Comparison among opsonic activity, antimeningococcal immunoglobulin G response, and serum bactericidal activity against meningococci in sera from vaccinees after immunization with a serogroup B outer membrane vesicle vaccine.

Opsonic activity in sera from 27 military recruits vaccinated with the Norwegian meningococcal serogroup B outer membrane vesicle vaccine was measured as respiratory burst with polymorphonuclear leukocytes as the effector cells and meningococci of the epidemic strain as the target. The results were compared with antimeningococcal IgG antibodies against an outer membrane vesicle coat in an enzyme-linked immunosorbent assay and with serum bactericidal activity. The vaccinees were immunized twice, with a 6-week interval between the two. The serum samples studied were collected at day zero, after 6 weeks, and after 12 weeks. Both serum bactericidal activity and respiratory burst were measured by adding external serum as the complement source. The results revealed a significant increase in specific IgG response, serum bactericidal activity, and respiratory burst after vaccination. We found a highly significant correlation between the responses in all three assays (P < 0.0001). The highest correlation was found between respiratory burst and antimeningococcal IgG response (r = 0.93). This result strongly indicates that respiratory burst is mediated almost exclusively by IgG antibodies. The correlation between antimeningococcal IgG response and serum bactericidal activity was slightly lower (r = 0.83). The correlation between respiratory burst and serum bactericidal activity was further reduced (r = 0.78), and some of the sera revealed a marked preference for only one of the activities. This result means that respiratory burst and serum bactericidal activity in part are induced by different mediators, and to obtain a more complete picture of the potential protective activity, both assays should be applied to survey a vaccine trial.