A linear B-cell epitope on the class 3 outer-membrane protein of Neisseria meningitidis recognized after vaccination with the Norwegian group B outer-membrane vesicle vaccine.

The class 3 outer-membrane protein (OMP) of Neisseria meningitidis is a potential target for bactericidal and opsonic antibodies in humans. Synthetic peptides spanning the class 3 OMP from the vaccine strain 44/76 (B:15:P1.7,16:L3,7) were synthesized on pins and screened with serum obtained from Norwegian adolescents immunized with a meningococcal serogroup B outer-membrane vesicle (OMV) vaccine. A strong IgG response to a single peptide (19FHQNGQVTEVTT30) located within loop 1 (VR1) was stimulated after three doses of OMV vaccine in three vaccinees selected on the basis of their antibody response to class 3 OMP. No clear linear B-cell epitopes were recognized by four different murine serotype 15-specific mAbs. A 23mer peptide (D63b2) containing loop 1 of the class 3 OMP was synthesized, and the IgG responses were measured in pre- and post-vaccination serum from 27 vaccinees. Specific IgG rose significantly in 37% of vaccinees 6 weeks after the second dose and in 74% of the vaccinees 6 weeks after the third dose of the OMV vaccine. Most immune sera reacted distinctly on immunoblots with denatured class 3 OMP, and the immunoblotting reactivity correlated strongly with concentration of the IgG antibodies specific for peptide D63b2. When added to a post-vaccination serum from one vaccinee, peptide D63b2 competed efficiently with the class 3 OMP for specific antibody binding on immunoblots and in pin ELISA. The results show that the significant part of the humoral response to the meningococcal class 3 OMP elicited by vaccination with the Norwegian OMV vaccine was directed against a single continuous epitope.