Mechanisms by which Staphylococcus aureus induces cytokines and cell death in human keratinocytes and mouse fibroblasts2016Background: Staphylococcus aureus is an important trigger of flares in atopic dermatitis. The exact mechanisms by which S. aureus induces inflammatory responses and cell death in the skin epithelium is unclear. The aim of this thesis was to elucidate the cellular and molecular mechanisms by which S. aureus induces it's pathogenic effects on keratinocyte and fibroblast cell lines.Methods: Human keratinocytes (HEKa), and mouse embryonic fibroblasts (MEF) from the NC/Nga dermatitis prone mouse strain were used to investigate the induction of Th2-promoting cytokines (IL-33 and TSLP) and cell death by S. aureus. Cytokine levels were measured by ELISA and cytotoxicity by flow cytometry.Results: Live, but not killed S. aureus or other staphylococcal species, induced release of Th2-promoting cytokines (IL-33 and TSLP) and necrosis in both human and mouse cell lines. Cytokines were not induced by TLR2 ligands, and anti-TLR2 antibodies did not inhibit release, suggesting that the TLR2 pathway was not involved. By contrast, the release of cytokines was induced by a secreted, heat-labile factor/s and could be blocked by protease and PAR2 inhibitors, suggesting that the protease-PAR2 pathway was critical. NC/Nga mouse fibroblasts that lacked soluble IL-33 (sST2) receptor were more sensitive to the effects of S. aureus than control MEF.Conclusions: S. aureus is unique amongst staphylococcal species in it's ability to induce an inflammatory response and cytotoxicity in human keratinocytes and mouse fibroblasts. The protease-PAR2 pathway is critical to this bioactivity. Development of specific inhibitors of this pathway may provide novel therapies for treating S. aureus -induced eczema flares.