The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of many transformed but also of non-transformed cells. In addition, TRAIL receptor activation has been reported to activate non-apoptotic signaling pathways. Here, we report an increased expression of TRAIL in peripheral blood T cells and monocytes from patients with atopic dermatitis (AD) compared with control individuals. High TRAIL expression was also observed in skin-infiltrating T cells of AD patients. Topical tacrolimus treatment reduced the total number of T cells in the skin, but the relative proportion of TRAIL-positive cells within both CD4+ and CD8+ cell populations did not change. TRAIL was demonstrated to induce the expression of interleukin-1 receptor antagonist (IL-1Ra) in keratinocytes in a caspase-independent manner in vitro. Moreover, increased expression of IL-1Ra was observed in keratinocytes of AD lesional skin. These data suggest that TRAIL-expressing inflammatory skin cells may contribute to the epidermal activation of the IL-1Ra gene in AD.