The application of Neisseria meningitidis serogroup B outer membrane vesicle as an adjuvant to induce specific antibody against the LPS of Brucella abortus S-99 in animal model

Abstract number: P1327

Siadat S.D., Norouzian D., Sharifat Salmani A., Ahmadi H., Nejati M., Kheirandish M., Zangeneh M., Hedayati M.H., Moshiri A., Siadat S.S., Shokohi S., Karbasian M., Salimi M.

Objective: Smoth lipopolysaccharide(S-LPS)of Brucella abortus can be candidated as a potent human vaccine. The adjuvants with microbial origins are more considerable among the other current adjuvants nowadays. The outer membrane vesicle(OMV)of Neisseria meningitidis serogroup B is one of the newly studied adjuvants with microbial origin.

Methods: The S-LPS of Brucella was extracted by Hot phenol-water with some modification as described previously. The noncovalent complex of S-LPS-OMV was injected subcutaneously into groups of ten mice with boosters on days 14 and 28 after the primary immunisation. The following groups were used as control: 1-LPS, 2-LPS plus incomplete Freunds adjuvan(IFA)and 3-LPS plus Freund's complete adjuvant (CFA). The mice were bled on days 0, 14, 28, 42.The humoral immune responses evaluated by detection of specific anti-LPS IgM and IgG titre via ELISA method.

Results: Anti-LPS IgG titre(demonstrated by ELISA)for LPS plus OMV has been increased 3.9, 3.18 and 1.58 fold after 14 days in comparison with the LPS, LPS plus IFA and LPS plus CFA control group. The application of LPS plus CFA led to higher level anti-LPS IgG titre than LPS plus IFA and LPS with 1.98 and 2.5 fold, respectively. The anti-LPS IgG titre in LPS plus IFA control group was not significantly increased in comparison with the LPS group. Booster doses have been effective to significantly increase anti-LPS IgG titre in all groups after 28 days. An increase in anti-LPS IgG titre following the second and third dose of LPS plus OMV induced 6 and 12.4 fold titres in comparison with the first dose. The highest anti-LPS IgG titre detected two weeks after the third dose(after 42 days)of LPS plus OMV.Comparative study of anti-LPS IgM titres were not revealed any significant level in all groups.

Conclusion: In this study, we showed that N. meningitidis serogroup B OMV in noncovalent complex with Brucella abortus S99 LPS induces high level of anti-LPS IgG and our purified OMV could act as an effective adjuvant. Since the application of most adjuvants is restricted because of hypersensitivity reactions and the safety of OMV in humans has been demonstrated in many studies, OMV would be a safe adjuvant which does not cause hypersensitivity and DTH reactions. Therefore noncovalent complex of OMV-B. abortus LPS may be a candidate for further development as a brucellosis vaccine for human use.