Bactericidal activity of a monoclonal antibody against a recombinant 40-kDa outer membrane protein of Porphyromonas gingivalis

Background: We have cloned the gene for a 40-kDa outer membrane protein (40 -kDa OMP) from Porphyromonas gingivalis 381. The recombinant (r)40-kDa OMP has become the subject of considerable interest because of its potential ro le in the development of a vaccine useful for passive immunization. To deve lop such a vaccine, it is essential to fully understand the functions of an ti-r40-kDa OMP antibody in the host defense against P. gingivalis. To that end, we developed a panel of monoclonal antibodies by immunizing mice with purified r40-kDa OMP. The objective of this study was to determine the bact ericidal activity on P. gingivalis by the IgG1 monoclonal antibody Pg-ompA2 . Methods: Bacterial growth measurement, a complement-mediated anti-P gingiva lis assay based on [H-3]thymidine uptake, and a C-14-release assay were per formed to test the bactericidal activity of Pg-ompA2 to P. gingiualis. Results: In the presence of complement, Pg-ompA2 was lethal to P. gingiuali s 381 as well as to the more virulent P. gingiualis strains, including ATCC 53977 and W83. Using component-deficient complement, we determined that Pg -ompA2 killed P. gingiualis by activating both the classical and alternativ e complement pathways. Conclusions: Pg-ompA2 has an in vitro complement-mediated bactericidal acti vity to P. gingiualis. Pg-ompA2 may contribute to the development of a loca l immunotherapy that can be applied in the gingival crevice of a patient wi th P. gingivalis-related periodontitis, or be a vaccine candidate.