Comparative immunogenicity of conjugates composed of the Staphylococcus aureus type 8 capsular polysaccharide bound to carrier proteins by adipic acid dihydrazide or N-succinimidyl-3-(2-pyridyldithio)propionate.

Staphylococcus aureus type 8 capsular polysaccharide (CP) was conjugated either to diphtheria toxoid or to Pseudomonas aeruginosa recombinant exoprotein A by using adipic acid dihydrazide (ADH) or N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) as the joining reagent. The polysaccharide/protein ratios of these two pairs of conjugates were similar. The two synthetic schemes bound the linker to the carboxyls of the type 8 CP by carbodiimide-mediated condensation. ADH was bound to the carboxyls of the protein, whereas SPDP reacted with the amino groups of the protein. Intermolecular linking of the carrier protein, caused by the carbodiimide during the conjugation reaction with the type 8 CP derivative, probably accounts for the larger size of the conjugates formed with ADH compared with those formed with SPDP. Both conjugates synthesized with ADH elicited higher levels of CP antibodies, especially after the first immunization, than did those prepared with SPDP. Similar levels of exoprotein A antibodies were elicited by both conjugates. Higher levels of diphtheria toxoid antibodies were elicited by the conjugate prepared with SPDP than by the one prepared with ADH. The basis for the differences in the immunogenicities of these two pairs of S. aureus type 8 CP conjugates is discussed.