Immunization of BALB/c mice with a combination of four recombinant Brucella abortus proteins, AspC, Dps, InpB and Ndk, confers a marked protection against a virulent strain of Brucella abortus

In this study, we assessed the protective efficacy of single subunit vaccines, encoded by the B. abortus 544 genes aspC, dps, yaeC and inpB, against B. abortus infection in mice. First, immunization with these antigens, with the exception of the YaeC protein, was found to elicit both humoral and cellular immune responses with IgG2a being dominant over IgG1. In addition, a massive production of IFN-γ but lower degree of IL-10 was observed, suggesting that all three antigens were able to induce predominantly cell-mediated immunity in response to B. abortus infection. Further investigation of a combined subunit vaccine (CSV) consisting of purified AspC, Dps, InpB and Ndk proteins showed a superior protective effect in mice against brucellosis. The intraperitoneal injection of this combination was shown to induce a remarkable production of IFN-γ and IL-2, which occurred in conjunction with an increase of blood CD4⁺ and CD8⁺ T cell proportions. In addition, the higher titer of IgG2a compared to IgG1 elicited by this CSV was obtained, suggesting that this CSV induced a typical T-helper-1-dominated immune response in vivo. Furthermore, the protection level induced by this combination was significantly higher than that induced by single antigens and was not significantly different compared to a group immunized with a live attenuated vaccine (RB51). Altogether, our findings suggest that the combination of different immunogenic antigens could be a useful approach for the development of a new, effective and safe brucellosis vaccine that can replace current vaccine strains.