Strain-Dependent Activation of Monocytes and Inflammatory Macrophages by Lipopolysaccharide of Porphyromonas gingivalis

Porphyromonas gingivalis is one of the pathogens associated with periodontal diseases, and its lipopolysaccharide (LPS) has been suggested as a possible virulence factor, acting by stimulation of host cells to secrete proinflammatory mediators. However, recent studies have shown that P. gingivalis LPS inhibited some components of the inflammatory response. The present study was designed to test the hypothesis that there are strain-dependent variations in the ability of P. gingivalis LPS to elicit the host inflammatory response. By using LPS preparations from two strains of P. gingivalis, W50 and A7346, the responses of mouse macrophages and human monocytes were evaluated by measuring the secretion of nitric oxide (NO) and tumor necrosis factor alpha (TNF-α). Both direct and indirect (priming) effects were investigated. LPS from Salmonella typhosa was used as a reference LPS. P. gingivalis A7436 LPS induced lower secreted levels of NO from the tested cells than S. typhosa LPS but induced similar levels of TNF-α. In contrast, LPS from P. gingivalis W50 did not induce NO or TNF-α secretion. Preincubation of macrophages with LPS from S. typhosa or P. gingivalis A7436 prior to stimulation with S. typhosa LPS upregulated NO secretion and downregulated TNF-α secretion, while preincubation with P. gingivalis W50 LPS enhanced both TNF-α and NO secretory responses. These results demonstrate that LPSs derived from different strains of P. gingivalis vary in their biological activities in vitro. The findings may have an impact on our understanding of the range of P. gingivalis virulence in vivo.