Porphyromonas gingivalis Lipopolysaccharide Isoforms Initiate Cytokine Tolerisation Responses in M1 and M2 Macrophages.

Objectives: Periodontitis is a chronic inflammatory disease characterised by excessive innate immune response to the oral biofilm bacteria. The pathogenesis of the disease manifests as periods of rapid progression and conversely, periods of remission. The “keystone” periopathogen Porphyromonas gingivalis has the ability to synthesise LPS isoforms, which differ in levels of endotoxin activity and in turn affect host immune response. Both pro-inflammatory M1 and regulatory M2 macrophages (MΦ’s) are hypothesised to be associated with the differential host response to this persistant pathogen. The objectives of this study are two-fold; i) to determine the sensitivity of M1 and M2 MΦ’s to endotoxin tolerance induced by LPS isoforms, and ii) to compare cytokine profiles to those produced by MΦ’s challenged with LPS extracted from subgingival plaque samples obtained from both healthy patients and those with chronic periodontitis.
Methods: The pro-monocyte THP-1 cell line was differentiated using PMA and Vitamin D3 into M1- and M2-like MΦ’s (respectively). These were pre-treated with Porphyromonas gingivalis LPS isoforms (m/z 1690 and 1435) and Escherichia coli K12 LPS for a period of 24 hours. Cells were then washed and stimulated for a further 18 hours. Macrophages were also treated with phenol-extracted LPS derived from the subgingival plaque samples. Supernatants were collected and levels of TNFα, IL-8, IL-10 and IL-18 secretion determined by sandwich ELISA.
Results: Our results indicate a differential LPS isoform-dependent cytokine profile between M1 and M2 MΦ’s in both the pre-stimulation and stimulation stages. Cytokine production suggests a link between LPS isoform-specific endotoxin tolerance and the response seen in M1 and M2 MΦ’s exposed to LPS extracted from patients.
Conclusions: The divergent cytokine production observed with tolerised M1 and M2 MΦ’s, identifies a mechanism whereby the pathogen is able to subvert and influence the immune response to its benefit by manipulating its LPS structure, potentially driving the progression of the disease.