Oxygen tension modulates oral epithelial cytokine response to bacterial stimuli

Studies have demonstrated that there is an inverse relationship between pocket depth and pocket oxygen tension. It has also been shown that deep pockets (7-10mm) are associated with moderate anaerobic bacteria such as P. intermedia, P. gingivalis and F. nucleatum). However, little is known about how the host tissues respond to colonising bacteria under differing oxygen tensions within the gingival crevice/periodontal pocket. Objectives: This study aimed to investigate the effect of three different oxygen tensions upon the cytokine response of gingival epithelial cells when exposed to 11 species of killed aerobic or anaerobic bacteria. Methods: Confluent monolayers of H400 oral epithelial cells were incubated in cell culture media pre-equilibrated at 2%, 10% or 21% oxygen and placed in a chamber of the same atmospheric oxygen percentage. The cultures were stimulated with S. mitis, A. actinomycetemcomitans, A. viscosus, S. constellatus, F. nucleatum nucleatum, P. micros, P. intermedia, T. forsythensis, P. gingivalis W83, LPS (15µg/ml) or vehicle control. After 3h, culture media was harvested and IL-8 and TNF-alpha levels measured by ELISA. Dissolved oxygen was measured in pre-equilibrated media by the Winkler test (range 3-4mg/l; ~55-75mmHg). Results: An oxygen-tension dependent effect on cytokine production was observed; IL-8 and TNF-alpha production were shown to be greatest at 2% oxygen and lowest at 21% oxygen for the majority of organisms tested. The greatest cytokine response was elicited by the anaerobic bacteria P. intermedia, T. forsythensis and P. gingivalis. Conclusions: These data demonstrate a greater pro-inflammatory host response to bacteria present in more anaerobic conditions (equivalent to deeper pockets), which may have implications for disease pathogenesis and/or therapy.