Direct control of regulatory T cells by keratinocytes

Mi-2β promotes immune evasion in melanoma by activating EZH2 methylation

Recent development of new immune checkpoint inhibitors has been particularly successfully in cancer treatment, but still the majority patients fail to benefit. Converting resistant tumors to immunotherapy sensitive will provide a significant improvement in patient outcome. Here we identify Mi-2β as a key melanoma-intrinsic effector regulating the adaptive anti-tumor immune response. Studies in genetically engineered mouse melanoma models indicate that loss of Mi-2β rescues the immune response to immunotherapy in vivo. Mechanistically, ATAC-seq analysis shows that Mi-2β controls the accessibility of IFN-γ-stimulated genes (ISGs). Mi-2β binds to EZH2 and promotes K510 methylation of EZH2, subsequently activating the trimethylation of H3K27 to inhibit the transcription of ISGs. Finally, we develop an Mi-2β-targeted inhibitor, Z36-MP5, which reduces Mi-2β ATPase activity and reactivates ISG transcription. Consequently, Z36-MP5 induces a response to immune checkpoint inhibitors in otherwise resistant melanoma models. Our work provides a potential therapeutic strategy to convert immunotherapy resistant melanomas to sensitive ones.

In vitro and in vivo anti-eczema effect of Artemisia annua aqueous extract and its component profiling

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia annua L. belongs to the Asteraceae family and has a long history of clinical application in China. It has been widely used for centuries to treat fever, malaria, jaundice and some skin diseases (such as scabies and sores). Modern pharmacological studies have shown that it has anti-inflammatory, immunomodulatory, antimalarial and antibacterial effects.

AIM OF STUDY

This study aimed to investigate the anti-eczema effect of A. annua aqueous extract (AAE), profile its potential bioactive components and try to explore its possible underlying mechanisms.

MATERIALS AND METHODS

The MTT assay was employed to assess the cytotoxicity of AAE. The anti-eczema effect of AAE was evaluated using both an in vitro 3D epidermal inflammation model and an in vivo guinea pig itching model. The bioactive components of AAE were characterized by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry coupled with the UNIFI platform.

RESULTS

In this study, we found that AAE is safe for primary human skin keratinocytes at concentrations ranging from 31.3 μg/mL to 250 μg/mL. Further investigations indicate that AAE can increase the itching threshold, inhibit the expression of the inflammatory cytokine TSLP, and promote the expression of FLG mRNA. Additionally, the utilization of UPLC-QTOF/MS and UNIFI platform enabled us to identify 61 potential bioactive components of AAE, with sesquiterpenes and phenolic acids being the most abundant components.

CONCLUSIONS

In this study, the anti-inflammatory and anti-itch effects of the A. annua extract were revealed, along with sesquiterpenes and phenolic acids were identified as potential bioactive components according to literature. The AAE extract holds potential for utilization in the treatment of eczema.

CD36-SREBP1 Axis Mediates TSLP Production in Obesity-Exacerbated Atopic Dermatitis

Obesity is associated with an increased risk of atopic dermatitis (AD) and may accelerate its development. Keratinocyte dysfunction has been observed in obesity-related skin diseases, including psoriasis and acanthosis nigricans, but is not fully understood in AD. In this study, we found that high-fat diet-induced obesity exacerbated AD-like dermatitis in mice, with elevated inflammatory molecules and increased CD36-SREBP1-related fatty acid accumulation in the lesional skin. Blocking CD36 or SREBP1 with chemical inhibitors effectively alleviated AD-like inflammation, decreased fatty acid accumulation, and downregulated TSLP expression in obese calcipotriol (MC903)-treated mice. Moreover, palmitic acid treatment induced TSLP overexpression in keratinocytes through the activation of the CD36-SREBP1 signaling pathway. The chromatin immunoprecipitation assay further revealed increased binding of SREBP1 to the TSLP promoter region. Our findings provide compelling evidence that obesity triggers the activation of the CD36-SREBP1-TSLP axis in keratinocytes, leading to epidermal lipid disorders and the aggravation of AD-like inflammation. By targeting CD36 or SREBP1, future combination therapies or modified treatment strategies could be developed to help manage patients with both obesity and AD.

Regulatory T cells in allergic inflammation

Regulatory T (Treg) cells maintain immune tolerance to allergens at the environmental interfaces in the airways, skin and gut, marshalling in the process distinct immune regulatory circuits operative in the respective tissues. Treg cells are coordinately mobilized with allergic effector mechanisms in the context of a tissue-protective allergic inflammatory response against parasites, toxins and potentially harmful allergens, serving to both limit the inflammation and promote local tissue repair. Allergic diseases are associated with subverted Treg cell responses whereby a chronic allergic inflammatory environment can skew Treg cells toward pathogenic phenotypes that both perpetuate and aggravate disease. Interruption of Treg cell subversion in chronic allergic inflammatory conditions may thus provide novel therapeutic strategies by re-establishing effective immune regulation.

Skin-derived TSLP stimulates skin migratory dendritic cells to promote the expansion of regulatory T cells

Therapeutic strategies that enhance regulatory T (Treg) cell proliferation or suppressive function hold promise for the treatment of autoimmune and inflammatory diseases. We previously reported that the topical application of the vitamin D3 analog MC903 systemically expands Treg cells by stimulating the production of thymic stromal lymphopoietin (TSLP) from the skin. Using mice lacking TSLP receptor expression by dendritic cells (DCs), we hereby show that TSLP receptor signaling in DCs is required for this Treg expansion in vivo. Topical MC903 treatment of ear skin selectively increased the number of migratory DCs in skin-draining lymph nodes (LNs) and upregulated their expression of co-stimulatory molecules. Accordingly, DCs isolated from skin-draining LNs but not mesenteric LNs or spleen of MC903-treated mice showed an enhanced ability to promote Treg proliferation, which was driven by co-stimulatory signals through CD80/CD86 and OX40 ligand. Among the DC subsets in the skin-draining LNs of MC903-treated mice, migratory XCR1- CD11b+ type 2 and XCR1- CD11b- double negative conventional DCs promoted Treg expansion. Together, these data demonstrate that vitamin D3 stimulation of skin induces TSLP expression, which stimulates skin migratory DCs to expand Treg cells. Thus, topical MC903 treatment could represent a convenient strategy to treat inflammatory disorders by engaging this pathway.

T helper 1 effector memory CD4+ T cells protect the skin from poxvirus infection

Poxvirus infections of the skin are a recent emerging public health concern, yet the mechanisms that mediate protective immunity against these viral infections remain largely unknown. Here, we show that T helper 1 (Th1) memory CD4+ T cells are necessary and sufficient to provide complete and broad protection against poxvirus skin infections, whereas memory CD8+ T cells are dispensable. Core 2 O-glycan-synthesizing Th1 effector memory CD4+ T cells rapidly infiltrate the poxvirus-infected skin microenvironment and produce interferon γ (IFNγ) in an antigen-dependent manner, causing global changes in gene expression to promote anti-viral immunity. Keratinocytes express IFN-stimulated genes, upregulate both major histocompatibility complex (MHC) class I and MHC class II antigen presentation in an IFNγ-dependent manner, and require IFNγ receptor (IFNγR) signaling and MHC class II expression for memory CD4+ T cells to protect the skin from poxvirus infection. Thus, Th1 effector memory CD4+ T cells exhibit potent anti-viral activity within the skin, and keratinocytes are the key targets of IFNγ necessary for preventing poxvirus infection of the epidermis.

Mining chicken ileal microbiota for immunomodulatory microorganisms

The gut microbiota makes important contributions to host immune system development and resistance to pathogen infections, especially during early life. However, studies addressing the immunomodulatory functions of gut microbial individuals or populations are limited. In this study, we explore the systemic impact of the ileal microbiota on immune cell development and function of chickens and identify the members of the microbiota involved in immune system modulation. We initially used a time-series design with six time points to prove that ileal microbiota at different succession stages is intimately connected to immune cell maturation. Antibiotics perturbed the microbiota succession and negatively affected immune development, whereas early exposure to the ileal commensal microbiota from more mature birds promoted immune cell development and facilitated pathogen elimination after Salmonella Typhimurium infection, illustrating that early colonization of gut microbiota is an important driver of immune development. Five bacterial strains, Blautia coccoides, Bacteroides xylanisolvens, Fournierella sp002159185, Romboutsia lituseburensis, and Megamonas funiformis, which are closely related to the immune system development of broiler chickens, were then screened out and validated for their immunomodulatory properties. Our results provide insight into poultry immune system-microbiota interactions and also establish a foundation for targeted immunological interventions aiming to combat infectious diseases and promote poultry health and production.

Epithelial cell-derived cytokine TSLP activates regulatory T cells by enhancing fatty acid uptake

Epithelial cells control a variety of immune cells by secreting cytokines to maintain tissue homeostasis on mucosal surfaces. Regulatory T (Treg) cells are essential for immune homeostasis and for preventing tissue inflammation; however, the precise molecular mechanisms by which epithelial cell-derived cytokines function on Treg cells in the epithelial tissues are not well understood. Here, we show that peripheral Treg cells preferentially respond to thymic stromal lymphoprotein (TSLP). Although TSLP does not affect thymic Treg differentiation, TSLP receptor-deficient induced Treg cells derived from naïve CD4⁺ T cells are less activated in an adoptive transfer model of colitis. Mechanistically, TSLP activates induced Treg cells partially through mTORC1 activation and fatty acid uptake. Thus, TSLP modulates the activation status of induced Treg through the enhanced uptake of fatty acids to maintain homeostasis in the large intestine.

Immunization with a Pneumococcal pep27 Mutant Strain Alleviates Atopic Dermatitis through the Upregulation of Regulatory T-Cell Activity and Epithelial Barrier Function and Suppressing TSLP Expression

Atopic dermatitis (AD) is an inflammatory disease driven in part by type 2 helper T (Th2) cytokines and skin barrier disruption alleviating the entry of allergens. Thymic stromal lymphopoietin (TSLP), an epithelial cell‒derived cytokine, is known to aggravate AD symptoms by activating Th2. In addition, regulatory T cells (Tregs) inhibit inflammatory cells such as Th2. However, the relationship between TSLP and Tregs in AD is unclear. A murine dermatitis model was induced by applying oxazolone to the ear skin of mice. Prophylactic and therapeutic responses were analyzed by immunizing mice intranasally with a pneumococcal pep27 mutant (Δpep27 mutant), attenuated strain by reducing the virulence of a pathogen. Intranasal immunization with a pneumococcal pep27 mutant could elicit anti-inflammatory Treg-relevant factors and epithelial barrier genes (loricrin, involucrin, filaggrin, and small proline-rich repeat proteins). Thus, pneumococcal pep27-mutant immunization suppressed epidermal collapse, IgE, TSLP, and upregulation of Th2 expression by upregulating Treg activity. In contrast, Treg inhibition aggravated AD symptoms through the upregulation of TSLP and Th2 and the repression of epithelial barrier function compared with that of the noninhibited pneumococcal Δpep27-mutant group. Taken together, immunization with pneumococcal Δpep27 mutant upregulated Treg and epithelial barrier function and inhibited TSLP and Th2 to relieve AD symptoms.

Combined application of dinitrofluorobenzene and ovalbumin induced AD-like dermatitis with an increase in helper T-cell cytokines and a prolonged Th2 response

BACKGROUND

The progression of acute-to-chronic atopic dermatitis is accompanied by multiple helper T-cell cytokine responses, but the mechanisms and relative importance of these changes remain unclear. There is no animal model for atopic dermatitis that recapitulates these cytokine responses.

OBJECTIVE

We sought to build a novel mouse model for atopic dermatitis (AD) that recapitulates these helper T-cell responses and some dynamic changes in cytokine responses in the progression of AD.

METHODS

Female BALB/c mice were subjected to the application of dinitrofluorobenzene (DNFB) and ovalbumin (OVA) to induce AD-like dermatitis. Skin lesions and serum were collected from mice in the acute and chronic phases to detect changes in cytokine responses and other features of AD.

RESULTS

Combined application of DNFB and OVA successfully induced AD-like dermatitis and histological changes as well as epidermal barrier dysfunction. In the acute phase of AD-like dermatitis, Th2-associated cytokines were mainly increased in serum and skin lesions. In the chronic phase of AD-like dermatitis, Th2-associated cytokines were still highly expressed, while Th1- and Th17-associated cytokines were also gradually increased. Compared with the acute phase, the JAK-STAT signaling pathway was highly expressed in the chronic phase of AD-like dermatitis.

CONCLUSION

The combined application of DNFB and OVA could be used to build a new mouse model for atopic dermatitis. This mouse model recapitulates the helper T-cell responses and some dynamic changes in cytokine responses in the progression of acute-to-chronic in human AD. The JAK-STAT signaling pathway plays a pivotal role in the chronicity of AD.

Advances in the modulation of ROS and transdermal administration for anti-psoriatic nanotherapies

Reactive oxygen species (ROS) at supraphysiological concentration have a determinate role in contributing to immuno-metabolic disorders in the epithelial immune microenvironment (EIME) of psoriatic lesions. With an exclusive focus on the gene-oxidative stress environment interaction in the EIME, a comprehensive strategy based on ROS-regulating nanomedicines is greatly anticipated to become the mainstay of anti-psoriasis treatment. This potential therapeutic modality could inhibit the acceleration of psoriasis via remodeling the redox equilibrium and reshaping the EIME. Herein, we present a marked overview of the current progress in the pathomechanisms of psoriasis, with particular concerns on the potential pathogenic role of ROS, which significantly dysregulates redox metabolism of keratinocytes (KCs) and skin-resident or -infiltrating cells. Meanwhile, the emergence of versatile nanomaterial-guided evolution for transdermal drug delivery has been attractive for the percutaneous administration of antipsoriatic therapies in recent years. We emphasize the underlying molecular mechanism of ROS-based nanoreactors for improved therapeutic outcomes against psoriasis and summarize up-to-date progress relating to the advantages and limitations of nanotherapeutic application for transdermal administration, as well as update an insight into potential future directions for nanotherapies in ROS-related skin diseases.

Emerging role for thymic stromal lymphopoietin-responsive regulatory T cells in colorectal cancer progression in humans and mice

Recruitment of regulatory T cells (T_regs) to tumors is a hallmark of cancer progression. Tumor-derived factors, such as the cytokine thymic stromal lymphopoietin (TSLP), can influence T_reg function in tumors. In our study, we identified a subset of T_regs expressing the receptor for TSLP (TSLPR⁺ T_regs) that were increased in colorectal tumors in humans and mice and largely absent in adjacent normal colon. This T_reg subset was also found in the peripheral blood of patients with colon cancer but not in the peripheral blood of healthy control subjects. Mechanistically, we found that this T_reg subset coexpressed the interleukin-33 (IL-33) receptor [suppressor of tumorigenicity 2 (ST2)] and had high programmed cell death 1 (PD-1) and cytotoxic lymphocyte-associated antigen 4 (CTLA-4) expression, regulated in part by the transcription factor Mef2c. T_reg-specific deletion of TSLPR, but not ST2, was associated with a reduction in tumor number and size with concomitant increase in T_H1 cells in tumors in chemically induced mouse models of colorectal cancer. Therapeutic blockade of TSLP using TSLP-specific monoclonal antibodies effectively inhibited the progression of colorectal tumors in this mouse model. Collectively, these data suggest that TSLP controls the progression of colorectal cancer through regulation of tumor-specific T_reg function and represents a potential therapeutic target that requires further investigation.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

Skin Immunity and Tolerance: Focus on Epidermal Keratinocytes Expressing HLA-G

Although the role of epidermal cells in skin regeneration has been extensively documented, their functions in immunity and tolerance mechanisms are largely underestimated. The aim of the present review was to outline the state of knowledge on resident immune cells of hematopoietic origin hosted in the epidermis, and then to focus on the involvement of keratinocytes in the complex skin immune networks acting in homeostasis and regeneration conditions. Based on this knowledge, the mechanisms of immune tolerance are reviewed. In particular, strategies based on immunosuppression mediated by HLA-G are highlighted, as recent advances in this field open up perspectives in epidermis-substitute bioengineering for temporary and permanent skin replacement strategies.

Thymic stromal lymphopoietin induces adipose loss through sebum hypersecretion

Emerging studies indicate that the immune system can regulate systemic metabolism. Here, we show that thymic stromal lymphopoietin (TSLP) stimulates T cells to induce selective white adipose loss, which protects against obesity, improves glucose metabolism, and mitigates nonalcoholic steatohepatitis. Unexpectedly, adipose loss was not caused by alterations in food intake, absorption, or energy expenditure. Rather, it was induced by the excessive loss of lipids through the skin as sebum. TSLP and T cells regulated sebum release and sebum-associated antimicrobial peptide expression in the steady state. In human skin, TSLP expression correlated directly with sebum-associated gene expression. Thus, we establish a paradigm in which adipose loss can be achieved by means of sebum hypersecretion and uncover a role for adaptive immunity in skin barrier function through sebum secretion.

Chromatin dynamics and epigenetics in skin stress adaptation

The skin, which is constantly exposed to a wide variety of environmental insults, maintains its integrity by rapidly responding to external signals. In the epidermis, most genes are set in transcriptionally poised conditions to prepare for the prompt induction of stress responding genes. Local chromatin dynamics, supported by an interplay between epigenetic regulators and transcription factors, underlies transcriptional responses upon stress exposure. This review summarizes the epigenetic mechanism regulating gene expression and discusses how stress signaling provokes chromatin reprogramming in the epidermis. Epigenetic regulators play a leading role in chromatin remodeling during stress adaptation, and the timely release and restoration of these factors are indispensable for an appropriate skin repair. Evidence for the epigenetic regulation of physiological responses in the skin is accumulating. The epigenetic environment under continuous stress stimuli may lead to the acquisition of stress tolerance, but at the same time, may also induce pathological hypersensitivity. This review describes the current understanding of epigenetics and provides the potential of epigenetic regulation in skin disease development.

Cutaneous innate immune tolerance is mediated by epigenetic control of MAP2K3 by HDAC8/9

The skin typically tolerates exposure to various microbes and chemicals in the environment. Here, we investigated how the epidermis maintains this innate immune tolerance to stimuli that are recognized by Toll-like receptors (TLRs). Loss of tolerance to TLR ligands occurred after silencing of the histone deacetylases (HDACs) HDAC8 and HDAC9 in keratinocytes. Transcriptional analysis identified MAP2K3 as suppressed by HDAC8/9 activity and a potential key intermediary for establishing this tolerance. HDAC8/9 influenced acetylation at H3K9 and H3K27 marks in the MAP2K3 promoter. Proteomic analysis further identified SSRP1 and SUPT16H as associated with HDAC8/9 and responsible for transcriptional elongation of MAP2K3. Silencing of MAP2K3 blocked the capacity of HDAC8/9 to influence cytokine responses. Relevance in vivo was supported by observations of increased MAP2K3 in human inflammatory skin conditions and the capacity of keratinocyte HDAC8/9 to influence dendritic cell maturation and T cell proliferation. Keratinocyte-specific deletion of HDAC8/9 also increased inflammation in mice after exposure to ultraviolet radiation, imiquimod, or Staphylococcus aureus These findings define a mechanism for the epidermis to regulate inflammation in the presence of ubiquitous TLR ligands.

Bone morphogenetic protein signaling regulates skin inflammation via modulating dendritic cell function

BACKGROUND

Bone morphogenetic proteins (BMPs) are members of the TGF-β family that signal via the BMP receptor (BMPR) signaling cascade, distinct from canonical TGF-β signaling. BMP downstream signaling is strongly induced within epidermal keratinocytes in cutaneous psoriatic lesions, and BMP7 instructs monocytic cells to acquire characteristics of psoriasis-associated Langerhans dendritic cells (DCs). Regulatory T (Treg)-cell numbers strongly increase during psoriatic skin inflammation and were recently shown to limit psoriatic skin inflammation. However, the factors mediating Treg-cell accumulation in psoriatic skin currently remain unknown.

OBJECTIVE

We sought to investigate the role of BMP signaling in Treg-cell accumulation in psoriasis.

METHODS

The following methods were used: immunohistology of patients and healthy controls; ex vivo models of Treg-cell generation in the presence or absence of Langerhans cells; analysis of BMP versus canonical TGF-β signaling in DCs and Treg cells; and modeling of psoriatic skin inflammation in mice lacking the BMPR type 1a in CD11c⁺ cells.

RESULTS

We here demonstrated a positive correlation between Treg-cell numbers and epidermal BMP7 expression in cutaneous psoriatic lesions and show that unlike Treg cells from healthy skin, a portion of inflammation-associated Treg cells exhibit constitutive-active BMP signaling. We further found that BMPR signaling licenses inflammation-associated Langerhans cell/DC to gain an enhanced capacity to promote Treg cells via BMPR-mediated CD25 induction and that this effect is associated with reduced skin inflammation.

CONCLUSIONS

Psoriatic lesions are marked by constitutive high BMP7/BMPR signaling in keratinocytes, which instructs inflammatory DCs to gain enhanced Treg-cell-stimulatory activity. Locally secreted BMP7 can directly promote Treg-cell generation through the BMP signaling cascade.

Regulatory T Cells but Not IL-10 Impair Cell-Mediated Immunity in Human Papillomavirus E7+ Hyperplastic Epithelium

High-risk human papillomavirus infection can induce cervical and other intraepithelial neoplasia and invasive cancers. A transgenic mouse expressing keratin 14 promotor-driven HPV16 E7 oncoprotein exhibits epithelial hyperplasia and mimics many features of human papillomavirus-related intraepithelial precancers. We have previously demonstrated that HPV16 E7-mediated epithelial hyperplasia suppresses T helper type 1 responses to intradermally delivered antigen and directs differentiation of CD4⁺ T cells towards a Foxp3⁺ regulatory phenotype (Treg). Here we establish that Foxp3⁺ Treg expansion from a transferred naive T-cell population is driven directly by the hyperplastic skin and is independent of pre-existing immune-modulated lymphocytes. However, depletion of endogenous CD25⁺ Tregs before priming of adoptively transferred T cells significantly improves antigen-specific CD8⁺ T-cell responses but not T helper type 1 responses. Deletion of IL-10 had no effect on Treg expansion, epidermal dendritic cell alteration, and suppression of induced T helper type 1 immunity in HPV16 E7-driven hyperplastic mice. Thus, HPV16 E7-mediated epithelial hyperplasia promotes expansion of peripheral Tregs in response to intradermal immunization that suppress antigen-specific CD8⁺ T-cell responses independently of IL-10, but depletion of these Tregs is not sufficient to restore T helper type 1 immunity.

Functional interactions between Mi-2β and AP1 complexes control response and recovery from skin barrier disruption

Keratinocytes respond to environmental signals by eliciting induction of genes that preserve skin's integrity. Here we show that the transcriptional response to stress signaling is supported by short-lived epigenetic changes. Comparison of chromatin accessibility and transcriptional changes induced by barrier disruption or by loss of the nucleosome remodeler Mi-2β identified their striking convergence in mouse and human keratinocytes. Mi-2β directly repressed genes induced by barrier disruption by restricting AP1-enriched promoter-distal sites, occupied by Mi-2β and JUNB at steady state and by c-JUN after Mi-2β depletion or stress signaling. Barrier disruption led to a modest reduction in Mi-2β expression and a further selective reduction of Mi-2β localization at stress response genes, possibly through competition with activated c-JUN. Consistent with a repressive role at stress response genes, genetic ablation of Mi-2β did not prevent reestablishment of barrier integrity but was required for return to homeostasis. Thus, a competition between Mi-2β-repressive and activating AP1 complexes may permit rapid transcriptional response to and resolution from stress signaling.

TSLP as druggable target - a silver-lining for atopic diseases?

Atopic diseases refer to common allergic inflammatory diseases such as atopic dermatitis (AD), allergic rhinitis (AR), and allergic asthma (AA). AD often develops in early childhood and may herald the onset of other allergic disorders such as food allergy (FA), AR, and AA. This progression of the disease is also known as the atopic march, and it goes hand in hand with a significantly impaired quality of life as well as a significant economic burden. Atopic diseases usually are considered as T helper type 2 (Th2) cell-mediated inflammatory diseases. Thymic stromal lymphopoietin (TSLP), an epithelium-derived pro-inflammatory cytokine, activates distinct immune and non-immune cells. It has been shown to be a master regulator of type 2 immune responses and atopic diseases. In experimental settings, the inhibition or knockout of TSLP signaling has shown great therapeutic potential. This, in conjunction with the increasing knowledge about the central role of TSLP in the pathogenesis of atopic diseases, has sparked an interest in TSLP as a druggable target. In this review, we will discuss the autocrine and paracrine effects of TSLP, how it regulates the tissue microenvironment and drives atopic diseases, which provide the rationale for the increasing interest in TSLP as a druggable target.

Dendritic cells and the skin environment

The skin is inhabited by several immune cell populations that serve as a first line of defence against pathogen invasion. Amongst these populations are dendritic cells, which play an essential sentinel function by taking up antigen or infectious agents and transporting them to the lymph node for T cell recognition and the priming of immune responses. In this review, we briefly summarise recent advances showing how skin dendritic cells are connected to a network of epithelial and stromal cells, which provide structural support, growth factors, spatial cues, contact with the external environment and the skin microbiome, and favour interactions with other immune cells. We propose that this network creates a unique skin environment that may condition dendritic cell phenotype and function.

Regulatory T cells in skin injury: At the crossroads of tolerance and tissue repair

Skin injury is a highly inflammatory process that is carefully regulated to mitigate tissue damage and allow for proper barrier repair. Regulatory T cells (Tregs) are crucial coordinators of the immune response to injury in several organs. Here, we review the emerging role of Tregs in facilitating skin repair after injury. We focus on recently discovered interactions between lymphocytes and nonhematopoietic cells during wound healing and discuss how these interactions are regulated both by "classical" suppressive mechanisms of Tregs and by "nonclassical" reparative Treg functions.

Anti-TSLP antibodies: Targeting a master regulator of type 2 immune responses

TSLP is an epithelial cell-derived cytokine synthesized in response to various stimuli, including protease allergens and microorganisms like viruses and bacteria. Biological functions of TSLP require heterodimer formation between the TSLP receptor (TSLPR) and IL-7 receptor-α, which polarize dendritic cells to induce type 2 inflammation and directly expand and/or activate Th2 cells, group 2 innate lymphoid cells, basophils, and other immune cells. TSLP is thus considered a master regulator of type 2 immune responses at the barrier surfaces of skin and the respiratory/gastrointestinal tract. Indeed, genetic, experimental, and clinical evidence suggests that the TSLP-TSLPR pathway is associated with the pathogenesis of allergic diseases such as atopic dermatitis (AD) and asthma. Tezepelumab (AMG-157/MEDI9929) is a human anti-TSLP antibody that prevents TSLP-TSLPR interactions. A phase 2 trial for moderate to severe AD showed that a greater but not statistically significant percentage of tezepelumab-treated patients showed clinical improvements compared to the placebo group. A phase 2 trial for uncontrolled, severe asthma showed significant decreases in asthma exacerbation rate and improved pulmonary function and asthma control for tezepelumab-treated patients. Levels of biomarkers of type 2 inflammation, such as blood/sputum eosinophil counts and fraction of exhaled nitric oxide decreased, however, clinical efficacy was observed irrespective of the baseline levels of these biomarkers. A blockade of the TSLP-TSLPR pathway likely will exert significant clinical effects on AD, asthma, and other allergic diseases. The efficacy of anti-TSLP antibodies compared to other biologics needs to be further examined.

Fucoxanthin Ameliorates Atopic Dermatitis Symptoms by Regulating Keratinocytes and Regulatory Innate Lymphoid Cells

Fucoxanthin (FX) is a xanthophyll that is contained abundantly in marine plants. The biological action of FX includes its antioxidant and anti-lipogenic activities, while the precise action of its mechanisms on skin cells has not yet been clarified. The current study examined the effect of FX in comparison with tacrolimus (TAC) on NC/Nga mice, which are an atopic dermatitis (AD) model. FX topical treatment dramatically ameliorated itching behavior over the TAC treatment, which was insufficient for improvement of AD symptoms. In Nc/Nga mice, FX or TAC applied to the skin inhibited eosinophil infiltration with decreased expression of Il-33. FX also stimulated Il-2, Il-5, Il-13, Il-10, and TGF-β expression levels, and Sca1⁺Il-10⁺TGF-β⁺ regulatory innate lymphoid cells (ILCreg) were dominantly observed in FX treated skin epidermal keratinocytes and dermal layers. This combined evidence demonstrated that FX exerts anti-inflammatory effects on keratinocytes and ameliorates AD symptoms by regulating ILCreg to normalize immune responses in an atopic dermatitis model.

Deriving a Boolean dynamics to reveal macrophage activation with in vitro temporal cytokine expression profiles

BACKGROUND

Macrophages show versatile functions in innate immunity, infectious diseases, and progression of cancers and cardiovascular diseases. These versatile functions of macrophages are conducted by different macrophage phenotypes classified as classically activated macrophages and alternatively activated macrophages due to different stimuli in the complex in vivo cytokine environment. Dissecting the regulation of macrophage activations will have a significant impact on disease progression and therapeutic strategy. Mathematical modeling of macrophage activation can improve the understanding of this biological process through quantitative analysis and provide guidance to facilitate future experimental design. However, few results have been reported for a complete model of macrophage activation patterns.

RESULTS

We globally searched and reviewed literature for macrophage activation from PubMed databases and screened the published experimental results. Temporal in vitro macrophage cytokine expression profiles from published results were selected to establish Boolean network models for macrophage activation patterns in response to three different stimuli. A combination of modeling methods including clustering, binarization, linear programming (LP), Boolean function determination, and semi-tensor product was applied to establish Boolean networks to quantify three macrophage activation patterns. The structure of the networks was confirmed based on protein-protein-interaction databases, pathway databases, and published experimental results. Computational predictions of the network evolution were compared against real experimental results to validate the effectiveness of the Boolean network models.

CONCLUSION

Three macrophage activation core evolution maps were established based on the Boolean networks using Matlab. Cytokine signatures of macrophage activation patterns were identified, providing a possible determination of macrophage activations using extracellular cytokine measurements.

Cytokine/chemokine profiles in squamous cell carcinoma correlate with precancerous and cancerous disease stage

Actinic Keratosis (AK), Intraepidermal Carcinoma (IEC), and Squamous Cell Carcinoma (SCC) are generally considered to be advancing stages of the same disease spectrum. However, while AK often regress spontaneously, and IEC often regress in response to immune-activating treatments, SCC typically do not regress. Therefore, it is vital to define whether fundamental immunological changes occur during progression to SCC. Here we show that proinflammatory cytokine expression, chemokine expression, and immune cell infiltration density change during progression to SCC. Our findings suggest a switch from predominantly proinflammatory cytokine production to chemokine production is a key feature of progression from precancer to cancer. Together, these observations propose a model that can underpin current research and open new avenues of exploration into the clinical significance of these profiles with respect to immunotherapeutic or other treatment outcomes.

Role of bulge epidermal stem cells and TSLP signaling in psoriasis

Psoriasis is a common inflammatory skin disease involving a cross‐talk between epidermal and immune cells. The role of specific epidermal stem cell populations, including hair follicle stem cells (HF‐SCs) in psoriasis is not well defined. Here, we show reduced expression of c‐JUN and JUNB in bulge HF‐SCs in patients with scalp psoriasis. Using lineage tracing in mouse models of skin inflammation with inducible deletion of c‐Jun and JunB, we found that mutant bulge HF‐SCs initiate epidermal hyperplasia and skin inflammation. Mechanistically, thymic stromal lymphopoietin (TSLP) was identified in mutant cells as a paracrine factor stimulating proliferation of neighboring non‐mutant epidermal cells, while mutant inter‐follicular epidermal (IFE) cells are lost over time. Blocking TSLP in psoriasis‐like mice reduced skin inflammation and decreased epidermal proliferation, VEGFα expression, and STAT5 activation. These findings unravel distinct roles of HF‐SCs and IFE cells in inflammatory skin disease and provide novel mechanistic insights into epidermal cell interactions in inflammation.

Choreographing Immunity in the Skin Epithelial Barrier

The skin interfaces with the external environment and is home to a myriad of immune cells that patrol the barrier to ward off harmful agents and aid in tissue repair. The formation of the cutaneous immune arsenal begins before birth and evolves throughout our lifetime, incorporating exogenous cues from microbes and inflammatory encounters, to achieve optimal fitness and function. Here, we discuss the context-specific signals that drive productive immune responses in the skin epithelium, highlighting key modulators of these reactions, including hair follicles, neurons, and commensal microbes. We thus also discuss the causal and mechanistic underpinning of inflammatory skin diseases that have been revealed in recent years. Finally, we discuss the non-canonical functions of cutaneous immune cells including their burgeoning role in epithelial regeneration and repair. The rapidly growing field of cutaneous immunity is revealing immune mechanisms and functions that can be harnessed to boost skin health and treat disease.

Sonic Hedgehog signaling limits atopic dermatitis via Gli2-driven immune regulation

Hedgehog (Hh) proteins regulate development and tissue homeostasis, but their role in atopic dermatitis (AD) remains unknown. We found that on induction of mouse AD, Sonic Hedgehog (Shh) expression in skin and Hh pathway action in skin T cells were increased. Shh signaling reduced AD pathology and the levels of Shh expression determined disease severity. Hh-mediated transcription in skin T cells in AD-induced mice increased Treg populations and their suppressive function through increased active transforming growth factor–β (TGF-β) in Treg signaling to skin T effector populations to reduce disease progression and pathology. RNA sequencing of skin CD4⁺ T cells from AD-induced mice demonstrated that Hh signaling increased expression of immunoregulatory genes and reduced expression of inflammatory and chemokine genes. Addition of recombinant Shh to cultures of naive human CD4⁺ T cells in iTreg culture conditions increased FOXP3 expression. Our findings establish an important role for Shh upregulation in preventing AD, by increased Gli-driven, Treg cell–mediated immune suppression, paving the way for a potential new therapeutic strategy.

Epithelial cell-derived cytokines: more than just signaling the alarm

The epithelial cell-derived cytokines thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 are central regulators of type 2 immunity, which drives a broad array of allergic responses. Often characterized as "alarmins" that are released by the barrier epithelium in response to external insults, these epithelial cell-derived cytokines were initially thought to act only early in allergic inflammation. Indeed, TSLP can condition dendritic cells to initiate type 2 responses, and IL-33 may influence susceptibility to asthma through its role in establishing the immune environment in the perinatal lungs. However, TSLP, IL-33, and IL-25 all regulate a broad spectrum of innate immune cell populations and are particularly potent in eliciting and activating type 2 innate lymphoid cells (ILC2s) that may act throughout allergic inflammation. Recent data suggest that a TSLP/ILC axis may mediate steroid resistance in asthma. Recent identification of memory Th2 cell subsets that are characterized by high receptor expression for TSLP, IL-33, and IL-25 further supports a role for these cytokines in allergic exacerbations. There is therefore growing interest in developing biologics that target TSLP, IL-33, and IL-25. This Review provides an overview of TSLP, IL-33, and IL-25 and the development of blocking antibodies that target these epithelial cell-derived cytokines.

Adventitial Stromal Cells Define Group 2 Innate Lymphoid Cell Tissue Niches

Type 2 lymphocytes promote both physiologic tissue remodeling and allergic pathology, yet their physical tissue niches are poorly described. Here, we used quantitative imaging to define the tissue niches of group 2 innate lymphoid cells (ILC2s), which are critical instigators of type 2 immunity. We identified a dominant adventitial niche around lung bronchi and larger vessels in multiple tissues, where ILC2s localized with subsets of dendritic and regulatory T cells. However, ILC2s were most intimately associated with adventitial stromal cells (ASCs), a mesenchymal fibroblast-like subset that expresses interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP). In vitro, ASCs produced TSLP that supported ILC2 accumulation and activation. ILC2s and IL-13 drove reciprocal ASC expansion and IL-33 expression. During helminth infection, ASC depletion impaired lung ILC2 and Th2 cell accumulation and function, which are in part dependent on ASC-derived IL-33. These data indicate that adventitial niches are conserved sites where ASCs regulate type 2 lymphocyte expansion and function.

Taking the lead - how keratinocytes orchestrate skin T cell immunity

The skin comprises a complex coordinated system of epithelial tissue cells and immune cells that ensure adequate immune reactions against trauma, toxins and pathogens, while maintaining tissue homeostasis. Keratinocytes form the outermost barrier of the skin, and sense changes in barrier integrity, intrusion of microbial components and stress molecules. Thus, they act as sentinels that continuously communicate the status of the organ to the cutaneous immune system. Upon damage the keratinocytes initiate a pro-inflammatory signaling cascade that leads to the activation of resident immune cells. Simultaneously, the tissue mediates and supports immune-suppressive functions to contain inflammation locally. After resolution of inflammation, the skin provides a niche for regulatory and effector memory T cells that can quickly respond to reoccurring antigens. In this review we discuss the central role of keratinocyte-derived signals in controlling cutaneous T cell immunity.

The atopic march: current insights into skin barrier dysfunction and epithelial cell-derived cytokines

Atopic dermatitis often precedes the development of other atopic diseases. The atopic march describes this temporal relationship in the natural history of atopic diseases. Although the pathophysiological mechanisms that underlie this relationship are poorly understood, epidemiological and genetic data have suggested that the skin might be an important route of sensitization to allergens. Animal models have begun to elucidate how skin barrier defects can lead to systemic allergen sensitization. Emerging data now suggest that epithelial cell-derived cytokines such as thymic stromal lymphopoietin (TSLP), IL-33, and IL-25 may drive the progression from atopic dermatitis to asthma and food allergy. This review focuses on current concepts of the role of skin barrier defects and epithelial cell-derived cytokines in the initiation and maintenance of allergic inflammation and the atopic march.

A tumor-myeloid cell axis, mediated via the cytokines IL-1α and TSLP, promotes the progression of breast cancer

Tumors actively manipulate the immune response through the production of factors that attract immune cells and subsequently alter their ability to recognize and effectively remove the tumor. While this immune evasion mechanism is an important aspect of tumor survival, the factors that serve as primary growth factors for the tumor are less understood. Here, we demonstrated a novel mechanism by which breast cancer cells manipulate tumor-infiltrating myeloid cells to maintain their survival. Tumor-derived interleukin 1α (IL-1α), acting on infiltrating myeloid cells, induced the expression of a critical tumor survival factor, the cytokine thymic stromal lymphopoietin (TSLP). TSLP promoted the survival of the tumor cells through induction of Bcl-2 expression. TSLP signaling was also required for metastasis to the lung. These studies define a novel IL-1α–TSLP-mediated crosstalk between tumor-infiltrating myeloid cells and tumor cells in the control of metastatic breast cancer.

Cytokine Signaling in the Development and Homeostasis of Regulatory T cells

Cytokine signaling is indispensable for regulatory T-cell (Treg) development in the thymus, and also influences the homeostasis, phenotypic diversity, and function of Tregs in the periphery. Because Tregs are required for establishment and maintenance of immunological self-tolerance, investigating the role of cytokines in Treg biology carries therapeutic potential in the context of autoimmune disease. This review discusses the potent and diverse influences of interleukin (IL)-2 signaling on the Treg compartment, an area of knowledge that has led to the use of low-dose IL-2 as a therapy to reregulate autoaggressive immune responses. Evidence suggesting Treg-specific impacts of the cytokines transforming growth factor β (TGF-β), IL-7, thymic stromal lymphopoietin (TSLP), IL-15, and IL-33 is also presented. Finally, we consider the technical challenges and knowledge limitations that must be overcome to bring other cytokine-based, Treg-targeted therapies into clinical use.

Antigen-specific Treg cells in immunological tolerance: implications for allergic diseases

Allergic diseases are chronic inflammatory disorders in which there is failure to mount effective tolerogenic immune responses to inciting allergens. The alarming rise in the prevalence of allergic diseases in recent decades has spurred investigations to elucidate the mechanisms of breakdown in tolerance in these disorders and means of restoring it. Tolerance to allergens is critically dependent on the generation of allergen-specific regulatory T (Treg) cells, which mediate a state of sustained non-responsiveness to the offending allergen. In this review, we summarize recent advances in our understanding of mechanisms governing the generation and function of allergen-specific Treg cells and their subversion in allergic diseases. We will also outline approaches to harness allergen-specific Treg cell responses to restore tolerance in these disorders.

HPV16E7-Induced Hyperplasia Promotes CXCL9/10 Expression and Induces CXCR3+ T-Cell Migration to Skin

Chemokines regulate tissue immunity by recruiting specific subsets of immune cells. Mice expressing the E7 protein of human papilloma virus 16 as a transgene from a keratin 14 promoter (K14.E7) show increased epidermal and dermal lymphocytic infiltrates, epidermal hyperplasia, and suppressed local immunity. Here, we show that CXCL9 and CXCL10 are overexpressed in non-hematopoietic cells in skin of K14.E7 mice when compared with non-transgenic animals, and recruit CXCR3⁺ lymphocytes to the hyperplastic skin. Overexpression of CXCL9 and CXCL10 is not observed in E7 transgenic mice with mutated Rb gene whose protein product cannot interact with E7 (K14.E7xRb^ΔL/ΔL) and in consequence lack hyperplastic epithelium. CXCR3⁺ T cells are preferentially recruited by CXCL9 and CXCL10 in supernatants of K14.E7 but not K14.E7xRb^ΔL/ΔL skin cultures in vitro. CXCR3 signalling promotes infiltration of a subset of effector T lymphocytes that enables donor lymphocyte deficient, E7-expressing skin graft rejection. Taken together, this suggests that recruitment of CXCR3⁺ T cells can be an important factor in the rejection of precancerous skin epithelium providing they can overcome local immunosuppressive mechanisms driven by skin-resident lymphocytes.

Secreted immunoregulatory proteins in the skin

The skin, thought initially to protect the body passively from pathogenic organisms and other environmental insults, is now recognised additionally as a sophisticated immune organ that actively regulates local immunity. Studies linking local innate and adaptive immunity to skin health and disease have revealed a complex network of cell communication and cytokine signalling. Here, we review the last 10 years of literature on this topic, and its relevance to skin immunity.

TSLP is a direct trigger for T cell migration in filaggrin-deficient skin equivalents

Mutations in the gene encoding for filaggrin (FLG) are major predisposing factors for atopic dermatitis (AD). Besides genetic predisposition, immunological dysregulations considerably contribute to its pathophysiology. For example, thymic stromal lymphopoietin (TSLP) is highly expressed in lesional atopic skin and significantly contributes to the pathogenesis of AD by activating dendritic cells that then initiate downstream effects on, for example, T cells. However, little is known about the direct interplay between TSLP, filaggrin-deficient skin and other immune cells such as T lymphocytes. In the present study, FLG knockdown skin equivalents, characterised by intrinsically high TSLP levels, were exposed to activated CD4⁺ T cells. T cell exposure resulted in an inflammatory phenotype of the skin equivalents. Furthermore, a distinct shift from a Th1/Th17 to a Th2/Th22 profile was observed following exposure of T cells to filaggrin-deficient skin equivalents. Interestingly, TSLP directly stimulated T cell migration exclusively in filaggrin-deficient skin equivalents even in the absence of dendritic cells, indicating a hitherto unknown role of TSLP in the pathogenesis of AD.