Cytokine milieu modulates release of thymic stromal lymphopoietin from human keratinocytes stimulated with double-stranded RNA

BackgroundThymic stromal lymphopoietin (TSLP) plays a key role in allergic diseases, such as atopic dermatitis (AD) and asthma. TSLP is highly expressed by keratinocytes in skin lesions of patients with AD, but environmental triggers for its release from keratinocytes with endogenous factors are not well understood. Patients with AD, in whom allergic sensitization is already established, are susceptible to viral dissemination.ObjectivesWe investigated TSLP's release from primary human keratinocytes stimulated with a Toll-like receptor (TLR) 3 ligand, polyinosinic-polycytidylic acid, which mimics viral double-stranded RNA (dsRNA), and its modulation by cytokines.MethodsPrimary human keratinocytes were stimulated with TLR ligands, cytokines, or both. TSLP released into culture supernatants was measured by means of ELISA.ResultsStimulation of keratinocytes with dsRNA induced release of TSLP and upregulated gene expression of TSLP and other cytokines and chemokines. The release of TSLP was enhanced by the addition of IL-4, IL-13, and/or TNF-α. With or without the TH2/TNF cytokines, the dsRNA-induced release of TSLP was upregulated by IFN-α and IFN-β and suppressed by IFN-γ, TGF-β, or IL-17.ConclusionsThe effect of the TLR3 ligand on keratinocytes suggests contribution of viral dsRNA to skin inflammations under the influence of a cytokine milieu. The results imply that viral dsRNA and a TH2 cytokine milieu might promote TH2-type inflammation through an induction of TSLP expression, suggesting that a vicious cycle exists between AD with TH2-type inflammation and viral infections and a possible blockade of this cycle by other cytokine milieus provided by cells, such as TH1, regulatory T, and TH17 cells.