Immune Response and Alveolar Bone Resorption in a Mouse Model ofTreponema denticolaInfection

Treponema denticola is considered to be an agent strongly associated with periodontal disease. The lack of an animal infection model has hampered the understanding ofT. denticola pathogenesis and the host's immune response to infection. In this study, we have established an oral infection model in mice, demonstrating that infection by oral inoculation is feasible. The presence ofT. denticola in the oral cavities of the animals was confirmed by PCR. Mice givenT. denticola developed a specific immune response to the bacterium. The antibodies generated from the infection were mainly of the immunoglobulin G1 subclass, indicating a Th2-tilted response. The antibodies recognized 11T. denticola proteins, of which a 62-kDa and a 53-kDa protein were deemed immunodominant. The two proteins were identified, respectively, as dentilisin and the major outer sheath protein by mass spectrometry. Splenocytes cultured from the infected mice no longer produced interleukin-10 and produced markedly reduced levels of gamma interferon relative to those produced by naïve splenocytes upon stimulation withT. denticola . Mandibles of infected mice showed significantly greater bone resorption (P < 0.01) than those of mock-infected controls.