The synthesis of Streptococcus pneumoniae polysaccharide-tetanus toxoid conjugates and the effect of chain length on immunogenicity

To study the relationship between length of pneumococcal polysaccharide and immunologic performance in rabbits we took well defined fragments of the capsular polysaccharides of S. pneumoniae types 3, 6A, 18C, 19F and 23F and pneumococcal C-polysaccharide and linked them terminally by reductive amination to tetanus toxoid. Contrary to other reports we found little variation in antibody titers with increasing length. In general the opsonophagocytic titers determined using activated HL60 cells and rabbit peritoneal cells correlated well with the antibody titers except for that of type 3, which despite the presence of high polysaccharide antibody titers gave unexpectedly low opsonophagocytic titers. The C-polysaccharide-conjugate was also immunogenic when injected in both rabbits and mice but gave low opsonophagocytic titers. It was demonstrated that opsonophagocytosis was solely dependent on the presence of phosophoryl choline-specific antibody and that the induction of these antibodies was species dependent.