Immunodeterminant specificity of human immunity to type III group B streptococcus.

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Abstract
The type III polysaccharide of group B. Streptococcus in its native state chemically consists of glucose, galactose, glucosamine, and sialic acid. The core of this polysaccharide lacks sialic acid and precipitates with type III antiserum to give a partial identity with the precipitate between the native antigen [Ag] and this serum. The core determinant is immunochemically similar to the capsular polysaccharide of type XIV S. pneumoniae, while the native type III group B streptococcal polysaccharide does not cross-react with type XIV pneumococcal antiserum. In human sera, it is antibody [Ab] directed to the native Ag which correlates very highly with opsonic immunity (r [correlation coefficient] = 0.94), while a poorer correlation exists between Ab to the core Ag and opsonins (r = 0.51 P < 0.001). In natural infections, an association exists between low levels of maternal Ab to the native Ag and risk of disease in the infant. This association is not true for Ab to the core structure, where infected infants and their mothers have much higher levels of Ab to the core than the native Ag. Infected infants are more likely to respond to infection by developing Ab to the native Ag. Immunization of 12 adults with multivalent pneumococcal polysaccharide induced significantly better Ab response to the core Ag than to the native, and this vaccine induced opsonic activity in only 1 recipient. Immunization of adults with type III group B streptococcal Ag induced Ab to the native determinant which correlated with opsonic activity. Native group B streptococcal polysaccharides may provide the best candidate Ag for immunization.