Type-specific opsonic antibodies evoked with a synthetic peptide of streptococcal M protein conjugated to polylysine without adjuvant.

A chemically synthesized copy (S-CB7) of a fragment (35 amino acid residues) of type 24 streptococcal M protein was covalently linked to polylysine with carbodiimide and injected subcutaneously into rabbits without adjuvant. Although the primary immune responses as measured by enzyme-linked immunosorbent assays at biweekly intervals were weak, the secondary responses as measured by both enzyme-linked immunosorbent assays and opsonophagocytic assays were as high as those obtained previously in rabbits immunized with the peptide conjugate emulsified in complete Freund adjuvant. Injection of murabutide, a synthetic muramyl dipeptide derivative of bacterial peptidoglycan, with the initial immunizing dose of peptide conjugate had no apparent effect on the secondary immune responses. These results indicate that protective immune responses may be raised against polylysine conjugates of chemically synthesized peptide copies of streptococcal M protein without adjuvant.