Recombinant Protein and DNA Vaccine Construct of Brucella abortus L7/L12 Gene Elicits Immune Response

Both cell mediated and humoral immune responses are required for recovery from Brucella abortus infection. In the development of vaccines capable of providing immunity against brucellosis, L7/L12 50S ribosomal protein has been demonstrated to be one of the protective immunogens of Brucella abortus. The recombinant Brucella abortus L7/L12 ribosomal protein previously produced in the E. coli system was purified by affinity chromatography. The DNA vaccine (pVL7/L12) construct was purified in bulk by endotoxin free reagents. The present study was designed to evaluate cell mediated immune response and humoral immune response after the intramuscular vaccination of mice with DNA vaccine alone (Group 1), recombinant protein alone (Group 2) and DNA vaccine followed by recombinant protein boosting (Group 3). The protective efficacy of the said vaccines also evaluated. Animals vaccinated with pVL7/L12 (DNA vaccine) alone did not develop L7/L12 specific antibodies at least until 60 days of vaccination. But recombinant protein induced a strong antibody titer (1:32000) after 60 days of post immunization which exhibited a dominance of immunoglobulin IgG2a over IgG1. L7/L12 DNA vaccine elicited a T-cell proliferation response and also induced the production of IFN-γ. The lymphocyte proliferation and IFNγ production was significantly higher (P<0.001) in Group 3 than the other groups. Group 3 also induced strong IgG2a response. The DNA vaccine followed by protein boosting induced a strong significant level of protection in mice against challenge with B. abortus 544. The level of protection in Group 3 was significantly higher than the DNA vaccine or recombinant protein alone. Altogether, the data generated in the present study suggested that L7/L12 DNA vaccine followed by recombinant protein boosting is a good candidate for use in future studies of vaccination against brucellosis.