Development of immunological method for prevention of dental caries using genetic engineering

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The first step for induction of dental caries by Streptococcus mutans is the adherence of the organism to tooth surfaces. Surface protein antigen (PAc) is considered to participatein the sucrose-independent attachment of the cell to acquired pellicles on tooth surfaces. On the other hand, glucosyltransferase (GTF) is important in the sucrose-dependent adherence of S.mutans.Our epitope mapping using many decapeptides showed that antigenic epitopes were located in the N-terminal A-repeat and middle region of PAc.Moreover, the A-repeat bound to salivary components. We have, therefore, constructed a fusion protein of the fragment corresponding to the A-repeat of PAc and the fragment corresponding to the sucrose-binding site of GTF-I,using an expression plasmid vector pTrc99A.Escherichia coli XL1-blue containing the chimeric plasmid pFPG22 expressed a fusion protein of PAc and GTF-I that reacted with both rabbit anti-PAc serum and antiGTF-I serum. Subcutaneous immunization with this fusion protein induced high titers of antibodies to both adherence factors, and these antibodies inhibited GTF-I, suggesting that the fusion protein may be useful for immunological prevention of dental caries.