TGF-β Is Required To Maintain the Pool of Immature Langerhans Cells in the Epidermis

The pivotal role of TGF-beta in Langerhans cell (LC) development has been previously established in TGF-beta-deficient mice, which lack epidermal LCs. As to whether TGF-beta also governs LC homeostasis and function remains elusive. To assess the role of TGF-beta-mediated control of cutaneous dendritic cells (DCs) in vivo, we generated mice with a conditional knockout of the TGF-beta receptor 1 (TbetaR1) under a DC-specific promoter (DC-TbetaR1(del) mice). While initial LC seeding occurred in DC-TbetaR1(del) mice, the cells disappeared from the epidermis during the first week of life. TbetaR1-deficient LCs demonstrated spontaneous maturation and gained migratory potential based on increased surface expression of MHC class II, costimulatory molecules, and CCR7 and downregulation of E-cadherin. In parallel to their early loss from the epidermis, migrating LCs were reduced in the dermis and skin-draining lymph nodes of adult DC-TbetaR1(del) mice, whereas the number of Langerin(+) dermal DCs was similar to wild-type. In the absence of LCs, low-dose contact hypersensitivity in DC-TbetaR1(del) mice was significantly diminished. In contrast, ear swelling was restored to wild-type levels when a higher hapten dose was applied to efficiently target TbetaR1-deficient dermal DCs. In conclusion, TGF-beta inhibits in vivo LC maturation and migratory phenotype, identifying TGF-beta as a critical factor controlling LC homeostasis in the steady state.