Fimbriae of Porphyromonas gingivalis induce opsonic antibodies that significantly enhance phagocytosis and killing by human polymorphonuclear leukocytes

Porphyromonas gingivalis, has been strongly implicated in the pathogenesis of human periodontitis. Fimbriae mediate adherence and colonization of the oral cavity by this organism and may, therefore, have potential for use as antigen in an anti-P. gingivalis vaccine. The purpose of our study was to d etermine whether P. gingivalis fimbriae have opsonic target sites and wheth er they are accessible on the cell surfaces and cross-reactive among P. gin givalis fimbral types and serotypes. Rabbits were immunized with a vaccine. The antiserum reacted with a 43-kDa fimbrillin monomer and a 43-kDa compon ent in whole-cell sonicates of P. gingivalis 33277, but it showed only very weak reactivity in the 43-kDa region of Western blots of a whole-cell soni cate of strain DPG3, a mutant that does not express functional fimbriae. Th e antibody enhanced chemiluminescence approximately six-fold relative to pr eimmune serum values and significantly enhanced phagocytosis and killing of P. gingivalis 33277 by human polymorphonuclear leukocytes. Peak opsonic ac tivity was observed at week 6 followed by a plateau that remained until wee k 16. The fimbria-deficient mutant DPG3 did not bind antifimbrial antibody and was not opsonized, whereas strain 381, the parent of the mutant, was op sonized. The specific antibody bound to and opsonized P. gingivalis strains 33277 and 381 (fimbria type I) but not W50, A7A-1-28, 9-14K-1 or FAY-19M-1 (fimbrial types II-V). Specific antibody bound to strain 2561 (fimbrial ty pe I) but, as assessed by chemiluminescence, did not opsonize it. While fim briae have opsonic target sites that are accessible on P. gingivalis cell s urfaces, the relevant opsonic target sites do not appear to be shared acros s serotypes or fimbrial types. Thus, a vaccine containing, as antigen, fimb rial protein from a single P. gingivalis strain would likely be ineffective against infections by P, gingivalis strains expressing other fimbrial type s.