Epidermal Langerhans Cells Research Articles

Abstract A102: Rescue of lost skin dendritic cells in melanoma is key for the resuscitation of antitumor T-cell responses

Abstract One major characteristic of skin-related cancers is the loss of skin-resident dendritic cell populations. In the tg(Grm1)EPv mouse model, ectopic expression of the metabotropic glutamate receptor-1 in melanocytes leads to a highly proliferative and antiapoptotic phenotype, resulting in melanoma formation within the dermis. The slow progression of these tumors allows for the in depth analysis of the immune infiltrate in growing tumors. We here show that total DCs (CD11c+ cells) are gradually lost as the tumor progresses. Mainly the dermal CD11b+ DCs are affected, whereas epidermal Langerhans cells remain unchanged. We hypothesized that extrinsic cell death of the DCs may be induced within the growing tumor. Indeed, the tumor tissue upregulated the expression of Fas ligand (FasL) that can induce extrinsic apoptosis in immature DCs that express Fas (CD95). Fas-mediated apoptosis depends on the activation of caspase-8 and mice in which the autoproteolytic cleavage site D387 is mutated to alanine (casp8D387A/casp8D387A) show strong resistance to Fas-mediated death. We compared the apoptosis induction in the different DC subsets in casp8WT/casp8WT and in casp8D387A/casp8D387A upon intradermal administration of an agonistic anti-CD95 antibody and we found that, indeed, CD11b+ DCs in WT mice are susceptible to apoptosis via CD95. In order to retrieve the intratumoral DCs, we treated tg(Grm1)EPv mice carrying tumor lesions with Flt3L and the percentages of the CD11b+ subset could be restored back to the levels of tumor-free mice. At the same time, T-cells from both the tumor and the tumor-draining lymph node were able to produce more cytotoxic cytokines. Our data thus indicate that the loss of DCs in melanoma depends on induction of apoptosis within the tumor; rescue of skin DCs may be a promising strategy in order to enhance the efficacy of existing immunotherapeutic strategies against skin-related cancers. Citation Format: Anastasia Prokopi, Christoph H. Tripp, Bart Tummers, Kerstin Komenda, Katharina Hutter, Giuseppe Cappellano, Lydia Bellmann, Mirjana Efremova, Zlatko Trajanoski, Suzie Chen, Bjorn E. Clausen, Douglas R. Green, Patrizia Stoitzner. Rescue of lost skin dendritic cells in melanoma is key for the resuscitation of antitumor T-cell responses [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A102.

Stat3 activation in epidermal keratinocytes induces Langerhans cell activation to form an essential circuit for psoriasis via IL-23 production

BackgroundPsoriasis is an inflammatory disease associated with aberrant crosstalk between the epidermis and immune system. However, the role of Langerhans cells (LCs) in psoriasis remains controversial. ObjectivesTo elucidate whether LCs are functionally involved in the development of psoriasis using a mouse model. MethodsTwo lines of transgenic mice were used and crossed. They included K5.Stat3C, the psoriasis-model mouse and langerin DTR knock-in (KI) mouse. We performed immunofluorescence staining for LCs in psoriatic lesion of human and model mice. Flow cytometric analyses were performed to compare between dendritic cells (DCs) and LCs in the epidermis and skin-draining lymph nodes (sDLNs). To assess cytokine/chemokine expression in the skin lesion or primary cultured keratinocytes, we performed RT-PCR, microarray analysis or intracellular staining on the flow cytometer. ResultsLCs were activated in psoriatic lesion of patients with psoriasis and K5.Stat3C mice. Compared with non-transgenic mice, K5.Stat3C mice constitutively showed an increased number of LCs in the sDLNs before psoriasis-like lesion developed. Stat3C transgenic keratinocytes expressed an elevated level of IL-1α. Psoriasis-like lesion in K5.Stat3C mice were attenuated in the absence of LCs, indicating that LCs were essential to the development of psoriasis-like lesion. Furthermore, we also recognized that epidermal LCs in psoriatic lesion of not only K5.Stat3C mice but also psoriasis patients produced IL-23. ConclusionsOur study suggests that Stat3 activation in keratinocytes may impact on LC activation in situ via IL-1α stimulation, at least in part, and that their presence may be essential for the pathogenesis of psoriasis through producing IL-23.

Differentiation of Langerhans Cells from Monocytes and Their Specific Function in Inducing IL-22-Specific Th Cells.

Human mucosal tissues and skin contain two distinct types of dendritic cell (DC) subsets, epidermal Langerhans cells (LCs) and dermal DCs, which can be distinguished by the expression of C-type lectin receptors, Langerin and DC-SIGN, respectively. Although peripheral blood monocytes differentiate into these distinct subsets, monocyte-derived LCs (moLCs) induced by coculture with GM-CSF, IL-4, and TGF-β1 coexpress both Langerin and DC-SIGN, suggesting that the environmental cues remain unclear. In this study, we show that LC differentiation is TGF-β1 dependent and that cofactors such as IL-4 and TNF-α promote TGF-β1-dependent LC differentiation into Langerin+DC-SIGN- moLCs but continuous exposure to IL-4 blocks differentiation. Steroids such as dexamethasone greatly enhanced TNF-α-induced moLC differentiation and blocked DC-SIGN expression. Consistent with primary LCs, dexamethasone-treated moLCs express CD1a, whereas monocyte-derived DCs (moDCs) express CD1b, CD1c, and CD1d. moDCs but not moLCs produced inflammatory cytokines after stimulation with CD1b and CD1d ligands mycolic acid and α-galactosylceramide, respectively. Strikingly, CD1a triggering with squalene on moLCs but not moDCs induced strong IL-22-producing CD4+ helper T cell responses. As IL-22 is an important cytokine in the maintenance of skin homeostasis, these data suggest that CD1a on LCs is involved in maintaining the immune barrier in the skin.

Pleiotropic Impacts of Macrophage and Microglial Deficiency on Development in Rats with Targeted Mutation of the Csf1r Locus.

We have produced Csf1r-deficient rats by homologous recombination in embryonic stem cells. Consistent with the role of Csf1r in macrophage differentiation, there was a loss of peripheral blood monocytes, microglia in the brain, epidermal Langerhans cells, splenic marginal zone macrophages, bone-associated macrophages and osteoclasts, and peritoneal macrophages. Macrophages of splenic red pulp, liver, lung, and gut were less affected. The pleiotropic impacts of the loss of macrophages on development of multiple organ systems in rats were distinct from those reported in mice. Csf1r−/− rats survived well into adulthood with postnatal growth retardation, distinct skeletal and bone marrow abnormalities, infertility, and loss of visceral adipose tissue. Gene expression analysis in spleen revealed selective loss of transcripts associated with the marginal zone and, in brain regions, the loss of known and candidate novel microglia-associated transcripts. Despite the complete absence of microglia, there was little overt phenotype in brain, aside from reduced myelination and increased expression of dopamine receptor-associated transcripts in striatum. The results highlight the redundant and nonredundant functions of CSF1R signaling and of macrophages in development, organogenesis, and homeostasis.

PEANUT ALLERGEN IMMUNOTHERAPY: ONLINE EDUCATION IMPROVES KNOWLEDGE OF ALLERGIST LEARNERS

Introduction A study was conducted to determine if an online educational intervention could improve knowledge and competence of allergists in the latest research on peanut allergen immunotherapies. Methods A 30-minute online educational intervention consisting of 3 video-based expert discussions among two faculty each covered topics related to the latest research on peanut allergen immunotherapy. Educational effect was evaluated with a repeated-pairs pre- to post-assessment study design in which each individual learner acts as his/her own control. A paired 2-tailed t-test evaluated whether the mean pre- and post-assessment scores significantly differed from one another and Pearson's X2 test measured changes in paired responses to individual questions. Cramer's V was used to calculate the effect size of the intervention. Data from the educational intervention were collected between September 28, 2017 and November 14, 2017. Results Participation in education resulted in statistically significant improvements and an extensive educational effect for allergists (n=155; P • Identification of the role of epidermal Langerhans cells in activating regulatory T cells (28% improvement) • Knowledge of safety of epicutaneous immunotherapy for peanut allergy (9% improvement) • Importance of the clinical relevance of a higher peanut protein threshold (105% improvement) • Confidence in discussing evidence regarding peanut allergen immunotherapy with patients (62% improvement) Conclusions Participation in online, video-based expert discussions of latest research in peanut allergen immunotherapies resulted in significant improvement in knowledge of allergists.

Development of a skin-friendly microemulsion for dermal allergen-specific immunotherapy

Due to their role in immune responses, the skin dendritic cells (i.e. epidermal Langerhans cells and dermal dendritic cells) have become of great interest to researchers in the past decades. A dermal administration of allergens could target these professional antigen-presenting cells directly and build up immunotolerance. Additionally, many of the adverse side effects, which are seen in the current state of the art specific immunotherapy routes, could be avoided.Therefore, in this study a penetration enhancing microemulsion was developed and its physicochemical properties were determined under several storage conditions. The influence of different preservatives on the microemulsion stability was observed. We examined epidermal penetration of Alexa Fluor-647 labelled bee-venom phospholipase A2 (Api m 1) using the Franz diffusion cell set up and confocal laser-scanning microscopy. First results of an in-vivo Api m 1-allergic mouse model indicated the protective efficacy of dermal AIT with our newly developed microemulsion.Summarily, the developed microemulsion is a suitable, stable drug delivery system for the topical administration of proteogenic allergens into the epidermis and is able to reach dendritic cells in the skin.

A protective Langerhans cell-keratinocyte axis that is dysfunctional in photosensitivity.

Photosensitivity, or skin sensitivity to ultraviolet radiation (UVR), is a feature of lupus erythematosus and other autoimmune and dermatologic conditions, but the mechanistic underpinnings are poorly understood. We identify a Langerhans cell (LC)-keratinocyte axis that limits UVR-induced keratinocyte apoptosis and skin injury via keratinocyte epidermal growth factor receptor (EGFR) stimulation. We show that the absence of LCs in Langerin-diphtheria toxin subunit A (DTA) mice leads to photosensitivity and that, in vitro, mouse and human LCs can directly protect keratinocytes from UVR-induced apoptosis. LCs express EGFR ligands and a disintegrin and metalloprotease 17 (ADAM17), the metalloprotease that activates EGFR ligands. Deletion of ADAM17 from LCs leads to photosensitivity, and UVR induces LC ADAM17 activation and generation of soluble active EGFR ligands, suggesting that LCs protect by providing activated EGFR ligands to keratinocytes. Photosensitive systemic lupus erythematosus (SLE) models and human SLE skin show reduced epidermal EGFR phosphorylation and LC defects, and a topical EGFR ligand reduces photosensitivity. Together, our data establish a direct tissue-protective function for LCs, reveal a mechanistic basis for photosensitivity, and suggest EGFR stimulation as a treatment for photosensitivity in lupus erythematosus and potentially other autoimmune and dermatologic conditions.

Cell-intrinsic regulation of murine epidermal Langerhans cells by protein S.

AXL, a member of the TYRO3, AXL, and MERTK (TAM) receptor tyrosine kinase family, has been shown to play a role in the differentiation and activation of epidermal Langerhans cells (LCs). Here, we demonstrate that growth arrest-specific 6 (GAS6) protein, the predominant ligand of AXL, has no impact on LC differentiation and homeostasis. We thus examined the role of protein S (PROS1), the other TAM ligand acting primarily via TYRO3 and MERTK, in LC function. Genetic ablation of PROS1 in keratinocytes resulted in a typical postnatal differentiation of LCs; however, a significant reduction in LC frequencies was observed in adult mice due to increased apoptosis. This was attributed to altered expression of cytokines involved in LC development and tissue homeostasis within keratinocytes. PROS1 was then excised in LysM+ cells to target LCs at early embryonic developmental stages, as well as in adult monocytes that also give rise to LCs. Differentiation and homeostasis of LCs derived from embryonic precursors was not affected following Pros1 ablation. However, differentiation of LCs from bone marrow (BM) precursors in vitro was accelerated, as was their capability to reconstitute epidermal LCs in vivo. These reveal an inhibitory role for PROS1 on BM-derived LCs. Collectively, this study highlights a cell-specific regulation of LC differentiation and homeostasis by TAM signaling.

Autoimmune disease severity is suppressed by type I interferon signaling in radioresistant cells

Abstract Type I interferons broadly modulate immune responses and can drive both anti-inflammatory and immunostimulatory programs. Vitiligo is an autoimmune disease where melanocytes are destroyed by autoreactive CD8+ T cells. We have previously shown in mice and human patient tissue that IFNγ and the induced downstream chemokines, CXCL9 and CXCL10 drive disease pathogenesis. Since type I interferon signaling can drive expression of multiple overlapping IFNγ target genes, we wanted to determine the role of type I interferon in disease progression. Interestingly, we found that type I interferon-deficient mice developed accelerated and severely enhanced vitiligo compared to WT control mice. These results suggest that in contrast to IFNγ, IFNAR signaling acts to suppress disease. We subsequently found that IFNAR signaling is not required on autoreactive CD8+ T cells or other radiosensitive immune cells but rather it is required on radioresistant cells to suppress vitiligo. In radioresistant IFNAR-deficient mice, autoreactive CD8+ T cells have significantly reduced levels of PD-1 expression which correlates to increased production of the effector cytokines TNFα and IFNγ. Generation of conditional knockout mice showed that epidermal radioresistant Langerhans cells and keratinocytes do not require IFNAR to suppress disease and we are currently investigating the role of IFNAR signaling on epidermal melanocytes. These studies will not only enhance our understanding of the role of IFNAR in promoting tissue specific tolerance, but will have broad insights into the role of IFNAR in other organ–specific autoimmune diseases, such as multiple sclerosis, in which IFNβ is an available treatment.

TGF-β1 regulates epidermal LCs in a Smad-independent pathway

Abstract Transforming growth factor-β1 (TGF-β1) is a key factor for Langerhans cell (LC) homeostasis and maintaining in the epidermis, but the underlying mechanisms in TGF-β signaling pathways remain elusive. Canonically, binding of TGF-β to TGF-βR activates Smad2 or Smad3, which subsequently heterodimerizes with Smad4 and then translocates into the nucleus acting as transcriptional regulators of TGF-β1 target genes. In order to investigate if Smad-dependent pathways are required for epidermal LC maintenance, we first crossed CSF1R-Cre and hLangerin-Cre transgenic mice with Smad2fl/fl and Smad4fl/fl, mice to generate the mutant mice with conditional Smad2 and Smad4 deletion at birth (CSF1Rcre) or 3 days after birth (hlangerinCre). Surprisingly, deletion of individual Smad2 or Smad4 in LCs did not significantly affect their ratios in skin and their expression of MHC-II, CD80 and CD86 in both models. The phagocytic capacity of LCs from KO mice was unaltered in vivo and in vitro compared to WT LCs. Furthermore, upon in vitro stimulation, MHC-II, CD80 and CD86 were comparably unregulated on LCs between KO and WT mice. We further tested LC number and maturation in conventional Smad3KO mice as well as Smad2/4 double KO mice induced by CSF1Rcre, the number and maturation of LCs are comparable between mutant and WT mice. Overall, our data suggest that conventional TGF-β/Smad2/3/4 signaling pathways may not be required for maintaining LC homeostasis and immature stage in the epidermis and LC maturation upon stimulation. The underlying mechanisms that Smad2/3/4-independent TGF-β pathways involved in LC maintenance and function remain to be further determined.

Glyteer, Soybean Tar, Impairs IL-4/Stat6 Signaling in Murine Bone Marrow-Derived Dendritic Cells: The Basis of Its Therapeutic Effect on Atopic Dermatitis.

Atopic dermatitis (AD) is a common inflammatory skin disease. Recent studies have revealed the involvement of T helper (Th)2 cytokines including Interleukin 4 (IL-4) in the pathogenesis of AD. Since epidermal Langerhans cells (LCs) and dermal myeloid dendritic cells (DCs) produce CCL17 and CCL22 that chemoattract Th2 cells, interfering with CCL17 and CCL22 production from LCs and dermal myeloid DCs may be beneficial in the treatment of AD. To investigate this, we stimulated murine bone marrow-derived DCs (BMDCs) with IL-4. IL-4 stimulation produced Ccl17 and Ccl22, which was attenuated by soybean tar Glyteer, a known aryl hydrocarbon receptor (Ahr) activator. Notably, Glyteer treatment blocked the nuclear translocation of Stat6 induced by IL-4 stimulation, suggesting that this treatment impairs the IL-4/Stat6 signaling pathway in BMDCs. Unexpectedly, Glyteer treatment did not potently upregulate the expression of Cyp1a1, a specific Ahr-responsive gene, suggesting that its inhibitory machinery for Ccl17 and Ccl22 expression is likely to operate in an Ahr-independent manner. These findings indicate that Glyteer may exhibit therapeutic potential for AD by downregulating the CCL17 and CCL22 production from DCs in a Th2-deviated microenvironment.

Indeterminate Cell Histiocytosis – Case Report and Review of Literature

Abstract Introduction. Indeterminate cell histiocytosis is a rare proliferative disorder of indeterminate dendritic cells, reported in only 50 case reports so far. It is clinically presented as yellow, red or brown papules and nodules that appear in otherwise healthy adult individuals. Indeterminate cells are distinct dendritic cells of the skin that have ultrastructural similarities to the epidermal Langerhans cells but do not contain the characteristic Birbeck’s granules and they are also langerin-negative, unlike LCH. Indeterminate cell histiocytosis is an exceptional entity with variable clinical, histopathologic or immunohistochemical findings, sharing morphologic and immunophenotypic features with both Langerhans- and non-Langerhans cell histiocytoses. Case Report. We present a case of indeterminate histiocytosis in a 77-year-old man with 3-year history of asymptomatic, multiple reddish and brown papules and nodules over the entire body, including the oral mucosa. Skin biopsy was done, and histopathological analysis with immunohistochemistry was performed. The positive ICH staining of cells for CD68, CD1a, and S-100 enabled us to diagnose ICH in our patient. Also, BRAF V600E mutation was detected in tumor tissue. The treatment was started with methotrexate that was effective for 6 months, but due to the disease recurrence, further therapy with thalidomide was advised, without effect. Conclusion. Indeterminate histiocytosis is a rare disease, therefore no standardized treatment has been established and the treatment options are limited.

Tacrolimus Reverses UVB Irradiation-Induced Epidermal Langerhans Cell Reduction by Inhibiting TNF-α Secretion in Keratinocytes via Regulation of NF-κB/p65.

Background: Topical calcineurin inhibitors including tacrolimus and pimecrolimus are used in the treatment of many inflammatory skin diseases mainly via blocking T-cell proliferation. Our previous studies found that pimecrolimus 1% cream could reverse high-dose ultraviolet B (UVB) irradiation-induced epidermal Langerhans cell (LC) reduction via inhibition of LC migration. We conducted this study to investigate the effects of topical tacrolimus 0.03% ointment on high-dose UVB-irradiated human epidermal LCs.Methods: Twenty fresh human foreskin tissues were randomly divided into four groups as follows: Control, Tacrolimus (0.03%), UVB (180 mJ/cm2), and UVB (180 mJ/cm2) + Tacrolimus (0.03%). Four time points were set as follows: 0, 18, 24, and 48 h. We collected culture medium and tissues at each time point. The percentage of CD1a+ cells in the medium was detected by means of flow cytometry. Each tissue was prepared for immunohistochemistry, real-time quantitative PCR, and western blot. HaCaT cells were cultured and divided into four groups: Control, Tacrolimus (1 μg/ml), UVB (30 mJ/cm2), and UVB (30 mJ/cm2) + Tacrolimus (1 μg/ml). The cells were incubated for 24 h and prepared for real-time quantitative PCR and western blot.Results: Topical tacrolimus significantly reversed high-dose UVB irradiation-induced epidermal LC reduction and CD1a+ cell increment in culture medium. Tacrolimus significantly inhibited UVB irradiation-induced tumor necrosis factor-α (TNF-α) and nuclear factor kappa B (NF-κB)/p65 mRNA and protein expression in HaCaT cells. Tacrolimus also significantly inhibited high-dose UVB irradiation-induced TNF-α expression in cultured tissues. Finally, TNF-α antagonist (recombinant human TNF-α receptor II: IgG Fc fusion protein) could significantly reverse UVB irradiation-induced epidermal LC reduction.Conclusion: Topical tacrolimus 0.03% could reverse UVB irradiation-induced epidermal LC reduction by inhibiting TNF-α secretion in keratinocytes via regulation of NF-κB/p65.

Skin Biopsy Findings in Patients With CMT1A: Baseline Data From the CLN-PXT3003-01 Study Provide New Insights Into the Pathophysiology of the Disorder.

Charcot-Marie-Tooth disease type 1A (CMT1A), the most common form of Charcot-Marie-Tooth diseases, is a demyelinating neuropathy caused by a deletion encompassing the gene coding for PMP22, a myelin protein of the peripheral nervous system. Although myelinated fibers are mostly involved in CMT1A, some patients experience neuropathic pain. We thus investigated whether unmyelinated fibers are lost in CMT1A. Skin biopsies were taken from the distal portion of the leg of 80 patients with CMT1A as part of the PXT30003-01 study and processed for quantification of intraepidermal nerve fiber density (IENFD). Mean IENFD was significantly lower in CMT1A patients than in healthy controls. Although the data were highly dispersed, IENFD tended to decrease with age and was higher overall in female patients and controls than male patients and controls. This study shows that small nerve fibers are affected in CMT1A and that this correlates with pin sensitivity. The density of epidermal Langerhans cells (LCs) was also significantly reduced in CMT1A patients, suggesting the involvement of LCs in neuropathic pain processes. These findings raise several questions concerning the interactions of Schwann cells and LCs with unmyelinated fibers in CMT1A. Moreover, they suggest that factors other than PMP22 gene dosage are involved in small fiber pathology in CMT1A.

CD45+, CD68+ and E-cadherin+ Expressions in Skin Dogs Naturally Infected by Leishmania infantum

Background: In canine leishmaniasis (CanL), infection occurs through phlebotomine vectors that inoculate the protozoan Leishmania infantum into the skin that infected macrophages and activated dendritic cells (CD). Dogs with CanL present variable clinical manifestations, being common the presence of cutaneous lesions. The aim of this study was to evaluate the expression of CD45+, CD68+ and E-cadherin+ associating the skin sentinels cells and to compare the clinical-dermatological manifestations in the skin of dogs naturally infected by L. infantum.Materials, Methods & Results: Dogs infected (n = 22) by L. infantum were divided into asymptomatic group (AD, n = 9), and symptomatic group (SD, n = 13), according criteria based on the presence or absence of skin changes. Dogs non-infected (CD, n = 5) were included as control group. Samples of skin biopsies collected from scapular region were processed by routine histology and labeled by immunohistochemistry with monoclonal antibodies against CD45+, CD68+ and E-cadherin+, and were described as none, mild, moderate and intense. SD presented keratoconjunctivitis, onychogryphose, lichenification, depigmentation, alopecia, hypotrichosis, erythematous dermatitis, exfoliative dermatitis, ulcerative dermatitis and crusted dermatitis, and the frequency these alterations was expressed as percentage. The results of hematological and biochemical parameters were analyzed by Kruskal-Wallis test followed by the Dunn’s test and expressed as mean ± standard deviation, with values P < 0.05. Leukocytosis (not significant), red blood cells, hematocrit and hemoglobin (P < 0.05), total protein serum (P < 0.05), globulins (P < 0.05), albumin and A/G ratio (P < 0.01) were altered in SD in relation to CD. Cutaneous cellular infiltration, composed by macrophages, plasma cells, lymphocytes and neutrophils, was observed in CD. There was an increase of expression of the markers in SD when compared to the other groups, as moderate CD68+ expression and L. infantum, and intense CD45+ and E-cadherin+ expressions.Discussion: Cutaneous involvement is very important in CanL, as it corresponds to where is the first interaction between the parasite and the immune system. Dermatological clinical signs, leukocytosis, anemia, globulins levels have been reported for dogs naturally infected by L. infantum. Inflammatory infiltrate was distributed at superficial and deep dermis, which was composed by mononuclear cells as macrophages, plasma cells, lymphocytes and neutrophils. To characterize the immune sentinels cells in the skin it was evaluated CD45+, CD68+ and E-cadherin+ expressions. In syntomatic dogs, our results revelead an increase of expression of these markers. CD45+ is one of the most abundant molecules expressed on the white blood cell surface in various mammals, while CD68+ is a myelomonocytic marker that seems to be retained during monocyte differentiation. In the skin, increased numbers of CD68+ are related to dendritic epidermal cells, which can be expressed as CD45+/CD1a-/HLA-DR+. DCs of the skin, particularly epidermal Langerhans cells (LCs), form networks anchored to neighboring keratinocytes via E-cadherin. Thus, CD45+, CD68+ and E-cadherin+ expressions may be related to activation of skin sentinels cells in dogs naturally infected by L. infantum. Our results indicated that CanL modify the CD45+, CD68+ and E-cadherin+ expressions, which characterize the immune sentinels cells activation that promove the recruitment the cellular infiltrate, which was composed by macrophages, plasma cells, lymphocytes and neutrophils. Thus, these informations may contribute to the follow-up of CanL progression in skin.

The Origin of Skin Dendritic Cell Network and Its Role in Psoriasis.

Dendritic cells (DCs) are heterogeneous groups of innate immune cells, which orchestrate immune responses by presenting antigens to cognate T cells and stimulating other types of immune cells. Although the term ‘DCs’ generally represent highly mixed subsets with functional heterogeneity, the classical definition of DCs usually denotes conventional DCs (cDCs). Skin contains a unique DC network mainly composed of embryo precursor-derived epidermal Langerhans cells (LCs) and bone marrow-derived dermal cDCs, which can be further classified into type 1 (cDC1) and type 2 (cDC2) subsets. Psoriasis is a chronic inflammatory skin disease, which is principally mediated by IL-23/IL-17 cytokine axis. In the psoriatic skins, DCs are prominent cellular sources for TNF-α and IL-23, and the use of blocking antibodies against TNF-α and IL-23 leads to a significant clinical improvement in psoriatic patients. Recent elegant human and mouse studies have shown that inflammation-induced inflammatory DCs, LCs, dermal cDC2, and monocyte-derived DCs are pivotal DC subsets in psoriatic inflammation. Thus, targeting specific pathogenic DC subsets would be a potential strategy for alleviating and preventing DC-derived IL-23-dependent psoriatic inflammation and other inflammatory dermatoses in the future.

Impaired epidermal Langerhans cell maturation in TGFβ-inducible early gene 1 (TIEG1) knockout mice.

TGF-β-inducible early gene 1 (TIEG1), also known as Krüppel-like factor 10 (Klf10), represents a major downstream transcription factor of transforming growth factor-β1 (TGF-β1) signaling. Epidermal Langerhans cells (LCs), a unique subpopulation of dendritic cells (DC), essentially mediates immune surveillance and tolerance. TGF-β1 plays a pivotal role in LC maintenance and function after birth, although the underpinning mechanisms remain elusive. Here, we hypothesized that TIEG1 might be involved in TGF-β1-mediated LC homeostasis and function. Utilizing TIEG1 null mice, we discovered that TIEG1 deficiency did not alter LC homeostasis at the steady state and LC repopulation at inflamed-state, as well as their antigen-uptake capacity, but significantly impaired their maturation ability, which was opposite to the fact that loss of TGF-β1 induced spontaneous LC maturation. Moreover, the ablation of TIEG1 enhanced skin contact hypersensitivity response. Our results suggested that TIEG1 is not a key molecule involved in TGF-β1-mediated homeostasis, while TIEG1-related signaling pathways regulate LC maturation and their function.

A case of Langerhans cell histiocytosis involving the cervical lymph node

Langerhans cell histiocytosis (LCH) is a heterogeneous disease, characterized by accumulation of dendritic cells with features similar to epidermal Langerhans cells. It is a rare entity that may involve various organ levels such as the skeletal, pulmonary, hematopoietic and lympho-vascular systems. The patient was a 1-year-old female presented with fever associated with otorrhea and palpable cervical lymph node for 4 days. Neck ultrasonography and Computed tomography imaging revealed multiple enlarged lymph nodes suggesting suspicious malignant morphology. Lymph node biopsy was performed under general anesthesia. Histological and immunophenotypic examination showed the lymph node to be consistent with LCH. The patient was given chemotherapy.

Cyclin D1 Is Expressed in Neoplastic Cells of Langerhans Cell Histiocytosis but Not Reactive Langerhans Cell Proliferations.

Langerhans cell histiocytosis (LCH) is characterized by frequent activating mutations involving the mitogen-activated protein kinase (MAPK) pathway. Therefore, downstream markers of MAPK pathway activation such as cyclin D1 may be useful as novel diagnostic markers of neoplasia in LCH. The goal of this study was to investigate cyclin D1 expression in LCH and reactive Langerhans cell accumulations using immunohistochemistry on archival tissue. All LCH cases tested (39/39) showed cyclin D1 expression in CD1a/Langerin cells. Most cases (22/39; 56%) showed strong cyclin D1 expression in the majority (≥50%) of lesional cells. Only a few cases (6/39; 15%) showed cyclin D1 expression in a small subset (<20%). Nearly all LCH cases (26/27; 96%) showed p-ERK expression by immunohistochemistry, parallel to cyclin D1 expression. CD1a Langerhans cells in all cases of florid dermatopathic lymphadenopathy and normal skin were negative for cyclin D1, as demonstrated by CD1a/cyclin D1 double staining. The majority of skin specimens (14/18; 78%) with dermatitis-related changes did not show cyclin D1 expression in the CD1a epidermal Langerhans cell aggregates. A minority (4/18; 22%) showed weak cyclin D1 staining in a small subset (5% to 10%) of CD1a Langerhans cells. We conclude that cyclin D1 is ubiquitously expressed in LCH, in keeping with the known near universal MAPK activation in this disease. Further, it is not significantly expressed in reactive Langerhans cell proliferations in lymph node or skin. Therefore, cyclin D1 immunohistochemistry may be useful in excluding non-neoplastic mimics of LCH.

Ontogeny and function of murine epidermal Langerhans cells.

Langerhans cells (LCs) are epidermis-resident antigen-presenting cells that share a common ontogeny with macrophages but function as dendritic cells (DCs). Their development, recruitment and retention in the epidermis is orchestrated by interactions with keratinocytes through multiple mechanisms. LC and dermal DC subsets often show functional redundancy, but LCs are required for specific types of adaptive immune responses when antigen is concentrated in the epidermis. This Review will focus on those developmental and functional properties that are unique to LCs.