Characterization of the binding of and the immune response to pneumococcal group 9 capsular polysaccharides.

The binding of Streptococcus pneumoniae 14C-9N and 14C-9V polysaccharides (PSs) to lymphocytes and polymorphonuclear leukocytes of human blood were studied. The quantity of 14C-9N and 14C-9V PSs bound to leukocytes was proportional to the number of leukocytes and the incubation time; the binding was temperature-dependent. The binding activity appeared to be specific, since the binding was inhibited by prior treatment with homologous group 9 PSs. The binding was also inhibited by prior treatment with cross-reactive group 9 PSs. The binding of 14C-9V PS to leukocytes was greater than that of 14C-9N PS. Reciprocal plot analysis revealed 6.4 X 10(4) binding sites for 9N PS on each lymphocyte and 9.5 X 10(4) binding sites for 9V PS on each lymphocyte, while the affinity constant for 9N PS was 3.7 X 10(9) M-1 and that for 9V PS was 9.4 X 10(8) M-1. Furthermore, there were 7.8 X 10(4) binding sites for 9N PS on each polymorphonuclear leukocyte and 1.2 X 10(5) binding sites for 9 V PS on each polymorphonuclear leukocyte, while the affinity constant for 9N PS was 1.6 X 10(9) M-1 and that for 9V PS was 8.5 X 10(8) M-1. There was a high degree of inhibition of the binding of 14C-9N PS to leukocytes by prior treatment with 9V PS, and a low degree of inhibition of the binding of 14C-9V PS to leukocytes by prior treatment with 9N PS. The high degree of inhibition of binding of 9V PS to leukocytes was not directly related to the production of cross-reactive antibodies to 9N PS. The serum antibody and the plaque-forming cell responses in mice immunized with 9V PS were significantly greater than responses in mice immunized with 9N PS.