Bactericidal activity of two IgG2a murine monoclonal antibodies with distinct fine specificities for group B Neisseria meningitidis capsular polysaccharide.

To analyze the fine specificity of the protective IgG response for the capsule of group B Neisseria meningitidis (Men B) induced after immunization with live bacteria, two specific IgG2a monoclonal antibodies (mAb) have been generated from hyperimmunized Balb/c and NZB mice (101C11 and 30H12). They specifically recognize in direct and competitive binding assays the capsular polysaccharides of Men B and Escherichia coli k1 on condition that the length of the polysaccharidic chain is sufficient to make a conformational structure (more than 15 monomers of alpha (2-->8) linked N-acetyl neuraminic acid). They do not interact with group A and group C Neisseria meningitidis polysaccharides in ELISA. A chemical derivative of the Men B polysaccharide, the N-propionylated Men B polysaccharide, considered as mimicking a unique bactericidal epitope on the surface of Men B is recognized by 101C11 but not by 30H12. The two mAb have, in vitro, a specific bactericidal activity against live Men B which do not seem serotype specific. Moreover, the killing of Men B mediated by 30H12 can be neutralized by an anti-idiotypic mAb (216F11) generated from A/J mice, immunized with polymerized 30H12. These data show that at least two distinct bactericidal epitopes exist on the surface of the Men B capsule.