Mucosal and Skin Langerhans Cells – Nurture Calls

MHC-II presentation by oral Langerhans cells impacts intraepithelial Tc17 abundance and Candida albicans oral infection via CD4 T cells

In a murine model (LCΔMHC-II) designed to abolish MHC-II expression in Langerhans cells (LCs), ∼18% of oral LCs retain MHC-II, yet oral mucosal CD4 T cells numbers are unaffected. In LCΔMHC-II mice, we now show that oral intraepithelial conventional CD8αβ T cell numbers expand 30-fold. Antibody-mediated ablation of CD4 T cells in wild-type mice also resulted in CD8αβ T cell expansion in the oral mucosa. Therefore, we hypothesize that MHC class II molecules uniquely expressed on Langerhans cells mediate the suppression of intraepithelial resident-memory CD8 T cell numbers via a CD4 T cell-dependent mechanism. The expanded oral CD8 T cells co-expressed CD69 and CD103 and the majority produced IL-17A [CD8 T cytotoxic (Tc)17 cells] with a minority expressing IFN-γ (Tc1 cells). These oral CD8 T cells showed broad T cell receptor Vβ gene usage indicating responsiveness to diverse oral antigens. Generally supporting Tc17 cells, transforming growth factor-β1 (TGF-β1) increased 4-fold in the oral mucosa. Surprisingly, blocking TGF-β1 signaling with the TGF-R1 kinase inhibitor, LY364947, did not reduce Tc17 or Tc1 numbers. Nonetheless, LY364947 increased γδ T cell numbers and decreased CD49a expression on Tc1 cells. Although IL-17A-expressing γδ T cells were reduced by 30%, LCΔMHC-II mice displayed greater resistance to Candida albicans in early stages of oral infection. These findings suggest that modulating MHC-II expression in oral LC may be an effective strategy against fungal infections at mucosal surfaces counteracted by IL-17A-dependent mechanisms.

The role of the epithelial sentinels, Langerhans cells and γδT cells, in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) arises in the oral epithelium, a tissue in which immune surveillance is mediated by its primary resident leukocytes, Langerhans cells (LCs), and γδT cells. Under steady-state conditions, LCs and γδT cells play a critical role in maintaining oral mucosal homeostasis. As antigen-presenting cells of stratified epithelia, LCs respond to various challenges faced by the epithelium, orchestrating innate, and adaptive immune responses in order to resolve them. γδT cells also sense diverse epithelial insults and react rapidly through cytokine production and cytolytic activity. These epithelial sentinels are also considered to be the first leukocytes in the oral epithelium to encounter early carcinogenic events that have the potential of becoming OSCC. As evident in many malignancies, leukocyte populations help prevent cancer development although they also promote tumor progression. OSCC is no exception, as studies have reported both anti- and pro-tumor roles of LCs and γδT cells. In this review, we summarize the ontogeny of LCs and γδT cells in the oral epithelium and discuss their role in OSCC.

The roles of tissue resident macrophages in health and cancer

As integral components of the immune microenvironment, tissue resident macrophages (TRMs) represent a self-renewing and long-lived cell population that plays crucial roles in maintaining homeostasis, promoting tissue remodeling after damage, defending against inflammation and even orchestrating cancer progression. However, the exact functions and roles of TRMs in cancer are not yet well understood. TRMs exhibit either pro-tumorigenic or anti-tumorigenic effects by engaging in phagocytosis and secreting diverse cytokines, chemokines, and growth factors to modulate the adaptive immune system. The life-span, turnover kinetics and monocyte replenishment of TRMs vary among different organs, adding to the complexity and controversial findings in TRMs studies. Considering the complexity of tissue associated macrophage origin, macrophages targeting strategy of each ontogeny should be carefully evaluated. Consequently, acquiring a comprehensive understanding of TRMs' origin, function, homeostasis, characteristics, and their roles in cancer for each specific organ holds significant research value. In this review, we aim to provide an outline of homeostasis and characteristics of resident macrophages in the lung, liver, brain, skin and intestinal, as well as their roles in modulating primary and metastatic cancer, which may inform and serve the future design of targeted therapies.

Guidelines for DC preparation and flow cytometry analysis of mouse nonlymphoid tissues

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various nonlymphoid tissues. DC are sentinels of the immune system present in almost every mammalian organ. Since they represent a rare cell population, DC need to be extracted from organs with protocols that are specifically developed for each tissue. This article provides detailed protocols for the preparation of single-cell suspensions from various mouse nonlymphoid tissues, including skin, intestine, lung, kidney, mammary glands, oral mucosa and transplantable tumors. Furthermore, our guidelines include comprehensive protocols for multiplex flow cytometry analysis of DC subsets and feature top tricks for their proper discrimination from other myeloid cells. With this collection, we provide guidelines for in-depth analysis of DC subsets that will advance our understanding of their respective roles in healthy and diseased tissues. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all coauthors, making it an essential resource for basic and clinical DC immunologists.

Langerhans cells shape postnatal oral homeostasis in a mechanical-force-dependent but microbiota and IL17-independent manner

The postnatal interaction between microbiota and the immune system establishes lifelong homeostasis at mucosal epithelial barriers, however, the barrier-specific physiological activities that drive the equilibrium are hardly known. During weaning, the oral epithelium, which is monitored by Langerhans cells (LC), is challenged by the development of a microbial plaque and the initiation of masticatory forces capable of damaging the epithelium. Here we show that microbial colonization following birth facilitates the differentiation of oral LCs, setting the stage for the weaning period, in which adaptive immunity develops. Despite the presence of the challenging microbial plaque, LCs mainly respond to masticatory mechanical forces, inducing adaptive immunity, to maintain epithelial integrity that is also associated with naturally occurring alveolar bone loss. Mechanistically, masticatory forces induce the migration of LCs to the lymph nodes, and in return, LCs support the development of immunity to maintain epithelial integrity in a microbiota-independent manner. Unlike in adult life, this bone loss is IL-17-independent, suggesting that the establishment of oral mucosal homeostasis after birth and its maintenance in adult life involve distinct mechanisms.

Tissue-specific macrophages: how they develop and choreograph tissue biology

Macrophages are innate immune cells that form a 3D network in all our tissues, where they phagocytose dying cells and cell debris, immune complexes, bacteria and other waste products. Simultaneously, they produce growth factors and signalling molecules - such activities not only promote host protection in response to invading microorganisms but are also crucial for organ development and homeostasis. There is mounting evidence of macrophages orchestrating fundamental physiological processes, such as blood vessel formation, adipogenesis, metabolism and central and peripheral neuronal function. In parallel, novel methodologies have led to the characterization of tissue-specific macrophages, with distinct subpopulations of these cells showing different developmental trajectories, transcriptional programmes and life cycles. Here, we summarize our growing knowledge of macrophage diversity and how macrophage subsets orchestrate tissue development and function. We further interrelate macrophage ontogeny with their core functions across tissues, that is, the signalling events within the macrophage niche that may control organ functionality during development, homeostasis and ageing. Finally, we highlight the open questions that will need to be addressed by future studies to better understand the tissue-specific functions of distinct macrophage subsets.

Neuroinflammation and neovascularization in diabetic eye diseases (DEDs): identification of potential pharmacotherapeutic targets

The goal of this review is to increase public knowledge of the etiopathogenesis of diabetic eye diseases (DEDs), such as diabetic retinopathy (DR) and ocular angiosarcoma (ASO), and the likelihood of blindness among elderly widows. A widow's life in North India, in general, is fraught with peril because of the economic and social isolation it brings, as well as the increased risk of death from heart disease, hypertension, diabetes, depression, and dementia. Neovascularization, neuroinflammation, and edema in the ocular tissue are hallmarks of the ASO, a rare form of malignant tumor. When diabetes, hypertension, and aging all contribute to increased oxidative stress, the DR can proceed to ASO. Microglia in the retina of the optic nerve head are responsible for causing inflammation, discomfort, and neurodegeneration. Those that come into contact with them will get blind as a result of this. Advanced glycation end products (AGE), vascular endothelial growth factor (VEGF), protein kinase C (PKC), poly-ADP-ribose polymerase (PARP), metalloproteinase9 (MMP9), nuclear factor kappaB (NFkB), program death ligand1 (PDL-1), factor VIII (FVIII), and von Willebrand factor (VWF) are potent agents for ocular neovascularisation (ONV), neuroinflammation and edema in the ocular tissue. AGE/VEGF, DAG/PKC, PARP/NFkB, RAS/VEGF, PDL-1/PD-1, VWF/FVIII/VEGF, and RAS/VEGF are all linked to the pathophysiology of DEDs. The interaction between ONV and ASO is mostly determined by the VWF/FVIII/VEGF and PDL-1/PD-1 axis. This study focused on retinoprotective medications that can pass the blood-retinal barrier and cure DEDs, as well as the factors that influence the etiology of neovascularization and neuroinflammation in the eye.

TRPV4 Activation Increases the Expression of CD207 (Langerin) of Monocyte-Derived Langerhans Cells without Affecting their Maturation

Langerhans cells (LCs) are the sole professional antigen-presenting cell normally found in the human epidermal compartment. Research into their physiological role is hindered by the fact that they are invariably activated during isolation from the skin. To overcome this challenge, we turned to a monocyte-derived LC (moLC) model, which we characterized with RNA sequencing, and compared the transcriptome of moLCs with that of donor-matched immature dendritic cells. We found that moLCs express markers characteristic of LC2 cells as well as TRPV4. TRPV4 is especially important in the skin because it has been linked to the conservation of the skin barrier, immunological responses, as well as acute and chronic itch, but we know little about its function on LCs. Our results show that TRPV4 activation increased the expression of Langerin and led to increased intracellular calcium concentration in moLCs. Regarding the functionality of moLCs, we found that TRPV4 agonism had a mitigating effect on their inflammatory responses because it decreased their cytokine production and T-cell activating capability. Because TRPV4 has emerged as a potential therapeutic target in dermatological conditions, it is important to highlight LCs as, to our knowledge, a previously unreported target of these therapies.

Neuro-epithelial-ILC2 crosstalk in barrier tissues

Group 2 innate lymphoid cells (ILC2s) contribute to the maintenance of mammalian barrier tissue homeostasis. We review how ILC2s integrate epithelial signals and neurogenic components to preserve the tissue microenvironment and modulate inflammation. The epithelium that overlies barrier tissues, including the skin, lungs, and gut, generates epithelial cytokines that elicit ILC2 activation. Sympathetic, parasympathetic, sensory, and enteric fibers release neural signals to modulate ILC2 functions. We also highlight recent findings suggesting neuro-epithelial-ILC2 crosstalk and its implications in immunity, inflammation and resolution, tissue repair, and restoring homeostasis. We further discuss the pathogenic effects of disturbed ILC2-centered neuro-epithelial-immune cell interactions and putative areas for therapeutic targeting.

BMPR1a is required for the optimal TGF-β1 dependent CD207+ Langerhans cell differentiation and limits skin inflammation via CD11c+ cells

The cytokine TGF-β1 induces epidermal Langerhans cell (LC) differentiation from human precursors, an effect mediated via bone morphogenetic protein receptor 1a (BMPR1a)/ALK3 signaling, as revealed from ectopic expression and receptor inhibition studies. Whether TGF-β1-BMPR1a signaling is required for LC differentiation in vivo remained incompletely understood. We found that TGF-β1 deficient mice show defective perinatal expansion and differentiation of LCs. LCs can be identified within the normal healthy human epidermis by anti-BMPR1a immunohistology staining. Deletion of BMPR1a in all (vav⁺) hematopoietic cells revealed that BMPR1a is required for the efficient TGF-β1-dependent generation of CD207⁺ LC-like cells from CD11c⁺ intermediates in vitro. Similarly, BMPR1a was required for the optimal induction of CD207 by preformed MHCII⁺ epidermal resident LC precursors in the steady-state. BMPR1a expression is strongly upregulated in epidermal cells in psoriatic lesions, and BMPR1a^ΔCD11c mice showed a defect in the resolution phase of allergic and psoriatic skin inflammation. Moreover, while LCs from these mice expressed CD207, BMPR1a counteracted LC activation and migration from skin explant cultures. Therefore, TGF-β1-BMPR1a signaling seems to be required for the efficient induction of CD207 during LC differentiation in the steady-state, and bone marrow-derived lesional CD11c⁺ cells may limit established skin inflammation via enhanced BMPR1a signaling.

Innate Phagocyte Polarization in the Oral Cavity

The oral cavity is a complex environment constantly exposed to antigens from food and the oral microbiota. Innate immune cells play an essential role in maintaining health and homeostasis in the oral environment. However, these cells also play a significant role in disease progression. This review will focus on two innate phagocytes in the oral cavity: macrophages and neutrophils, and examine their roles during homeostasis and disease development, with a focus on periodontal disease and cancer. Macrophages have a well-known ability to polarize and be activated towards a variety of phenotypes. Several studies have found that macrophages’ polarization changes can play an essential role in maintaining health in the oral cavity and contribute to disease. Recent data also finds that neutrophils display phenotypic heterogeneity in the oral cavity. In both cases, we focus on what is known about how these cellular changes alter these immune cells’ interactions with the oral microbiota, including how such changes can lead to worsening, rather than improving, disease states.

Early antitumor activity of oral Langerhans cells is compromised by a carcinogen

Early diagnosis of oral squamous cell carcinoma (OSCC) remains an unmet clinical need. Therefore, elucidating the initial events of OSCC preceding tumor development could benefit OSCC prognosis. Here, we define the Langerhans cells (LCs) of the tongue and demonstrate that LCs protect the epithelium from carcinogen-induced OSCC by rapidly priming αβT cells capable of eliminating γH2AX⁺ epithelial cells, whereas γδT and natural killer cells are dispensable. The carcinogen, however, dysregulates the epithelial resident mononuclear phagocytes, reducing LC frequencies, while dendritic cells (DCs), macrophages, and plasmacytoid DCs (pDCs) populate the epithelium. Single-cell RNA-sequencing analysis indicates that these newly differentiated cells display an immunosuppressive phenotype accompanied by an expansion of T regulatory (Treg) cells. Accumulation of the Treg cells was regulated, in part, by pDCs and precedes the formation of visible tumors. This suggests LCs play an early protective role during OSCC, yet the capacity of the carcinogen to dysregulate the differentiation of mononuclear phagocytes facilitates oral carcinogenesis.

A model of impaired Langerhans cell maturation associated with HPV induced epithelial hyperplasia

Langerhans cells (LC) are skin-resident antigen-presenting cells that regulate immune responses to epithelial microorganisms. Human papillomavirus (HPV) infection can promote malignant epithelial transformation. As LCs are considered important for controlling HPV infection, we compared the transcriptome of murine LCs from skin transformed by K14E7 oncoprotein and from healthy skin. We identified transcriptome heterogeneity at the single cell level amongst LCs in normal skin, associated with ontogeny, cell cycle, and maturation. We identified a balanced co-existence of immune-stimulatory and immune-inhibitory LC cell states in normal skin that was significantly disturbed in HPV16 E7-transformed skin. Hyperplastic skin was depleted of immune-stimulatory LCs and enriched for LCs with an immune-inhibitory gene signature, and LC-keratinocyte crosstalk was dysregulated. We identified reduced expression of interleukin (IL)-34, a critical molecule for LC homeostasis. Enrichment of an immune-inhibitory LC gene signature and reduced levels of epithelial IL-34 were also found in human HPV-associated cervical epithelial cancers.

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Single cell atlas of Langerhans cells in cutaneous skin

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Stimulatory and inhibitory Langerhans cell states are in balance

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Inhibitory Langerhans cell states dominate HPV-transformed hyperplastic skin

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Langerhans cell imbalance is associated with disrupted IL-34 signaling

Distinct human Langerhans cell subsets orchestrate reciprocal functions and require different developmental regulation

Langerhans cells (LCs) play a pivotal role in skin homeostasis, and the heterogeneity of LCs has long been considered. In this study, we have identified two steady-state (LC1 and LC2) and two activated LC subsets in the epidermis of human skin and in LCs derived from CD34⁺ hemopoietic stem cells (HSC-LCs) by utilizing single-cell RNA sequencing and mass cytometry. Analysis of HSC-LCs at multiple time-points during differentiation revealed that EGR1 and Notch signaling were among the top pathways regulating the bifurcation of LC1 and LC2. LC1 were characterized as classical LCs, mainly related to innate immunity and antigen processing. LC2 were similar to monocytes or myeloid dendritic cells, involving in immune responses and leukocyte activation. LC1 remained stable under inflammatory microenvironment, whereas LC2 were prone to being activated and demonstrated elevated expression of immuno-suppressive molecules. We revealed distinct human LC subsets that require different developmental regulation and orchestrate reciprocal functions.

Shaped by the epithelium - postnatal immune mechanisms of oral homeostasis

The first encounter of mucosal barriers with the microbiota initiates host-microbiota feedback loops instructing the tailored development of both the immune system and microbiota at each mucosal site. Once established, balanced immunological interactions enable symbiotic relationships with the microbiota in adult life. This process has been extensively investigated in the mammalian monolayer epithelium-covered intestine and lung mucosae; however, the postnatal mechanisms engaged by the oral mucosa to establish homeostasis are currently being discovered. Here, we discuss the early life dialogue between the oral mucosa and the microbiota, with particular emphasis on the central role the multilayer epithelium plays to protect the oral mucosa. These intricate and unique postnatal immunological processes shape oral homeostasis, which can potentially affect buccal and systemic health in adult life.

Addressing Full-Thickness Skin Defects: A Review of Clinically Available Autologous Skin Replacements

Autologous keratinocyte culture, and combinations of scaffolds, different cell types, solutions of macromolecules, or growth factors have contributed to the resurfacing of full-thickness skin defects. Ideally, a treatment for full-thickness skin defects should not merely reestablish continuity of the surface of the skin but should restore its structure to allow skin to function as a dynamic biological factory that can participate in protein synthesis, metabolism, and cell signaling, and form an essential part of the body's immune, nervous, and endocrine systems. This paper provides a review of clinically available autologous skin replacements, highlighting the importance of regenerating an organ that will function physiologically.

Immunology of Acute and Chronic Wound Healing

Skin wounds greatly affect the global healthcare system, creating a substantial burden on the economy and society. Moreover, the situation is exacerbated by low healing rates, which in fact are overestimated in reports. Cutaneous wounds are generally classified into acute and chronic. The immune response plays an important role during acute wound healing. The activation of immune cells and factors initiate the inflammatory process, facilitate wound cleansing and promote subsequent tissue healing. However, dysregulation of the immune system during the wound healing process leads to persistent inflammation and delayed healing, which ultimately result in chronic wounds. The microenvironment of a chronic wound is characterized by high quantities of pro-inflammatory macrophages, overexpression of inflammatory mediators such as TNF-α and IL-1β, increased activity of matrix metalloproteinases and abundance of reactive oxygen species. Moreover, chronic wounds are frequently complicated by bacterial biofilms, which perpetuate the inflammatory phase. Continuous inflammation and microbial biofilms make it very difficult for the chronic wounds to heal. In this review, we discuss the role of innate and adaptive immunity in the pathogenesis of acute and chronic wounds. Furthermore, we review the latest immunomodulatory therapeutic strategies, including modifying macrophage phenotype, regulating miRNA expression and targeting pro- and anti-inflammatory factors to improve wound healing.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

Resident Innate Immune Cells in the Cornea

The cornea is a special interface between the internal ocular tissue and the external environment that provides a powerful chemical, physical, and biological barrier against the invasion of harmful substances and pathogenic microbes. This protective effect is determined by the unique anatomical structure and cellular composition of the cornea, especially its locally resident innate immune cells, such as Langerhans cells (LCs), mast cells (MCs), macrophages, γδ T lymphocytes, and innate lymphoid cells. Recent studies have demonstrated the importance of these immune cells in terms of producing different cytokines and other growth factors in corneal homeostasis and its pathologic conditions. This review paper briefly describes the latest information on these resident immune cells by specifically analyzing research from our laboratory.

Novel Concepts: Langerhans Cells in the Tumour Microenvironment

Langerhans cells (LCs) are immune cells that reside in the stratified epithelium of the skin and mucosal membranes. They play a range of roles in the skin, including antigen presentation and maintenance of peripheral tolerance. Reports of LC numbers have been variable in different cancer types, with the majority of studies indicating a reduction in their number. Changes in the cytokine profile and other secreted molecules, downregulation of surface molecules on cells and hypoxia all contribute to the regulation of LCs in the tumour microenvironment. Functionally, LCs have been reported to regulate immunity and carcinogenesis in different cancer types. An improved understanding of the function and biology of LCs in tumours is essential knowledge that underpins the development of new cancer immunotherapies.

"Structural imprinting" of the cutaneous immune effector function

Keratinization provides tolerance to desiccation and mechanical durability. Loricrin, which is an epidermal thiol-rich protein, efficiently stabilizes terminally differentiated keratinocytes and maintains redox homeostasis. The discovery of the largely asymptomatic loricrin knockout (LKO) phenotype decades ago was rather unpredicted. Nevertheless, when including redox-driven, NF-E2-related factor 2-mediated backup responses, LKO mice provide opportunities for the observation of altered or "quasi-normal" homeostasis. Specifically, given that the tissue structure, as well as the local metabolism, transmits immunological signals, we sought to dissect the consequence of truncated epidermal differentiation program from immunological perspectives. Through a review of the aggregated evidence, we have attempted to generate an integrated view of the regulation of the peripheral immune system, which possibly occurs within the squamous epithelial tissue with truncated differentiation. This synthesis might not only provide insights into keratinization but also lead to the identification of factors intrinsic to the epidermis that imprint the immune effector function.

Notch-Mediated Generation of Monocyte-Derived Langerhans Cells: Phenotype and Function

Langerhans cells (LCs) in the skin are a first line of defense against pathogens but also play an essential role in skin homeostasis. Their exclusive expression of the C-type lectin receptor Langerin makes them prominent candidates for immunotherapy. For vaccine testing, an easily accessible cell platform would be desirable as an alternative to the time-consuming purification of LCs from human skin. Here, we present such a model and demonstrate that monocytes in the presence of GM-CSF, TGF-β1, and the Notch ligand DLL4 differentiate within 3 days into CD1a+Langerin+cells containing Birbeck granules. RNA sequencing of these monocyte-derived LCs (moLCs) confirmed gene expression of LC-related molecules, pattern recognition receptors, and enhanced expression of genes involved in the antigen-presenting machinery. On the protein level, moLCs showed low expression of costimulatory molecules but prominent expression of C-type lectin receptors. MoLCs can be matured, secrete IL-12p70 and TNF-α, and stimulate proliferation and cytokine production in allogeneic CD4+ and CD8+ T cells. In regard to vaccine testing, a recently characterized glycomimetic Langerin ligand conjugated to liposomes demonstrated specific and fast internalization into moLCs. Hence, these short-term in vitro‒generated moLCs represent an interesting tool to screen LC-based vaccines in the future.

Distorted frequency of dendritic cells and their associated stimulatory and inhibitory markers augment the pathogenesis of pemphigus vulgaris

The objective of this study was to investigate the frequency and functionality of DCs and its associated stimulatory and inhibitory markers in the pathogenesis of PV Active PV patients (n = 30) having both skin and oral lesions, and 30 healthy controls were recruited in the study. The frequency of DCs was determined by flow cytometry followed by the primary culture by using recombinant IL-4 (250 IU/ml) and GM-CSF (600 IU/ml). The culture supernatant was used for ELISA. RNA was isolated from sorted DCs and used for the mRNA expression of DC-associated stimulatory (CD40 and CD80) and inhibitory (PSGL1 and ILT3) markers. Tissue localization of Langerhans cells was done by immunohistochemistry. In this study, altered frequency of myeloid DC (mDC) and plasmacytoid DC (pDC) was seen in the circulation of PV patients. The primary culture of patient-derived DCs showed anomalous cytokine profiling. In the culture supernatant of DCs, elevated levels of TNF-ɑ and IL-12 were detected in PV patients. Meanwhile, reverse trend was found in the case of IFN-ɑ and IL-10 cytokine levels. Similarly, a discrepancy in the expression of DC-associated stimulatory (CD40 and CD80) and inhibitory (PSGL1 and ILT3) markers suggested their possible involvement in the immunopathogenesis of PV. An elevated number of tissue localizing Langerhans cells was also observed in the perilesional skin. This study indicates the distorted frequency and functionality of DCs in the immunopathogenesis of PV. Targeting these functional markers in the future may generate novel therapeutic options for better management of PV.

Niche rather than origin dysregulates mucosal Langerhans cells development in aged mice

Unlike epidermal Langerhans cells (LCs) that originate from embryonic precursors and are self-renewed locally, mucosal LCs arise and are replaced by circulating bone marrow (BM) precursors throughout life. While the unique lifecycle of epidermal LCs is associated with an age-dependent decrease in their numbers, whether and how aging has an impact on mucosal LCs remains unclear. Focusing on gingival LCs we found that mucosal LCs are reduced with age but exhibit altered morphology with that observed in aged epidermal LCs. The reduction of gingival but not epidermal LCs in aged mice was microbiota-dependent; nevertheless, the impact of the microbiota on gingival LCs was indirect. We next compared the ability of young and aged BM precursors to differentiate to mucosal LCs. Mixed BM chimeras, as well as differentiation cultures, demonstrated that aged BM has intact if not superior capacity to differentiate into LCs than young BM. This was in line with the higher percentages of mucosal LC precursors, pre-DCs, and monocytes, detected in aged BM. These findings suggest that while aging is associated with reduced LC numbers, the niche rather than the origin controls this process in mucosal barriers.

Dermatological diseases presented before COVID-19: Are patients with psoriasis and superficial fungal infections more vulnerable to the COVID-19?

Recent studies have focused on the comorbid conditions of the COVID‐19. According to the current studies, numerous diseases including lung disease, cardiovascular disease and immunosuppression appear to be at higher risk for severe forms of the COVID‐19. To date, there are no data in the literature on the comorbid dermatologic diseases and COVID‐19. We tried to analyze the previous dermatological comorbidity of 93 patients with COVID‐19 (51 males, 42 females) who presented to the dermatology outpatient clinics for the last 3 years. The most common dermatologic diseases in patients with COVID‐19 who have dermatologic diseases for the last 3 years were superficial fungal infections (24, 25.8%), seborrheic dermatitis (11, 11.8%), actinic keratosis (10, 10.8%), psoriasis (6, 6.5%), and eczema (6, 6.5%), respectively. In addition, the number of COVID‐19 patients who presented to dermatology in the last 3 months was 17 (11 men, 6 women). The median age of these patients was 58 (minimum 18, maximum 80) years, and the most common dermatologic diseases before diagnosed COVID‐19 were superficial fungal infections (5, 25%), psoriasis (4, 20%), and viral skin diseases (3, 15%). The possible similarity between cutaneous and mucosal immunity and immunosuppression suggests that patients with some dermatologic diseases especially superficial fungal infections and psoriasis may be more vulnerable to the COVID‐19.

The developing immune network in human prenatal skin

Establishment of a well‐functioning immune network in skin is crucial for its barrier function. This begins in utero alongside the structural differentiation and maturation of skin, and continues to expand and diversify across the human lifespan. The microenvironment of the developing human skin supports immune cell differentiation and has an overall anti‐inflammatory profile. Immunologically inert and skewed immune populations found in developing human skin promote wound healing, and as such may play a crucial role in the structural changes occurring during skin development.

BMP7 aberrantly induced in the psoriatic epidermis instructs inflammation-associated Langerhans cells

BACKGROUND

Epidermal hyperplasia represents a morphologic hallmark of psoriatic skin lesions. Langerhans cells (LCs) in the psoriatic epidermis engage with keratinocytes (KCs) in tight physical interactions; moreover, they induce T-cell-mediated immune responses critical to psoriasis.

OBJECTIVE

This study sought to improve the understanding of epidermal factors in psoriasis pathogenesis.

METHODS

BMP7-LCs versus TGF-β1-LCs were phenotypically characterized and their functional properties were analyzed using flow cytometry, cell kinetic studies, co-culture with CD4 T cells, and cytokine measurements. Furthermore, immunohistology of healthy and psoriatic skin was performed. Additionally, in vivo experiments with Jun^f/fJunB^f/fK5cre-ER^T mice were carried out to assess the role of bone morphogenetic protein (BMP) signaling in psoriatic skin inflammation.

RESULTS

This study identified a KC-derived signal (ie, BMP signaling) to promote epidermal changes in psoriasis. Whereas BMP7 is strictly confined to the basal KC layer in the healthy skin, it is expressed at high levels throughout the lesional psoriatic epidermis. BMP7 instructs precursor cells to differentiate into LCs that phenotypically resemble psoriatic LCs. These BMP7-LCs exhibit proliferative activity and increased sensitivity to bacterial stimulation. Moreover, aberrant high BMP signaling in the lesional epidermis is mediated by a KC intrinsic mechanism, as suggested from murine data and clinical outcome after topical antipsoriatic treatment in human patients.

CONCLUSIONS

These data indicate that available TGF-β family members within the lesional psoriatic epidermis preferentially signal through the canonical BMP signaling cascade to instruct inflammatory-type LCs and to promote psoriatic epidermal changes. Targeting BMP signaling might allow to therapeutically interfere with cutaneous psoriatic manifestations.