The cell adhesion molecule E-cadherin is a major component of adherens junctions and marks Langerhans cells (LC), the only dendritic cell (DC) population of the epidermis. LC form a dense network and ...attach themselves to the surrounding keratinocytes via homophilic E-cadherin binding. LC activation, mobilization, and migration require a reduction in LC E-cadherin expression. To determine whether E-cadherin plays a role in regulating LC homeostasis and function, we generated CD11c-specific E-cadherin knockout mice (CD11c-Ecaddel). In the absence of E-cadherin−mediated cell adhesion, LC numbers remained stable and similar as in control mice, even in aged animals. Intriguingly, E-cadherin−deficient LC displayed a dramatically changed morphology characterized by a more rounded cell body and fewer dendrites than wild-type cells. Nevertheless, maturation and migration of LC lacking E-cadherin was not altered, neither under steady-state nor inflammatory conditions. Accordingly, CD11c-Ecaddel and control mice developed comparable contact hypersensitivity reactions and imiquimod-triggered psoriatic skin inflammation, indicating that E-cadherin on LC does not influence their ability to orchestrate T cell-mediated immunity. In conclusion, our data demonstrate that E-cadherin is dispensable to maintain LC in the epidermis and does not regulate LC maturation, migration, and function.
Langerhans cells (LCs) constitute a network of immune sentinels in the skin epidermis that is seeded during embryogenesis. Whereas the development of LCs has been extensively studied, much less is ...known about the homeostatic renewal of adult LCs in "nonmanipulated" animals. Here, we present a new multicolor fluorescent fate mapping system and quantification approach to investigate adult LC homeostasis. This novel approach enables us to propose and provide evidence for a model in which the adult epidermal LC network is not formed by mature coequal LCs endowed with proliferative capabilities, but rather constituted by adjacent proliferative units composed of "dividing" LCs and their terminally differentiated daughter cells. Altogether, our results demonstrate the general utility of our novel fate-mapping system to follow cell population dynamics in vivo and to establish an alternative model for LC homeostasis.
Background & Aims The pathogenesis of inflammatory bowel disease (IBD) is associated with a dysregulated mucosal immune response. Expression of the tumor necrosis factor (TNF) superfamily member 14 ...(TNFSF14, also known as LIGHT homologous to lymphotoxins, exhibits inducible expression, and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes) on T cells is involved in their activation; transgenic expression of LIGHT on T cells in mice promotes inflammation in multiple organs, including intestine. We investigated the roles for LIGHT in recovery from intestinal inflammation in mice. Methods We studied the role of LIGHT in intestinal inflammation using Tnfsf14−/− and wild-type mice. Colitis was induced by transfer of CD4+ CD45RBhigh T cells into Rag1−/− or Tnfsf14−/− Rag1−/− mice, or by administration of dextran sulfate sodium to Tnfsf14−/− or wild-type C57BL/6J mice. Mice were weighed, colon tissues were collected and measured, and histology analyses were performed. We measured infiltrating cell populations and expression of cytokines, chemokines, and LIGHT. Results After administration of dextran sulfate sodium, Tnfsf14−/− mice developed more severe colitis than controls, based on their reduced survival, accelerated loss of body weight, and histologic scores. LIGHT protected mice from colitis via the lymphotoxin β receptor and was expressed mainly by myeloid cells in the colon. Colons of Tnfsf14−/− mice also had increased accumulation of innate immune cells and higher levels of cytokines than colons from control mice. LIGHT, therefore, appears to regulate inflammation in the colon. Conclusions Tnfsf14−/− mice develop more severe colitis than control mice. LIGHT signals through the lymphotoxin β receptor in the colon to regulate the innate immune response and mediate recovery from intestinal inflammation.
An immunoregulatory role of aryl hydrocarbon receptor (AhR) has been shown in conventional alpha beta and gamma delta T cells, but its function in skin gamma delta T cells (dendritic epidermal T ...cells DETC) is unknown. In this study, we demonstrate that DETC express AhR in wild-type mice, and are specifically absent in the epidermis of AhR-deficient mice (AhR-KO). We show that DETC precursors are generated in the thymus and home to the skin. Proliferation of DETC in the skin was impaired in AhR-KO mice, resulting in a >90% loss compared with wild type. Surprisingly, DETC were not replaced by alpha beta T cells or conventional gamma delta T cells, suggesting a limited time frame for seeding this niche. We found that DETC from AhR-KO mice failed to express the receptor tyrosine kinase c-Kit, a known growth factor for gamma delta T cells in the gut. Moreover, we found that c-kit is a direct target of AhR, and propose that AhR-dependent c-Kit expression is potentially involved in DETC homeostasis. DETC are a major source of GM-CSF in the skin. Recently, we had shown that impaired Langerhans cell maturation in AhR-KO is related to low GM-CSF levels. Our findings suggest that the DETCs are necessary for LC maturation, and provide insights into a novel role for AhR in the maintenance of skin-specific gamma delta T cells, and its consequences for the skin immune network.
Psoriasis is an autoinflammatory skin disease of unknown etiology. Topical application of Aldara cream containing the Toll-like receptor (TLR)7 agonist Imiquimod (IMQ) onto patients induces flares of ...psoriasis. Likewise, in mice IMQ triggers pathological changes closely resembling psoriatic plaque formation. Key cytokines like IL-23 and type-I IFN (IFN-I), both being produced mainly by dendritic cells (DCs), have been implicated in psoriasis. Although plasmacytoid DCs (pDCs) are the main source of IFNα and thought to initiate disease, conventional DCs (cDCs) appear to maintain the psoriatic lesions. Any role of cDCs during lesion formation remains elusive. Here, we report that selective activation of TLR7 signaling specifically in CD11c(+) DCs was sufficient to induce psoriasiform skin disease in mice. Intriguingly, both pDCs and the IFN-I pathway were dispensable for the development of local skin inflammation. Selective TLR7 triggering of Langerin(+) DCs resulted in attenuated disease, whereas their depletion did not alter the severity of skin lesions. Moreover, after IMQ-painting, IL-23 was exclusively produced by Langerin(neg) DCs in vivo. In conclusion, TLR7-activated Langerin(neg) cDCs trigger psoriatic plaque formation via IL-23-mediated activation of innate IL-17/IL-22-producing lymphocytes, independently of pDCs or IFN-I. These results suggest therapeutic targeting of IL-23 production by cDCs to refine current treatment strategies for psoriasis.
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor involved in adaptive cell functions, and it is highly active in the epidermis. AhR ligands can accelerate keratinocyte ...differentiation, but the precise role of AhR in the skin barrier is unknown. Our study showed that transepidermal water loss, a parameter of skin barrier integrity, is high in AhR-deficient mice. Experiments with conditionally AhR-deficient mouse lines identified keratinocytes as the primary cell population responsible for high transepidermal water loss. Electron microscopy showed weaker intercellular connectivity in the epidermis of keratinocytes in AhR-knockout mice, and gene expression analysis identified many barrier-associated genes as AhR targets. Moreover, AhR-deficient mice had higher interindividual differences in their microbiome. Interestingly, removing AhR ligands from the diet of wild-type mice mimicked AhR deficiency with respect to the impaired barrier; conversely, re-addition of the plant-derived ligand indole-3-carbinol rescued the barrier deficiency even in aged mice. Our results suggest that functional AhR expression is critical for skin barrier integrity and that AhR represents a molecular target for the development of therapeutic approaches for skin barrier diseases, including by dietary intervention.
Tumors activate β‐catenin in DCs to suppress CD8 immunity by inhibiting cross‐priming; β‐catenin‐suppressed CD8 immunity could be rescued by enhancing cross‐priming.
Whereas CD8+ T cells are ...essential for anti‐tumor immunity, tumors often evade CD8+ T cell surveillance by immunosuppression. As the initiators of antigen‐specific immune responses, DCs are likely to play a central role in regulating the balance between immunity and tolerance to tumor antigens and are specialized in their ability to cross‐present exogenous tumor antigens on MHC class I molecules to initiate CD8+ T cell immunity. However, it remains unclear whether and how tumors modulate DC functions to suppress CD8+ T cell responses. We have shown previously that β‐catenin signaling in DCs promotes DC‐mediated CD4+ T cell tolerance. Here, we tested the hypothesis that β‐catenin in DCs mediates tumor‐induced suppression of CD8+ T cell immunity by inhibiting the ability of DCs in cross‐priming. β‐Catenin was activated in DCs by multiple tumors in vivo and in vitro. B16 melanoma‐bearing mice, when vaccinated with DC‐targeting anti‐DEC‐205 mAb fused with tumor antigens, exhibited dampened CD8+ immunity, similar to DC‐β‐cateninactive mice. DCs from DC‐β‐cateninactive and tumor‐bearing mice were deficient in cross‐priming, and antigen‐specific CD8+ T cells primed in these mice resulted in dampened CD8+ memory responses. Importantly, DC‐β‐catenin−/− mice completely abrogate tumor‐mediated inhibition of cross‐priming, suggesting that tumor‐induced inhibition of cross‐priming is dependent on β‐catenin. Finally, enhancing cross‐priming at the priming or recall phase rescued β‐catenin‐suppressed CD8+ immunity in DC‐β‐cateninactive and tumor‐bearing mice. Thus, β‐catenin‐mediated inhibition of cross‐priming represents a new and potentially general mechanism that tumors employ to achieve immunosuppression.
Innate lymphoid cells (ILCs) are important regulators of early infection at mucosal barriers. ILCs are divided into three groups based on expression profiles, and are activated by cytokines and ...neuropeptides. Yet, it remains unknown if ILCs integrate other signals in providing protection. We show that signaling through herpes virus entry mediator (HVEM), a member of the tumor necrosis factor (TNF) receptor superfamily, in ILC3 is important for host defense against oral infection with the bacterial pathogen Yersinia enterocolitica. HVEM stimulates protective interferon-γ (IFN-γ) secretion from ILCs, and mice with HVEM-deficient ILC3 exhibit reduced IFN-γ production, higher bacterial burdens and increased mortality. In addition, IFN-γ production is critical as adoptive transfer of wild-type but not IFN-γ-deficient ILC3 can restore protection to mice lacking ILCs. We identify the TNF superfamily member, LIGHT, as the ligand inducing HVEM signals in ILCs. Thus HVEM signaling mediated by LIGHT plays a critical role in regulating ILC3-derived IFN-γ production for protection following infection.
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•ILC3 are required for early host defense during Y. enterocolitica infection•IFN-γ from CCR6− ILC3 is essential for protection of mice from Yersinia•HVEM expression by ILC3 is important for IFN-γ production following infection•LIGHT is the ligand for HVEM signaling in regulating ILC3-derived IFN-γ production
Seo et al. find that IFN-γ-producing ILC3 in the small intestine are required for host protection against Yersinia enterocolitica infection. HVEM signaling in ILC3, mediated by the ligand LIGHT, is critical for regulating IFN-γ production for protection following infection.
Dermatitis is often associated with an allergic reaction characterized by excessive type 2 responses leading to epidermal acanthosis, hyperkeratosis, and dermal inflammation. Although factors like ...IL-4, IL-13, and thymic stromal lymphopoietin (TSLP) are thought to be instrumental for the development of this type of skin disorder, other cytokines may be critical. Here, we show that the tumor necrosis factor (TNF) superfamily protein LIGHT (homologous to lymphotoxin, exhibits inducible expression, and competes with HSV glycoprotein D for binding to HVEM, a receptor expressed on T lymphocytes) is required for experimental atopic dermatitis, and LIGHT directly controls keratinocyte hyperplasia, and production of periostin, a matricellular protein that contributes to the clinical features of atopic dermatitis as well as other skin diseases such as scleroderma. Mice with a conditional deletion of the LIGHT receptor HVEM (herpesvirus entry mediator) in keratinocytes phenocopied LIGHT-deficient mice in exhibiting reduced epidermal thickening and dermal collagen deposition in a model of atopic dermatitis driven by house dust mite allergen. LIGHT signaling through HVEM in human epidermal keratinocytes directly induced proliferation and periostin expression, and both keratinocyte-specific deletion of HVEM or antibody blocking of LIGHT-HVEM interactions after disease onset prevented expression of periostin and limited atopic dermatitis symptoms. Developing reagents that neutralize LIGHT-HVEM signaling might be useful for therapeutic intervention in skin diseases where periostin is a central feature.
Langerhans cells (LCs) are dendritic cells (DCs) residing in epithelia, where they critically regulate immunity and tolerance. The p14 adaptor molecule is part of the late endosomal/LAMTOR (lysosomal ...adaptor and mitogen-activated protein kinase and mammalian target of rapamycin mTOR activator/regulator) complex, thereby contributing to the signal transduction of the extracellular signaling-regulated kinase (ERK) and the mTOR cascade. Furthermore, p14 represents an important regulator for endosomal sorting processes within the cell. Mutated, dysfunctional p14 leads to a human immunodeficiency disorder with endosomal/lysosomal defects in immune cells. Because p14 participates in the regulation of endosomal trafficking, growth factor signaling, and cell proliferation, we investigated the role of p14 in mouse DCs/LCs using a conditional knockout mouse model. p14-deficient animals displayed a virtually complete loss of LCs in the epidermis early after birth due to impaired proliferation and increased apoptosis of LCs. Repopulation analysis after application of contact sensitizer leads to the recruitment of a transient LC population, predominantly consisting of short-term LCs. The underlying molecular mechanism involves the p14-mediated disruption of the LAMTOR complex which results in the malfunction of both ERK and mTOR signal pathways. Hence, we conclude that p14 acts as a novel and essential regulator of LC homeostasis in vivo.
•DC-specific ablation of p14 leads to the disruption of the LC network in situ by inducing apoptosis and proliferation deficiency in LCs.•p14 deficiency affects ERK/mTOR signaling in DCs and results in transient recruitment of circulation-derived short-term LCs to the skin.
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