Development of immunological sensitization and alveolar bone loss in gnotobiotic rats infected with Actinomyces viscosus Ny 1

Development of sensitization in rats monoassocialed with Actinomyces viscosus Ny 1 was estimated by titrating serum agglutinins and by measuring the anamnestic, in vitro response of spleen T lymphocytes to two antigen fractions. These parameters of the immune response were compared with the development of alveolar bone loss using germfree rats as controls. At 46 days of age, 19 days after monoassociation, we observed (i) a mean serum antibody litre of (log 2 ) 3.6, (ii) considerable antigen‐dependent T‐cell proliferation, and (iii) statistically significant amounts of alveolar bone loss. Thereafter, sensitization to A. viscosus and total bone loss increased cuncomitantly until the end of the experiment at 88 days of age. However, the rate of bone loss decreased with time at some sites, suggesting that negative feedback mechanisms by suppressor cells enable bone remodeling. These results demonstrate that, in experimental periodontal disease elicited by A. viscosus. the immune response to dental plaque bacteria and bone loss occur simultaneously.