Porphyromonas gingivalis Lipopolysaccharide Contains Multiple Lipid A Species That Functionally Interact with Both Toll-Like Receptors 2 and 4

Abstract

The innate host response to lipopolysaccharide (LPS) obtained from Porphyromonas gingivalis is unusual in that different studies have reported that it can be an agonist for Toll-like receptor 2 (TLR2) as well as an antagonist or agonist for TLR4. In this report it is shown that P. gingivalis LPS is highly heterogeneous, containing more lipid A species than previously described. In addition, purification of LPS can preferentially fractionate these lipid A species. It is shown that an LPS preparation enriched for lipid A species at m/z 1,435 and 1,450 activates human and mouse TLR2, TLR2 plus TLR1, and TLR4 in transiently transfected HEK 293 cells coexpressing membrane-associated CD14. The HEK cell experiments further demonstrated that cofactor MD-2 was required for functional engagement of TLR4 but not of TLR2 nor TLR2 plus TLR1. In addition, serum-soluble CD14 effectively transferred P. gingivalis LPS to TLR2 plus TLR1, but poorly to TLR4. Importantly, bone marrow cells obtained from TLR2؊/؊ and TLR4 ؊/؊ mice also responded to P. gingivalis LPS in a manor consistent with the HEK results, demonstrating that P. gingivalis LPS can utilize both TLR2 and TLR4. No response was observed from bone marrow cells obtained from TLR2 and TLR4 double-knockout mice, demonstrating that P. gingivalis LPS activation occurred exclusively through either TLR2 or TLR4. Although the biological significance of the different lipid A species found in P. gingivalis LPS preparations is not currently understood, it is proposed that the presence of multiple lipid A species contributes to cell activation through both TLR2 and TLR4.

IL-8 and IDO Expression by Human Gingival Fibroblasts via TLRs

“…It has been shown that highly purified P. gingivalis LPS possess lipid A heterogeneity, which may contribute to their ability to interact with either TLR2 or TLR4 (39). P. gingivalis LPS at a concentration of 50 g/ml used in our study predominantly stimulated HGFs via TLR2 and to a lesser extend via TLR4 (InvivoGen product information).…”

Subversion of Innate Immunity by Periodontopathic Bacteria via Exploitation of Complement Receptor-3

“…Interestingly, P. gingivalis appears to be biased toward preferentially activating TLR2 both in vitro and in vivo (Burns et al, 2006;Hajishengallis et al, 2006a). Although bacterial LPS in general is a strong TLR4 agonist, P. gingivalis seems to deviate from the norm in that it expresses a heterogeneous mixture of lipid A species, which can induce cell activation through TLR2 or TLR4 (weakly) or even antagonize TLR4-induced cell activation (Darveau et al, 2004;Dixon and Darveau, 2005). Therefore, by altering the proportions of its different lipid A moieties, P. gingivalis may increase its virulence through manipulation of the innate response in ways that predominant activation of TLR2 over TLR4, may allow effective exploitation of CR3.…”

Importance of heterogeneity in Porhyromonas gingivalis lipopolysaccharide lipid A in tissue specific inflammatory signalling

“…TLR2 and cluster of differentiation (CD) 14 mRNA were regulated differentially in human gingival epithelia while the modulation of hBD-2 expression was suggested to occur through co-operation of both TLR2 and TLR4 [46]. In another study, multiple lipid A species interacted functionally with both TLR2 and TLR4 [15]. However, as already mentioned, the TLR2 agonist activity in P. gingivalis is most likely due to a lipoprotein, and treatment of LPS with lipoproteinase as free LPS substantially attenuated the TLR2 engaging activity [17].…”

“…In terms of bone loss, in vitro and in vivo experiments have provided conflicting data. For example, when P. gingivalis is co-cultured with bone cells in vitro , the effect on bone resorbing cells appears to be mediated through engagement of both TLR2 and TLR4 [15,19]. However, similar experiments conducted in experimental animals orally infected with P. gingivalis predominantly show bone loss to be mediated by TLR2 [20–22].…”