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Effect of aluminum ions on chemical and immunological properties of meningococcal group B polysaccharide

Soluble salts of aluminum were examined for their capacity to complex with purified meningococcal group B polysaccharide. The formation of the complexes resulted, first, in a markedly reduced rate of internal esterification at acid pH and, consequently, prolonged stability of the antigen as measured by its reactivity with antibody at pH 4 and, second, in an increased resistance to neuraminidase. Al3+ complexes of B polysaccharides were tested for immunogenicity in mice and found to be no better than the purified polysaccharide in the Na+ or Ca2+ form. However, when Neisseria meningitidis type 6 protein (outer membrane) complexed to B polysaccharide was tested, a substantial increase in anti-B titers was detected, whereas antiprotein titers remained unchanged. The possibility of using combinations of metal-polysaccharide-outer membrane protein complexes as vaccines for humans is discussed.