The Interrelationships Between Bone-Loss, Host Response and Porphyromonas gingivalis Strains

Background: Although Porphyromonas gingivalis (P. gingivalis) infected mice were extensively used as a model for periodontal disease, strain dependent immune response and the resulted bone loss need further clarification. Objectives: To evaluate the effect of oral infection with different P. gingivalis strains on the mouse immune response and its correlation to alveolar bone loss (ABL). Materials and Methods: The mouse oral infection model (experimental periodontitis) was used to evaluate ABL. Mice were orally infected with three P. gingivalis strains (381, 33277, 53977) or a vehicle. Forty-two days following infection maxillae were analyzed for volumetric ABL using micro computed-tomography. Levels of serum anti-P. gingivalis IgG were evaluated at 12 and 42 days. The cytokine response to the three P. gingivalis strains was tested using the subcutaneous chamber model. Four groups of BALB/c mice were infected with the different P. gingivalis strains or saline and chamber exudates were analyzed for cytokines. Results: The P. gingivalis 53977-infected group showed the highest ABL which was significantly different from the P. gingivalis 381 and 33277-infected groups. In-addition, the humoral response to P. gingivalis 53977 infected-group was similar to the non-infected mice, and significantly lower than in the P. gingivalis 381 and 33277-infected groups. All cytokines levels were increased following P. gingivalis challenges at 2 and 48 hours post-infection. At 96 hours post-infection, IL-1β levels stayed significantly higher in the P. gingivalis 53977-infected group only, while IL-4 levels remained significantly higher in the P. gingivalis 381-infected group. Conclusions: The high levels of ABL induced by oral infection with P. gingivalis 53977 were inversely correlated to the humoral response to this bacterium. In-addition, the ABL was correlated with an elevated pro-inflammatory response.