Expression of thymic stromal lymphopoietin (TSLP) in allergic rhinitis: Induction of tight junction proteins in human nasal epithelial cells and dendritic cells by epithelial-derived TSLP

Thymic stromal lymphopoietin (TSLP) is an interleukin 7-like cytokine that triggers dendritic cell (DC)-mediated T helper 2-type inflammatory responses and is considered to be a master switch for allergic inflammation such as that in asthma and atopic dermatitis. Furthermore, proinflammatory cytokines and Toll-like receptor ligands can induce TSLP production in human bronchial epithelial cells and human keratinocytes. We first found high expression of endogenous TSLP in the epithelium of allergic rhinitis with recruitment and infiltration of DCs. In culture, the TSLP production in human nasal epithelial cells was markedly and significantly increased by treatment with the proinflammatory cytokines interleukin 1β/tumor necrosis factor-α and a Toll-like receptor 2 ligand, P3CSK4. Since it is also thought that TSLP expression not only activates DCs but also affects the epithelial barrier in allergic rhinitis, we investigated the effects of TSLP on tight junctions of human nasal epithelial cells and DCs in vitro. Treatment with TSLP enhanced the barrier function of human nasal epithelial cells in vitro together with an increase of the tight junction proteins claudin-1,-4,-7, and occludin. Furthermore, TSLP could exclusively induce claudin-7 expression in mouse DC line XS52, which expressed tight junction molecules claudin-1,-3,-4,-6,-7,-8, occludin and tricellulin.These findings suggest that nasal epithelial-derived TSLP plays an important role in allergic rhinitis as well as asthma and atopic dermatitis and may control tight junctions of epithelial cells and DCs to preserve the epithelial barrier and promote direct sampling of antigens by DCs.