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ObjectivesDevelopment of an efficacious vaccine against brucellosis has been a challenge for scientists for many years. At present, there is no licensed vaccine against human brucellosis. To overcome this problem, currently, antigenic determinants of Brucella cell wall such as Lipopolysaccharide (LPS) are considered as potential candidates to develop subunit vaccines.MethodsIn this study, Brucella abortus LPS was used for conjugation to Neisseria meningitidis serogroup B outer membrane vesicle (OMV) as carrier protein using carbodiimide and adipic acid–mediated coupling and linking, respectively. Groups of eight BALB/c mice were injected subcutaneously with 10 μg LPS alone, combined LPS + OMV and conjugated LPS–OMV on 0 days, 14 days, 28 days and 42 days. Anti-LPS IgG was measured in serum.ResultsThe yield of LPS to OMV in LPS–OMV conjugate was 46.55%, on the basis of carbohydrate content. The ratio for LPS to OMV was 4.07. The LPS–OMV conjugate was the most immunogenic compound that stimulated following the first injection with increased IgG titer of ∼5-fold and ∼1.3-fold higher than that produced against LPS and LPS in noncovalent complex to OMV (LPS + OMV), respectively. The highest anti-LPS IgG titer was detected 2 weeks after the third injection (Day 42) of LPS–OMV conjugate. The conjugated compound elicited higher titers of IgG than LPS + OMV, that showed a 100–120-fold rise of anti-LPS IgG in mice.ConclusionThese results indicate that our conjugated LPS–OMV can be used as a brucellosis vaccine, but further investigation is required.

This review presents a brief outline of our current knowledge of the structure and chemical composition of the outer membrane vesicles (OMVs), originating from the surface of Gram negative bacteria including their outer membrane proteins and lipopolysaccharides. Moreover, the functional roles and applications of OMVs in medical research such as OMV-based vaccines, OMV adjuvants properties, OMV carriers in conjugated vaccines as well as in drug vehicles and delivery systems are discussed. Finally, new applications of these macromolecules as biotechnological tools are briefly presented.

The purpose of the present study was to evaluate the immunogenicity and protective efficacy of the truncated form of outer membrane protein 2b (TOmp2b) from Brucella abortus in BALB/c mice. Three immunization regimens Protein/Protein, DNA/DNA and DNA/Protein were used. Immunization of mice with all vaccine strategies elicited a strong specific IgG responses (IgG2a titers over IgG1) and provided T helper1 (Th1) oriented immune responses. Furthermore, Protein/Protein (Pro/Pro-) and DNA/Pro- vaccinated groups conferred protection levels against B. abortus challenge not significantly different from those induced by B. abortus RB51 vaccine stain. In conclusion, TOmp2b is potential to stimulate specific immune responses and to confer cross protection against B. melitensis and B. abortus infection. Therefore, TOmp2b could be introduced as a new subunit vaccine candidate against Brucella infection.

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