Protein-conjugated synthetic di- and trisaccharides of pneumococcal type 17F exhibit a different immunogenicity and antigenicity than tetrasaccharide.

Overlapping synthetic disaccharide, trisaccharide and tetrasaccharide, derived from pneumococcal polysaccharide type 17F (PS17F), were coupled to keyhole limpet haemocyanin (KLH). The conjugates were tested in mice. The disaccharide-KLH and especially trisaccharide-KLH, in combination with Quil A, induced high titres of high-avidity anti-PS17F IgG. Both conjugates protected mice against challenge with Streptococcus pneumoniae 17F. Tetrasaccharide-KLH, although able to elicit anti-tetrasaccharide antibodies, induced a minimal non-protective anti-PS17F IgG response of low avidity. The tetrasaccharide-KLH conjugate, in contrast to the other conjugates, failed to bind rabbit anti-PS17F IgG.