Evaluation of a DNA vaccine encoding Brucella BvrR in BALB/c mice

Brucellosis is an important neglected zoonotic disease, and the pathogens responsible are Brucellae. In order to evaluate the immunogenicity and protective efficacy of a DNA vaccine encoding Brucella BvrR, the recombinant plasmid pCDNA-BvrR was constructed by inserting the BvrR gene fragment into a pCDNA3.0 vector. The His(6)-tagged BvrR was purified with His-trap FF crude affinity chromatography and verified with an anti-histidine monoclonal antibody by western blot analysis. The specific immunoglobulin antigens and their isotypes were detected by indirect ELISA. The recombinant His(6)-BvrR protein was expressed and purified by affinity chromatography. The optical density 450 value of immunoglobulin G (IgG) in the pCDNA-BvrR group was significantly increased compared with the pCDNA3.0 vector or PBS groups (P<0.05), and the pCDNA3.0 vector and PBS groups exhibited no significant difference (P>0.05). BvrR induced specific antibodies with a dominance of IgG2a over IgG1 and the T cell-proliferative response, in addition to a typical T helper-1 (Th1)-dominated immune response in mice. The splenocytes from mice of the pCDNA-BvrR group demonstrated significant proliferative activity compared with the pCDNA3.0 vector group. The present results indicated that immunization with BvrR induced a specific Th1-type immune response in mice. Subsequent to challenging with B. abortus S19, it was identified that the DNA vaccine pCDNA-BvrR induced a significant level of protection in BALB/c mice by evaluating systemic bacterial clearance. These results suggested that BvrR may be a good candidate for a DNA vaccine against brucellosis.