Immunochemical Analysis and Immunogenicity of the Type II Group B

streptococcal (GBS) type-specific antisera and the type II-specific polysaccharide is evaluated from a struc-tural and immunologic viewpoint. Although all GBS type-specific polysaccharides are composed of the same monosaccharides, the type II antigen is more complex structurally and contains these sugars in a molar ratio different from the other antigens. Type II polysaccharide has two side chains. One contains only sialic acid and is less susceptible to acid cleavage than sialic acid residues found on types III, Ia, and Ib poly-saccharides. The other side chain is composed of ga-lactose as the only sugar. Immunochemical studies demonstrate that the type II polysaccharide has several immunodeterminants. One of these determinants is likely to be the side-chain galactose, while sialic acid appears to comprise part of another immunodeter-minant, more complex than sialic acid alone. A series of cross-reactions is demonstrated between the type II native antigen and antisera to serotypes Ia, III, and Ib by a sensitive radioactive antigen-binding assay, which account for additional, complex immunodeter-minants. The strongest of these cross-reactions is with type Ia antiserum and the weakest with lb antiserum. Since Ia and lb polysaccharides differ in only one link-age, these findings suggest that the trisaccharide BD