Entry into afferent lymphatics and maturation in situ of migrating murine cutaneous dendritic cells

STR typing of skin swabs from individuals after an allogeneic hematopoietic stem cell transplantation

One of the pre-requisites for forensic DNA analysis is the fact that all nucleated cells of a person carry the same genetic information. However, this is not the case for individuals who have received an allogeneic hematopoietic stem cell or bone marrow transplantation, as all new cells formed by the bone marrow no longer show the genetic information of the recipient but that of the donor, while all other cells still carry the original information before transplantation. Thus, STR typing of a blood sample after successful transplantation yields a DNA profile that differs from the recipient's original profile and corresponds to the donor genotype instead. Evidence from a routine case suggests that transplanted individuals may show donor alleles in skin swabs, as well. In order to examine this issue more closely, various skin swabs from 28 patients who have received an allogeneic hematopoietic stem cell transplantation were examined in this study. Swabs from the right and left palm, the back of the hand, one of the two upper arms, and the neck were collected from each person. Ninety-one of the 140 resulting swabs delivered useful results. All of those samples showed mixtures of recipient and donor DNA with different mixture ratios and the proportions of donor and recipient alleles revealed inter- and intra-individual differences. Those results were discussed with respect to graft versus host disease.

Ex-Vivo Skin Explant Culture Is a Model for TSLP-Mediated Skin Barrier Immunity

The skin is the outermost barrier protecting the body from pathogenic invasion and environmental insults. Its breakdown initiates the start of skin inflammation. The epidermal growth factor (EGFR) on keratinocytes protects this barrier, and its dysfunction leads to atopic dermatitis-like skin disease. One of the initial cytokines expressed upon skin barrier breach and during atopic dermatitis is TSLP. Here, we describe the expression and secretion of TSLP during EGFR inhibition and present an ex-vivo model, which mimics the early events after barrier insult. Skin explants floated on culture medium at 32 °C released TSLP in parallel to the activation of the resident Langerhans cell network. We could further show the up-regulation and activation of the AP-1 family of transcription factors during atopic-like skin inflammation and its involvement in TSLP production from the skin explant cultures. Inhibition of the c-Jun N-terminal kinase pathway led to a dose-dependent blunting of TSLP release. These data indicate the involvement of AP-1 during the early stages of atopic-like skin inflammation and highlight a novel therapeutic approach by targeting it. Therefore, skin explant cultures mimic the early events during skin barrier immunity and provide a suitable model to test therapeutic intervention.

A recombinant oncolytic Newcastle virus expressing MIP-3α promotes systemic antitumor immunity

BACKGROUND

The oncolytic Newcastle disease virus (NDV) is inherently able to trigger the lysis of tumor cells and induce the immunogenic cell death (ICD) of tumor cells and is also an excellent gene-engineering vector. The macrophage inflammatory protein-3α (MIP-3α) is a specific chemokine for dendritic cells (DCs). Thus, we constructed a recombinant NDV expressing MIP-3α (NDV-MIP3α) as an in vivo DC vaccine for amplifying antitumor immunities.

METHODS

The recombinant NDV-MIP3α was constructed by the insertion of MIP-3α cDNA between the P and M genes. Western blotting assay and ELISA were used to detect MIP-3α, HMGB1, IgG, and ATP in the supernatant and sera. The chemotaxis of DCs was examined by Transwell chambers. The phenotypes of the immune cells (eg, DCs) were analyzed by flow cytometry. The antitumor efficiency of NDV-MIP3α was observed in B16 and CT26 tumor-bearing mice. Immunofluorescence and immunohistochemistry were applied to observe the ecto-calreticulin (CRT) and intratumoral attraction of DCs. Adoptive transfer of splenocytes and antibodies and depletion of T-cell subsets were used to evaluate the relationship between antitumor immunities and the role of the T-cell subtype.

RESULTS

The findings show that NDV-MIP3α has almost the same capabilities of tumor lysis and induction of ICD as the wild-type NDV (NDV-WT). MIP-3α secreted by NDV-MIP3α could successfully attract DCs in vitro and in vivo. Both B16 and CT26 cells infected with NDV-MIP3α could strongly promote DC maturation and activation. Compared with NDV-WT, intratumoral injection of NDV-MIP3α and the adoptive transfer of T lymphocytes from mice injected with NDV-MIP3α resulted in a significant suppression of B16 and CT26 tumor growth. The NDV-MIP3α-induced production of tumor-specific cellular and humoral immune responses was dependent on CD8⁺ T cells and partially on CD4⁺ T cells. A significant reversion of tumor microenvironments was found in the mice injected with NDV-MIP3α.

CONCLUSIONS

Compared with NDV-WT, the recombinant NDV-MIP3α as an in vivo DC vaccine demonstrates enhanced antitumor activities through the induction of stronger system immunities and modulation of the tumor microenvironment. This strategy may be a potential approach for the generation of an in vivo DC vaccine.

Dendritic Epidermal T Cells in Allergic Contact Dermatitis

Allergic contact dermatitis (ACD) is a common inflammatory skin disease with a prevalence of approximately 20% in the European population. ACD is caused by contact allergens that are reactive chemicals able to modify non-immunogenic self-proteins to become immunogenic proteins. The most frequent contact allergens are metals, fragrances, and preservatives. ACD clinically manifests as pruritic eczematous lesions, erythema, local papules, and oedema. ACD is a T cell-mediated disease, involving both CD4⁺ and CD8⁺ T cells. In addition, γδ T cells appear to play an important role in the immune response to contact allergens. However, it is debated whether γδ T cells act in a pro- or anti-inflammatory manner. A special subset of γδ T cells, named dendritic epidermal T cells (DETC), is found in the epidermis of mice and it plays an important role in immunosurveillance of the skin. DETC are essential in sensing the contact allergen-induced stressed environment. Thus, allergen-induced activation of DETC is partly mediated by numerous allergen-induced stress proteins expressed on the keratinocytes (KC). Several stress proteins, like mouse UL-16-binding protein-like transcript 1 (Mult-1), histocompatibility 60 (H60) and retinoic acid early inducible-1 (Rae-1) α-ε family in mice and major histocompatibility complex (MHC) class I-chain-related A (MICA) in humans, are upregulated on allergen-exposed KC. Allergen-induced stress proteins expressed on the KC are consequently recognized by NKG2D receptor on DETC. This review focuses on the role of γδ T cells in ACD, with DETC in the spotlight, and on the role of stress proteins in contact allergen-induced activation of DETC.

Production of Extracellular Adenosine by CD73+ Dendritic Cells Is Crucial for Induction of Tolerance in Contact Hypersensitivity Reactions

Dendritic cells (DCs) express the ecto-5'-nucleotidase CD73 that generates immunosuppressive adenosine (Ado) by dephosphorylation of extracellular Ado monophosphate and diphosphate. To investigate whether CD73-derived Ado has immune-suppressive activity, 2,4-dinitrothiocyanobenzene (DNTB) was applied to skin of wild-type (WT) or CD73-deficient (CD73^-/-) mice, followed by sensitization and challenge with 2,4-dinitrofluorobenzene. In this model, we show the induction of tolerance by DNTB against 2,4-dinitrofluorobenzene only in WT but not in CD73^-/- mice. Analysis of skin DCs showed increased expression of CD73 after application of DNTB in WT mice. That was accompanied by elevated concentrations of extracellular Ado in the lymph node. Moreover, T cells expressed markers for anergy, namely EGR2 and NDRG1 in DNTB-treated WT mice and they exhibited impaired proliferation upon ex vivo re-stimulation. Similarly, in vitro we observed that Ado-producing WT DCs, but not CD73^-/- DCs, rendered transgenic T cells from OTII mice (OTII T cells) hyporeactive, decreased their T-cell costimulatory signaling, and induced up-regulation of EGR2 and NDRG1. Thus, these data show that expression of CD73 by DCs, which triggers elevated levels of extracellular Ado, is a crucial mechanism for the induction of anergic T cells and tolerance.

Silkworm dropping extract ameliorate trimellitic anhydride-induced allergic contact dermatitis by regulating Th1/Th2 immune response

Allergic contact dermatitis (ACD) is an inflammatory skin disease caused by hapten-specific immune response. Silkworm droppings are known to exert beneficial effects during the treatment of inflammatory diseases. Here, we studied whether topical treatment and oral administration of silkworm dropping extract (SDE) ameliorate trimellitic anhydride (TMA)-induced ACD. In ACD mice model, SDE treatment significantly suppressed the increase in both ear thickness and serum IgE levels. Furthermore, IL-1β and TNF-α levels were reduced by SDE. In allergic responses, SDE treatment significantly attenuated the production of the Th2-associated cytokine IL-4 in both ear tissue and draining lymph nodes. However, it increased the production of the Th1-mediated cytokine IL-12. Thus, these results showed that SDE attenuated TMA-induced ACD symptoms through regulation of Th1/Th2 immune response. Taken together, we suggest that SDE treatment might be a potential agent in the prevention or therapy of Th2-mediated inflammatory skin diseases such as ACD and atopic dermatitis.

ABBREVIATIONS

ACD: allergic contact dermatitis; AD: atopic dermatitis; APC: antigen presenting cells; CCL: chemokine (C-C motif) ligand; CCR: C-C chemokine receptor; Dex: dexamethasone; ELISA: enzyme-linked immunosorbent assay; IFN: interferon; Ig: immunoglobulin; IL: interleukin; OVA: ovalbumin; PS: prednisolone; SDE: silkworm dropping extract; Th: T helper; TMA: trimellitic anhydride; TNF: tumor necrosis factor.

Functional Specialization of Skin Dendritic Cell Subsets in Regulating T Cell Responses

Dendritic cells (DC) are a heterogeneous family of professional antigen-presenting cells classically recognized as most potent inducers of adaptive immune responses. In this respect, Langerhans cells have long been considered to be prototypic immunogenic DC in the skin. More recently this view has considerably changed. The generation of in vivo cell ablation and lineage tracing models revealed the complexity of the skin DC network and, in particular, established the existence of a number of phenotypically distinct Langerin⁺ and negative DC populations in the dermis. Moreover, by now we appreciate that DC also exert important regulatory functions and are required for the maintenance of tolerance toward harmless foreign and self-antigens. This review summarizes our current understanding of the skin-resident DC system in the mouse and discusses emerging concepts on the functional specialization of the different skin DC subsets in regulating T cell responses. Special consideration is given to antigen cross-presentation as well as immune reactions toward contact sensitizers, cutaneous pathogens, and tumors. These studies form the basis for the manipulation of the human counterparts of the murine DC subsets to promote immunity or tolerance for the treatment of human disease.

The clash of Langerhans cell homeostasis in skin: Should I stay or should I go?

Langerhans cells (LC), the skin epidermal contingent of dendritic cells (DC), possess an exceptional life cycle and developmental origin. LC, like all mature blood cells, develop from haematopoietic stem cells (HSC) through successive steps of lineage commitment and differentiation. However, LC development is different to that of other DC subsets and not yet fully understood. Haematopoietic cell fate decisions are instructed by specific growth factors and cytokines produced in specialized microenvironments or niches. Upon ligand binding the cognate surface receptors on HSC and further restricted progenitor cells regulate the signalling pathways that eventually leads to the execution of lineage-determining genetic programs. In this review we focus on a specific set of surface receptor kinases that have been identified as critical regulators of LC development using genetically modified mice. Recent studies suggest for some of these kinases to impact on LC/LC progenitor interaction with the local niche by regulating adhesion and/or migration. During embryonic development, in wound healing and aberrantly in tumour invasion the same kinase receptors control a genetic program known as epithelial-to-mesenchymal-transition (EMT). We will discuss how EMT and its reverse program of mesenchymal-to-epithelial-transition (MET) can serve as universal concepts operating also in LC development.

The late endosomal adaptor molecule p14 (LAMTOR2) represents a novel regulator of Langerhans cell homeostasis

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.

Langerhans cells protect from allergic contact dermatitis in mice by tolerizing CD8(+) T cells and activating Foxp3(+) regulatory T cells

Allergic contact dermatitis is the most frequent occupational disease in industrialized countries. It is caused by CD8(+) T cell-mediated contact hypersensitivity (CHS) reactions triggered at the site of contact by a variety of chemicals, also known as weak haptens, present in fragrances, dyes, metals, preservatives, and drugs. Despite the myriad of potentially allergenic substances that can penetrate the skin, sensitization is relatively rare and immune tolerance to the substance is often induced by as yet poorly understood mechanisms. Here we show, using the innocuous chemical 2,4-dinitrothiocyanobenzene (DNTB), that cutaneous immune tolerance in mice critically depends on epidermal Langerhans cells (LCs), which capture DNTB and migrate to lymph nodes for direct presentation to CD8(+) T cells. Depletion and adoptive transfer experiments revealed that LCs conferred protection from development of CHS by a mechanism involving both anergy and deletion of allergen-specific CD8(+) T cells and activation of a population of T cells identified as ICOS(+)CD4(+)Foxp3(+) Tregs. Our findings highlight the critical role of LCs in tolerance induction in mice to the prototype innocuous hapten DNTB and suggest that strategies targeting LCs might be valuable for prevention of cutaneous allergy.

Targeting skin dendritic cells to improve intradermal vaccination

Vaccinations in medicine are typically administered into the muscle beneath the skin or into the subcutaneous fat. As a consequence, the vaccine is immunologically processed by antigen-presenting cells of the skin or the muscle. Recent evidence suggests that the clinically seldom used intradermal route is effective and possibly even superior to the conventional subcutaneous or intramuscular route. Several types of professional antigen-presenting cells inhabit the healthy skin. Epidermal Langerhans cells (CD207/langerin(+)), dermal langerin(neg), and dermal langerin(+) dendritic cells (DC) have been described, the latter subset so far only in mouse skin. In human skin langerin(neg) dermal DC can be further classified based on their reciprocal expression of CD1a and CD14. The relative contributions of these subsets to the generation of immunity or tolerance are still unclear. Yet, specializations of these different populations have become apparent. Langerhans cells in human skin appear to be specialized for induction of cytotoxic T lymphocytes; human CD14(+) dermal DC can promote antibody production by B cells. It is currently attempted to rationally devise and improve vaccines by harnessing such specific properties of skin DC. This could be achieved by specifically targeting functionally diverse skin DC subsets. We discuss here advances in our knowledge on the immunological properties of skin DC and strategies to significantly improve the outcome of vaccinations by applying this knowledge.

Review article: lymphatic system and associated adipose tissue in the development of inflammatory bowel disease

BACKGROUND

The lymphatic system plays critical roles in tissue fluid homoeostasis, immune defence and metabolic maintenance. Lymphatic vessels transport lymph, proteins, immune cells and digested lipids, allowing fluid and proteins to be returned to the blood stream, lipids to be stored and metabolized and antigens to be sampled in lymph nodes. Lymphatic drainage is mainly driven by rhythmic constrictions intrinsic to the vessels and critically modulated by fluid pressure and inflammatory mediators.

AIM

To collect and discuss the compelling available information linking the lymphatic system, adiposity and inflammation.

METHODS

A literature search was performed through PubMed focusing on lymphatic system, inflammation, immune cells and fat transport and function in the context of IBD.

RESULTS

Evidence collected allows us to propose the following working model. Compromised lymph drainage, reported in IBD, leads to oedema, lymphangiogenesis, impaired immune cell trafficking and lymph leakage. Lymph factor(s) stimulate adipose tissue to proliferate and produce cytokines, which affect immune cell functions and exacerbate inflammation.

CONCLUSIONS

Understanding the lymphatic system's role in immune cell trafficking and immune responses, contribution to fat transport, distribution, metabolism and implication in the pathogenesis of chronic intestinal inflammation may provide the basis for new therapeutic strategies and improved quality-of life.

Langerhans cells and more: langerin-expressing dendritic cell subsets in the skin

Langerhans cells (LCs) are antigen-presenting dendritic cells (DCs) that reside in epithelia. The best studied example is the LC of the epidermis. By electron microscopy, their identifying feature is the unique rod- or tennis racket-shaped Birbeck granule. The phenotypic hallmark is their expression of the C-type lectin receptor langerin/CD207. Langerin, however, is also expressed on a recently discovered population of DC in the dermis and other tissues of the body. These 'dermal langerin(+) dendritic cells' are unrelated to LCs. The complex field of langerin-negative dermal DCs is not dealt with here. In this article, we briefly review the history, ontogeny, and homeostasis of LCs. More emphasis is laid on the discussion of functional properties in vivo. Novel models using genetically engineered mice are contributing tremendously to our understanding of the role of LCs in eliciting adaptive immune responses against pathogens or tumors and in inducing and maintaining tolerance against self antigens and innocuous substances in vivo. Also, innate effector functions are increasingly being recognized. Current activities in this area are reviewed, and possibilities for future exploitation of LC in medicine, e.g. for the improvement of vaccines, are contemplated.

Revisiting the tolerogenicity of epidermal Langerhans cells

Langerhans cells (LC) are unique members of the dendritic cell (DC) family residing in the epidermis of skin and mucosa. Specific autocrine and environmental factors shape the biology of LC, such as TGF-beta1, IL-10, vitamin D(3), UV light or neuropeptides, which are required for LC development but also influence their capacity to induce immunity or tolerance. Both, immunogenic and tolerogenic functions require antigen transport from the skin to the draining lymph nodes, but the LC maturation grade directs the differential outcome. In this review, we recapitulate early indications for LC tolerogenicity and oppose them to more recent findings with gene-targeted mice, which dramatically challenged some of the early results. The newly discovered Langerin(+) dermal DC subset (DDC) seems to be responsible also for many tolerogenic effects that were initially attributed to steady state migratory LC. Transfer of antigens from LC to other DC subsets as well as transport of HIV are discussed as part of the complex interactions between LC and other cells or as mechanisms of immune evasion. Finally, the first clinical trials on allergy therapies targeting skin DC in the steady state are mentioned as they may open the door to curative tolerogenic therapies.

Epifluorescence intravital microscopy of murine corneal dendritic cells

Purpose. Dendritic cells (DCs) are antigen-presenting cells vital for initiating immune responses. In this study the authors examined the in vivo migratory capability of resident corneal DCs to various stimuli. Methods. The authors used mice expressing enhanced yellow fluorescent protein (eYFP) under control of the CD11c promoter to visualize corneal DCs. To assess the distribution and mobility of DCs, normal corneas were imaged in vivo and ex vivo with fluorescence microscopy. Intravital microscopy was used to examine the responses of resident central and peripheral corneal DCs to silver nitrate injury, lipopolysaccharide, microspheres, and tumor necrosis factor (TNF-alpha). In some experiments, TNF-alpha injection was used to first induce centripetal migration of DCs to the central cornea, which was subsequently reinjected with microspheres. Results. In normal corneas, DCs were sparsely distributed centrally and were denser in the periphery, with epithelial-level DCs extending into the epithelium. Videomicroscopy showed that though cell processes were in continuous movement, cells generally did not migrate. Within the first 6 hours after stimulation, neither central nor peripheral corneal DCs exhibited significant lateral migration, but central corneal DCs assumed extreme morphologic changes. An increased number of DCs in the TNF-alpha-stimulated central cornea were responsive to subsequent microsphere injection by adopting a migratory behavior, but not with increased speed. Conclusions. In vivo imaging reveals minimal lateral migration of corneal DCs after various stimuli. In contrast, DCs within the central cornea after initial TNF-alpha injection are more likely to respond to a secondary insult with lateral migration.

Layer-by-layer-assembled multilayer films for transcutaneous drug and vaccine delivery

We describe protein- and oligonucleotide-loaded layer-by-layer (LbL)-assembled multilayer films incorporating a hydrolytically degradable polymer for transcutaneous drug or vaccine delivery. Films were constructed based on electrostatic interactions between a cationic poly(beta-amino ester) (denoted Poly-1) with a model protein antigen, ovalbumin (ova), and/or immunostimulatory CpG (cytosine-phosphate diester-guanine-rich) DNA oligonucleotide adjuvant molecules. Linear growth of nanoscale Poly-1/ova bilayers was observed. Dried ova protein-loaded films rapidly deconstructed when rehydrated in saline solutions, releasing ova as nonaggregated/nondegraded protein, suggesting that the structure of biomolecules integrated into these multilayer films is preserved during release. Using confocal fluorescence microscopy and an in vivo murine ear skin model, we demonstrated delivery of ova from LbL films into barrier-disrupted skin, uptake of the protein by skin-resident antigen-presenting cells (Langerhans cells), and transport of the antigen to the skin-draining lymph nodes. Dual incorporation of ova and CpG oligonucleotides into the nanolayers of LbL films enabled dual release of the antigen and adjuvant with distinct kinetics for each component; ova was rapidly released, while CpG was released in a relatively sustained manner. Applied as skin patches, these films delivered ova and CpG to Langerhans cells in the skin. To our knowledge, this is the first demonstration of LbL films applied for the delivery of biomolecules into skin. This approach provides a new route for storage of vaccines and other immunotherapeutics in a solid-state thin film for subsequent delivery into the immunologically rich milieu of the skin.

The cutaneous biochemical redox barrier: a component of the innate immune defenses against sensitization by highly reactive environmental xenobiotics

Contact allergy to environmental xenobiotics is a common and important problem, but it is unclear why some chemicals are potent sensitizers and others weak/nonsensitizers. We explored this by investigating why similar chemicals, 2,4-dinitrochlorobenzene (DNCB) and 2,4-dinitrothiocyanobenzene (DNTB), differ in their ability to induce contact hypersensitivity (CHS). DNCB induced CHS in humans, whereas at similar doses DNTB did not. However, following DNCB sensitization, DNTB elicited CHS in vivo and stimulated DNCB-responsive T cells in vitro, suggesting that differences in response to these compounds lie in the sensitization phase. In contrast to DNCB, DNTB failed to induce emigration of epidermal Langerhans cells in naive individuals. Examination for protein dinitrophenylation in skin revealed that DNCB penetrated into the epidermis, whereas DNTB remained bound to a thiol-rich band within the stratum corneum. DNTB reacted rapidly with reduced glutathione in vitro and was associated with a decrease in the free thiol layer in the stratum corneum, but not in the nucleated epidermis. By contrast, DNCB required GST facilitation to react with gluthathione and, following penetration through the stratum corneum, depleted thiols in the viable epidermis. Chemical depletion of the thiol-rich band or removing it by tape stripping allowed increased penetration of DNTB into the epidermis. Our results suggest that the dissimilar sensitizing potencies of DNCB and DNTB in humans are determined by a previously undescribed outer epidermal biochemical redox barrier, a chemical component of the innate immune defense mechanisms that defend against sensitization by highly reactive environmental chemicals.

The human skin/chick chorioallantoic membrane model accurately predicts the potency of cosmetic allergens

The current standard method for predicting contact allergenicity is the murine local lymph node assay (LLNA). Public objection to the use of animals in testing of cosmetics makes the development of a system that does not use sentient animals highly desirable. The chorioallantoic membrane (CAM) of the chick egg has been extensively used for the growth of normal and transformed mammalian tissues. The CAM is not innervated, and embryos are sacrificed before the development of pain perception. The aim of this study was to determine whether the sensitization phase of contact dermatitis to known cosmetic allergens can be quantified using CAM-engrafted human skin and how these results compare with published EC3 data obtained with the LLNA. We studied six common molecules used in allergen testing and quantified migration of epidermal Langerhans cells (LC) as a measure of their allergic potency. All agents with known allergic potential induced statistically significant migration of LC. The data obtained correlated well with published data for these allergens generated using the LLNA test. The human-skin CAM model therefore has great potential as an inexpensive, non-radioactive, in vivo alternative to the LLNA, which does not require the use of sentient animals. In addition, this system has the advantage of testing the allergic response of human, rather than animal skin.

Identification of three distinct subsets of migrating dendritic cells from oral mucosa within the regional lymph nodes

To investigate the phenotypic and migrational properties of oral mucosal dendritic cells (OMDCs), fluorescein isothiocyanate (FITC) was painted onto mouse buccal mucosa and the expression patterns of functional molecules in FITC-bearing migrating DCs within the regional lymph nodes (RLNs) were analysed. We found three distinct subpopulations of migrating OMDCs within the RLNs: CD11c(hi) CD207(-) (F1), CD11c(int/lo) CD207(-) (F2) and CD11c(int/lo) CD207(+) (F3). The F1 DCs reached the RLNs earlier (after 24 hr) but diminished immediately. Additionally, F1 DCs expressed high levels of CD11b. The F2 DCs migrated continuously to the RLNs and maintained the highest ratio of all three fractions. The F3 DCs migrated slowly to the RLNs and demonstrated a late peak at 96 hr. In addition, F3 DCs showed the highest CD205 expression levels of all three subsets. All fractions of migrating OMDCs expressed CD80, CD86 and major histocompatibility complex class II at high levels, suggesting that all OMDCs are in a mature stage and have the potential for antigen presentation. All migrating OMDCs lacked CD8alpha expression. Taken together, our results indicate that the lack of CD207 is one factor that identifies submucosal DCs. Both F1 and F2 DCs lack CD207; F1 DCs are resident and F2 DCs are newly recruited following FITC application. The F3 DCs, which express CD207, are mucosal Langerhans cells that migrate later. The identification of OMDC subsets should facilitate further studies investigating the functional roles of each fraction.

Visualizing dendritic cell migration within the skin

Dendritic cells (DCs) within the skin are a heterogeneous population of cells, including Langerhans cells of the epidermis and at least three subsets of dermal DCs. Collectively, these DCs play important roles in the initiation of adaptive immune responses following antigen challenge of the skin as well as being mediators of tolerance to self-antigen. A key functional aspect of cutaneous DCs is their migration both within the skin and into lymphatic vessels, resulting in their emigration to draining lymph nodes. Here, we discuss our current understanding of the requirements for successful DC migration in and from the skin, and introduce some of the microscopic techniques developed in our laboratory to facilitate a better understanding of this process. In particular, we detail our current use of multi-photon excitation (MPE) microscopy of murine skin to dissect the migratory behavior of DCs in vivo.

Application of a Systems Biology Approach to Skin Allergy Risk Assessment

We have developed an in silico model of the induction of skin sensitisation, in order to characterise and quantify the contribution of each pathway to the overall biological process. This analysis has been used to guide our research on skin sensitisation and in vitro test development programmes, and provides a theoretical rationale for the interpretation and integration of non-animal predictive data for risk assessment (RA) purposes. The in vivo mouse Local Lymph Node Assay (LLNA) is now in widespread use for the evaluation of skin sensitisation potential and potency. Recent changes in European Union (EU) legislation (i.e. the 7th Amendment to the EU Cosmetics Directive) have made the development of non-animal approaches to provide the data for skin sensitisation RA a key business need. Several in vitro predictive assays have already been developed for the prediction of skin sensitisation. However, these are based on the determination of a small number of pathways within the overall biological process, and our understanding of the relative contribution of these individual pathways to skin sensitisation induction is limited. To address this knowledge gap, a “systems biology” approach has been used to construct a computer-based mathematical model of the induction of skin sensitisation, in collaboration with Entelos, Inc. The biological mechanisms underlying the induction phase of skin sensitisation are represented by nonlinear ordinary differential equations and defined by using information from over 500 published papers. By using the model, we have identified knowledge gaps for future investigative research, and key factors that have a major influence on the induction of skin sensitisation (e.g. TNF-α production in the epidermis). The relative contribution of each of these key pathways has been assessed by determining their contributions to the overall process (e.g. sensitiser-specific T-cell proliferation in the draining lymph node). This information provides a biologically-relevant rationale for the interpretation and potential integration of diverse types of non-animal predictive data. Consequently, the Skin Sensitisation Physiolab® (SSP) platform represents one approach to integration that is likely to prove an invaluable tool for hazard evaluation in a new framework for consumer safety RA.

Blood-derived dermal langerin+ dendritic cells survey the skin in the steady state

Langerin is a C-type lectin receptor that recognizes glycosylated patterns on pathogens. Langerin is used to identify human and mouse epidermal Langerhans cells (LCs), as well as migratory LCs in the dermis and the skin draining lymph nodes (DLNs). Using a mouse model that allows conditional ablation of langerin⁺ cells in vivo, together with congenic bone marrow chimeras and parabiotic mice as tools to differentiate LC- and blood-derived dendritic cells (DCs), we have revisited the origin of langerin⁺ DCs in the skin DLNs. Our results show that in contrast to the current view, langerin⁺CD8⁻ DCs in the skin DLNs do not derive exclusively from migratory LCs, but also include blood-borne langerin⁺ DCs that transit through the dermis before reaching the DLN. The recruitment of circulating langerin⁺ DCs to the skin is dependent on endothelial selectins and CCR2, whereas their recruitment to the skin DLNs requires CCR7 and is independent of CD62L. We also show that circulating langerin⁺ DCs patrol the dermis in the steady state and migrate to the skin DLNs charged with skin antigens. We propose that this is an important and previously unappreciated element of immunosurveillance that needs to be taken into account in the design of novel vaccine strategies.

Production of monoclonal antibodies that recognize the extracellular domain of mouse langerin/CD207

Langerin CD207 is a type II transmembrane protein. It is responsible for the formation of Birbeck granules, which are intracellular organelles within Langerhans cells, the dendritic cells of stratified squamous epithelia like the epidermis. Because current anti-CD207 antibodies have limitations, we prepared new monoclonals by immunizing rats with the extracellular region of mouse Langerin followed by a boost with enriched Langerhans cells (LCs). We secured a large panel of mAbs, most of which reacted with the carboxy terminal carbohydrate recognition domain. These mAbs could be used to immunoblot and immunoprecipitate mouse Langerin and to stain the cell surface and intracellular pools of CD207 by FACS analysis. Labeling of Birbeck granules was also achieved by immunoelectron microscopy. Anti-CD207 identified LCs in the epidermis and skin draining lymph nodes of BALB/c and C57BL/6 mice, but BALB/c mice had an additional Langerin(+) population in spleen, thymus and mesenteric lymph node. This additional subset had higher levels of CD8 and CD205 than epidermal LCs, and also had a less mature phenotype, i.e., lower MHC II, CD40 and CD86. Subcutaneous injection of IgG but not IgM forms of these new anti-CD207 mAbs led to rapid and selective labeling of the Langerin(+) cells in skin draining lymph nodes as well as spleen. The new IgG anti-CD207 mAbs should be useful for further research on LCs and dendritic cells including an evaluation of the consequences of antigen delivery within anti-CD207 mAbs in vivo.

An inflammation-induced mechanism for leukocyte transmigration across lymphatic vessel endothelium

The exit of antigen-presenting cells and lymphocytes from inflamed skin to afferent lymph is vital for the initiation and maintenance of dermal immune responses. How such an exit is achieved and how cells transmigrate the distinct endothelium of lymphatic vessels are unknown. We show that inflammatory cytokines trigger activation of dermal lymphatic endothelial cells (LECs), leading to expression of the key leukocyte adhesion receptors intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and E-selectin, as well as a discrete panel of chemokines and other potential regulators of leukocyte transmigration. Furthermore, we show that both ICAM-1 and VCAM-1 are induced in the dermal lymphatic vessels of mice exposed to skin contact hypersensitivity where they mediate lymph node trafficking of dendritic cells (DCs) via afferent lymphatics. Lastly, we show that tumor necrosis factor alpha stimulates both DC adhesion and transmigration of dermal LEC monolayers in vitro and that the process is efficiently inhibited by ICAM-1 and VCAM-1 adhesion-blocking monoclonal antibodies. These results reveal a CAM-mediated mechanism for recruiting leukocytes to the lymph nodes in inflammation and highlight the process of lymphatic transmigration as a potential new target for antiinflammatory therapy.

Murine CXCL14 is dispensable for dendritic cell function and localization within peripheral tissues

Dendritic cells (DCs) have long been recognized as key regulators of immune responses. However, the process of their recruitment to peripheral tissues and turnover during homeostasis remains largely unknown. The chemokine CXCL14 (BRAK) is constitutively expressed in skin and other epithelial tissues. Recently, the human chemokine was proposed to play a role in the homeostatic recruitment of macrophage and/or DC precursors toward the periphery, such as skin. Although so far no physiological function could be demonstrated for the murine CXCL14, it shows a remarkable homology to the human chemokine. In order to elucidate the in vivo role of CXCL14, we generated a mouse defective for this chemokine. We studied various components of the immune system with emphasis on monocytes/macrophages and DC/Langerhans cell (LC) populations in different tissues during steady state but did not find a significant difference between knockout (CXCL14(-)(/)(-)) and control mice. Functionally, LCs were able to become activated, to migrate out of skin, and to elicit a delayed type of hypersensitivity reaction. Overall, our data indicate that murine CXCL14 is dispensable for the homeostatic recruitment of antigen-presenting cells toward the periphery and for LC functionality.

Sympathetic nervous system influence on the innate immune response

Our studies focused on the sympathetic nervous system (SNS) influence on dendritic cells (DCs), which play a crucial role in the innate immune response. We found that DCs express a variety of adrenergic receptors (ARs) with alpha1-ARs playing a stimulatory and beta2-ARs an inhibitory effect on DCs migration. beta2-ARs in skin and bone marrow-derived DCs when stimulated by bacterial toll-like receptors (TLRs) agonists respond to norepinephrine (NE) by decreased interleukin-12 (IL-12) and increased IL-10 production which in turn downregulates inflammatory cytokine production and CCR7 expression and thus their migration ability leading to reduced T helper-1 (Th1) priming. We also found that contact sensitizers that may induce a predominant Th1 response, do so by inhibiting the local NE turnover in the skin. The SNS seems therefore to contribute in shaping the information conveyed by DCs to T cells and thus in inducing the appropriate adaptive immune response. In this sense, the SNS physiological influence may allow Th2 priming to fight infections sustained by extracellular pathogens and limit the risk for organ-specific autoimmune reactions associated with excessive Th1 priming and inhibition of T regulatory cell functions. More recently, we found that preconditioning of the skin by beta-adrenergic antagonist and the TLR2 agonist S. Aureus peptidoglycan (PGN) may instruct a Th1 adaptive response to a soluble protein antigen. On the contrary, when the TLR4 agonist E. Coli lipopolysaccharide was used, the presence of the beta-adrenergic antagonist was not effective. These effects were consonant with the pattern of TLRs expression shown by epidermal keratinocytes (EKs) but not by skin DCs. As beta-ARs signaling defects together with S. Aureus infections are thought to serve as initiation and/or persistence factors for numerous Th1-sustained autoimmune inflammatory skin diseases, we might have disclosed at least part of the relevant pathogenetic mechanism.

Subtoxic concentrations of allergenic haptens induce LC migration and maturation in a human organotypic skin explant culture model: a novel method for identifying potential contact allergens

The accelerated migration of Langerhans cells (LCs) out of the epidermis and up-regulation of maturation markers, upon treatment with subtoxic concentrations of chemicals, were used as the criteria to determine the potential of allergenic chemicals capable of inducing a hapten-specific delayed-type hypersensitivity reaction. Here we report the findings of a study in which seven chemicals, coded and tested in a blind fashion, were classified as contact allergens or non-allergens using the human organotypic skin explant culture (hOSEC) model. All chemicals that were identified as a contact sensitizer on decoding induced a definite decrease in the number of CD1a and HLA-DR-positive epidermal LCs in the epidermis of the skin explants, as determined by both semiquantitative immunohistochemistry and quantitative flow cytometric analysis. A significant increase in the number of CD83(+) cells was accompanied by up-regulation of activation molecules in the epidermis of hOSEC exposed specifically to contact allergens. In contrast, there were only minor alterations in epidermal LC numbers, expression of CD83 and other activation markers by LCs when the biopsies were treated with non-toxic concentrations of non-allergenic irritants and vehicles. The data suggest that an increased epidermal LC migration and maturation accompanied by increased expression of activation markers could be used as end-point determinants to screen allergens in a non-animal alternative hOSEC model.

Adenoviral gene transfer of stromal cell-derived factor-1 to murine tumors induces the accumulation of dendritic cells and suppresses tumor growth

The human CXC chemokine, stromal cell-derived factor 1 (SDF-1alpha), is known to function in vitro as a chemotactic factor for lymphocytes, monocytes, and dendritic cells. In the context that dendritic cells are powerful antigen-presenting cells, we hypothesized that adenoviral gene transfer of SDF-1alpha to tumors might inhibit growth of preexisting tumors through attracting dendritic cells to the tumor. AdSDF-1alpha mediated the expression of SDF-1alpha mRNA and protein in A549 cells in vitro, and the supernatant of the AdSDF-1alpha-infected A549 cells showed chemotactic activity for dendritic cells. When syngeneic murine CT26 colon carcinoma tumors (BALB/c) and B16 melanoma and Lewis lung cell carcinoma (C57Bl/6) were injected with AdSDF-1alpha (5 x 10(8) plaque-forming units), there was an accumulation of dendritic cells and CD8(+) cells within the tumor and significant inhibition of tumor growth compared with tumors injected with PBS or AdNull (control vector). The injection of AdSDF-1alpha into tumors induced the inflammatory enlargement and the accumulation of dendritic cells in the draining lymph node. Intratumoral AdSDF-1alpha administration elicited tumor-specific CTLs and adoptive transfer of splenocytes from AdSDF-1alpha-treated mice resulted in the elongation of survival after tumor challenge. Interestingly, in wild-type and CD4(-/-) mice but not in CD8(-/-) mice, AdSDF-1alpha inhibited the growth of the tumor. These observations suggest that adenoviral gene transfer of SDF-1alpha may be a useful strategy to accumulate dendritic cells in tumors and evoke antitumor immune responses to inhibit tumor growth.

Differentiation to the CCR2+ inflammatory phenotype in vivo is a constitutive, time-limited property of blood monocytes and is independent of local inflammatory mediators

It is proposed that CCR2+ monocytes are specifically recruited to inflammatory sites, whereas CCR2- monocytes are recruited to normal tissue to become resident macrophages. Whether these subsets represent separate lineages, how differential trafficking is regulated and whether monocytes undergo further differentiation is uncertain. Using a mouse model of autoimmune uveoretinitis we examined monocyte trafficking to the inflamed retina in vivo. We show that bone marrow-derived CD11b+ F4/80- monocytes require 24 to 48 h within the circulation and lymphoid system before acquiring the CCR2+ phenotype and trafficking to the inflamed retina is enabled. This phenotype, and the capacity to traffic were lost by 72 h. Monocyte CCR2 expression followed a similar time course in normal mice indicating that differentiation to an inflammatory phenotype is a constitutive, time-limited property, independent of local inflammatory mediators. Phenotypic analysis of adoptively transferred cells indicated that circulating inflammatory monocytes also differentiate into CD11c+ and B220+ dendritic cells and F4/80+ tissue macrophages in vivo. Our data supports the hypothesis of continuous extravasation and progressive differentiation over time of inflammatory monocytes in the circulation rather than replication within the actively inflamed tissue, and supports the concept of myeloid dendritic cell differentiation from trafficking monocytes under physiological conditions in vivo.

Migratory Langerhans cells in mouse lymph nodes in steady state and inflammation

Dendritic cells cells induce immunity or-in the steady state-maintain peripheral tolerance. Little is known in that regard about Langerhans cells. Therefore, we investigated migrating Langerhans cells in the steady-state versus inflammation. Increased numbers of Langerhans cells, as determined by immunostaining for Langerin/CD207, appeared in the lymph nodes in response to a contact allergen. Whereas a large proportion of Langerhans cells expressed CD86 in the steady state, CD40, and CD80 were found on a smaller percentage. During inflammation, more CD40(+), CD80(+), CD274/B7-H1/PD-L1(+), and CD273/B7-DC/PD-L2(+) Langerhans cells were found in the lymph nodes, and they expressed higher levels of these molecules. CD275/inducible T cell co-stimulator (ICOS) ligand was not detected. Langerhans cells in the nodes of contact allergen-treated mice produced more IL-12p40/70. This correlated with more interferon-gamma being produced by activated lymph node T cells. Epicutaneous immunization with ovalbumin under inflammatory conditions led to a more vigorous proliferation of antigen-specific CD4 T cells in vitro and in vivo as compared with immunization in the steady state. The latter modality, however did not induce strong CD4 T cell tolerance in this model. Thus, the overall phenotype of Langerhans cells is not an indicator for their immunogenic or tolerogenic potential.

Langerhans cells are strongly reduced in the skin of transgenic mice overexpressing follistatin in the epidermis

Activins are members of the transforming growth factor-beta (TGF-beta) family and are important for skin morphogenesis and wound healing. TGF-beta1 is necessary for the population of the epidermis with Langerhans cells (LC). However, a role for activin in LC biology is not known. To address this question, we analyzed skin from transgenic mice overexpressing the activin antagonist follistatin in the epidermis. Using immunofluorescence, we observed a striking decrease in the number of LC in the epidermis of transgenic mice in comparison to wild-type mice. Nevertheless, these LC expressed normal levels of major histocompatibility complex (MHC)-class II and Langerin/ CD207 in situ. In explant cultures of whole ear skin the number of dendritic cells (DC), which migrated into the culture medium, was reduced. This reduction was even more pronounced in cultures of epidermal sheets. Virtually all emigrated cutaneous DC displayed typical morphology with cytoplasmic "veils", showed translocation of MHC-class II to the surface membrane, and expressed the maturation marker 2A1. Thus, cutaneous DC from transgenic mice seemed to mature normally. These results demonstrate that overexpression of follistatin in the epidermis affects LC trafficking but not maturation and suggest a novel role of the follistatin-binding partner activin in LC biology.

Accelerated dendritic-cell migration and T-cell priming in SPARC-deficient mice

On their path to draining lymph nodes, epidermal Langerhans cells traverse collagen-dense connective tissue before reaching lymphatic vessels. The matricellular protein SPARC (secreted protein, acidic and rich in cysteine), which is induced during inflammation and tissue repair, organizes collagen deposition in tissue stroma. We analyzed Langerhans cell and dendritic-cell migration and its impact on T-cell priming in SPARC-null (SPARC–/–) and SPARC-sufficient (SPARC+/+) mice. Although the same number of Langerhans cells populate the ear skin of SPARC–/– and SPARC+/+ mice, more Langerhans cells were found in the lymph nodes draining antigen-sensitized ears of SPARC–/– mice and significantly more Langerhans cells migrated from null-mice-derived ear skin explants. Such favored Langerhans cell migration is due to the host environment, as demonstrated by SPARC+/+>SPARC–/– and reciprocal chimeras, and have a profound influence on T-cell priming. Contact-, delayed type-hypersensitivity and naive T-cell receptor-transgenic T-cell priming, together indicate that the lack of SPARC in the environment accelerates the onset of T-cell priming by hastening Langerhans cell/dendritic-cell migration.

Constitutive expression of alpha interferon by skin dendritic cells confers resistance to infection by foot-and-mouth disease virus

The role of dendritic cells (DC) in the initiation of immune responses against foot-and-mouth disease virus (FMDV) is poorly understood. We analyzed the innate response of freshly isolated swine skin DC to the virus and show a rapid induction of beta interferon (IFN-beta) mRNA but not IFN-alpha mRNA. However, these DC secreted both IFN-alpha and IFN-beta proteins in response to live virus but not killed virus. Furthermore, the surface expression of swine major histocompatibility complex class II (SLA II) or CD80/CD86 molecules and antigen processing functions were not affected by FMDV exposure. Given the demonstrated sensitivity of FMDV to IFN-alpha/beta, there was no productive or nonproductive infection of these cells. Finally, freshly isolated skin DC constitutively expressed intracellular IFN-alpha protein in the absence of stimulation, with no detectable secretion of the cytokine until virus exposure. In situ analysis of these DC showed that these cells express and store IFN-alpha in uninfected animals. This is the first demonstration of the constitutive expression of IFN-alpha in resident, tissue-derived DC and indicates that skin DC can play an important role in the innate immune response of swine to viral infections.

Disruption of the langerin/CD207 gene abolishes Birbeck granules without a marked loss of Langerhans cell function

Langerin is a C-type lectin expressed by a subset of dendritic leukocytes, the Langerhans cells (LC). Langerin is a cell surface receptor that induces the formation of an LC-specific organelle, the Birbeck granule (BG). We generated a langerin(-/-) mouse on a C57BL/6 background which did not display any macroscopic aberrant development. In the absence of langerin, LC were detected in normal numbers in the epidermis but the cells lacked BG. LC of langerin(-/-) mice did not present other phenotypic alterations compared to wild-type littermates. Functionally, the langerin(-/-) LC were able to capture antigen, to migrate towards skin draining lymph nodes, and to undergo phenotypic maturation. In addition, langerin(-/-) mice were not impaired in their capacity to process native OVA protein for I-A(b)-restricted presentation to CD4(+) T lymphocytes or for H-2K(b)-restricted cross-presentation to CD8(+) T lymphocytes. langerin(-/-) mice inoculated with mannosylated or skin-tropic microorganisms did not display an altered pathogen susceptibility. Finally, chemical mutagenesis resulted in a similar rate of skin tumor development in langerin(-/-) and wild-type mice. Overall, our data indicate that langerin and BG are dispensable for a number of LC functions. The langerin(-/-) C57BL/6 mouse should be a valuable model for further functional exploration of langerin and the role of BG.

Illuminating the landscape of in vivo immunity: insights from dynamic in situ imaging of secondary lymphoid tissues

A central feature of the immune system is the migratory behavior of its cellular components. Thus, fully understanding the generation and maintenance of immune responses must include consideration of how hematopoietic cells home to, interact within, and exit from secondary lymphoid organs as well as peripheral tissues. Recent advances in in situ imaging techniques now permit direct observation of these events in their physiologic settings with high spatiotemporal resolution. This review summarizes progress in this area of investigation from a lymphocentric perspective. We highlight controversies, point out key unanswered questions, and briefly outline what we believe are some of the near-term directions that in situ microscopic analysis of the immune system will take.

CCR7 governs skin dendritic cell migration under inflammatory and steady-state conditions

The CC chemokine receptor CCR7 has been identified as a key regulator of homeostatic B and T cell trafficking to secondary lymphoid organs. Data presented here demonstrate that CCR7 is also an essential mediator for entry of both dermal and epidermal dendritic cells (DC) into the lymphatic vessels within the dermis while this receptor is dispensable for the mobilization of Langerhans cells from the epidermis to the dermis. Moreover, a distinct population of CD11c(+)MHCII(high) DC showing low expression of the costimulatory molecules CD40, CD80, and CD86 in wild-type animals was virtually absent in skin-draining lymph nodes of CCR7-deficient mice under steady-state conditions. We provide evidence that these cells represent a semimature population of DC that is capable of initiating T cell proliferation under conditions known to induce tolerance. Thus, our data identify CCR7 as a key regulator that governs trafficking of skin DC under both inflammatory and steady-state conditions.

[Tolerance induction towards nickel. From animal model to humans]

Nickel is the most common contact allergen in humans. Until recently, many questions concerning tolerance mechanisms to nickel were unresolved. Besides human ex vivo, intervention and observation studies, the establishment of a reproducible mouse model has contributed to the analysis of these mechanisms. A more detailed understanding of the pathogenesis of nickel allergy and tolerance towards nickel by investigations in an animal model and in human studies is a prerequisite for developing specific prevention and therapy of nickel allergy. With this article, we provide a review of the investigations concerning nickel allergy and give perspectives towards oral tolerance induction to nickel in the animal model and in humans.

APCs in the anterior uveal tract do not migrate to draining lymph nodes

The migration of APCs from sites of infection and their maturation are critical elements in the generation of immune responses. However, the paths by which intraocular Ags migrate to draining lymph nodes are not known because the eye has limited lymphatic vessels. To date, only dendritic cells from the cornea and conjunctiva have been shown to emigrate. We demonstrate that phagocytic APCs in the anterior uveal tissues of the murine eye that ingest fluorescent latex beads do not migrate to regional lymph nodes. The beads are ingested in the uveal tract by cells expressing MHC class II, CD11c, or F4/80. Using intravital time-lapse videomicroscopy to monitor iris APC migration after anterior chamber injection of fluorescent Ag, fluorescently labeled APCs fail to move at multiple observation times, even in the presence of Ag and LPS. Whereas an as yet unidentified ocular nonphagocytic APC subset might migrate from the anterior uveal tissues, it is more probable that immune responses in the draining lymph nodes are engendered by soluble Ag escaping the eye through interstitial spaces. The inability of anterior uveal tissue APCs to migrate to lymph nodes may contribute to deviant immune responses that dominate after Ags are introduced into the anterior chamber.

A Model System Using Tape Stripping for Characterization of Langerhans Cell-Precursors In Vivo

Little is known about the immigration of bone marrow-derived progenitors of Langerhans cells (LC) into the epidermis. We developed an in vivo system based on the tape stripping method that allowed us to study the immigration of LC into the epidermis after intradermal injection of bone marrow-derived dendritic cells (DC). Tape stripping induced a mechanical disruption of the epidermal barrier that led to skin inflammation and subsequent emigration of LC and dermal DC from the skin. Emigrating LC and dermal DC were observed in lymphatic vessels, and the numbers of LC and dermal DC in the draining lymph node increased. Up to 500 times more injected precursors migrated into tape-stripped epidermis as compared with unstripped epidermis. Newly immigrated cells were slender with one or two dendrites and acquired a more dendritic morphology after 2-4 days. They were both MHC II-positive and negative and they did not express Langerin/CD207, nor macrophage-mannose receptor/CD206 and Fc-epsilon receptor I. In contrast, all cells that had entered the epidermis expressed CD11c and CCR6, suggesting that they were LC. We conclude that this experimental system may serve as a valuable tool for the further characterization of LC-precursors and the conditions necessary for LC-immigration into the epidermis.

Activation of the D Prostanoid Receptor 1 Regulates Immune and Skin Allergic Responses

The mobilization of Langerhans cells (LCs) from epithelia to the draining lymph nodes is an essential process to initiate primary immune responses. We have recently shown that in mice, PGD2 is a potent inhibitor of epidermal LC emigration. In this study, we demonstrate that activation of the D prostanoid receptor 1 (DP1) impedes the TNF-alpha-induced migration of human LCs from skin explants and strongly inhibits the chemotactic responses of human LC precursors and of maturing LCs to CC chemokine ligands 20 and 19, respectively. Using a murine model of atopic dermatitis, a chronic Th2-type allergic inflammatory disease, we demonstrate that the potent DP1 agonist BW245C dramatically decreases the Ag-specific T cell activation in the skin draining lymph nodes and markedly prevents the skin lesions following repeated epicutaneous sensitization with OVA. Interestingly, analysis of the local response indicates that BW245C treatment strongly reduces the recruitment of inflammatory cells into the dermis and disrupts the Th1/Th2 balance, probably through the increased production of the immunoregulatory cytokine IL-10, in the skin of sensitized mice. Taken together, our results suggest a new function for DP1 in the regulation of the immune and inflammatory responses. We propose that DP1 activation by specific agonists may represent a strategy to control cutaneous inflammatory Th2-associated diseases.

Neuronal repellent Slit2 inhibits dendritic cell migration and the development of immune responses

One of the essential functions of dendritic cells is to take up Ags in peripheral tissues and migrate into secondary lymphoid organs to present Ags to lymphocytes for the induction of immune responses. Although many studies have demonstrated that the migration of dendritic cells is closely associated with the development of immune responses, little is known about factors that inhibit dendritic cell migration and control the extent of immune responses to Ag stimulation. We show that Slit2, a neuronal repellent factor, is up-regulated in the skin by allergen sensitization and down-regulates the migration of Langerhans cells. The effect is mediated by direct interaction of Slit2 with cells that express a Slit-specific receptor, Robo1. Slit2-mediated inhibition of Langerhans cell migration results in suppression of contact hypersensitivity responses. These findings provide insights into a novel mechanism by which Slit2 functions as an anti-inflammatory factor for the initiation of immune responses.

Prostaglandin E2-EP4 signaling initiates skin immune responses by promoting migration and maturation of Langerhans cells

Antigen-specific immune responses in the skin are initiated by antigen uptake into Langerhans cells and the subsequent migration of these cells to draining lymph nodes. Although prostaglandin E2 (PGE2) is produced substantially in skin exposed to antigen, its role remains unclear. Here we show that although Langerhans cells express all four PGE receptor subtypes, their migration to regional lymph nodes was decreased only in EP4-deficient (Ptger4-/-) mice and in wild-type mice treated with an EP4 antagonist. An EP4 agonist promoted the migration of Langerhans cells, increased their expression of costimulatory molecules and enhanced their ability to stimulate T cells in the mixed lymphocyte reaction in vitro. Contact hypersensitivity to antigen was impaired in Ptger4-/- mice and in wild-type mice treated with the EP4 antagonist during sensitization. PGE2-EP4 signaling thus facilitates initiation of skin immune responses by promoting the migration and maturation of Langerhans cells.