Immunochemical and Protective Properties of Conjugated Capsular Polysaccharide of Streptococcus pneumoniae Serotype 9N

Abstract

Conjugates of Streptococcus pneumoniae type 9N capsular polysaccharide with tetanus toxoid have been prepared. Their interactions with specific antibodies to tetanus toxoid and polysaccharide 9N were assessed, and the conjugate with optimal ratio between polysaccharide and carrier protein was chosen for further investigations (3 : 4, wt/wt). Adsorption characteristics of tetanus toxoid and polysaccharide on aluminum hydroxide were determined using the quantitative ELISA for further in vivo experiments; the optimum ratio of the conjugate and adjuvant was proved to be ≤1 : 1 (wt/wt). Repetitive immunization with selected conjugate adsorbed on aluminum hydroxide evoke the anti-PS antibody with titers equal to 70 400 (p < 0.001) which were 140-fold higher comparing to those for the unconjugated form of the antigen. The investigation of the formation of protective immunity from Streptococcus pneumoniae serotype 9N was performed by intranasal challenge of wild-type mice and revealed that the titers of bacterial contamination in the lungs of immunized mice were 10-fold lower comparing with non-immunized mice 72 h after the challenge (p > 0.05).