Chemistry and immunochemistry of the pneumococcal polysaccharide vaccine with special reference to cross-reactions and immunologic factors.

This review summarizes data on the cross-reactions observed among the subtypes of Streptococcus pneumoniae. Types 6A and 6B; 19F, 19A, 19B, and 19C; 18F, 18A, 18B, and 18C; and 23F, 23A, and 23B were examined with use of radioimmunoassay for measurement of inhibition of binding; the cross-reactions are discussed in terms of the known chemical structures of the antigens involved. Cross-reactions observed with use of rabbit antisera proved to be an unreliable guide to the responses observed thus far in humans. Cross-reactions of pneumococcal capsular polysaccharide antigens with other bacterial antigens are mentioned. These cross-reactions are analyzed with the idea of maximizing the effectiveness of the pneumococcal vaccine. Immunologic factors that may determine the quality and/or quantity of the immune response to immunization are discussed. These factors include antigenic competition and influence of preimmunization levels of antibody. Antigenic competition, although not a major concern with the present vaccine, may determine the upper limit of the number of capsular types that can be present in a single vaccine. The preimmunization level of antibody may determine the specificity of the antibody produced after vaccination.