, there were no significant changes in the lymphocyte proliferation of the mice in the subunit vaccine group and the blank group when stimulated with the corresponding immune proteins. The survival rate (60%) of the CyaY and HPSNAG-1330 groups was higher than that of the inactivated vaccine group (40%), and which of the other groups was lower than that of the inactivated vaccine group. The above results proved that CyaY and HPSNAG-1330 proteins can induce effective immune protection responses in mice. At the same time, the lesions of the spleens and lungs of the mice in CyaY and the HPSNAG-1330 are relatively mild. So, the protective effect of these two proteins is better than that of inactivated vaccine. In this study, two subunit antigens with immune-protective properties were screened by mouse immunization experiments, which provided materials for subsequently combined immunization of multiple antigens using pig model experiments.

Key words: Glaesserella parasuis, recombinant subunit vaccine, evaluation of the immune effect