Skin Immunity Research Articles

Skin microbiota-host interactions.

The skin is a complex and dynamic ecosystem that is inhabited by bacteria, archaea, fungi and viruses. These microbes-collectively referred to as the skin microbiota-are fundamental to skin physiology and immunity. Interactions between skin microbes and the host can fall anywhere along the continuum between mutualism and pathogenicity. In this Review, we highlight how host-microbe interactions depend heavily on context, including the state of immune activation, host genetic predisposition, barrier status, microbe localization, and microbe-microbe interactions. We focus on how context shapes the complex dialogue between skin microbes and the host, and the consequences of this dialogue for health and disease.

Non-classical Immunity Controls Microbiota Impact on Skin Immunity and Tissue Repair

Mammalian barrier surfaces are constitutively colonized by numerous microorganisms. We explored how the microbiota was sensed by the immune system and the defining properties of such responses. Here, we show that a skin commensal can induce Tcell responses in a manner that is restricted to non-classical MHC class I molecules. These responses are uncoupled from inflammation and highly distinct from pathogen-induced cells. Commensal-specific Tcells express a defined gene signature that is characterized by expression of effector genestogether with immunoregulatory and tissue-repairsignatures. As such, non-classical MHCI-restricted commensal-specific immune responses not only promoted protection to pathogens, but also accelerated skin wound closure. Thus, the microbiota can induce a highly physiological and pleiotropic form of adaptive immunity that couples antimicrobial function with tissue repair. Our work also reveals that non-classical MHC class I molecules, an evolutionarily ancient arm of the immune system, can promote homeostatic immunity to the microbiota.

Redefining the Role of Langerhans Cells As Immune Regulators within the Skin.

Langerhans cells (LC) are a unique population of tissue-resident macrophages that form a network of cells across the epidermis of the skin, but which have the ability to migrate from the epidermis to draining lymph nodes (LN). Their location at the skin barrier suggests a key role as immune sentinels. However, despite decades of research, the role of LC in skin immunity is unclear; ablation of LC results in neither fatal susceptibility to skin infection nor overt autoimmunity due to lack of immune regulation. Our understanding of immune processes has traditionally been centered on secondary lymphoid organs as sites of lymphocyte priming and differentiation, which is exemplified by LC, initially defined as a paradigm for tissue dendritic cells that migrate to draining LN on maturation. But, more recently, an awareness of the importance of the tissue environment in shaping effector immunity has emerged. In this mini-review, we discuss whether our lack of understanding of LC function stems from our lymph node-centric view of these cells, and question whether a focus on LC as immune regulators in situ in the skin may reveal clearer answers about their function in cutaneous immunology.

Microbiome in the Gut-Skin Axis in Atopic Dermatitis.

The microbiome is vital for immune system development and homeostasis. Changes in microbial composition and function, termed dysbiosis, in the skin and the gut have recently been linked to alterations in immune responses and to the development of skin diseases, such as atopic dermatitis (AD). In this review, we summarize the recent findings on the gut and skin microbiome, highlighting the roles of major commensals in modulating skin and systemic immunity in AD. Although our understanding of the gut-skin axis is only beginning, emerging evidence indicates that the gut and skin microbiome could be manipulated to treat AD.

Polymeric immunoglobulin receptor in dojo loach (Misgurnus anguillicaudatus): Molecular characterization and expression analysis in response to bacterial and parasitic challenge

The polymeric immunoglobulin receptor (pIgR) is an essential component of the mucosal immune system in jawed vertebrates including teleost fish, which mediate transepithelial transport of secretory immunoglobulins (sIgs) to protect organisms against environmental pathogens. In this study, we firstly cloned and identified the pIgR from dojo loach (Misgurnus anguillicaudatus). The full-length cDNA of Ma-pIgR was of 1145 bp, containing an open reading frame (ORF) of 1101 bp encoded a predicted protein of 336 amino acids. The structure of Ma-pIgR is comprised of a signal peptide, a transmembrane region, an intracellular region and an extracellular region with two Ig-like domains (ILDs), which are similar to their counterparts described in other teleosts. Multiple sequence alignment and phylogenetic analysis showed the dojo loach is closely related to the fish family Cyprinidae. The transcriptional level of Ma-pIgR was detected by quantitative real-time PCR (qRT-PCR) in different tissues and high expression was found in liver, skin, kidney, eye, fin and gills. Two infection models of the loach with bacteria (Aeromonas hydrophila) and parasite (Ichthyophthirius multifiliis) were constructed for the first time. Histological studies showed the goblet cells in skin significantly increased and the ratio of gill length to width also significantly changed after challenged with A.hydrophila. Both challenge experiments resulted in the significant up-regulated expression of Ma-pIgR not only in kidney and spleen, but also in skin and gills. Our results suggest that pIgR may play an important role in skin and gill mucosal immunity to protect the loach against bacteria and parasite.

Prophenoloxidase-Mediated Ex Vivo Immunity to Delay Fungal Infection after Insect Ecdysis.

Skin immunity protects animals from airborne pathogen infection. Unlike mammals, arthropods, including insects, undergo periodic ecdysis to grow and develop. Newly molted insects emerge with unsclerotized thin cuticles but successfully escape pathogenic infections during the post-molt period. Here we show that prophenoloxidases (PPOs) in molting fluids remain bioactive on the integument and impede fungal infection after ecdysis. We found that the purified plasma PPOs or recombinant PPOs could effectively bind to fungal spores (conidia) by targeting the cell wall components chitin and β-1,3-glucan. Pretreatment of the spores of the fungal pathogen Beauveria bassiana with PPOs increased spore hydrophilicity and reduced spore adhesion activity, resulting in a significant decrease in virulence as compared with mock infection. We also identified a spore-secreted protease BPS8, a member of peptidase S8 family of protease that degrade PPOs at high levels to benefit fungal infection, but which at lower doses activate PPOs to inhibit spore germination after melanization. These data indicate that insects have evolved a distinct strategy of ex vivo immunity to survive pathogen infections after ecdysis using PPOs in molting fluids retained on the underdeveloped and tender integument of newly molted insects for protection against airborne fungal infection.

9-cis-Retinoic acid induces a distinct regulatory dendritic cell phenotype that modulates murine delayed-type allergy.

Hand eczema, which is frequently caused by delayed-type allergy, is treated with 9-cis-retinoic acid (9cisRA). However, knowledge on how 9cisRA modulates skin immunity is sparse. As dendritic cells (DCs) are central in the pathogenesis of contact allergy, we investigated 9cisRA modulation of DC function in murine contact hypersensitivity (CHS). 9cisRA-differentiated DCs (9cisRA-DCs) were analysed for phenotype and function. In vivo 9cisRA-DCs were tested in the CHS model. 9cisRA induces the differentiation of a distinct CD103- CD207- regulatory DC phenotype. CD11c+ DCs differentiated with 9cisRA have lower expression of major histocompatibility complex-II and costimulatory molecules, but conversely have higher expression of the inhibitory coreceptor PD1-L. 9cisRA-DC culture does not induce the expression of proinflammatory cytokines, but strongly enhances osteopontin (OPN) secretion. 9cisRA-DCs are compromised in the induction of T cell proliferation in vitro, but efficiently convert naive T cells into regulatory T cells (Tregs). Notably, OPN-deficient 9cisRA-DCs show a loss of Treg-inducing function, which is re-established by substituting OPN. In vivo, in allergic mice, allergen-primed 9cisRA-DCs suppress allergic inflammation and induce Treg accumulation in skin draining lymph nodes. This study describes 9cisRA-mediated differentiation of a distinct DC phenotype that relies on OPN for Treg transformation and suppresses established CHS through Treg induction.

Proteomic Profiling of Sweat Exosome Suggests its Involvement in Skin Immunity

Healthy human skin sustains an effective immune defense mechanism, formed by a complex physical and chemical epidermal barrier that coordinates with different cellular components of the skin immune system. However, the mechanism by which skin cells regulate local immune homeostasis in health and disease contexts is not well known. To investigate whether exosomes exist in sweat, sweat samples from healthy individuals were collected after aerobic exercise. Sweat exosome was isolated via differential ultracentrifugation, observed under transmission electron microscopy, measured by dynamic light scattering, and confirmed by immunoblot. Further, shotgun liquid chromatography (LC)-mass spectrometry (MS)/MS analysis was conducted to investigate the proteomic profiling of sweat exosome. Secreted exosome was detected in human sweat. A total of 1,062 proteins were identified in sweat exosome, including 997 different proteins compared with sweat proteomics and 896 unique proteins compared with urine, saliva, and plasma exosomes. Diverse antimicrobial peptides and immunological factors were found in sweat exosome, suggesting the involvement of exosome in skin immunity. This study provides direct evidence that secreted exosomes exist in human sweat. The proteomic profiling of sweat exosome provides insight into sweat features and the potential physiological significance of exosomes in immune homeostasis.

Local immune response of two mucosal surfaces of the European seabass, Dicentrarchus labrax, fed tryptophan- or methionine-supplemented diets

Immune responses relies on an adequate provision of multiple nutrients that sustain the synthesis of key effector molecules. These needs are depicted in the already reported increase of circulating free amino acids in fish under stressful conditions. Since aquaculture and the inherent fish welfare are an emergent call, the immunomodulatory effects of amino acids on gut- and skin-associated lymphoid tissues of the European seabass (Dicentrarchus labrax) were studied under unstressed conditions and after an inflammatory insult. To achieve this goal, fish were distributed in duplicate tanks (fifteen fish per tank) and were fed for 14 days with methionine or tryptophan-supplemented diets at 2× dietary requirement level (MET and TRP, respectively) or a control diet meeting the amino acids requirement levels (CTRL). Afterwards, samples of skin and posterior gut were collected from 6 fish per dietary treatment for the assessment of the immune status while the remaining animals were intraperitoneally-injected with inactivated Photobacterium damselae subsp. piscicida and subsequently sampled either 4 or 24 h post-injection.The immune status of both mucosal surfaces was poorly affected, although a tryptophan effect was denoted after bacterial inoculation, with several immune-related genes up-regulated in the gut at 4 h post-injection, which seems to suggest a neuroendocrine-immune systems interaction. In contrast, skin mucosal immunity was inhibited by tryptophan dietary supplementation. Regarding methionine, results were often statistically non-significant, though increasing trends were denoted in a few parameters.Overall, dietary methionine did not significantly affect neither gut nor skin immunity, whereas tryptophan supplementation seems to induce modulatory mechanisms that might be tissue-specific.

Lower levels of interleukin-1β gene expression are associated with impaired Langerhans' cell migration in aged human skin.

SummaryLangerhans’ cells (LC) play pivotal roles in skin immune responses, linking innate and adaptive immunity. In aged skin there are fewer LC and migration is impaired compared with young skin. These changes may contribute to declining skin immunity in the elderly, including increased skin infections and skin cancer. Interleukin‐1β (IL‐1β) and tumour necrosis factor‐α (TNF‐α) are mandatory signals for LC migration and previous studies suggest that IL‐1β signalling may be dysregulated in aged skin. Therefore, we sought to explore the mechanisms underlying these phenomena. In skin biopsies of photoprotected young (< 30 years) and aged (> 70 years) human skin ex vivo, we assessed the impact of trauma, and mandatory LC mobilizing signals on LC migration and gene expression. Biopsy‐related trauma induced LC migration from young epidermis, whereas in aged skin, migration was greatly reduced. Interleukin‐1β treatment restored LC migration in aged epidermis whereas TNF‐α was without effect. In uncultured, aged skin IL‐1β gene expression was lower compared with young skin; following culture, IL‐1β mRNA remained lower in aged skin under control and TNF‐α conditions but was elevated after culture with IL‐1β. Interleukin‐1 receptor type 2 (IL1R2) gene expression was significantly increased in aged, but not young skin, after cytokine treatment. Keratinocyte‐derived factors secreted from young and aged primary cells did not restore or inhibit LC migration from aged and young epidermis, respectively. These data suggest that in aged skin, IL‐1β signalling is diminished due to altered expression of IL1B and decoy receptor gene IL1R2.

Staphylococcus aureus from atopic dermatitis skin alters cytokine production triggered by monocyte-derived Langerhans cell

BackgroundAtopic dermatitis (AD) is one of the most common chronic inflammatory skin diseases. The skin of patients with AD presents as a disbalance of the microbiome with a strong colonization by Staphylococcus aureus, which positively correlates with the severity of the disease. However, the effect of colonized S. aureus on the skin immune system has not been fully elucidated. ObjectiveThe aim of this study is to explore whether S. aureus isolated from AD skin is able to skew T cell responses via Langerhans cells (LC) as compared to a standard strain of S. aureus and S. epidermidis. MethodsWe prepared monocyte-derived LC (MoLC) from healthy controls and patients with AD, and stimulated MoLC with a standard strain of S. aureus NCTC8325, S. aureus TF3378 isolated from AD skin, or S. epidermidis. Stimulated MoLC were co-cultured with autologous CD4pos T cells and then T cell responses were analyzed by T cell polarization assays, cytokine analysis and real-time PCR. ResultsMoLC stimulated by S. aureus TF3378 induced significantly high and rapid proliferation of T cells as compared to those by S. aureus NCTC8325 and S. epidermidis. Cytokine productions from T cells cultured with S. aureus TF3378-stimulated MoLC showed significantly high amounts of IL-2 and less IFN-γ production with imbalanced Th1/Th2 (decreased TBX21/GATA3 ratio) mRNA expression. The T cell proliferation with increased IL-2 production via S. aureus TF3378-stimulated MoLC was diminished by treatment of proteinase K. ConclusionS. aureus TF3378 on AD skin can skew T cell responses via LC toward imbalanced Th1/Th2 skin immunity.

Psoriasiform skin disease in transgenic pigs with high-copy ectopic expression of human integrins α2 and β1.

ABSTRACTPsoriasis is a complex human-specific disease characterized by perturbed keratinocyte proliferation and a pro-inflammatory environment in the skin. Porcine skin architecture and immunity are very similar to that in humans, rendering the pig a suitable animal model for studying the biology and treatment of psoriasis. Expression of integrins, which is normally confined to the basal layer of the epidermis, is maintained in suprabasal keratinocytes in psoriatic skin, modulating proliferation and differentiation as well as leukocyte infiltration. Here, we generated minipigs co-expressing integrins α2 and β1 in suprabasal epidermal layers. Integrin-transgenic minipigs born into the project displayed skin phenotypes that correlated with the number of inserted transgenes. Molecular analyses were in good concordance with histological observations of psoriatic hallmarks, including hypogranulosis and T-lymphocyte infiltration. These findings mark the first creation of minipigs with a psoriasiform phenotype resembling human psoriasis and demonstrate that integrin signaling plays a key role in psoriasis pathology.

Oral warfarin intake affects skin inflammatory cytokine responses in rats

Warfarin is an anticoagulant used in prevention/prophylaxis of thromboembolism. Besides the effects on coagulation, non-hemorrhagic reactions have also been documented. Although cutaneous reactions were reported in some patients, the impact on skin immunity was not explored. In the present paper, the effect of 30-day oral warfarin intake on skin cytokine responses in rats was analyzed. Increased release of inflammatory cytokines (TNF, IL-1β and IL-10) was noted by skin explants from rats which received warfarin, but without effect on IL-6. No impact on epidermal cell cytokine secretion was seen, except a tendency of an increase of IL-6 response to stimulation with microbial product lipopolysaccharide (LPS). Topical application of contact allergen dinitrochlorobenzene (DNCB) resulted in slight (numerical solely) increase of TNF release by skin explants of warfarin-treated animals, while epidermal cells responded by increased secretion of all four cytokines examined. The data presented provide new information on the potential of oral warfarin to modulate skin innate immune activity.

Light-Emitting Diode at 460 ± 20 nm Increases the Production of IL-12 and IL-6 in Murine Dendritic Cells.

Light emitting diode (LED) therapy has been proposed as an option for the treatment of many skin inflammatory processes. Dendritic cells (DCs) are important cells of skin that participate in the initiation and activation of skin immunity. The modulation of these cells by LED could explain much of its effects. Thus, the aim of this study was to examine the effects of LED at 460 ± 20 nm on cytokine production and the expression of surface markers on DCs. DCs were obtained from mouse bone marrow-derived dendritic cells (BMDCs). The LED was applied giving a fluence of 3.3, 8.2, or 16.5 J/cm2 on BMDCs or lipopolysaccharide (LPS)-matured BMDCs. The production of cytokine was analyzed by enzyme linked immunosorbant assay (ELISA) and the expression of DC co- and stimulatory was analyzed markers by cytometry. LED increases IL-12p40 and IL-6 production in both nonstimulated BMDCs and LPS-matured BMDCs. The expression of MHC-II molecule was inhibited and the expression of the CD86 molecule was increased in nonstimulated BMDCs but not in LPS-matured BMDCs. The production of tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10) and the expression of CD40 were not altered. These results demonstrate that LED stimulated cytokine production in BMDCs, suggesting a proinflammatory role in the tested conditions and maybe it can increase DC maturation.

Orf virus infection

Orf virus (ORFV) is an important pathogen responsible for a highly contagious zoonotic viral infection that threatens those who handle sheep and goats. Orf virus is the prototype of the Parapoxvirus genus, and its resilience in the environment and ability to reinfect its host has contributed to the spread and maintenance of the infection in many species. In healthy humans, the disease usually resolves spontaneously within 3 to 6weeks. There is no specific treatment and many different approaches such as use of imiquimod, cidofovir, curettage, shave excision, cryotherapy, and electrocautery have all been reported to be successful, without supporting evidence from controlled clinical trials. Throughout its interaction with the different hosts, ORFV has evolved a strategy for immune evasion via the development of an array of virulence factors. The interaction of ORFV with the immune system has been the subject of research for decades. Whole inactivated ORFV has been used as a type of immunomodulating drug; a so called paramunity inducer proposed as both a preventative and a therapeutic immunomodulator across various species. Additional research on the remarkable strategies underlying ORFV infection could lead to improved understanding of skin immunity.

Forensic aspects of gene expression signatures for age determination in bruises as evaluated in an experimental porcine model.

Determining the age of bruises and the force used to inflict the trauma is of crucial importance in both human and veterinary forensic pathology. In the present study, the expression of more than 50 different genes in subcutaneous fat and muscle tissue from experimental bruises in pigs was investigated. The aim was to evaluate if expression signatures of selected genes were capable of determining bruises according to age and the force of impact. Eighteen experimental pigs were anesthetized, and on each animal four blunt traumas were inflicted on the back with a low, moderate or high force. The pigs were euthanized from 1 to 10h after infliction of the trauma and subcutaneous fat and muscle tissues were sampled. As control, subcutaneous fat and muscle tissues were sampled from two un-injured pigs. Quantitative real-time polymerase chain reaction was performed to evaluate mRNA expression of genes involved in inflammation, tissue damage and repair. Expression signatures of thirteen selected genes in subcutaneous fat but not in muscle tissue reflected the age of bruises with a precision of approximately ±2h. Moreover, the gene expression signature in the subcutaneous fat was to some extend able to separate bruises inflicted with different forces. Expression signatures of selected genes in the subcutaneous fat will increase the precision of the age determination of bruises in pigs. Further, due to the similarity of porcine and human skin physiology and immunity, these results might also provide valuable information in human forensic science.

Specific interaction between defined skin commensal and dermal IL-17A-producing gamma delta T cells.

Abstract The skin is home to a diverse and complex microbiota that play an important role in tissue homeostasis and local immunity. We have previously shown that Staphylococcus epidermidis promotes IL-17A-producing CD8+ T cells that enhance innate barrier immunity and limit pathogen invasion. However, the ability of other defined skin microbes and/or microbes-derived products to modulate skin immunity is still poorly characterized. T cells expressing low level of gamma delta TCR (gdT) are a dermal population of T lymphocytes that are committed to produce IL-17A and can mediate both innate and adaptive-like immune responses. Here, we show that cutaneous colonization with Corynebacterium accolens, a dominant member of the human and murine skin microbiota, induces IL-17A-producing gdT cells in the skin of specific-pathogen free mice. Intriguingly this ability is conserved amongst other species from the same genus supporting the idea that a canonical constituent shared by members of this taxon may be mediating this effect. Using a mutant strain of C. accolens lacking the corynemycolic acid synthase enzyme, we found that corynemycolic acids, a major component of the cell envelope, are important for the induction of IL-17A-producing gdT cells. Furthermore, mice associated with C. accolens displayed increased skin inflammation in an experimental model of psoriasis, a disease associated with an increase of IL-17A-producing gdT cells. Together these results uncover a novel mode of interaction between the skin microbiota and the skin immune system and highlight the important role that the skin microbiota may have in the pathogenesis of skin inflammatory disorders.

MiRNAs are required for embryonic development of Langerhans Cells

Abstract Langerhans cells (LCs) are epidermal-resident dendritic cells that play important roles in skin immunity and tolerance. Recent fate-mapping studies have demonstrated that adult LCs derive predominantly from fetal liver monocytes with a minor contribution of yolk sac-derived macrophages. However, the role of epigenetic regulations in embryonic development of LCs remains unclear. MicroRNAs (miRNAs) are small, noncoding RNAs that negatively regulate gene expression of their mRNA targets. We and others recently reported that miRNAs are key players in regulating immune cell development and function, including LCs. To further study the role of miRNAs in LC ontogeny, we generated CSF1rCreDicerf/fKO mice in which miRNAs are deficient in myeloid lineage cells including LCs. As expected, the frequency of LCs was drastically reduced in Dicer KO adult mice. Interestingly, there was also a significant reduction (p=0.027) of epidermal LCs in Dicer KO embryos at E18.5, suggesting that miRNAs are crucial for embryonic development of LCs. Given the differential expression of miR-150 and miR-155 in embryonic LC development, we generated CSF1rCremiR-150f/fKI and CSF1rCremiR-155f/fKI mice in which expression of miR-150 and miR-155 is upregulated in LC-lineage, respectively. Surprisingly, neither strain caused defective LC development in fetal or adult epidermis. Overall, this is the first study to demonstrate that miRNAs are required for embryonic LC development. Furthermore, although overexpression of miR-150 or miR-155 is dispensable for LC ontogeny, the specific miRNAs responsible for proper LC development deserve to be further explored.

019 Functional changes in Langerhans cells (LCs) may partially explain alterations in skin immunity with aging

019 Functional changes in Langerhans cells (LCs) may partially explain alterations in skin immunity with aging

Downregulation of AQP2 in the anterior vaginal wall is associated with the pathogenesis of female stress urinary incontinence.

The pathogenesis of stress urinary incontinence (SUI) is unclear. Aquaporins (AQPs) are a family of transmembrane proteins that transport water and small solutes, including glycerol, across cell membranes. AQPs have been demonstrated to serve a role in skin hydration, cellular proliferation, migration, immunity, wound healing and vascular remodeling in multiple organs. Furthermore, studies have confirmed that abnormal synthesis and degradation of collagens in extracellular matrix (ECM) remodeling contributes to SUI, by altering normal tissue architecture and mechanical properties. The authors previously demonstrated that AQP2 expressed in the human endometrium varies during the menstrual cycle. However, it is unknown whether AQP2 serves a role in the pathogenesis of SUI in the urethral supporting tissue. In the present study, AQP2 location and expression was examined in the anterior vaginal wall, and investigated the association between AQP2 and collagen I/III in female SUI. Western blotting, immunohistochemistry and immunofluorescence were used to measure AQP2 expression levels, and to reveal the location of AQP2 in the anterior vaginal wall, as well as fibroblasts in SUI and non‑SUI. The association between AQP2 and collagen I/III was subsequently investigated by AQP2‑small interfering RNA knockdown and overexpression 2 in fibroblasts. AQP2 expression in the anterior vaginal wall was significantly increased in women without SUI compared with those with SUI (P<0.05). Downregulation of AQP2 significantly decreased the mRNA and protein expression of collagenI/III, while AQP2 overexpression significantly increased the mRNA and protein expression of collagen I/III in fibroblasts (P<0.05). AQP2 was demonstrated to be expressed in the anterior vaginal wall and fibroblasts, and to regulate the expression level of collagen I/III in the anterior vaginal wall and fibroblasts, suggesting that AQP2 is associated with the pathogenesis of female SUI through collagen metabolism during ECM remodeling.