Porphyromonas gingivalis lipopolysaccharide: an unusual pattern recognition receptor ligand for the innate host defense system

Lipopolysaccharide (LPS) is a key inflammatory mediator. Due to its ability to potently activate host inflammatory and innate defense responses, it ha s been proposed to function as an important molecule that alerts the host o f potential bacterial infection. However, although highly conserved, LPS co ntains important structural differences among different bacterial species t hat can significantly alter host responses. For example, LPS obtained from Porphyromonas gingivalis: an etiologic agent for periodontitis; causes a hi ghly unusual host innate host response. II is an agonist for human monocyte s and an antagonist for human endothelial cells. Correspondingly, although it activates p38 MAP kinase in human monocytes, P. gingivalis LPS does not activate p38 nor ERK MAP kinase in endothelial cells. In Fact, P. gingivali s LPS is an effective inhibitor of Escherichia coli LPS induced p38 phospho rylation. These data show that P. gingivalis LPS modulates host defenses in endothelial cells by interfering with MAP kinase activation. In addition, P. gingivalis LPS is unusual in that it engages TLR-2 but not TLR-4 when ex amined in stably transfected CHO cell lines. We propose that, since LPS is a key ligand for the human innate host defense system, these unusual proper ties of P. gingivalis LPS are associated with the bacterium's role in the p athogenesis of periodontitis.