Strain-dependent activation of the mouse immune response is correlated with Porphyromonas gingivalis-induced experimental periodontitis

Aims: To evaluate the effect of oral infection with three Porphyromonas gingivalis strains on alveolar bone loss (ABL) and its correlation with the mouse immune response. Materials and Methods: Mice were orally infected with P. gingivalis strains 381, 33277 and 53977. After 42 days, maxillae were analysed for ABL using micro-computed tomography and the serum for anti-P.gingivalis IgG1 and IgG2a levels. The cytokine response to P. gingivalis was tested using the subcutaneous chamber model. Results: The P. gingivalis 53977-infected group showed the highest ABL, which was significantly different from all other groups (p<0.001). In addition, the humoral response to P. gingivalis 53977 was significantly lower than the response to P. gingivalis 381 and 33277 (p≤0.01). The IgG2a/IgG1 ratio was higher in the P. gingivalis 33277-infected group (1.6) compared with the P. gingivalis 381-infected group (0.51). Four days post-infection, interleukin (IL)-1β levels remained significantly higher in the P. gingivalis 53977-infected group only (1198.2±260.0, p<0.05), while IL-4 levels remained significantly higher in the P. gingivalis 381-infected group (265.8±131.6, p<0.05). Conclusions: The high levels of ABL induced by P. gingivalis 53977 were inversely correlated with the humoral response to this bacterium. In addition, ABL was correlated with an elevated pro-inflammatory response.