Measurement of opsonophagocytic activity of antibodies specific toNeisseria meningitidis serogroup A capsular polysaccharide-serogroup B outer membrane vesicle conjugate in animal model

Preparation and Evaluation of a New Lipopolysaccharide-based Conjugate as a Vaccine Candidate for Brucellosis

Objectives

Development 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.

Methods

In 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.

Results

The 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.

Conclusion

These results indicate that our conjugated LPS–OMV can be used as a brucellosis vaccine, but further investigation is required.

Outer membrane vesicle: a macromolecule with multifunctional activity

Nowadays adjuvants are extensively used as immuno-stimulatory and immuno-modulatory compounds as components of subunit and combination vaccine formulations. The adjuvants of microbial origin are more frequently used among currently used licensed or experimental adjuvants. The outer membrane vesicle (OMV) of Neisseria meningitidis is among the newly studied components of microbial origin, which could be applied as an adjuvant. Although the potency of OMV as a carrier (conjugated to a hapten) is now proven, the adjuvant properties of OMV have particular significance as a potential target for protective immunity. Since it has immune-stimulatory activity, OMV has been utilized in vaccine development. This commentary reviews the different applications of OMV as potential adjuvant in the field of vaccine development.