No abstract

No abstract

Background: Thymic stromal lymphopoietin (TSLP), highly expressed by keratinocytes in skin lesions of atopic dermatitis patients and bronchial epithelial cells in asthma, plays a key role in allergic diseases. Information on triggers for the release of TSLP in keratinocytes is still limited. Keratinocytes express Toll-like receptor (TLR) 5, the ligand for which is flagellin, the major structural protein of the flagella of Gram-negative bacteria. IL-4, IL-13 and TNF-α (Th2/TNF) are associated with allergic diseases. TGF-α, one of the ligands for the epidermal growth factor receptor, is overexpressed in keratinocytes in atopic dermatitis. We investigated the induction of TSLP expression in keratinocytes stimulated with flagellin and its modulation by the Th2/TNF cytokines and TGF-α. Methods: Primary human keratinocytes were stimulated with flagellin with or without cytokines. The TSLP released was measured by ELISA. Gene expression was analyzed by quantitative real-time PCR. Results: Stimulation of keratinocytes with flagellin induced the release of TSLP protein and upregulation of the gene expression of TSLP and other pro-inflammatory molecules. The flagellin-induced release of TSLP was enhanced by the Th2/TNF cytokines or TGF-α. Small interfering RNA-mediated knockdown of TLR5 expression suppressed the flagellin-induced TSLP gene expression. Conclusions: Flagellin induces TSLP expression in keratinocytes via TLR5 and the expression can be upregulated by a cytokine milieu with Th2/TNF or TGF-α, suggesting that exposure of barrier-defective skin to Gram-negative bacteria or environmental flagellin contributes to the initiation and/or amplification of Th2-type skin inflammation including atopic dermatitis through the induction of TSLP expression in keratinocytes.

No abstract

Background: Thymic stromal lymphopoietin (TSLP), highly expressed by keratinocytes in skin lesions in atopic dermatitis and bronchial epithelial cells in asthma, plays a key role in allergic diseases. Double-stranded RNA (dsRNA) stimulates keratinocytes to release TSLP in vitro. Objective: To examine the potential of glucocorticoids and calcineurin inhibitors to suppress dsRNA-induced release of TSLP from keratinocytes. Methods: Primary human kerarinocytes were stimulated with dsRNA in the presence of IL-4, IL-13 and TNF-α. TSLP release was measured by ELISA. The effects of glucocorticoids and 2 calcineurin inhibitors, cyclosporin A and FK506/tacrolimus, were analyzed. Results: The glucocorticoids inhibited dsRNA-induced release of TSLP. The inhibitory effect became saturated (50–70% reduction) at concentrations higher than 10^–10M. Cyclosporin A inhibited the release of TSLP by 50–60% at 10^–5 and 10^–4M. FK506 had no effect at 10^–5M or less, but almost completely inhibited the release of TSLP at 10^–4M. No synergistic effect was obtained with a glucocorticoid plus either of the calcineurin inhibitors. An additive inhibitory effect was obtained with a glucocorticoid plus 10^–5M cyclosporin A. Glucocorticoid inhibited dsRNA-induced TSLP transcription in the absence of Th2/TNF cytokines. Conclusions: Glucocorticoids inhibited the dsRNA-induced release of TSLP in the atopic cytokine milieu at much lower concentrations than calcineurin inhibitors, suggesting that they could be effective in the treatment of atopic dermatitis when exogenous or endogenous dsRNA is involved in the pathogenesis. In addition, the in vitro system established in this study would be useful for screening of therapeutic reagents which target TSLP expression.