Antibodies to meningococcal class 1 outer-membrane protein and its variable regions in patients with systemic meningococcal disease

Summary Antibodies to the meningococcal serosubtype-specific P1. 7, 16 protein and its variable regions (VR) were analysed in 28 convalescent sera drawn 8-36 months after systemic meningococcal disease by immunoblotting and enzyme immunoassay (EIA) methods. EIA antigens were the meningococcal P1. 7, 16 protein, produced in Bacillussubtilis, and peptides covering its VR1 (P1. 7 region) and VR2 (P1. 16 region) inserted into a bacterial penicillinase protein. In the immunoblotting method, three meningococcal reference strains were used; they expressed either the P1. 7, 16 protein, or only its VR1 or VR2 epitopes in their class 1 proteins. Both methods showed a strong IgG response in four sera to P1. 7, 16 and VR2, but not to VR1; 18 sera had no or weak anti-class 1 protein activity. The six remaining sera were positive only on blots. The VR2-specific sera had 30-fold higher bactericidal activity than those with negligible P1. 7, 16 responses. Previous vaccination of the patients with a B: 15: P1. 7, 16 meningococcal vaccine was associated with a strong anti-P1. 7, 16 and anti-VR2 booster response that declined with time. The subtype-specific antibody activity in some sera indicated colonisation after disease by meningococci with class 1 proteins different from the strain that had caused disease.