Characterization of the cross-reaction between type 19F(19) and 19A(57) pneumococcal capsular polysaccharides: compositional analysis and immunological relation determined with rabbit typing antisera.

The immunological relation, physicochemical characteristics, and chemical composition of type 19F(19) and 19A(57) within the cross-reactive group 19 pneumococcal capsular polysaccharides were studied. By using rabbit hyperimmune diagnostic antisera in agglutination, immunodiffusion, quantitative precipitation, and absorption assays, extensive cross-antigenicity and cross-immunogenicity were demonstrable between the disease-associated types 19F(19) and 19A(57). Types 19B(58) and 19C(59), rarely associated with human disease, were extensively cross-reactive with each other but reacted weakly with types 19F(19) and 19A(57). Both types 19F(19) and 19A(57) polysaccharides contained trace amounts of protein and nucleic acid and had comparable molecular sizes as determined by gel filtration. Compositional analysis showed type 19F(19) to contain rhamnose, glucose, N-acetylmannosamine, and a phosphate ester. Type 19A(57) contained these four moieties, and in addition, contained fucose, galactose, and N-acetylglucosamine. Plans for using this information to evaluate current and proposed formulation of multivalent pneumococcal polysaccharide vaccines are discussed.