Host responses against periodontopathic bacterial challenge

Objectives: We previously reported that Porphyromonas gingivalis and Tannerella forsythia, which had cysteine proteinase activities, induced larger abscess formation comparing to other bacteria. We also reported that P. gingivalis, deficient of gingipain activities, had weak abscess forming ability. However, much remains to be clarified in regarding host responses at an abscess area. We report here the host responses of mice after injection of various bacterial strains. We also determined the effect of gingipain activities on the destruction of host tissue.

Methods: Live bacterial cells were subcutaneously injected to C57/BL6 mice. Four days after injection, mice were killed and host responses were evaluated histologically and histochemically.

Results: P. gingivalis and T. forsythia induced large abscess formations that were surrounded by eosin-positive fibrous connected tissues. However, the abscesses in P. gingivalis-injected mice were not completely surrounded by connective tissues and the fibers were irregularly arranged. Neutrophils and acid phosphatase (ACP)-positive cells densely infiltrated tissues injected with these two bacteria. Other bacterial strains including gram-positive bacteria induced smaller abscesses that were clearly surrounded by connective tissues. The fibers were regularly arranged and were completely different from the findings in P. gingivalis and T. forsythia- induced abscesses; as well the numbers of ACP-positive cells were much smaller. In mice injected with gingipain-deficient mutant, only micro abscesses surrounded by dense connective tissue were observed. The infiltration of neutrophils was localized around the lesions.

Conclusion: From these results, P. gingivalis and T. forsythia were determined to induce severe inflammation that differed from that induced by other bacteria. The cysteine proteinase activities appeared to have a significant role in the tissue destruction. This work was in part supported by a Grant-in-Aid for Scientific Research (18592296) and Grants-in-Aid for Frontier Research from the Ministry of Education, Science, Sports and Culture, Japan.