Immunization of a combination of four recombinant Brucella abortus proteins Adk, Ndk, L7/L12 and SecB induced protective immune responses in BALB/c mice against a virulent strain B. abortus 544 infection

This study investigated the efficacy of four Brucella (B.) abortus recombinant proteins, namely adenylate kinase (Adk), nucleoside diphosphate kinase (Ndk), 50S ribosomal protein (L7/L12) and preprotein translocase subunit (SecB), as a combined subunit vaccine (CSV) against B. abortus infection in BALB/c mice. Immunoblotting assay showed that these four recombinant proteins as well as pcold-TF vector reacted individually with Brucella-positive serum, but not with Brucella-negative serum. The peripheral blood CD4+ T cell population was increased in CSV-immunized mice compared to PBS and pcold-TF vector groups. In addition, CSV and pcold-TF groups displayed induced IgG1 and IgG2a antibodies production compared to PBS and RB51 group, whereas IgG2a titer was higher than IgG1 titer in CSV group. The secretion profiles of IgG1 and IgG2a production together with an enhancement of CD4+ T cell population suggested that CSV did not only induce T helper 1 (Th1) T cell immunity but also humoral immunity. Therein, Th1 T cell immunity is more predominant in eliminating intracellular bacteria B. abortus. Furthermore, CSV immunization significantly reduced the bacterial burden in the spleen as well as the spleen weight in comparison to PBS and pcold-TF groups. Altogether, combination of these antigens could be potential to induce protective immunity against B. abortus infection in animals.