Macrophage tolerance response to Aggregatibacter actinomycetemcomitans lipopolysaccharide induces differential regulation of tumor necrosis factor-alpha, interleukin-1 beta and matrix metalloproteinase 9 secretion.
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.


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.


CONCLUSIONS
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.
Tanabe
S-I
SI
Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Quebec City, Quebec, Canada.
Grenier
D
D
D016976:Aggregatibacter actinomycetemcomitans / Q000737:chemistry; D006801:Humans; D007108:Immune Tolerance / Q000276:immunology*; D053583:Interleukin-1beta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000276:immunology* / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000276:immunology*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D020298:U937 Cells
D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D020780:Matrix Metalloproteinase 9