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.