Maturing Langerin- dendritic cells control expansion of Foxp3+ regulatory T cells in the skin after ultraviolet B exposure

Dendritic cells (DCs) are critical regulators of Foxp3+ regulatory T (Treg) cell-homeostasis. Recent reports have suggested that Langerin+ DCs, especially epidermal Langerhans cells (LCs), play an important role in inducing Treg cells. We investigated the roles of Langerin+ DCs in expanding Treg cells after ultraviolet B (UVB) exposure. We found that Treg cells were expanded in UVB-exposed skin in vivo even without Langerin+ DCs including LCs. In the UVB-exposed skin, Langerin- DCs showed a mature phenotype, and the Treg-expansion induced by UVB was significantly abrogated by CD86/CD80 blockade. Thus, maturing Langerin- DCs, rather than LCs and Langerin+ dermal DCs, are the main contributors to UVB-induced Treg expansion in the skin. These results indicate that a new mechanism for UVB-mediated tolerance, which can provide a new concept of treatment using DC-mediated tolerance.