The effect of stress on the inflammatory response to Porphyromonas gingivalis in a mouse subcutaneous chamber model

Background: The impact of emotional stress on the outcome of infectious diseases was studied in animal models and humans, but data related to the effect of stress on periodontal infection are limited. Using the subcutaneous chamber model in mice, the present study was carried out to investigate the effect of stress on the host response to Porphyromonas gingivalis. Methods: Mice with subcutaneous chambers (2 per animal) were divided into 4 treatment groups: cold-stress; isolation-stress; corticosterone (CS)-injected; and controls. On the third day of stress conditions, heat-killed P. gingivalis were injected into the chambers. The chambers were sampled 1 and 5 days later and analyzed for leukocyte number, tumor necrosis factor (TNF)-α levels, and interferon (IFN)-γ levels. Results: Injection of P. gingivalis induced the migration of leukocytes into the chambers and increased the intrachamber levels of IFN-γ and TNF-α. There were no significant differences in cell number and IFN-γ levels between the different treatment groups, but the levels of TNF-α were significantly lower in the isolation-stress and cold-stress groups compared to control animals. CS-injected animals were not different from controls. In addition, the levels of TNF-α in the stressed animals were lower on the fifth day post-injection than on the first day, but not in the CS and control group. Conclusions: The results suggest that the levels of TNF-α induced by P. gingivalis in the infection site are downregulated in stressed animals, and CS is not the sole mediator responsible. The stress-induced reduction in TNF-α levels might have an impact on the pathogenesis of periodontal disease in humans experiencing emotional stress.