Class-specific human bactericidal antibodies to capsular and noncapsular surface antigens of Neisseria meningitidis.

Bactericidal and enzyme-linked immunosorbent assays were used to determine the immunoglobulin classes responsible for group- and type-specific immunity to Neisseria meningitidis among healthy, unvaccinated individuals and persons who received group-B N meningitidis polysaccharide-serotype-2 protein vaccine. Bactericidal antibodies to the group B polysaccharide were primarily IgM; only a few individuals had both IgM and IgG antibodies. IgG bactericidal antibodies were detected only in those individuals with high IgM-antibody levels to group B meningococci. Increased levels of bactericidal antibodies to the group-B polysaccharide were infrequently found in vaccinees, possibly because of high prevaccination bactericidal-antibody levels. Bactericidal antibodies to the group-C polysaccharide were IgM, IgG, or both. Vaccine-induced antibodies to lipopolysaccharide were not bactericidal for a group-C serotype-2 strain with the lipopolysaccharide immunotype of the vaccine strain.