Antigenic Specificity of Bactericidal Antibodies in Antisera to Neisseria meningitidis

Abstract

The antigenic specificity of bactericidal antibodies to Neisseria meningitidis was tested by radioactive bactericidal and antigen-binding assays. All meningococci tested for polysaccharide serogroups A, B, and Y shared one or more of the seven defined type-specific antigens of group C. Bactericidal tests with human convalescent sera and immune rabbit sera showed that killing of 14 different group B strains was variable and correlated better with antibodies to the serotype antigens than with antibodies to the polysaccharide. Purified antibodies to polysaccharides of group A or C were bactericidal to all homologous serogroup strains tested. However, purified antibodies to polysaccharides of each of three group B strains were active only against the immunizing strain and a few others. The polysaccharides of each of the three group B strains were indistinguishable on the basis of studies of inhibition of antibody binding and inhibition of bactericidal activities. The data suggest that antibodies to the polysaccharide antigen of group B meningococci may be less important in immunity than antibodies to groups A and C polysaccharides. The presence of antigenic ally similar surface serotype antigens in many strains of serogroups A, B, C, and Y explains the observed cross-reactivity of bactericidal activity in serum after infection.