Sphingolipid Synthesis By Porphyromonas gingivalis Dampens The Inflammatory Response

Objectives: Porphyromonas gingivalis, like other bacteria belonging to the phylum Bacteroidetes synthesize sphingolipids (SLs). Our studies have discovered that synthesis of sphingolipids (SLs) by P. gingivalis dampens the inflammatory response of THP-1 macrophages to this bacterium and that this immunosuppression does not require physical cell-to-cell contact between the host cells and P. gingivalis (transwell experiments). Our working hypothesis is that secreted outer membrane vesicles (OMVs) have the ability to mitigate the immune response. The goal of this study was to determine if various nutrients and growth condition altered the production and immunomodulatory properties of OMVs produced by the wild-type strain W83 and the SL-null mutant.
Methods: Outer membrane vesicles (OMV) were isolated from strain W83 and an SL-null mutant strain (W83ΔSPT). P. gingivalis was grown in either rich bacterial medium (TSBHK) or tissue culture medium (RPMI with 10% fetal bovine serum). OMV’s from each respective sample were then added to THP-1 cells, a macrophage like cell line derived from an acute monocytic leukemia patient. Samples were collected at 6 hrs and 24 hrs and Luminex immunoassays were performed to determine the effects of the various OMVs on the cytokine levels produced by the THP-1 cells.
Results: Our data demonstrate that OMVs produced by the SL-null strain elicit a robust inflammatory response (elevated IL-1β, IL-6, IL-10, IL-8, RANTES, and TNFα) from THP1 macrophages while OMVs produced by the parent strain W83 do not.


Conclusions: Our data suggest that SL synthesis is central to the ability of P. gingivalis to manipulate an inflammatory response by THP-1 cells. Future studies will include more detailed analysis of the role of growth parameters on the immunoregulatory properties of OMVs with an overall goal to elucidate the underlying mechanisms that dampen the inflammatory response.