Biological activities of lipopolysaccharides from oral bacteria and their relevance to the pathogenesis of chronic periodontitis.

Chronic periodontitis is a major cause of tooth loss in adults and is a consequence of the colonisation of the subgingival region by organisms such as Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum. Lipopolysaccharide (LPS) is a constituent of the cell walls of all of these bacteria and is found in large quantities on the surfaces of periodontally-diseased teeth. LPS from oral bacteria has a marked effect on most types of cell found in the periodontal tissues including macrophages, lymphocytes, fibroblasts and osteoblasts. Fibroblasts and macrophages respond to oral LPS by secreting a range of cytokines, and other effector molecules, with inflammatory, immunomodulatory and tissue-destroying capabilities. Lymphocytes are stimulated by LPS to produce a wide range of antibodies with different specificities, hence exacerbating the inflammatory response. By its actions on bone cells, LPS can stimulate bone resorption and inhibit bone formation resulting in erosion of the tooth-supporting alveolar bone. There is, therefore, considerable evidence implicating LPS in the pathogenesis of chronic periodontitis. However, the possible involvement of other biologically-active bacterial components must not be overlooked.