A flow cytometric opsonophagocytic assay for measurement of functional antibodies elicited after immunisation with the Neisseria meningitidis serogroup A capsular polysaccharide-serogroup B outer membrane vesicle conjugate vaccine in animal model

Abstract number: p578

Kheirandish  M., Siadat  S.D., Behzadiyannejad  Q., Tabaraiee  B., Ahmadi  H., Najar Pirayeeh  S., Nejati  M., Mahmoodi  K.

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) was 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 immunization. The following groups were used as control: CPSA; OMV-PorA; 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.

Results: 

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

Conclusion: 

Our results indicated that the CPSA- -OMV-PorA conjugate could be as a candidate for bivalent vaccine toward serogroup A and B meningococci.