Identification of a repeated epitope recognized by human serum antibodies in a surface protein antigen of Streptococcus mutans.

This study determined the antigen determinants of a 190-kDa protein antigen of Streptococcus mutans that is involved in the initial attachment to the tooth surface. In 5 subjects, the reactivities of serum antibodies to 7 overlapping surface protein antigen fragments covering the entire antigen molecule and 19 sequential overlapping synthetic 19-mer peptides covering the entire A-region of the surface protein antigen were examined with enzyme-linked immunosorbent assay (ELISA). The study showed that the A-region of the antigen is strongly immunogenic in humans and contains several widely distributed epitopes. In addition, an amino acid sequence of the one of dominant epitopes in a certain subject was identified as LTAENTAI with ELISA inhibition assays using the relevant truncated peptides. This epitope was located both at the positions from L-346 to I-364 and L-430 to E-437 of the antigen molecule, and serum antibodies against the epitope were found in 3 of the 5 subjects.