Chemical structure of and immune response to polysaccharides of Streptococcus pneumoniae

By use of rabbit antisera, extensive cross-reactions were demonstrated among pneumococcal (Danish) types 6A and 6B, types 9N, 9A, 9L, and 9V, and types 19F and 19A. The structural similarity of the group 6 polysaccharides was associated with extensive immunogenicity in humans. In contrast, immunization of humans with type 19F or 19A may not induce sufficient cross-protection. The type 19F polysaccharide has the structure of a linear polymer of N-acetylmannosamine-glucose-rhamnose phosphate. Danish type 19A (type 57 in the United States system) polysaccharide contains this repeating unit and, in addition, has side chains of N-acetylglucosamine-galactose phosphate and fucose phosphate. Maternal immunization with type 19F or type 6A polysaccharide during pregnancy elicited high antibody formation in the offspring. Young mice, which received an additional dose of polysaccharide at two weeks of age, showed a higher antibody response than did those that did not receive polysaccharide. These studies reveal that the extensive cross-immunogenicity of pneumococcal group polysaccharides has a basis in chemical structure. Maternal immunization with pneumococcal polysaccharides may enhance the immune response of neonates.