Biological and immunological characteristics of Brucella abortus S99 major outer membrane proteins

Introduction and objective: Outer membrane proteins (OMPs) of Brucella are considered as immunogenic structures which can be used to design and develop a subunit vaccine for human brucellosis. Brucella abortus S99 OMPs promote the synthesis of high levels of specific anti-Brucella IgG molecules in rabbits when administrated with lipopolysaccharide (LPS). The objective of this study is evaluation of the efficacy of B. abortus major OMPs with LPS in the induction of immune response against brucellosis. Materials and methods: OMPs were derived from B. abortus by sequential extraction of sonicated cells with ultracentrifugation and predigestion with lysozyme. Proteins could be separated by anion-exchange chromatography and gel-filtration. Based on SDS-PAGE profiles, porins have been dominantly purified among three different classes of B. abortus OMPs. Sera of immunized rabbits against B. abortus porins were analyzed by enzyme-linked immunosorbent assay (ELISA). LPS of B. abortus and complete Freudʹs adjuvant (CFA) were also applied to elicit higher levels of anti-Brucella antibodies. Results: ELISA confirmed the potency of porins and porins combination with CFA and LPS to promote humoral specific response. Among the above-mentioned compounds, a combination of porins + LPS or porins + CFA has been the most potent immunogenic compound to induce higher titer of antibody against B. abortus S99 in the animal model. Conclusion: The application of a complex of Brucella LPS and porins as an effective method to elicit protective and long-lasting immunity against Brucella infection and would be studied to design and develop a subunit vaccine for human brucellosis.