EPITOPE MAPPING OF B-CELL DETERMINANTS ON THE 15-KILODALTON LIPOPROTEIN OF TREPONEMA-PALLIDUM (TPP15) WITH SYNTHETIC PEPTIDES

The antigenicity of the 15-kDa lipoprotein of Treponema pallidum (Tpp1 5 or TpN15) was comprehensively evaluated in epitope-scanning studies with overlapping deca- and octapeptides and polyclonal rabbit and huma n infant immunoglobulins (Igs) and antisera. This approach enabled us to identify potentially important regions and to determine the optimal dilutions of Igs or antisera for use in further studies. IgM and IgG from both species were capable of recognizing multiple, continuous epi topes. A total of 13 peptides, principally clustered in the central re gions of the protein, were recognized by all syphilitic sera and Ig fr actions. On the basis of window analyses, frequency profiles, and alan ine substitution studies, five heptapeptides were selected for mimetic studies. Two of these five immunodominant, continuous epitopes initia lly appeared to be species specific; however, antisera elicited agains t mimetics of all five epitopes were polyspecific, recognizing similar motifs on several other treponemal proteins, including those of aviru lent organisms. The only mimetic which yielded positive reactions with infant IgM and syphilitic sera in the absence of cross-reactions with rabbit antisera to avirulent treponemes was the variant of the VMYASS G motif. These findings are relevant to the development of simple, ine xpensive assays for the serodiagnosis of active syphilis.