Immunogenicity and protective immunity induced by synthetic peptides associated with putative immunodominant regions of Streptococcus mutans glucan-binding protein B

Glucan-binding protein B (GbpB) from Streptococcus mutans has been shown to induce protective immunity to dental caries in experimental models. Having recently sequenced the gbpB gene, our objective in this study was to identify immunogenic regions within the GbpB sequence for use in subunit vaccines. Potential regions of immunogenicity were sought by use of a matrix-based algorithm (EpiMatrix) to estimate the binding characteristics of peptides derived from the GbpB sequence by using a database of known major histocompatibility complex class II binding alleles. Screening the entire sequence revealed several peptides with estimated high binding probabilities. Two N-terminal 20-mer peptides (SYI and QGQ) subtending two of these regions were synthesized. A preliminary experiment, in which these peptides were synthesized in the multiple antigenic peptide format and were used to subcutaneously immunize Sprague-Dawley rats twice at a 21-day interval, revealed that the SYI peptide induced a higher percentage of responses to the inciting peptide as well as to intact GbpB, as measured by enzyme-linked immunosorbent assay. The effect of immunization with the SYI Peptide construct on the cariogenicity of S. mutans was then investigated by immunizing weanling Sprague-Dawley rats twice at a 9-day interval with SYI or with phosphate-buffered saline. All rats were then orally infected with S. mutans strain SJ. After a 78-day infection period, the SYI-immunized groups had significant reductions in dental caries on both smooth and occlusal surfaces compared with the sham-immunized group. Thus, these experiments indicated that at least one linear sequence, derived from the N-terminal third of GbpB, was sufficiently immunogenic to induce a protective immune response in this experimental rat model for dental caries.