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IntroductionTwo in vitro systems for the generation of human dendritic cells (DCs) are widely used for basic and clinically oriented research: monocyte-derived DCs (moDCs) and hematopoietic progenitor cell (HPC)-derived DCs. In the first system, granulocytemacrophage colony-stimulating factor (GM-CSF) plus interleukin-4 (IL-4) are added to peripheral blood monocytes to generate moDCs. 1 This system is most widely applied for generating human DCs. In the second model, CD34 ϩ HPCs are stimulated in transforming growth factor ␤1 (TGF-␤1)-supplemented serumfree cultures (containing basic DC cytokines GM-CSF, tumor necrosis factor ␣ [TNF␣], stem cell factor [SCF] with or without Flt3L) for generating Langerhans cells (LCs), a DC subtype that resides within epithelial tissue. 2,3 Exclusion of TGF-␤1 from this latter culture system abrogates LC differentiation and de-represses a program of monocyte generation from CD34 ϩ cells. 3 When these latter HPC cultures are initiated in the presence of serum without TGF-␤1, 2 pathways of CD1a ϩ DCs are simultaneously generated, ie LCs and non-LC interstitial/dermal-type DCs. 4 These populations arise from 2 separate precursor pathways at culture day 5. A CD1a ϩ CD14 Ϫ precursor gives rise to LCs, whereas a CD1a Ϫ CD14 ϩ precursor can give rise to non-LC DCs, which share many features with moDCs generated from peripheral blood monocytes. 4,5 This CD1a Ϫ CD14 ϩ intermediate population can be further subdivided into 2 functional subsets based on CD11b (CD11b ϩ CD14 ϩ versus CD11b Ϫ CD14 ϩ monocytic cells). CD11b ϩ CD14 ϩ cells can be induced by GM-CSF plus IL-4 to develop into intDC/moDCs or by M-CSF to macrophage differentiation. Conversely, CD11b Ϫ CD14 ϩ intermediates, which represent early monocytic cells, retain LC differentiation capacity in the presence of TGF-␤1. 6 Therefore, a CD14 ϩ monocytic precursor can be induced to develop along 2 separate pathways in vitro depending on IL-4 (moDCs) versus TGF-␤1 (LCs) cytokine signals.IL-4 versus TGF-␤1 antagonize each other's function to induce moDCs versus LCs. Neutralizing anti-TGF-␤1 mAb represses LC generation in favor of CD14 ϩ monocyte generation. 7 Similarly, the addition of IL-4 to TGF-␤1-supplemented LC generation cultures of CD34 ϩ cells represses LC differentiation in favor of inducing non-LC DC differentiation. 7 Conversely, the addition of TGF-␤1 to GM-CSF plus IL-4-containing moDC cultures of peripheral blood monocytes polarizes these cells toward an LC-like phenotype. 8 In line with this, TGF-␤1 in the epidermal microenvironment is critical for LC differentiation in vivo. [9][10][11] Functional differences between moDCs versus LCs are increasingly recognized. However, very little is known about the molecular mechanisms controlling the lineage commitment of these cells to develop into different DC subsets (ie, LCs and non-LC moDCs).We recently performed mechanistic studies on the involvement of family members of the nuclear hormone receptor system, ie, retinoid X receptor-alpha (RXR␣) and vitamin D 3 receptor (VDR) i...

The epithelial signaling protein and transcriptional regulator β-catenin has recently been implicated in hematopoietic dendritic cell (DC) differentiation as well as in DC-mediated tolerance. We here observed that epidermal Langerhans cells (LCs) but not interstitial/dermal DCs express detectable β-catenin. LCs are unique among the DC family members in that LC networks critically depend on epithelial adhesion molecules as well as on the cytokine transforming growth factor-β1 (TGF-β1). However, despite the important functions of LCs in the immune system, the molecular mechanisms governing LC differentiation and maintenance remain poorly defined. We found that TGF-β1 induces β-catenin in progenitor cells undergoing LC differentiation and that β-catenin promotes LC differentiation. Vitamin D, another epidermal signal, enhanced TGF-β1-mediated β-catenin induction and promoted the expression of multiple epithelial genes by LCs. Moreover, full-length vitamin D receptor (VDR) promoted, whereas a truncated VDR diminished, the positive effects of ectopic β-catenin on LC differentiation. Therefore, we here identified β-catenin as a positive regulator of LC differentiation in response to TGF-β1 and identified a functional interaction between β-catenin and VDR in these cells.

Langerhans cells (LCs) are a unique subset of dendritic cells (DCs) that express epithelial adhesion molecules, allowing them to form contacts with epithelial cells and reside in epidermal/epithelial tissues. The dynamic regulation of epithelial adhesion plays a decisive role in the life cycle of LCs. It controls whether LCs remain immature and sessile within the epidermis or mature and egress to initiate immune responses. So far, the molecular machinery regulating epithelial adhesion molecules during LC maturation remains elusive. Here, we generated pure populations of immature human LCs in vitro to systematically probe for gene-expression changes during LC maturation. LCs downregulate a set of epithelial genes including E-cadherin, while they upregulate the mesenchymal marker N-cadherin known to facilitate cell migration. In addition, N-cadherin is constitutively expressed by monocyte-derived DCs known to exhibit characteristics of both inflammatory-type and interstitial/dermal DCs. Moreover, the transcription factors ZEB1 and ZEB2 (ZEB is zinc-finger E-box-binding homeobox) are upregulated in migratory LCs. ZEB1 and ZEB2 have been shown to induce epithelial-to-mesenchymal transition (EMT) and invasive behavior in cancer cells undergoing metastasis. Our results provide the first hint that the molecular EMT machinery might facilitate LC mobilization. Moreover, our study suggests that N-cadherin plays a role during DC migration. Keywords: Cell migration r Dendritic cells r Epithelial-to-mesenchymal transition r Langerhans cells r MaturationAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionLangerhans cells (LCs) represent a subset of dendritic cells (DCs), specialized to fulfill innate and adaptive immune functions within Correspondence: Prof. Herbert Strobl e-mail: herbert.strobl@medunigraz.at the epidermis [1]. LCs are unique among DC family in their expression of multiple epithelial adhesion-associated molecules such as E-cadherin, claudin-1, TROP-2, EpCAM, desmoplakin, zonula occludin, and cytokeratin 8/18 [1][2][3]. These epithelial * These authors contributed equally to this work.www.eji-journal.eu 554Sabine Konradi et al. Eur. J. Immunol. 2014. 44: 553-560 features allow LCs to form cell contacts with epidermal keratinocytes and organize into networks. Upon activation, LCs mature and upregulate T-cell costimulatory molecules (MHCII, CD40, 80, 83, 86) [4]. LC maturation is accompanied by LC emigration from the skin to the lymph node to induce immune responses [1]. The downregulation of E-cadherin adhesion is a crucial step in initiating LC emigration from the epidermis [5][6][7]. However, the mechanism regulating E-cadherin adhesion during LC maturation remains elusive. During embryonic and cancer development, epithelial cells can convert from a stationary to a motile/metastatic phenotype, thereby undergoing a transformation process called epithelialto-mesenchymal transition (EMT) [8]. EMT involves cytoskeletal rearrangements dr...