BACKGROUND" Human thymic stromal lymphopoietin (TSLP) is expressed in the human asthmatic lung and activates dendritic cells (DCs) to strongly induce proallergic T-helper type 2 (Th2) cell responses, suggesting that TSLP plays a critical role in the pathophysiology of human asthma. Th2 cells are predominantly involved in mild asthma, whereas a mixture of Th1 and Th2 cells with neutrophilic inflammation, probably induced by Th17, affects more severe asthmatic disease. Exacerbation of asthmatic inflammation is often triggered by airway-targeting RNA viral infection; virus-derived double-stranded RNA, Toll-like receptor (TLR)3 ligand, activates bronchial epithelial cells to produce pro-inflammatory mediators, including TSLP.
Objective: Because TSLPR-expressing DCs express TLR3, we examined how the relationship between TSLP and TLR3 ligand stimulation influences DC activation.
Methods: CD11c(+)DCs purified from adult peripheral blood were cultured in TLR ligands containing media with or without TSLP and then co-cultured with allogeneic naïve CD4(+)T cells.
Results: CD11c(+) DCs responded to a combination of TSLP and TLR3 ligand, poly(I : C), to up-regulate expression of the functional TSLP receptor and TLR3. Although TSLP alone did not induce IL-23 production by DCs, poly(I : C) alone primed DCs for the production of IL-23, and a combination of TSLP and poly(I : C) primed DCs for further production of IL-23. The addition of poly(I : C) did not inhibit TSLP-activated DCs to prime naïve CD4(+) T cells to differentiate into inflammatory Th2 cells. Furthermore, DCs activated by a combination of TSLP and poly(I : C) primed more naïve CD4(+) T cells to differentiate into Th17-cytokine-producing cells with a central memory T cell phenotype compared with DCs activated by poly(I : C) alone.
Conclusions: These results suggest that through DC activation, human TSLP and TLR3 ligands promote differentiation of Th17 cells with the central memory T cell phenotype under Th2-polarizing conditions.