NFκB activation in keratinocytes determines Th1 vs. Th2 type responses

Objective: The aim of our study is to establish the mechanism by which periodontal pathogens are able to establish chronic infection in the oral cavity resulting in tissue destruction and loss of tooth support.

Methods: Human Oral keratinocytes (HOKs) with intact NFκB and those with constitutively active as well as NFκB knock down HOKs were used in co-cultures of immune effectors in the presence of F. nucleatum. Levels of cell death and released cytokines/chemokines were determined using multiplex cytokine array, 51Cr release assay and Annexin V and propidium iodide staining.

Results: Addition of F. nucleatum elevated secretion of TNF-α, IFN-γ, IL-6, IL-1β, GM-CSF and increased the secretion of key chemokines in the co-cultures of immune effectors with HOKs. Increased induction of IFN-γ in these co-cultures, was directly proportional to the levels of cell death induced in HOKs by F. nucleatum, and depended on the levels of NFκB expression in HOKs. Thus, an inverse secretion of IFN-γ over IL-6 was seen when NFκB was suppressed by an IκB super-repressor in HOKs, whereas elevation in NFκB was inhibitory to the release of IFN-γ in these co-cultures. Since induction of cell death by F. nucleatum was seen in TNF-α+/+ but not in TNF-α-/- cells, TNF-α is one of the major mediators of cell death by F. nucleatum.

Conclusions: Inability of HOKs to maintain high NFκB induction during infection with F. nucleatum could be the underlying mechanism of chronic periodontal infection, since HOKs induce large levels of TNF-α secretion during their interaction with immune effectors resulting in greater death of HOKs, and continuous recruitment of inflammatory effectors. Therefore, the status of NFκB activation by the oral microflora in oral epithelial cells can determine the extent and the type of Th1 vs. Th2 type inflammatory responses by the immune effectors induced during periodontal disease.

R01-12880