Immunomodulatory and superantigen activities of bacteria associated with adult periodontitis

Abstract

Immune dysfunctions are frequently associated with chronic inflammatory diseases. Several investigators have reported that patients with severe periodontitis show reduced or negligible levels of proliferative responses of peripheral blood and gingival lymphocytes to periodontopathic organisms. The purpose of this study was to evaluate the influences of products from Porphyromonas gingivalis (P. gingivalis) and Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) on lymphocytes obtained from periodontally diseased and non-diseased individuals in order to extend our understanding of the possible role of such bacterial components as immune modulators. Pooled cultures of either P. gingivalis or A. actinomycetemcomitans were disrupted using glass beads in a bead mill to prepare whole cell homogenates. These homogenates were then co-cultured with human peripheral blood mononuclear cells (PBMC) and known lymphocyte stimulators. Cultures were pulsed with tritiated thymidine, harvested, and radio label incorporation was determined. Responses to toxic shock syndrome toxin-1 (TSST-1) and pokeweed mitogen (PWM) were inhibited at high concentrations of bacterial homogenate. However, as the concentration was reduced, responses induced by PWM were restored while TSST-1 induced responses remained inhibited. Such results suggest that P. gingivalis and A. actinomycetemcomitans contain potent immunosuppressants with differential influences on lymphocyte population. These effects on B- and T-cells are independent of periodontal disease status and appear to exert their influence through non-toxic mechanisms. In addition, work currently underway presently indicates that obligate oral anaerobic bacteria such as P. gingivalis produce substances with some of the characteristics of superantigens.