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BACKGROUND AND OBJECTIVE: The lipopolysaccharide of Aggregatibacter actinomycetemcomitans, a potent stimulator of the immune system, induces the secretion of inflammatory mediators that modulate periodontal tissue destruction. In this study, we investigated the tolerance response of human macrophages to stimulation with A. actinomycetemcomitans lipopolysaccharide. MATERIAL AND METHODS: U937 monocytes were differentiated into adherent macrophage-like cells by treatment with phorbol myristic acid. Macrophage-like cells were then pretreated for 24 h with either 0.01 or 0.1 microg/mL LPS A. actinomycetemcomitans. Culture medium supernatants were removed and cells were restimulated with LPS at 1 microg/mL. Cell-free supernatants were collected after 24 h of stimulation and analyzed by ELISA for TNF-alpha, IL-1 beta, IL-6, IL-8, PGE(2) and MMP-9. RESULTS: Phorbol myristic acid-differentiated U937 macrophages treated with low doses of lipopolysaccharide developed tolerance to subsequent lipopolysaccharide treatments, resulting in significantly reduced secretion of tumor necrosis factor-alpha. However, this tolerance response was associated with increased secretion of interleukin-1 beta and matrix metalloproteinase 9, whereas the secretion of interleukin-6, interleukin-8 and prostaglandin E(2) was unaffected. Phosphatidylinositol-3'-kinase inhibitors added during the tolerance-induction period markedly attenuated the increase in interleukin-1 beta secretion but had no effect on tumor necrosis factor-alpha. CONCLUSION: This study showed that A. actinomycetemcomitans lipopolysaccharide can induce a tolerance response in macrophages that alters the secretion of two important inflammatory mediators as well as of the tissue-degrading enzyme matrix metalloproteinase-9. This phenomenon may play a role in modulating the host inflammatory response and the progression of periodontitis. [ABSTRACT FROM AUTHOR]

Lectins were used to characterize glycoconjugates on the cell surface of Treponema denticola, a suspected periodontopathogen. Bacteria were first screened by light microscopy using fluorescein isothiocyanate-coupled lectins. Wheat germ agglutinin (WGA) showed a high reactivity to T. denticola. While the WGA-binding activity was accentuated following heating or detergent treatments of bacterial cells, the reaction was inhibited by incorporation of competing carbohydrates. Scanning and transmission electron microscope studies were conducted in order to characterize the distribution of the WGA-binding sites on the cell surface of T. denticola. Data from these studies confirmed that heat treatment increases the percentage of labeled profiles and suggest that the WGA-binding sites are concentrated on specific regions on the spirochete surface. Initial biochemical analysis indicated that the high reactivity to WGA resides in a peptidoglycan fraction. [ABSTRACT FROM AUTHOR]

Background and Objective: The lipopolysaccharide of Aggregatibacter actinomycetemcomitans, a potent stimulator of the immune system, induces the secretion of inflammatory mediators that modulate periodontal tissue destruction. In this study, we investigated the tolerance response of human macrophages to stimulation with A. actinomycetemcomitans lipopolysaccharide., Material and Methods: U937 monocytes were differentiated into adherent macrophage-like cells by treatment with phorbol myristic acid. Macrophage-like cells were then pretreated for 24 h with either 0.01 or 0.1 microg/mL LPS A. actinomycetemcomitans. Culture medium supernatants were removed and cells were restimulated with LPS at 1 microg/mL. Cell-free supernatants were collected after 24 h of stimulation and analyzed by ELISA for TNF-alpha, IL-1 beta, IL-6, IL-8, PGE(2) and MMP-9., Results: Phorbol myristic acid-differentiated U937 macrophages treated with low doses of lipopolysaccharide developed tolerance to subsequent lipopolysaccharide treatments, resulting in significantly reduced secretion of tumor necrosis factor-alpha. However, this tolerance response was associated with increased secretion of interleukin-1 beta and matrix metalloproteinase 9, whereas the secretion of interleukin-6, interleukin-8 and prostaglandin E(2) was unaffected. Phosphatidylinositol-3'-kinase inhibitors added during the tolerance-induction period markedly attenuated the increase in interleukin-1 beta secretion but had no effect on tumor necrosis factor-alpha., Conclusion: This study showed that A. actinomycetemcomitans lipopolysaccharide can induce a tolerance response in macrophages that alters the secretion of two important inflammatory mediators as well as of the tissue-degrading enzyme matrix metalloproteinase-9. This phenomenon may play a role in modulating the host inflammatory response and the progression of periodontitis.

Using an agar-skim milk gel method, over 300 oral bacterial isolates were tested for their ability to produce trypsin or chymotrypsin inhibitor. Eleven bacterial strains, including seven isolates identified as Bacteroides intermedius, were found to inhibit both proteolytic activities. The inhibitory factors of the 11 bacterial strains could be divided into two categories: i) heat-stable and dialysable, and ii) heat-labile and non-dialysable. The protease inhibitor activity of B. intermedius strains, which belongs to the latter category, was found in a membrane fraction as well as in a membrane-free extract. Furthermore, three strains of B. intermedius showed this inhibitory activity in the culture supernatant. In combination with plasma-derived protease inhibitors, the production of these additional protease inhibitors by oral bacteria could protect the host from tissue degradation.