Immunogenic and protective properties of meningococcal serotype 2a protein in the hen-embryo model.

The ability of serotype 2 outer membrane protein (SP-2) of Neisseria meningitidis strain M986 serogroup B, serotype 2a (B, 2a) to stimulate antibody formation in hens and to confer protection against meningococcal challenge to embryos from immunised hens was investigated. Hens, housed with roosters, were immunised with 100 micrograms of SP-2 once a week for 5 weeks to maintain consistent levels of serum antibody during the study. Antibodies in sera of hens, yolks and plasma of 13-day-old embryos reacted in enzyme-linked immunosorbent assays and immunodiffusion with outer membrane vesicles (OMV) from serotypes 2a, 2b and 2c and most of the other prototype group B strains of N. meningitidis. Cross-reactivity of hen sera with most OMV appeared after only one injection of SP-2. Embryos from immunised hens were protected against challenge with up to 10,000 LD50 doses of either the homologous strain M986 (B, 2a) or strain M1011 (B, 2a). Protection was also evident against strains 614 (W135, 2a), S5896 (Y, 2c) and 2241 (C, 2a), but not against strain 78704 (C, 2a) despite strong cross-reactivity of antibody with OMV of this strain. Embryos were only partially protected against strain 78069 (B, 2b) and were fully susceptible to strain 2996 (B, 2b). Some protection was also obtained against meningococcal strains M1080 (B, 1), M982 (B,9), S3032 (B, 12), 79001 (B, 12), 79694 (B, 15-related) but not strain 77252 (B, nontypable). These results suggest that proteins extracted from both serotype 2a and 2b meningococci would provide the broadest protection against infection with group B, serotype 2 meningococci and that antibody, presumably directed against common peptides in the major outer membrane proteins, can prevent infection by some other disease-associated serotypes of N. meningitidis.