Comparative Immunogenicity of Vaccines Prepared from Capsular Polysaccharides of Group C Neisseria meningitidis O.Acetyl.Positive and O.Acetyl.Negative Variants and Escherichia coli K92 in Adult Volunteers

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Abstract
Three structurally and antigenically similar capsular polysaccharides, two derived from group C Neisseria meningitidis (O-acetyl-positive and O-acetyl-negative variants) and one from Escherichia coli K92, which cross-reacts with polysaccharide from group C N. meningitidis, were compared for their ability to induce anticapsular and bactericidal antibodies to group C N. meningitidis in adult volunteers. All three vaccines elicited group C-specific serum antibodies. The vaccine derived from the 0acetyl- negative variant was the most immunogenic of the three vaccines. With use of radiolabeled O-acetyl-positive group C N. meningitidis polysaccharide antigen, the geometric mean titers of antibody in serum were 41.7 µg/ml to the O-acetyl-negative variant, 22.8 µg/ml to the O-acetyl-positive variant, and 7.1 µg/ml to E. coli K92. Antibodies induced by all three vaccines were bactericidal for both of the group C N. meningitidis polysaccharide variants. An inverse relation between the comparative immunogenicity of the O-acetyl-negative polysaccharide and the virulence of group C N. meningitidis was found.