Immunization with a combination of recombinant Brucella abortus proteins induces T helper immune response and confers protection against wild‐type challenge in BALB/c mice

Summary

Protective efficiency of a combination of four recombinant Brucella abortus ( B. abortus) proteins, namely, ribosomal protein L7/L12, outer membrane protein (OMP) 22, OMP25 and OMP31, was evaluated as a combined subunit vaccine (CSV) against B. abortus infection in RAW 264.7 cell line and murine model. Four proteins were cloned, expressed and purified, and their immunocompetence was analysed. BALB/c mice were immunized subcutaneously with single subunit vaccines (SSVs) or CSV. Cellular and humoral immune responses were determined by ELISA. Results of immunoreactivity showed that these four recombinant proteins reacted with Brucella‐positive serum individually but not with Brucella‐negative serum. A massive production of IFN‐γ and IL‐2 but low degree of IL‐10 was observed in mice immunized with SSVs or CSV. In addition, the titres of IgG2a were heightened compared with IgG1 in SSV‐ or CSV‐immunized mice, which indicated that SSVs and CSV induced a typical T‐helper‐1‐dominated immune response in vivo. Further investigation of the CSV showed a superior protective effect in mice against brucellosis. The protection level induced by CSV was significantly higher than that induced by SSVs, which was not significantly different compared with a group immunized with RB51. Collectively, these antigens of Brucella could be potential candidates to develop subunit vaccines, and the CSV used in this study could be a potential candidate therapy for the prevention of brucellosis.

Abstract

In this report, we described the production of a combination of four different immunogenic antigens rL7/L12, rOMP22, rOMP25 and rOMP31 as single (SSV) and combined subunit vaccines (CSV) and evaluated their immunogenicity in a murine model. Moreover, CSV led to markedly enhanced humoral and cellular immune responses. This response subsequently induced a superior protective effect that was equivalent to the protection conferred by RB51 administration. Furthermore, CSV affected expression levels of proinflammatory cytokines in murine macrophages. CSV also enhanced peripheral blood T lymphocyte activity. These results indicated that CSV may be a potential suitable CSV candidate against brucellosis.