Cutting Edge: Proinflammatory and Th2 Cytokines Synergize to Induce Thymic Stromal Lymphopoietin Production by Human Skin Keratinocytes

We recently showed that dendritic cells (DCs) activated by thymic stromal lymphopoietin (TSLP) prime naive CD4 + T cells to differentiate into T helper type 2 (Th2) cells that produced high amounts of tumor necrosis factor-α (TNF-α), but no interleukin (IL)-10. Here we report that TSLP induced human DCs to express OX40 ligand (OX40L) but not IL-12. TSLP-induced OX40L on DCs was required for triggering naive CD4 + T cells to produce IL-4, -5, and -13. We further revealed the following three novel functional properties of OX40L: (a) OX40L selectively promoted TNF-α, but inhibited IL-10 production in developing Th2 cells; (b) OX40L lost the ability to polarize Th2 cells in the presence of IL-12; and (c) OX40L exacerbated IL-12–induced Th1 cell inflammation by promoting TNF-α, while inhibiting IL-10. We conclude that OX40L on TSLP-activated DCs triggers Th2 cell polarization in the absence of IL-12, and propose that OX40L can switch IL-10–producing regulatory Th cell responses into TNF-α–producing inflammatory Th cell responses.

Atopic dermatitis is a highly pruritic chronic inflammatory skin disorder affecting 10-20% of children worldwide. Symptoms can persist or begin in adulthood. It is also the most common cause of occupational skin disease in adults. This disease results from an interaction between susceptibility genes, the host's environment, pharmacological abnormalities, skin barrier defects, and immunological factors. New management approaches have evolved from advances in our understanding of the pathobiology of this common skin disorder.

The role of transforming growth factor-beta (TGF-beta) in inhibiting T cell functions has been studied with dominant-negative TGF-beta receptor transgenic models; however, the full impact of TGF-beta signaling on T cells and the mechanisms by which TGF-beta signals remain poorly understood. Here we show that mice with T cell-specific deletion of TGF-beta receptor II developed lethal inflammation associated with T cell activation and differentiation. In addition, TGF-beta signaling positively regulated T cell development and homeostasis. Development of CD8+ T cells and NKT cells, maintenance of peripheral Foxp3-expressing regulatory T cells, and survival of CD4+ T cells all depended on TGF-beta signaling. Both T helper 1 (Th1) differentiation and survival of activated CD4+ T cells required T-bet, the TGF-beta-regulated transcription factor, which controlled CD122 expression and IL-15 signaling in Th1 cells. This study reveals pleiotropic functions of TGF-beta signaling in T cells that may ensure a diverse and self-tolerant T cell repertoire in vivo.