Abstract: Based on the N-terminal gene of LppA protein of Mycoplasma mycoides subsp. capri (Mmc) Guizhou strain, the eukaryotic recombinant expression plasmid pVAX1-LppA was constructed, and the immune effect was analyzed to provide new ideas for the prevention and control of mycoplasmal pneumonia of sheep and goats (MPSG). Mice were immunized with the constructed eukaryotic recombinant expression plasmid pVAX1-LppA (50, 100, 150 μg), pVAX1 empty vector, and PBS, respectively. The levels of antibodies and cytokines (IL-2, IFN-γ and IL-4) in sera of mice were detected by ELISA. The proliferation of splenic lymphocytes was detected by MTT assay and the ratio of CD4⁺, CD8⁺ T lymphocytes to total cells was detected by flow cytometry. The protective efficiency of mice was evaluated by the challenge test. The lungs of mice were collected for preparation of sections to observe the pathological changes. The results showed that compared with the empty vector pVAX1 and PBS control groups, the levels of antibodies and cytokines (IL-2, IFN-γ, IL-4) in mice in the recombinant plasmid pVAX1-LppA group were significantly increased, the proliferation ability of spleen cells was stronger, and the proportion of CD4⁺ and CD8⁺ T lymphocytes in total cells increased significantly. The recombinant plasmid pVAX1-LppA had a certain ability to protect mice from Mmc challenge. The lung pathological damage was significantly reduced, and the number of cases was decreased post immunization. The maximum protection rate of 100 μg recombinant plasmid pVAX1-LppA was 80%. The results showed that LppA protein had good immunogenicity, and the recombinant plasmid pVAX1-LppA could activate strong humoral and cellular immune responses, which could be used as a candidate vaccine for MPSG.

Key words: Mycoplasma mycoides subsp.capri, LppA protein, DNA vaccine, immune effect