Considerations on the use of Neisseria meningitidis class 5 proteins as meningococcal BC vaccine components.

This investigation was carried out to evaluate the importance of individual meningococcal surface class 5 protein with respect to antibody induction and its functional activity. Two groups of mice were immunized with two vaccine preparations differing in the presence or absence of class 5 protein. The ELISA results show that both vaccines were immunogenic and elicited mainly IgG antibodies against the major classes of meningococcal surface proteins, and the absence of class 5 protein in the vaccine produced a significant change in the overall units ml-1 of antibodies against the homologous strain. The infant rat model and the bactericidal assay were used to evaluate the functional antibody activity. Our results showed that (1) even using two different challenge doses (10(6) and 10(7) bacteria/animal), mortality could not be detected when followed up at 48 h; (2) there was protection as determined by the infant rat model and bactericidal activity using sera from both vaccinated groups; (3) there were no differences in the bactericidal titres between these groups; (4) in the infant rat model there were no differences in the index of bacteraemia among the infected animals (counts ml-1 of blood); and (5) there were differences in the incidence of bacteraemia. This is the first evidence that some immunological differences in the vaccine response could be attributed to the absence of class 5 protein by using infant rat model but not by using the bactericidal assay.