Protection of BALB/c mice against Brucella abortus 544 challenge by vaccination with bacterioferritin or P39 recombinant proteins with CpG oligodeoxynucleotides as adjuvant

The P39 and the bacterioferrin (BFR) antigens of Brucella melitensis 16M we re previously identified as T dominant antigens able to induce both delayed -type hypersensivity in sensitized guinea pigs and in vitro gamma interfero n (IFN-gamma) production by peripheral blood mononuclear cells from infecte d cattle. Here, we analyzed the potential for these antigens to function as a subunitary vaccine against Brucella abortus infection in BALB/c mice, an d we characterized the Immoral and cellular immune responses induced. Mice were injected with each of the recombinant proteins alone or adjuvanted wit h either CpG oligodeoxynucleotides (CpG ODN) or non-CpG ODN. Mice immunized with the recombinant antigens with CpG ODN were the only group demonstrati ng both significant IFN-gamma production and T-cell proliferation in respon se to either Brucella extract or to the respective antigen. The same conclu sion holds true for the antibody response, which was only demonstrated in m ice immunized with recombinant antigens mixed with CpG ODN. The antibody ti ters (both immunoglobulin G1 [IgG1] and IgG2a) induced by P39 immunization were higher than the titers induced by BFR (only IgG2a). Using a B. abortus 544 challenge, the level of protection was analyzed and compared to the pr otection conferred by one immunization with the vaccine strain B19. Immuniz ation with P39 and CpG ODN gave a level of protection comparable to the one conferred by B19 at 4 weeks postchallenge, and the mice were still signifi cantly protected at 8 weeks postchallenge, although to a lesser extent than the B19-vaccinated group. Intriguingly, no protection was detected after B FR vaccination. All other groups did not demonstrate any protection.