Major outer membrane proteins from Porphyromonas gingivalis: strain variation, distribution, and clinical significance in periradicular lesions.

Porphyromonas gingivalis has been implicated in both marginal periodontitis and periapical infection. This study examined the major outer membrane proteins, from P. gingivalis, which related to periradicular lesions. Outer membrane protein profiles of P. gingivalis ATCC 33277 and W83 were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and N-terminal amino acid analysis. Most outer membrane proteins, such as RagA, gingipains, and OmpA-like proteins, were found in both strains in a similar distribution pattern; however, the migration positions of Lys-gingipain and RagB were inverted in SDS-PAGE. Western blot analysis showed that RagA, RagB, and OmpA-like proteins were found in all of the P. gingivalis strains tested. The antiserum of W83 against RagB reacted poorly to some strains, such as ATCC 33277. When strains phylogenetically related to P. gingivalis were examined, RagA and OmpA homologs were immunologically detected in several strains. However, none of the RagB homologs were detected in any strain analyzed, suggesting that RagB is unique to P. gingivalis. To examine immunoreactive antigens in P. gingivalis, sera from patients with periradicular lesions were used. More than half of the sera showed strong reactions to P. gingivalis cell components, especially RagB. Our results indicate that a major outer membrane protein, RagB, is a possible virulence factor in periradicular lesions.