Fractionation and characterization of surface antigens from group A Neisseria meningitidis.

Group A meningococcal surface components were first subjected to fractionation with a mixture of chloroform-methanol. Sodium dodecyl sulfate-acrylamide gel electrophoresis of the aqueous phase containing 30 to 40% of the original material revealed only two polypeptide components and a slowly migrating carbohydrate component. The soluble fraction of the interphase was found to contain most of the bacterial surface proteins and the chloroform-methanol phase essentially all of the lipid components. The components of the aqueous phase were further fractionated by use of the hydrophobic affinity column, 4-phenylbutylamino-Sepharose and gradient elution with NaCl to yield fractions I and II. Fraction II was further separated into a minor and a major component (IIb) with Sepharose G-200. Fraction I contained the group A polysaccharide in ionic linkages with a minor polypeptide component (6%). It elicited bactericidal antibodies in rabbits and protected mice against homologous challenge, whereas the polysaccharide alone was non-immunogenic in these animals. Fraction IIb was a polysaccharide-polypeptide complex with unknown linkages; it induced a low concentration of rabbit antibodies that were bactericidal to group A and C meningococci. Mice vaccinated with fraction IIb were most resistant to homologous challenge and the resistance was also extended to challenges with group B and C cells. Fractions I and IIb appeared to be useful alternatives to the currently employed group-specific polysaccharide vaccines for the protection against drug-resistant meningococci. A simplified procedure for the preparation of group-specific polysaccharide was presented.