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Comparison among opsonic activity and serum bactericidal activity against Meningococci in rabbit sera from vaccines after immunisation with the Neisseria meningitidis serogroup A capsular polysaccharide-serogroup B outer membrane vesicle conjugate vaccine

Abstract number: 1733_584

Siadat S., Najafi Barzegar H., Behzadiyannejad Q., Tabaraiee B., Ahmadi H., Nourouzian Shamasbi D., Najar Peerayeh S., Nejati M., Zangeneh M., Adibi Motlagh B.

Introduction: Production of effective vaccine formulations is dependent on the availability of assays for the measurement of protective immune responses. Antibody- and complement-mediated phagocytosis is the main defence mechanism against Neisseria meningitidis.

Methods: Therefore, a newly developed phagocytosis assay based on flow cytometry (flow assay) and the serum bactericidal assay (SBA) were using sera obtained from rabbit postvaccination with a bivalent conjugate of Neisseria meningitidis serogroup A capsular polysaccharide (CPSA) to serogroup B outer membrane vesicle containing PorA (OMV-PorA), an OMV-PorA of Neisseria meningitidis serogroup B and the CPSA (as control), was done in order to evaluation of the potential efficacy of (experimental) meningococcal vaccines. The conjugate and control were injected intramuscularly into groups of five rabbit with boosters on days 14, 28 and 42 after the primary immunisation. The following groups were used as control: 1: CPSA; 2: OMV-PorA; 3: normal saline. The serum on days 0, 14, 28, 42 and 56 were collected and stored at -20°C for next analysis.

Phagocytic function of and intracellular oxidative burst generation by rabbit PMN, against Neisseria meningitidis serogroup A and B, were measured with flow cytometer (Coulter Epics-XL-Profile USA), using dihydrorhodamine-123 as probes, respectively. In these experiments non-heat-inactivated standard strain Neisseria meningitidis serogroup A (CSBPI, G-243) and B (CSBPI, G-245) were used. SBA titers are given as reciprocal Log2 values of the dilution giving at least 50% killing of the inoculum measured as colony forming units.

Results: The results of SBA titers and quantitative flow cytometric analysis of rabbit PMN function in hyperimmun sera with the glycoprotein conjugate revealed a highly significant increase in opsonophagocytic responses and bactericidal antibody against serogroup A meningococci after 56 day in comparison with the CPSA and OMV-PorA control group (P < 0.05). Opsonophagocytic responses and bactericidal activity against serogroup B meningococci of the conjugate showed no significant difference in comparison with the OMV-PorA containing control (P > 0.05).

Conclusion: Both SBA and opsonic activity are crucial for the protection against meningococcal disease, Our results indicated that the CPSA–OMV-PorA conjugate could be as a candidate for bivalent vaccine toward serogroup A and B meningococci.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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