P. gingivalis Induced & Naturally Occurring Effects of iNOS

Objectives: iNOS may play a role in periodontal disease pathogenesis by sustaining NFκB in osteoclasts during IL-1 stimulated bone resorption. The aim of this study was to investigate P. gingivalis-induced local and systemic effects in iNOS knockout mice. Methods: P. gingivalis W50 infection was established in the periodontal tissues of iNOS-/- and iNOS+/+ mice. Seventy days later, jaws were defleshed and stained to delineate the CEJ. Alveolar bone loss (mm²) was measured morphometrically by a sole blinded operator using a dissecting microscope and a computer assisted image analysis system. A separate group of uninfected iNOS-/- and iNOS+/+ mice were aged naturally. In order to examine the immune response to P. gingivalis infection, a murine abscess model was established. Serum cytokine (IL-4, IL-10, IL-12, IFN-γ and TNF-α) and antibody (IgG1, IgG2a or IgM) responses were measured by ELISA, and splenic lymphocytes analysed by FACS at day 10. Results: A significantly greater amount of alveolar bone loss (P<0.0001) occurred in the P. gingivalis-infected iNOS-/- mice, compared to iNOS+/+ mice at day 70. Equal levels of progressive bone loss occurred in both uninfected iNOS-/- and iNOS+/+ mice from week 6 to 30. Moderate amounts of serum IL-12 and small amounts of IL-10 were detected in the P. gingivalis-infected iNOS-/- mice, while both cytokines were absent in iNOS+/+ mice. A similar percentage of IL-4, IL-10 and IFN-γ positive CD4 and CD8 T cells were detected in both iNOS-/- and iNOS+/+ mice. IgG1 was the dominant antibody detected in P. gingivalis infected mice. Conclusions: iNOS appears to be protective against P. gingivalis-induced alveolar bone loss. Elimination of iNOS appears to enhance IL-12 production, which may implicate this cytokine in inflammation-induced tissue destruction. This research was supported by ADRF.