Epidermal Langerhans Cells Research Articles

Aedes aegypti Mosquito Probing Enhances Dengue Virus Infection of Resident Myeloid Cells in Human Skin.

The most prevalent arthropod-borne viruses, including the dengue viruses, are primarily transmitted by infected mosquitoes. However, the dynamics of dengue virus (DENV) infection and dissemination in human skin following Aedes aegypti probing remain poorly understood. We exposed human skin explants to adult female Ae. aegypti mosquitoes following their infection with DENV-2 by intrathoracic injection. Skin explants inoculated with a similar quantity of DENV-2 by a bifurcated needle were used as controls. Quantitative in situ imaging revealed that DENV replication was greatest in keratinocytes in the base of the epidermis, accounting for 50-60% of all infected cells regardless of the route of inoculation. However, DENV inoculation by Ae. aegypti probing resulted in an earlier and increased viral replication in the dermis, infecting twice as many cells at 24 h when compared to needle inoculation. Within the dermis, enhanced replication of DENV by Ae. aegypti infected mosquitoes was mediated by increased local recruitment of skin-resident macrophages, dermal dendritic cells, and epidermal Langerhans cells relative to needle inoculation. An enhanced but less pronounced influx of resident myeloid cells to the site of mosquito probing was also observed in the absence of infection. Ae. aegypti probing also increased recruitment and infection of dermal mast cells. Our findings reveal for the first time that keratinocytes are the primary targets of DENV infection following Ae. aegypti inoculation, even though most of the virus is inoculated into the dermis during probing. The data also show that mosquito probing promotes the local recruitment and infection of skin-resident myeloid cells in the absence of an intact vasculature, indicating that influx of blood-derived neutrophils is not an essential requirement for DENV spread within and out of skin.

Macrophage Functions in Psoriasis: Lessons from Mouse Models.

Psoriasis is a systemic autoimmune/autoinflammatory disease that can be well studied in established mouse models. Skin-resident macrophages are classified into epidermal Langerhans cells and dermal macrophages and are involved in innate immunity, orchestration of adaptive immunity, and maintenance of tissue homeostasis due to their ability to constantly shift their phenotype and adapt to the current microenvironment. Consequently, both macrophage populations play dual roles in psoriasis. In some circumstances, pro-inflammatory activated macrophages and Langerhans cells trigger psoriatic inflammation, while in other cases their anti-inflammatory stimulation results in amelioration of the disease. These features make macrophages interesting candidates for modern therapeutic strategies. Owing to the significant progress in knowledge, our review article summarizes current achievements and indicates future research directions to better understand the function of macrophages in psoriasis.

Isolation and characterization of epidermal Langerhans cells from human skin

Isolation and characterization of epidermal Langerhans cells from human skin

Yinxieling decoction ameliorates psoriasis by regulating the differentiation and functions of Langerhans cells via the TGF-β1/PU.1/IL-23 signal axis.

Langerhans cells (LCs) play a critical role in skin immune responses and the development of psoriasis. Yinxieling (YXL) is a representativeChinese herbal medicine for the treatment of psoriasis in South China. It was found to improve psoriasis without obvious side effects in the clinic. Here we attempted to clarify whether and how YXL regulates the differentiation and functions of LCs in Imiquimod (IMQ)-induced psoriasis in vivo and induced LCs in vitro. The Psoriasis Area Severity Index (PASI) score was used to evaluate the efficacy of YXL for IMQ-induced psoriasis-like mice. Flow cytometry was utilized to analyze the effects of YXL, to regulate the differentiation, migration, maturation, and antigen presentation of LCs. The results show that YXL significantly alleviated skin inflammation, as reduced in PASI score and classic psoriasis characteristics in pathological sections. Although there was no effect on the proportion of total DCs in the skin-draining lymph nodes, the expression of epidermal LCs and its transcription factor PU.1 were both markedly inhibited. LCs were also prevented from migrating from epidermal to skin-draining lymph nodes and mature. In addition, the number of LCs carrying antigens in the epidermis increased, which suggested that YXL could effectively prevent LCs from presenting antigens. In vitro, YXL had a significant impact on inhibiting the differentiation of LCs. Further data showed that YXL decreased the relative expression of transforming growth factor-β (TGFβ) messenger RNA (mRNA) and interleukin-23 (IL-23) mRNAs. Thus, YXL alleviates psoriasis by regulating differentiation, migration, maturation, and antigen presentation via the TGFβ/PU.1/IL-23 signal axis.

HDAC3 Is Required for Pathognomonic Features of Langerhans Cell Histiocytes

Langerhans cell histiocytosis (LCH) is a pediatric inflammatory myeloid neoplasm that develops due to dysregulated myeloid cell development. BRAFV600E is the most common disease-causing mutation and constitutively activates the mitogen-activated protein kinase (MAPK) pathway in myeloid lineage precursors leading to the key pathognomonic features of LCH cells. Enhanced myelopoiesis and reduced CCR7 expression promote accumulation of LCH cells in tissues by simultaneously increasing the production of pathological DCs and preventing tissue egress. Furthermore, LCH cells acquire an oncogene induced senescence-associated secretory phenotype (SASP) that depends on mammalian target of rapamycin (mTOR), which is hallmarked by increased expression of anti-apoptotic proteins, inflammatory cytokines, and matrix metalloproteinases enhancing survival of LCH cells and promoting recruitment of inflammatory immune cells forming characteristic granulomatous lesions. These pathognomonic features result in the accumulation of LCH cells in any organ causing a wide range of clinical symptoms. Frontline therapy for LCH involves combination chemotherapy and steroidal anti-inflammatories, or MAPK inhibitors, which have significant toxicity and fail to eliminate disease causing precursors. New therapeutic approaches are urgently needed. Here, using multiple genetic mouse models, we show that normal epidermal Langerhans cells (LCs) depend on HDAC3 for their development, differentiation, and survival. Integrative RNA and chromatin-immunoprecipitation-sequencing show loss of HDAC3 abrogates the expression of master regulators of myeloid development and function including Csf1r, Spi1, Id2 and Runx3. LCH cells are also known to rely on Csf1r and Pu.1 for their development and homeostasis, thus we hypothesized that LCH cells similarly rely on HDAC3 for their development and survival. CD11c Cre LSL-BRAFV600E ( BRAFV600E CD11c) mice develop severe multifocal LCH with pronounced lesion development in their livers and lungs, hepatosplenomegaly, and a reduced lifespan due to the accumulation of pathological dendritic cells (DCs). We generated BRAFV600E CD11c HDAC3 fl/fl ( BRAFV600E HD3KO) mice, which produce pathological DCs that simultaneously express BRAFV600E and harbor a conditional deletion in the deacetylase domain of HDAC3. Compared to BRAFV600E CD11c mice, BRAFV600E HD3KO mice exhibited significantly less hepatosplenomegaly, reduced lesional burden (Panel A), attenuated disease progression, and improved survival indicating reduced LCH disease burden. Compared to BRAFV600E CD11c flow cytometry showed BRAFV600E HD3KO had reduced numbers of LCH cells in lungs and livers linking improved disease outcomes to abrogation of pathological DCs. Flow cytometric analysis of circulating myeloid cells further found reduced frequency of circulating DCs and DC progenitors, indicating that a lack of HDAC3 activity prevents the development of pathological DCs (Panel B). LCH-like cells can be generated in vitro by culturing BRAFV600E CD11c bone marrow with granulocyte-monocyte colony-stimulating factor (GM-CSF), providing a valuable drug screening tool. Treating LCH-like cells with RGFP966, an HDAC3-specific inhibitor, increased apoptosis indicated by annexin-V and DAPI staining, reduced expression of Bcl-2, increased CCR7 expression, and decreased S6 phosphorylation (an indication of decreased mTOR activity), showing that pharmacological inhibition of HDAC3 may prove therapeutically efficacious by abrogating pathognomonic features of LCH cells. Together, our findings identify HDAC3 as a critical epigenetic regulator for both healthy and pathological LCs. We further show, HDAC3 is required for multiple pathognomonic features of LCH cells and could be a promising drug target. Furthermore, if HDAC3 is required for the development of pathological DC and DC progenitors, HDAC3 blockade would address a great need in treatment of patients with LCH.

Dengue Virus Infects Human Skin Langerhans Cells through Langerin for Dissemination to Dendritic Cells

Dengue virus (DENV) is the most disease-causative flavivirus worldwide. DENV as a mosquito-borne virus infects human hosts through the skin; however, the initial target cells in the skin remain unclear. In this study, we have investigated whether epidermal Langerhans cells (LCs) play a role in DENV acquisition and dissemination. We have used a human epidermal exvivo infection model as well as isolated LCs to investigate infection by DENV. Notably, both immature and mature LCs were permissive to DENV infection invitro and exvivo, and infection was dependent on C-type lectin receptor langerin because blocking antibodies against langerin significantly reduced DENV infection invitro and exvivo. DENV-infected LCs efficiently transmitted DENV to target cells such as dendritic cells. Moreover, DENV exposure increased the migration of LCs from epidermal explants. These results strongly suggest that DENV targets epidermal LCs for infection and dissemination in the human host. These findings could provide potential drug targets to combat the early stage of DENV infection.

216 Human epidermal Langerhans cells emigrate and induce a tolerogenic immune response in response to tick feeding and tick-borne pathogens

216 Human epidermal Langerhans cells emigrate and induce a tolerogenic immune response in response to tick feeding and tick-borne pathogens

Cross-presenting Langerhans cells are required for the early reactivation of resident CD8+ memory T cells in the epidermis

Tissue-resident memory CD8+ T cells (TRM) reside at sites of previous infection, providing protection against reinfection with the same pathogen. In the skin, TRM patrol the epidermis, where keratinocytes are the entry site for many viral infections. Epidermal TRM react rapidly to cognate antigen encounter with the secretion of cytokines and differentiation into cytotoxic effector cells, constituting a first line of defense against skin reinfection. Despite the important protective role of skin TRM, it has remained unclear, whether their reactivation requires a professional antigen-presenting cell (APC). We show here, using a model system that allows antigen targeting selectively to keratinocytes in a defined area of the skin, that limited antigen expression by keratinocytes results in rapid, antigen-specific reactivation of skin TRM. Our data identify epidermal Langerhans cells that cross-present keratinocyte-derived antigens, as the professional APC indispensable for the early reactivation of TRM in the epidermal layer of the skin.

Positive and ecobiological contribution in skin photoprotection of ectoine and mannitol combined in vivo with UV filters.

Chronic exposure to ultraviolet (UV) irradiation causes immunosuppression, photoaging, and carcinogenesis by induction of a cascade of skin damages. Sunscreens currently on the market are not absorbing UV rays uniformly throughout the full UV range, high sun protection factor (SPF) sunscreens absorb most of UVB rays but are less effective in absorbing the UVA part of the spectrum. In the context, one approach could consist of preserving the skin natural resources and mechanisms, which is the foundation of the ecobiological approach, by combing UV filters and antioxidants to enhance their photoprotective effect. First, the photoprotection properties of ectoine and mannitol association were characterized by the quantification of glutathione, reactive oxygen species, and double-stranded DNA breaks and by the epidermal Langerhans cells functionality. Second, the protection of squalene oxidation, catalase activity, and trans-urocanic acid (UCA) by the ectoine and mannitol association combined or not with SPF30 UV filters was assessed in vivo via non-invasive skin samplings in 10 subjects on irradiated areas. Using in vitro irradiated skin cell models, we demonstrated that this association significantly preserved intracellular glutathione levels, reduced DNA strand breaks induced by oxidative stress, and maintained Langerhans cell functionality. In vivo this association combined with UV filters presented significantly higher protection of three natural defense systems altered by UV compared to UV filters alone: squalene oxidation, catalase activity, and preservation of trans-UCA. This study demonstrates the ecobiological potential of combining UV filters with biological protection to increase skin photoprotection provided by specific active ingredients with antioxidative and immunosuppressive properties.

Structural Changes of Cutaneous Immune Cells in Patients With Type 1 Diabetes and Their Relationship With Diabetic Polyneuropathy.

Diabetic polyneuropathy (DPN) is a complication of diabetes characterized by pain or lack of peripheral sensation, but the underlying mechanisms are not yet fully understood. Recent evidence showed increased cutaneous macrophage infiltration in patients with type 2 diabetes and painful DPN, and this study aimed to understand whether the same applies to type 1 diabetes. The study included 104 participants: 26 healthy controls and 78 participants with type 1 diabetes (participants without DPN [n = 24], participants with painless DPN [n = 29], and participants with painful DPN [n = 25]). Two immune cells, dermal IBA1+ macrophages and epidermal Langerhans cells (LCs, CD207+), were visualized and quantified using immunohistological labeling and stereological counting methods on skin biopsies from the participants. The IBA1+ macrophage infiltration, LC number density, LC soma cross-sectional area, and LC processes were measured in this study. Significant difference in IBA1+ macrophage expression was seen between the groups (p = 0.003), with lower expression of IBA1 in participants with DPN. No differences in LC morphologies (LC number density, soma cross-sectional area, and process level) were found between the groups (all p > 0.05). In addition, IBA1+ macrophages, but not LCs, correlated with intraepidermal nerve fiber density, Michigan neuropathy symptom inventory, (questionnaire and total score), severity of neuropathy as assessed by the Toronto clinical neuropathy score, and vibration detection threshold in the whole study cohort. This study showed expressional differences of cutaneous IBA1+ macrophages but not LC in participants with type 1 diabetes-induced DPN compared with those in controls. The study suggests that a reduction in macrophages may play a role in the development and progression of autoimmune-induced diabetic neuropathy.

CD1a-mediated immunity from a molecular perspective

Human CD1a is a non-polymorphic glycoprotein that presents lipid antigens to T cells. The most obvious role of CD1a is associated with its expression on Langerhans cells in epidermis, where it is involved in responses to pathogens. Antigen-specific T cells are believed to co-recognise CD1a presenting bacterial antigens such as species of lipopeptides from Mycobacterium tuberculosis. Further, human skin contains large amount of endogenous lipids that can activate distinct subsets of CD1a-restricted autoreactive T cells, mostly belonging to the αβ lineage, which are abundant in human blood and skin and are important for skin homeostasis in healthy individuals. CD1a and CD1a-restricted T cells have been linked to certain autoimmune conditions such as psoriasis, atopic dermatitis and contact hypersensitivity becoming a potential candidate for clinical interventions. A significant progress has been made in the last twenty years towards our understanding of the molecular processes that orchestrate CD1a-lipid binding, antigen presentation and mechanism of CD1a recognition by αβ and γδ T cells. This review summarises the recent developments within the field of CD1a-mediated immunity from a molecular perspective.

The immunological effects of intradermal particle-based vaccine delivery using a novel microinjection needle studied in a human skin explant model.

For intradermal (ID) immunisation, novel needle-based delivery systems have been proposed as a better alternative to the Mantoux method. However, the penetration depth of needles in the human skin and its effect on immune cells residing in the different layers of the skin has not been analyzed. A novel and user-friendly silicon microinjection needle (Bella-muTM) has been developed, which allows for a perpendicular injection due to its short needle length (1.4-1.8mm) and ultrashort bevel. We aimed to characterize the performance of this microinjection needle in the context of the delivery of a particle-based outer membrane vesicle (OMV) vaccine using an ex vivo human skin explant model. We compared the needles of 1.4 and 1.8mm with the conventional Mantoux method to investigate the depth of vaccine injection and the capacity of the skin antigen-presenting cell (APC) to phagocytose the OMVs. The 1.4mm needle deposited the antigen closer to the epidermis than the 1.8mm needle or the Mantoux method. Consequently, activation of epidermal Langerhans cells was significantly higher as determined by dendrite shortening. We found that five different subsets of dermal APCs are able to phagocytose the OMV vaccine, irrespective of the device or injection method. ID delivery using the 1.4mm needle of a OMV-based vaccine allowed epidermal and dermal APC targeting, with superior activation of Langerhans cells. This study indicates that the use of a microinjection needle improves the delivery of vaccines in the human skin.

Basal Cell Carcinoma in Xeroderma Pigmentosa: Reduced CD1a Expression as a Sensitive Predictor of Recurrence.

Xeroderma pigmentosa (XP) is a rare genetic disorder that is characterized by defective DNA repair after ultraviolet induced damage with a great tendency for recurrent cutaneous malignancies including basal cell carcinoma (BCC). BCC is frequently linked to impaired local immune response with a major role played by Langerhans cells (LCs). The current study aims at investigating LCs in BCC specimens of XP and non-XP patients, in a trial to study its possible impact on tumor recurrence. It included 48 retrospective cases of primary facial BCC (18 for XP patients and 30 for non-XP controls). Each group was subdivided, based on the 5 years follow-up data, into recurrent and non-recurrent BCC groups. LCs were assessed immunohistochemically using the sensitive marker; CD1a. Results showed significantly reduced LCs count (intratumoral, peritumoral, and in perilesional epidermis) in XP patients compared with non-XP controls ( P ˂0.001 for all). Intratumoral ( P =0.008), peritumoral ( P =0.005), and perilesional epidermal ( P =0.02) LCs mean values were significantly lower in recurrent versus non-recurrent BCC specimens. Also, within each group (XP and controls), LCs were of significantly lower means in recurrent versus non-recurrent cases ( P ≤0.001 for all). Regarding recurrent BCC cases, peritumoral LCs showed a significant positive correlation with 1ry BCC duration ( P =0.05). Also, intratumoral and peritumoral LCs correlated positively with BCC relapse interval ( P =0.04 for both). Among non-XP controls, periocular tumors had the least LCs count (22.00±3.56), whereas tumors located in the rest of the face had the greatest count (29.00±0.00) ( P =0.02). Sensitivity and specificity of LCs to predict BCC recurrence in XP patients reached 100% in intartumoral area and perilesional epidermis when cutoff points were less than 9.5 and 20.5, respectively. In conclusion; reduced LC count in primary BCC specimens of XP patients and also in normal subjects could help to predict its recurrence. Thus, it might be identified as a risk factor for relapse to apply new strict therapeutic and preventive measures. This presents new avenue for the immunosurveillance against skin cancer relapse. However, being the first study to investigate that link in XP patients recommends further research to confirm.

Staphylococcal phosphatidylglycerol antigens activate human T cells via CD1a.

Expressed on epidermal Langerhans cells, CD1a presents a range of self-lipid antigens found within the skin; however, the extent to which CD1a presents microbial ligands from bacteria colonizing the skin is unclear. Here we identified CD1a-dependent T cell responses to phosphatidylglycerol (PG), a ubiquitous bacterial membrane phospholipid, as well as to lysylPG, a modified PG, present in several Gram-positive bacteria and highly abundant in Staphylococcus aureus. The crystal structure of the CD1a-PG complex showed that the acyl chains were buried within the A'- and F'-pockets of CD1a, while the phosphoglycerol headgroup remained solvent exposed in the F'-portal and was available for T cell receptor contact. Using lysylPG and PG-loaded CD1a tetramers, we identified T cells in peripheral blood and in skin that respond to these lipids in a dose-dependent manner. Tetramer+CD4+ T cell lines secreted type 2 helper T cell cytokines in response to phosphatidylglycerols as well as to co-cultures of CD1a+ dendritic cells and Staphylococcus bacteria. The expansion in patients with atopic dermatitis of CD4+ CD1a-(lysyl)PG tetramer+ T cells suggests a response to lipids made by bacteria associated with atopic dermatitis and provides a link supporting involvement of PG-based lipid-activated T cells in atopic dermatitis pathogenesis.

Interoperability of RTN1A in dendrite dynamics and immune functions in human Langerhans cells.

Skin is an active immune organ where professional antigen-presenting cells such as epidermal Langerhans cells (LCs) link innate and adaptive immune responses. While Reticulon 1A (RTN1A) was recently identified in LCs and dendritic cells in cutaneous and lymphoid tissues of humans and mice, its function is still unclear. Here, we studied the involvement of this protein in cytoskeletal remodeling and immune responses toward pathogens by stimulation of Toll-like receptors (TLRs) in resident LCs (rLCs) and emigrated LCs (eLCs) in human epidermis ex vivo and in a transgenic THP-1 RTN1A+ cell line. Hampering RTN1A functionality through an inhibitory antibody induced significant dendrite retraction of rLCs and inhibited their emigration. Similarly, expression of RTN1A in THP-1 cells significantly altered their morphology, enhanced aggregation potential, and inhibited the Ca2+ flux. Differentiated THP-1 RTN1A+ macrophages exhibited long cell protrusions and a larger cell body size in comparison to wild-type cells. Further, stimulation of epidermal sheets with bacterial lipoproteins (TLR1/2 and TLR2 agonists) and single-stranded RNA (TLR7 agonist) resulted in the formation of substantial clusters of rLCs and a significant decrease of RTN1A expression in eLCs. Together, our data indicate involvement of RTN1A in dendrite dynamics and structural plasticity of primary LCs. Moreover, we discovered a relation between activation of TLRs, clustering of LCs, and downregulation of RTN1A within the epidermis, thus indicating an important role of RTN1A in LC residency and maintaining tissue homeostasis.

Clinicodermoscopic and immunopathological profile of non-infectious non-eczematous inflammatory tattoo reactions: A retrospective study from a tertiary care centre of East India.

Introduction Tattoo-associated complications are on the rise due to the popularity of decorative tattoos in recent years. The exact pathogeneses of various tattoo reaction patterns are still unclear, and their dermoscopic details are sparsely reported. Aim We aimed to retrospectively study the clinical, dermoscopic and immunopathological details of patients with non-infectious, non-eczematous inflammatory tattoo reaction patterns in a tertiary care centre of East India. Method The clinical, dermoscopic and pathological details of all the patients who had non-infectious, non-eczematous inflammatory tattoo reactions were collected. In all the cases, immunohistochemistry was done for CD1a, CD3, CD4, CD8, FoxP3, CD20 and CD56. Results A total of five patients of skin phototypes IV and V and six tattoo reactions were analysed. Five lesions had reactions at the site of a black tattoo, and one at the site of red tattoo. Clinically, the patients presented with erythematous or blue-grey flat-topped to verrucous papules and plaques. Dermoscopic features were dominated by a central white to pink-white structureless area, a peripheral grey-white to bluish-white structureless area, white scales, comedo-like opening with keratotic plugging, milia-like cysts and shiny white structures. Pathologically, except for one lesion that only showed a lichenoid reaction pattern in the red tattoo, all had a combination of reaction patterns. Immunohistochemistry showed increased epidermal and dermal Langerhans cells, predominantly CD8 positive T cells in the epidermis and dermis, sparse dermal B cells and CD4 positive T cells, reduced T regulatory cells and a complete absence of CD56 positive NK cells. Limitations Small sample size was the limitation of the study. Conclusion The clinical morphology and dermoscopy may not differentiate between various types of non-infectious non-eczematous inflammatory tattoo reactions. The immunological profile supports a delayed hypersensitivity reaction due to contact sensitisation to tattoo pigment, and CD8 positive T cells play a central role in executing various pathological reaction patterns, both in the epidermis and dermis.

Transcriptional programming of immunoregulatory responses in human Langerhans cells.

Human epidermal Langerhans cells (LCs) maintain immune homeostasis in the skin. To examine transcriptional programming of human primary LCs during homeostasis, we performed scRNA-seq analysis of LCs before and after migration from the epidermis, coupled with functional assessment of their regulatory T cell priming capabilities. The analysis revealed that steady-state LCs exist in a continuum of maturation states and upregulate antigen presentation genes along with an immunoregulatory module including the genes IDO1, LGALS1, LAMTOR1, IL4I, upon their migration. The migration-induced transition in genomic state is accompanied by the ability of LCs to more efficiently prime regulatory T cell responses in co-culture assays. Computational analyses of the scRNAseq datasets using SCENIC and Partial Information Decomposition in Context identified a set of migration-induced transcription factors including IRF4, KLF6 and RelB as key nodes within a immunoregulatory gene regulatory network. These findings support a model in which efficient priming of immunoregulatory responses by LCs is dependent on coordinated upregulation of a migration-coupled maturation program with a immunoregulation-promoting genomic module.

Multi-System Langerhans Cell Histiocytosis as a Mimic of IgG4-Related Disease: A Case Report and Literature Review

Langerhans cell histiocytosis (LCH) is a rare disease characterized by the clonal accumulation and/or proliferation of specific dendritic cells resembling normal epidermal Langerhans cells (LCs). Clinical manifestations are variable, depending on the affected tissues or organs, however, LCH with elevated serum IgG4 has not been reported. Herein, we reported a 26-year-old Chinese female multi-system LCH (MS-LCH) who first presented with central diabetes insipidus (CDI), accompanied by panhypopituitarism and hepatic dysfunction. Diagnostic investigations were strongly suspicious of IgG4-RD because of elevated serum IgG4 levels during the process. Furtherly, thyroid and lymph node involvement and biopsy led to the diagnosis of MS-LCH; the strongly positive staining of CD1a, S100, CD207 (langerin), and Ki67 was found. Moreover, after systemic treatment with five cycles of chemotherapy, many lesions were greatly improved. Since both LCH and IgG4-RD are orphan diseases that can affect any organ, the differential diagnosis is challenging, especially when LCH is associated with unexplained serum IgG4 elevation. In this article, the case of a young woman suffering from MS-LCH that affected organs including the pituitary, thyroid, lymph node, and liver was summarized, and relevant literature was reviewed to better equip the diagnosis and treatment in its early stages.

542 Murine epidermis harbors functionally distinct langerhans cell subsets

Epidermal Langerhans cells (LCs) derive from embryonic myeloid progenitors at the steady-state and monocyte progenitors under inflammatory conditions. LCs have the capacity to induce both immunity and tolerance in the skin, but how a single population of LCs mediates both these functions has perplexed researchers for decades. We hypothesized that LCs in murine epidermis have functionally heterogenous subpopulations. We employed single-cell RNA sequencing (scRNAseq) and scATACseq to identify transcriptional and epigenetic heterogeneity in LCs during late embryonic development, adult steady-state and inflamed-state. We found three transcriptionally distinct clusters in adult at steady-state: ATF3hiCD207lo (cLC1), ATF3loCD207hi (cLC2), and CD207+ cells expressing keratinocyte (KC) genes (kLCs). Ingenuity pathway analysis showed LC1 had downregulated immunostimulatory pathways and LC2 had upregulated immunostimulatory pathways. LCs from ATF3 knockout mice promoted Th1/2/17 immunity in co-culture experiments, confirming the immunotolerant function of cLC1s. cLC1 and cLC2 clusters had corresponding scATACseq clusters but kLCs did not, suggesting that kLCs may acquire their KC-“fingerprint” through interactions with KCs. scRNAseq analyses of E18.5 pre-LCs and 3 weeks post UVC-treatment also identified ATF3hi and ATF3lo clusters, but kLCs were neither present at E18.5 nor after UVC treatment. Overall, our single cell analyses uncover murine epidermal LC subsets with distinct functions during late embryonic development, steady-state and inflamed-state.

006 IL-6 enhances IL-6 expression by epidermal langerhans cells (LCs)

Exposure of endothelial cells (ECs) to the neuropeptide calcitonin gene-related peptide (CGRP) endows them with the ability, as bystanders, to bias the outcome of LC antigen (Ag) presentation to T cells toward the Th17 pole and our previous work indicates that EC IL-6 production mediates most of this effect. Preliminary experiments suggested that IL-6 could enhance IL-6 expression by LCs. We have further examined this effect as IL-6 released by CGRP-exposed ECs may stimulate LCs to produce additional IL-6, potentially involved in regulating the outcome of Ag presentation.