Opposing roles of IL-17A and IL-25 in the regulation of TSLP production in human nasal epithelial cells.

Background: The importance of IL-17A, IL-17F, and IL-25 in allergic rhinitis (AR), as well as their possible role in regulation on thymic stromal lymphopoietin (TSLP) production in nasal epithelial cells, is not well understood.

Objective: To determine the possible regulation of IL-17A, IL-17F, and IL-25 on TSLP production in the initiation of allergic responses.

Methods: The levels of IL-17A, IL-17F, IL-25, and TSLP in nasal lavages of patients with AR were measured using an enzyme-linked immunosorbent assay (ELISA) and compared with that in normal controls. Then, primary human nasal epithelial cells (HNECs) were stimulated with dsRNA (0-75 microg/ml), as well as IL-17A (100 ng/ml), IL-17F (100 ng/ml), and IL-25(100 ng/ml). The mRNA expression of IL-17A, IL-17F, IL-25, TSLP, as well as the chemokines CCL20, IL-8, and eotaxin was analyzed using quantitative real-time PCR, and their protein levels in the supernatants of cultured HNECs were determined by ELISA.

Results: Both TSLP and IL-17 cytokines are significantly elevated in patients with AR. dsRNA was found to increase the production of IL-17F, IL-25, TSLP, CCL20, and IL-8 in HNECs. Furthermore, IL-25 significantly enhanced dsRNA-induced TSLP production in primary HNECs and was dominant to the inhibitory effect of IL-17A on TSLP regulation.

Conclusions: Our study provides the first evidence that both IL-17F and IL-25 can be induced by dsRNA in HNECs. Despite of the opposing effects of IL-17A and IL-25 on TSLP regulation in HNECs, IL-25 was dominant to IL-17A, providing a plausible explanation for the simultaneous upregulation of IL-17 cytokines and TSLP in patients with AR.