Langerhans cells (LCs) are bone marrow (BM)–derived epidermal dendritic cells (DCs) that develop from precursors found in the dermis. Epidermal LCs are absent in transforming growth factor (TGF) β1-deficient mice. It is not clear whether TGFβ1 acts directly on LC precursors to promote maturation or whether it acts on accessory cells, which in turn affect LC precursors. In addition, the physiologic source of TGFβ1 is uncertain because BM chimera experiments showed that neither hematopoietic nor nonhematopoietic-derived TGFβ1 is required for LC development. To address these issues, we created mice transgenic for a bacterial artificial chromosome (BAC) containing the gene for human Langerin into which Cre recombinase had been inserted by homologous recombination (Langerin-Cre). These mice express Cre selectively in LCs, and they were bred to floxed TGFβRII and TGFβ1 mice, thereby generating mice with LCs that either cannot respond to or generate TGFβ1, respectively. Langerin-Cre TGFβRII mice had substantially reduced numbers of epidermal LCs, demonstrating that TGFβ1 acts directly on LCs in vivo. Interestingly, Langerin-Cre TGFβ1 mice also had very few LCs both in the steady state and after BM transplantation. Thus, TGFβ1 derived from LCs acts directly on LCs through an autocrine/paracrine loop, and it is required for LC development and/or survival.

SUMMARY Mice lacking epidermal Langerhans cells (LC) develop exaggerated contact-hypersensitivity (CHS) responses due to the absence of LC during sensitization/initiation. Examination of T cell responses reveals that the absence of LC leads to increased numbers of hapten-specific CD4 and CD8 T cells but does not alter cytokine expression or development of Treg. CHS responses and antigen-specific T cells are increased in mice in which MHC-II is ablated specifically in LC suggesting that direct cognate interaction between LC and CD4 cells is required for LC suppression. LC-derived IL-10 is also required for optimal inhibition of CHS. Both LC-derived IL-10 mediated suppression and full LC activation require LC expression of MHC-II. These data support a model in which cognate interaction of LC with CD4 T cells enables LC to inhibit expansion of antigen-specific responses via elaboration of IL-10.

Langerhans cells (LCs) are bone marrow (BM) -derived epidermal dendritic cells (DCs) that develop from precursors found in the dermis. Epidermal LCs are absent in transforming growth factor (TGF) ␤ 1-defi cient mice. It is not clear whether TGF ␤ 1 acts directly on LC precursors to promote maturation or whether it acts on accessory cells, which in turn affect LC precursors. In addition, the physiologic source of TGF ␤ 1 is uncertain because BM chimera experiments showed that neither hematopoietic nor nonhematopoietic-derived TGF ␤ 1 is required for LC development. To address these issues, we created mice transgenic for a bacterial artifi cial chromosome (BAC) containing the gene for human Langerin into which Cre recombinase had been inserted by homologous recombination (Langerin-Cre). These mice express Cre selectively in LCs, and they were bred to fl oxed TGF ␤ RII and TGF ␤ 1 mice, thereby generating mice with LCs that either cannot respond to or generate TGF ␤ 1, respectively. Langerin-Cre TGF ␤ RII mice had substantially reduced numbers of epidermal LCs, demonstrating that TGF ␤ 1 acts directly on LCs in vivo. Interestingly, Langerin-Cre TGF ␤ 1 mice also had very few LCs both in the steady state and after BM transplantation. Thus, TGF ␤ 1 derived from LCs acts directly on LCs through an autocrine/paracrine loop, and it is required for LC development and/or survival.