A flow cytometric opsonophagocytic assay for measurement of functional antibodies elicited after immunization with outer membrane vesicle of Neisseria meningitidis serogroup B.

Opsonophagocytosis mediated by antibody and complement is the major defense mechanism for clearing Neisseria meningitidis from the host. Therefore, a newly developed phagocytosis assay based on flow cytometry (flow assay) was using sera obtained from rabbit postvaccination with outer membrane vesicle of N. meningitidis serogroup B, was done in order to evaluation of the potential efficacy of (experimental) meningococcal vaccines. The Outer Membrane Vesicles (OMVs) and control were injected intramuscularly into groups of five rabbit with boosters on 14, 28 and 42 days after the primary immunization. The serum on 0, 14, 28, 42 and 56 days were collected and stored at -20 degrees C for next analysis. Phagocytic function of and intracellular oxidative burst generation by rabbit polymorphonuclear (PMN), against N. meningitidis serogroup B, was measured with flow cytometer, using dihydrorhodamine-123 as probes, respectively. We use a Coulter Epics XL-profile (USA) with an argon laser operating at 488 nm. The results of quantitative flow cytometric analysis of rabbit PMN function in hyperimmun sera with OMVs revealed a highly significant increase in opsonophagocytic responses against serogroup B meningococci after 56 day in comparison with the control group (p < 0.05). Present results indicated that OMVs could be as a candidate for vaccine toward serogroup B meningococci and a new standard flow cytometric method to measure the opsonophagocytosis activity by rabbit PMNs was shown by this study.