Isolation and Characterization of Neisseria meningitidis Groups A, C, X, and Y Polysaccharide Antigens.

To prepare Neisseria meningitidis groups A, C, X, and Y polysaccharide antigens, culture supernatant fluids were subjected to serial processes of salt precipitation, alkaline hydrolysis, ethyl alcohol precipitation, and Sephadex G-200 chromatography. This method resulted in the isolation of large quantities of group antigens. All are acidic polysaccharides, the group C antigen being a polymer of n-acetyl neuraminic acid. Thiobarbituric acid assay failed to reveal sialic acids in the other group antigens. Protein was undetectable by absorption at 280 nm or by Folin analysis. These antigens are of similar molecular size, the majority of which are excluded by Sephadex G-200. They migrate in the upper one-third of sucrose density gradients and are retained by 5% acrylamide gel. All are highly group-specific and react only with homologous hyperimmune antisera in hemagglutination, complement fixation, and immunodiffusion systems. As little as 0.03 mumoles of n-acetyl neuraminic acid in group C antigen inhibits the hemagglutination of group C-sensitized red cells. All antigens are immunogenic in rabbits. These techniques afford a simplified method for the production of relatively large yields of highly specific group antigens which participate in multiple immunologic systems.