Immunogenicity of peptides coupled with multiple T-cell epitopes of a surface protein antigen of Streptococcus mutans

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Abstract
A surface protein antigen (PAc) of Streptococcus mutans, in particular the A‐region of the molecule, has been noted as a possible target of effective dental caries vaccine. We have previously shown that two peptides of 19 amino acids (residues 361–379, NAKATYEAALKQYEADLAA, and residues 301–319, ANAANEADYQAKLTAYQTE), which correspond to parts of the A‐region, contain both T‐ and B‐cell epitopes for the induction of cross‐reacting antibodies to the PAc. In this study, for development of an appropriate antigen as a peptide vaccine for use in prophylactic dentistry, we analysed in detail the localization of the T‐ and B‐cell epitopes of PAc(361–379) peptide and the T‐cell epitope of PAc(301–319) peptide in B10 congenic mice. In four murine major histocompatibility complex (MHC) haplotypes (H‐2f, d, a and k), PAc(361–377) peptide showed T‐ and B‐cell epitopes forming a cluster. It was found that the antibody which was induced by the immunization with the peptide was strongly cross‐reactive with recombinant (r)PAc. Meanwhile, PAc(305–318) peptide, recognised by five strains of mice of different MHC haplotypes (H‐2f, d, a, k and s), also bore multiple T‐cell epitopes. PAc(361–377) peptide coupled to PAc(305–318) significantly elevated cross‐reacting antibody levels compared to immunization with PAc(361–377) only in four H‐2 haplotypes. Moreover, a peptide with PAc(305–318) coupled to the N‐terminal region of PAc(361–377) produced significant cross‐reacting antibody against rPAc, even in B10.S mice which had not responded to immunization with PAc(361–379) peptide. Therefore, it was suggested that coupling among the peptides forming a cluster might be effective in increasing immunogenicity. These results may provide us with a useful strategy for the design of peptide‐based vaccines for S. mutans in the future.