Thymic stromal lymphopoietin-activated invariant natural killer T cells trigger an innate allergic immune response in atopic dermatitis

Background: Although invariant natural killer T (iNKT) cells have been shown to play a critical role in the pathogenesis of asthma, the role of iNKT cells in atopic dermatitis (AD) has not been well evaluated. Objective: We investigated whether iNKT cells in patients with AD increased and whether iNKT cells were activated by thymic stromal lymphopoietin (TSLP), which is highly expressed in keratinocytes of AD. Methods: We assessed the population of iNKT cells in PBMCs of patients with AD and healthy controls (HCs) using flow cytometry. Immunohistochemistry was used to evaluate iNKT cells and TSLP expression in AD and HC skin. We also evaluated whether iNKT cells expressed the TSLP receptor, the effects of TSLP on iNKT cells, and iNKT cell-dendritic cell interactions in a TSLP-rich environment. Results: There were more iNKT cells among PBMCs of patients with moderate to severe AD than mild AD (P < .05) and HC (P < .001). The number of iNKT cells was significantly larger in severe AD skin lesions than in mild (P < .001) or moderate AD skin lesions (P < .05). TSLP expression increased in lesional skin (P < .001) but not in the sera of patients with AD (P = .729) compared with HC. iNKT cells expressed TSLP receptor protein and mRNA. TSLP directly activated iNKT cells to secrete IL-4 and IL-13, and the concurrent addition of dendritic cells further activated IFN-gamma expression. Conclusion: Increased iNKT cells activated by TSLP, especially in patients with severe AD, might play an essential role in the innate allergic immune response in AD. (J Allergy Clin Immunol 2010;126:290-9.)