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

Background

Thymic 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.

Objectives

We 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.

Methods

Primary human keratinocytes were stimulated with TLR ligands, cytokines, or both. TSLP released into culture supernatants was measured by means of ELISA.

Results

Stimulation 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 T_H2/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.

Conclusions

The 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 T_H2 cytokine milieu might promote T_H2-type inflammation through an induction of TSLP expression, suggesting that a vicious cycle exists between AD with T_H2-type inflammation and viral infections and a possible blockade of this cycle by other cytokine milieus provided by cells, such as T_H1, regulatory T, and T_H17 cells.

Key words: Thymic stromal lymphopoietin, keratinocyte, double-stranded RNA, cytokine milieu, atopic dermatitis, viral exposure, viral infection, vicious cycle, promotion and blockade

Abbreviations used: AD, Atopic dermatitis, DC, Dendritic cell, dsRNA, Double-stranded RNA, Pam₃CSK₄, (S)-[2,3-Bis(palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-Cys-(S)-Ser-(S)-Lys₄-OH, 3HCl, poly I:C, Polyinosinic-polycytidylic acid, TLR, Toll-like receptor, Treg, Regulatory T, TSLP, Thymic stromal lymphopoietin