IDENTIFICATION OF MURINE PROTECTIVE EPITOPES ON THE PORPHYROMONAS-GINGIVALIS FIMBRILLIN MOLECULE

Fimbriae from Porphyromonas gingivalis are believed to play an importa nt role in the pathogenesis of periodontal diseases. The aim of the pr esent study was to identify the fimbrial protective T-cell epitopes in CBA/J mice. A truncated protein corresponding to amino acids 1 to 198 , PgF1-198, was generated and allowed us to demonstrate that the N ter minus of the protein contains T-cell epitopes, With synthetic peptides , an immunodominant sequence was identified between amino acids 103 an d 122. The corresponding peptide, PgF-P8, induced T-cell proliferation after in vitro restimulation of in vivo-primed cells, giving a stimul ation index comparable to the one obtained with r-fimbrillin, and indu ced production of both Th1 and Th2 cytokines. Growth supernatant conta ined significant levels of interleukin 2 (IL-2), gamma interferon, IL- 4 (28 pg/ml), and tumor necrosis factor alpha. Immunization of mice wi th r-fimbrillin, PgF1-198, and PgF-P8 induced production of antibodies specific to r-fimbrillin and PgF-P8. In addition, by using the mouse chamber model we found that mice immunized with PgF-P8 were dramatical ly protected against a normally lethal injection of P. gingivalis, Ani mals immunized with PgF-P8 40 days prior to challenge showed a 60% sur vival rate when challenged with P. gingivalis, compared with just 25% survival in control animals and just 5% survival in mice immunized wit h PgF-P8 only 21 days prior to challenge. Although the protection depe nded on the time of immunization before the bacterial challenge, it di d not correlate with in vivo local cytokine production (IL-2, IL-4, IL -6, tumor necrosis factor alpha, and gamma interferon), specific antib ody levels, or the isotype of anti-PgF-P8 antibodies produced.