Aa Colonization and Induced Bone Loss in Three Rat Strains

Objective: To compare colonization, induced IgG, and alveolar bone loss in Aggregatibacter actinomycetemcomitans (Aa)-inoculated Fawn Hooded Hypertensive (FHH), Dahl Salt Sensitive (DSS) and Norway Brown (BN) rats. Methods: Each rat strain was divided into a non-inoculated control group and a group inoculated with Aa wildtype strain Aa1005rif. Blood samples were taken pre-inoculation and at twelve weeks. Colonization was assessed 12 weeks after inoculation. Control and Aa-inoculated rats for each strain were assessed for Aa specific IgG antibody by ELISA, and horizontal bone loss by cemento-enamel junction (CEJ) to alveolar bone crest (ABC) distance measurement for six molars at ten sites. Colonization and antibody titer were compared between groups by ANOVA and post-hoc testing. Diseased rats were defined as having two sites per quadrant that had CEJ-ABC levels significantly greater than the control group site mean. Results: The mean anti-Aa IgG level of all the Aa-inoculated rat strains was elevated relative to their uninoculated control group. BN rats showed an IgG level to Aa significantly higher than uninoculated controls (p<0.05). The mean IgG level of the FHH Aa-inoculated group was significantly lower than Aa-inoculated BN and DSS groups, (p<0.05). Colonization of FHH rats by Aa1005rif was significantly higher than the DSS and NB inoculated rats (p<0.05 ). Only the FHH rats showed a significant association between Aa inoculation and disease (Fisher's exact test p=0.001) Conclusion: Aa colonized more readily and caused more disease in FHH rats than the other rat strains. FHH IgG-specific response to Aa was significantly lower than the Aa-inoculated NB and DSS strains. The increased susceptibility of the FHH to Aa colonization and Aa-induced bone loss could be in part due to a diminished IgG response to Aa infection.