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Immune response and periodontal bone loss in germfree rats immunized and infected with Actinobacillus actinomycetemcomitans.

Experiments were performed to determine the effect of delayed-type hypersensitivity (DTH; cell mediated immunity) on subsequent periodontal bone loss in monoinfected (Actinobacillus actinomycetemcomitans [A actinomycetemcomitans]) gnotobiotic rats. Foot pad swelling reactions to A actinomycetemcomitans sonicate were used to monitor both immediate hypersensitivity and DTH. DTH was present in A actinomycetemcomitans immunized (I) animals when initially challenged with A actinomycetemcomitans. This DTH was maintained throughout the experimental period Sham-immunized (SI) animals did not show DTH until after 30 days of infection. The cellular infiltrate in the gingiva of immunized animals was relatively more mononuclear than the infiltrate of SI animals Serum IgG antibody to A actinomycetemcomitans was significantly elevated in I compared to SI animals. The relationship between the foot pad swelling and serum antibody levels suggested that an active Arthus type reaction was observed A actinomycetemcomitans injected rats demonstrated an Arthus-type reaction throughout the duration of the experiment SI animals only showed this reaction 30 days after immunization; the extent of swelling was always less than in the I group. Immunized rats demonstrated significantly elevated horizontal bone loss after infection for 90 days. The data suggest that a “mixed” hypersensitivity reaction to A actinomycetemcomitans occurs in presensitized rats and that the presence of this hypersensitivity can be associated with increased periodontal bone loss.