Evidence that vitamin D(3) promotes mast cell-dependent reduction of chronic UVB-induced skin pathology in mice

Vitamin D and allergic diseases

In recent years, the relationship between vitamin D and allergic diseases has received widespread attention. As a fat-soluble vitamin, vitamin D plays a crucial role in regulating the immune system and may influence the onset and progression of diseases such as atopic dermatitis, allergic rhinitis, and asthma. To understand the underlying mechanisms, we have summarized the current research on the association between vitamin D and allergic diseases. We also discuss the impact of vitamin D on the immune system and its role in the course of allergic diseases, particularly focusing on how vitamin D supplementation affects the treatment outcomes of these conditions. We aim to provide a theoretical basis and practical guidance for optimizing the management and treatment of allergic diseases by modulating vitamin D levels.

Vitamin D Influences the Activity of Mast Cells in Allergic Manifestations and Potentiates Their Effector Functions against Pathogens

Mast cells (MCs) are abundant at sites exposed to the external environment and pathogens. Local activation of these cells, either directly via pathogen recognition or indirectly via interaction with other activated immune cells and results in the release of pre-stored mediators in MC granules. The release of these pre-stored mediators helps to enhance pathogen clearance. While MCs are well known for their protective role against parasites, there is also significant evidence in the literature demonstrating their ability to respond to viral, bacterial, and fungal infections. Vitamin D is a fat-soluble vitamin and hormone that plays a vital role in regulating calcium and phosphorus metabolism to maintain skeletal homeostasis. Emerging evidence suggests that vitamin D also has immunomodulatory properties on both the innate and adaptive immune systems, making it a critical regulator of immune homeostasis. Vitamin D binds to its receptor, called the vitamin D receptor (VDR), which is present in almost all immune system cells. The literature suggests that a vitamin D deficiency can activate MCs, and vitamin D is necessary for MC stabilization. This manuscript explores the potential of vitamin D to regulate MC activity and combat pathogens, with a focus on its ability to fight viruses.

The Role of Vitamins in the Pathogenesis of Asthma

Vitamins play a crucial role in the proper functioning of organisms. Disturbances of their levels, seen as deficiency or excess, enhance the development of various diseases, including those of the cardiovascular, immune, or respiratory systems. The present paper aims to summarize the role of vitamins in one of the most common diseases of the respiratory system, asthma. This narrative review describes the influence of vitamins on asthma and its main symptoms such as bronchial hyperreactivity, airway inflammation, oxidative stress, and airway remodeling, as well as the correlation between vitamin intake and levels and the risk of asthma in both pre- and postnatal life.

COVID-19 and Multiple Sclerosis: A Complex Relationship Possibly Aggravated by Low Vitamin D Levels

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an exceptionally transmissible and pathogenic coronavirus that appeared at the end of 2019 and triggered a pandemic of acute respiratory disease, known as coronavirus disease 2019 (COVID-19). COVID-19 can evolve into a severe disease associated with immediate and delayed sequelae in different organs, including the central nervous system (CNS). A topic that deserves attention in this context is the complex relationship between SARS-CoV-2 infection and multiple sclerosis (MS). Here, we initially described the clinical and immunopathogenic characteristics of these two illnesses, accentuating the fact that COVID-19 can, in defined patients, reach the CNS, the target tissue of the MS autoimmune process. The well-known contribution of viral agents such as the Epstein-Barr virus and the postulated participation of SARS-CoV-2 as a risk factor for the triggering or worsening of MS are then described. We emphasize the contribution of vitamin D in this scenario, considering its relevance in the susceptibility, severity and control of both pathologies. Finally, we discuss the experimental animal models that could be explored to better understand the complex interplay of these two diseases, including the possible use of vitamin D as an adjunct immunomodulator to treat them.

Focus on mast cells in the tumor microenvironment: Current knowledge and future directions

Mast cells (MCs) are crucial cells participating in both innate and adaptive immune processes that play important roles in protecting human health and in the pathophysiology of various diseases, such as allergies, cardiovascular diseases, and autoimmune diseases. In the context of tumors, MCs are a non-negligible population of immune cells in the tumor microenvironment (TME). In most tumor types, MCs accumulate in both the tumor tissue and the surrounding tissue. MCs interact with multiple components of the TME, affecting TME remodeling and the tumor cell fate. However, controversy persists regarding whether MCs contribute to tumor progression or trigger an anti-tumor immune response. This review focuses on the context of the TME to explore the specific properties and functions of MCs and discusses the crosstalk that occurs between MCs and other components of the TME, which affect tumor angiogenesis and lymphangiogenesis, invasion and metastasis, and tumor immunity through different mechanisms. We also anticipate the potential role of MCs in cancer immunotherapy, which might expand upon the success achieved with existing cancer therapies.

Utilizing mast cells in a positive manner to overcome inflammatory and allergic diseases

Mast cells (MCs) are immune cells widely distributed in the body, accompanied by diverse phenotypes and functions. Committed mast cell precursors (MCPs) leave the bone marrow and enter the blood circulation, homing to peripheral sites under the control of various molecules from different microenvironments, where they eventually differentiate and mature. Partly attributable to the unique maturation mechanism, MCs display high functional heterogeneity and potentially plastic phenotypes. High plasticity also means that MCs can exhibit different subtypes to cope with different microenvironments, which we call “the peripheral immune education system”. Under the peripheral immune education system, MCs showed a new character from previous cognition in some cases, namely regulation of allergy and inflammation. In this review, we focus on the mucosal tissues, such as the gastrointestinal tract, to gain insights into the mechanism underlying the migration of MCs to the gut or other organs and their heterogeneity, which is driven by different microenvironments. In particular, the immunosuppressive properties of MCs let us consider that positively utilizing MCs may be a new way to overcome inflammatory and allergic disorders.

Mast Cells and Vitamin D Status: A Clinical and Biological Link in the Onset of Allergy and Bone Diseases

The immune system is made up by an extremely composite group of cells, whose regulated and harmonious activity is fundamental to maintain health. The mast cells are an essential effector of inflammatory response which is characterized by a massive release of mediators accumulated in cytoplasmic secretory granules. However, beyond the effects on immune response, mast cells can modify bone metabolism and are capable of intervening in the genesis of pathologies such as osteoporosis and osteopenia. Vitamin D is recognized to induce changes in bone metabolism, but it is also able to influence immune response, suppressing mast cell activation and IgE synthesis from B cells and increasing the number of dendritic cells and IL-10-generating regulatory T cells. Vitamin D deficit has been reported to worsen sensitization and allergic manifestations in several different experimental models. However, in clinical situations, contradictory findings have been described concerning the correlation between allergy and vitamin D deficit. The aim of this review was to analyze the close relationships between mast cells and vitamin D, which contribute, through the activation of different molecular or cellular activation pathways, to the determination of bone pathologies and the onset of allergic diseases.

Novel Insights Into the Immune-Regulatory Functions of Mast Cells in the Cutaneous Immune Response

Skin is a frontline organ that is continuously exposed to external stimuli, including pathogens. Various immune cells reside in the skin under physiological conditions and protect the body from the entry of pathogens/antigens by interacting with each other and orchestrating diverse cutaneous immune responses. To avoid unnecessary inflammation and tissue damage during the elimination of external pathogens and antigens, skin possesses regulatory systems that fine-tune these immune reactions. Mast cells (MCs) are one of the skin-resident immune cell populations that play both effector and regulatory functions in the cutaneous immune response. So far, the interleukin-10-mediated mechanisms have mostly been investigated as the regulatory mechanisms of MCs. Recent studies have elucidated other regulatory mechanisms of MCs, such as the maintenance of regulatory T/B cells and the programmed cell death protein-1/programmed cell death-ligand 1-mediated inhibitory pathway. These regulatory pathways of MCs have been suggested to play important roles in limiting the excessive inflammation in inflammatory skin diseases, such as contact and atopic dermatitis. The regulatory functions of MCs may also be involved in the escape mechanisms of antitumor responses in skin cancers, such as melanoma. Understanding and controlling the regulatory functions of skin MCs may lead to novel therapeutic strategies for inflammatory skin diseases and skin cancers.

Exploring the Immune-Boosting Functions of Vitamins and Minerals as Nutritional Food Bioactive Compounds: A Comprehensive Review

Food components have long been recognized to play a fundamental role in the growth and development of the human body, conferring protective functionalities against foreign matter that can be severe public health problems. Micronutrients such as vitamins and minerals are essential to the human body, and individuals must meet their daily requirements through dietary sources. Micronutrients act as immunomodulators and protect the host immune response, thus preventing immune evasion by pathogenic organisms. Several experimental investigations have been undertaken to appraise the immunomodulatory functions of vitamins and minerals. Based on these experimental findings, this review describes the immune-boosting functionalities of micronutrients and the mechanisms of action through which these functions are mediated. Deficiencies of vitamins and minerals in plasma concentrations can lead to a reduction in the performance of the immune system functioning, representing a key contributor to unfavorable immunological states. This review provides a descriptive overview of the characteristics of the immune system and the utilization of micronutrients (vitamins and minerals) in preventative strategies designed to reduce morbidity and mortality among patients suffering from immune invasions or autoimmune disorders.

Immunopathogenesis and management of polymorphic light eruption

Polymorphic light eruption (PLE) is the most common immunologically mediated photodermatosis, demonstrating many abnormalities caused by critical failure of ultraviolet (UV)-induced immunosuppression. The unique expression of antimicrobial peptides in PLE, which is most likely determined by alteration of microbiome components upon UV exposure, implicates their possible triggering role and pathogenic significance in the eruption. The review aims to clarify current knowledge regarding the immunological disturbances correlated with PLE that serve a base for better understanding of molecular pathogenesis of the disease and the development of new therapeutic strategies. Preventive treatment with broad-spectrum suncreens and sunscreens containing DNA repair enzymes, as well as natural photohardening with graduate exposure to sunlight in early spring could be sufficient in milder cases. Antioxidants and topical calcipotriol are promising approach for adjuvant prevention. Phototherapy, mainly with narrow band UVB rays, is more appropriate method in severe cases of the disease. The established treatment options for PLE include local and systemic glucocorticoids, systemic nonsedative antihistamines for itch relief, and rarely, immunosuppressive drugs in the refractory cases. Like medical photohardening, afamelanotide has the potential of photoprotection by inducing a melanization of the skin. Afamelanotide is believed to be a possible new treatment option for very severe and refractory cases of PLE. Targeting the main pruritogenic cytokine, IL-31, opens a new road for the development of novel therapeutic approaches to combat moderate and severe itching in cases of PLE with intense pruritus.

The emerging role of mast cells in skin cancers: involved cellular and molecular mechanisms

Skin cancers are the most common cancers worldwide. They can be divided into nonmelanoma skin cancers (NMSC) including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and less common lymphomas and merkel cell carcinoma, and melanomas. Melanomas comprise less than 5% of skin cancer rate but are responsible for more than 90% of skin cancer death. Mast cells (MCs) are multifunctional cells that play an important role in inflammatory and allergic reactions. They attract other key players of the immune system by releasing cytokines. Healthy human skin comprises MCs under physiological status, and the number can increase under certain conditions including skin malignancies postulating their possible role in pathogenesis of and immunity against skin cancers. MCs respond to cytokines released by tumor stromal cells, release mediators (including histamine and tryptase), and induce the neovascularization, degradation of extracellular matrix (ECM), and induce mitogenesis. However, MCs may use molecular mechanisms to exert immunosuppressive activity including releasing complement C3, lower expression of CD40L, and overexpression of enzymes with vitamin D3 metabolizing activity including CYP27A1 and CYP27B1. This review summarizes the current knowledge on the role of MCs in pathogenesis and immunity against skin cancers.

Essential sufficiency of zinc, ω-3 polyunsaturated fatty acids, vitamin D and magnesium for prevention and treatment of COVID-19, diabetes, cardiovascular diseases, lung diseases and cancer

Despite the development of a number of vaccines for COVID-19, there remains a need for prevention and treatment of the virus SARS-CoV-2 and the ensuing disease COVID-19. This report discusses the key elements of SARS-CoV-2 and COVID-19 that can be readily treated: viral entry, the immune system and inflammation, and the cytokine storm. It is shown that the essential nutrients zinc, ω-3 polyunsaturated fatty acids (PUFAs), vitamin D and magnesium provide the ideal combination for prevention and treatment of COVID-19: prevention of SARS-CoV-2 entry to host cells, prevention of proliferation of SARS-CoV-2, inhibition of excessive inflammation, improved control of the regulation of the immune system, inhibition of the cytokine storm, and reduction in the effects of acute respiratory distress syndrome (ARDS) and associated non-communicable diseases. It is emphasized that the non-communicable diseases associated with COVID-19 are inherently more prevalent in the elderly than the young, and that the maintenance of sufficiency of zinc, ω-3 PUFAs, vitamin D and magnesium is essential for the elderly to prevent the occurrence of non-communicable diseases such as diabetes, cardiovascular diseases, lung diseases and cancer. Annual checking of levels of these essential nutrients is recommended for those over 65 years of age, together with appropriate adjustments in their intake, with these services and supplies being at government cost. The cost:benefit ratio would be huge as the cost of the nutrients and the testing of their levels would be very small compared with the cost savings of specialists and hospitalization.

IL-10 in Mast Cell-Mediated Immune Responses: Anti-Inflammatory and Proinflammatory Roles

Mast cells (MCs) play critical roles in Th2 immune responses, including the defense against parasitic infections and the initiation of type I allergic reactions. In addition, MCs are involved in several immune-related responses, including those in bacterial infections, autoimmune diseases, inflammatory bowel diseases, cancers, allograft rejections, and lifestyle diseases. Whereas antigen-specific IgE is a well-known activator of MCs, which express FcεRI on the cell surface, other receptors for cytokines, growth factors, pathogen-associated molecular patterns, and damage-associated molecular patterns also function as triggers of MC stimulation, resulting in the release of chemical mediators, eicosanoids, and various cytokines. In this review, we focus on the role of interleukin (IL)-10, an anti-inflammatory cytokine, in MC-mediated immune responses, in which MCs play roles not only as initiators of the immune response but also as suppressors of excessive inflammation. IL-10 exhibits diverse effects on the proliferation, differentiation, survival, and activation of MCs in vivo and in vitro. Furthermore, IL-10 derived from MCs exerts beneficial and detrimental effects on the maintenance of tissue homeostasis and in several immune-related diseases including contact hypersensitivity, auto-immune diseases, and infections. This review introduces the effects of IL-10 on various events in MCs, and the roles of MCs in IL-10-related immune responses and as a source of IL-10.

The dark side of daylight: photoaging and the tumor microenvironment in melanoma progression

Continued thinning of the atmospheric ozone, which protects the earth from damaging ultraviolet radiation (UVR), will result in elevated levels of UVR reaching the earth's surface, leading to a drastic increase in the incidence of skin cancer. In addition to promoting carcinogenesis in skin cells, UVR is a potent extrinsic driver of age-related changes in the skin known as "photoaging." We are in the preliminary stages of understanding of the role of intrinsic aging in melanoma, and the tumor-permissive effects of photoaging on the skin microenvironment remain largely unexplored. In this Review, we provide an overview of the impact of UVR on the skin microenvironment, addressing changes that converge or diverge with those observed in intrinsic aging. Intrinsic and extrinsic aging promote phenotypic changes to skin cell populations that alter fundamental processes such as melanogenesis, extracellular matrix deposition, inflammation, and immune response. Given the relevance of these processes in cancer, we discuss how photoaging might render the skin microenvironment permissive to melanoma progression.

Sex Differences in Photoprotective Responses to 1,25-Dihydroxyvitamin D3 in Mice Are Modulated by the Estrogen Receptor-β

Susceptibility to photoimmune suppression and photocarcinogenesis is greater in male than in female humans and mice and is exacerbated in female estrogen receptor-beta knockout (ER-β-/-) mice. We previously reported that the active vitamin D hormone, 1,25-dihydroxyvitamin D3 (1,25(OH)2D), applied topically protects against the ultraviolet radiation (UV) induction of cutaneous cyclobutane pyrimidine dimers (CPDs) and the suppression of contact hypersensitivity (CHS) in female mice. Here, we compare these responses in female versus male Skh:hr1 mice, in ER-β-/-/-- versus wild-type C57BL/6 mice, and in female ER-blockaded Skh:hr1 mice. The induction of CPDs was significantly greater in male than female Skh:hr1 mice and was more effectively reduced by 1,25(OH)2D in female Skh:hr1 and C57BL/6 mice than in male Skh:hr1 or ER-β-/- mice, respectively. This correlated with the reduced sunburn inflammation due to 1,25(OH)2D in female but not male Skh:hr1 mice. Furthermore, although 1,25(OH)2D alone dose-dependently suppressed basal CHS responses in male Skh:hr1 and ER-β-/- mice, UV-induced immunosuppression was universally observed. In female Skh:hr1 and C57BL/6 mice, the immunosuppression was decreased by 1,25(OH)2D dose-dependently, but not in male Skh:hr1, ER-β-/-, or ER-blockaded mice. These results reveal a sex bias in genetic, inflammatory, and immune photoprotection by 1,25(OH)2D favoring female mice that is dependent on the presence of ER-β.

Vitamin D and Immune Regulation: Antibacterial, Antiviral, Anti-Inflammatory

Regulation of immune function continues to be one of the most well-recognized extraskeletal actions of vitamin D. This stemmed initially from the discovery that antigen presenting cells such as macrophages could actively metabolize precursor 25-hydroxyvitamin D (25D) to active 1,25-dihydroxyvitamin D (1,25D). Parallel observation that activated cells from the immune system expressed the intracellular vitamin D receptor (VDR) for 1,25D suggested a potential role for vitamin D as a localized endogenous modulator of immune function. Subsequent studies have expanded our understanding of how vitamin D exerts effects on both the innate and adaptive arms of the immune system. At an innate level, intracrine synthesis of 1,25D by macrophages and dendritic cells stimulates expression of antimicrobial proteins such as cathelicidin, as well as lowering intracellular iron concentrations via suppression of hepcidin. By potently enhancing autophagy, 1,25D may also play an important role in combatting intracellular pathogens such as M. tuberculosis and viral infections. Local synthesis of 1,25D by macrophages and dendritic cells also appears to play a pivotal role in mediating T-cell responses to vitamin D, leading to suppression of inflammatory T helper (Th)1 and Th17 cells, and concomitant induction of immunotolerogenic T-regulatory responses. The aim of this review is to provide an update on our current understanding of these prominent immune actions of vitamin D, as well as highlighting new, less well-recognized immune effects of vitamin D. The review also aims to place this mechanistic basis for the link between vitamin D and immunity with studies in vivo that have explored a role for vitamin D supplementation as a strategy for improved immune health. This has gained prominence in recent months with the global coronavirus disease 2019 health crisis and highlights important new objectives for future studies of vitamin D and immune function. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Hydroxylumisterols, Photoproducts of Pre-Vitamin D3, Protect Human Keratinocytes against UVB-Induced Damage

Lumisterol (L3) is a stereoisomer of 7-dehydrocholesterol and is produced through the photochemical transformation of 7-dehydrocholesteol induced by high doses of UVB. L3 is enzymatically hydroxylated by CYP11A1, producing 20(OH)L3, 22(OH)L3, 20,22(OH)2L3, and 24(OH)L3. Hydroxylumisterols function as reverse agonists of the retinoic acid-related orphan receptors α and γ (RORα/γ) and can interact with the non-genomic binding site of the vitamin D receptor (VDR). These intracellular receptors are mediators of photoprotection and anti-inflammatory activity. In this study, we show that L3-hydroxyderivatives significantly increase the expression of VDR at the mRNA and protein levels in keratinocytes, both non-irradiated and after UVB irradiation. L3-hydroxyderivatives also altered mRNA and protein levels for RORα/γ in non-irradiated cells, while the expression was significantly decreased in UVB-irradiated cells. In UVB-irradiated keratinocytes, L3-hydroxyderivatives inhibited nuclear translocation of NFκB p65 by enhancing levels of IκBα in the cytosol. This anti-inflammatory activity mediated by L3-hydroxyderivatives through suppression of NFκB signaling resulted in the inhibition of the expression of UVB-induced inflammatory cytokines, including IL-17, IFN-γ, and TNF-α. The L3-hydroxyderivatives promoted differentiation of UVB-irradiated keratinocytes as determined from upregulation of the expression at the mRNA of involucrin (IVL), filaggrine (FLG), and keratin 14 (KRT14), downregulation of transglutaminase 1 (TGM1), keratins including KRT1, and KRT10, and stimulation of ILV expression at the protein level. We conclude that CYP11A1-derived hydroxylumisterols are promising photoprotective agents capable of suppressing UVB-induced inflammatory responses and restoring epidermal function through targeting the VDR and RORs.

Enzyme-treated soy protein supplementation in low protein diet enhanced immune function of immune organs in on-growing grass carp

A 56 days feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on immune function of immune organs (head kidney, spleen and skin) in on-growing grass carp. A total of 540 on-growing grass carp (initial average weight: 325.72 ± 0.60 g) were fed six diets, which included a normal protein diet (28% crude protein) and five low protein diets (26% crude protein) supplemented with graded levels of ETSP (0.0, 0.8, 1.2, 1.6 and 2.0%). At the end of feeding period, a challenge test was performed by infection with Aeromonas hydrophila for two weeks. The results indicated that (1) reducing dietary protein content from 28 to 26% decreased antibacterial substances and aggravated inflammatory responses of above three immune organs; (2) under the condition of reducing protein level in diet, 0.8-1.2% ETSP supplementation reversed these above adverse effects on immune function of above three immune organs; (3) suitable ETSP supplementation-decreased inflammatory responses were partly associated with [IκB kinase β (IKKβ)/inhibitor of κBα (IκBα)/nuclear factor kappa B (NF-κB) p65 and p52 or NF-κB p65] signaling and [target of rapamycin (TOR)/(S6K1, 4E-BP)] signaling in above three immune organs. (4) On the basis of C3 content (head kidney), C4 content (spleen) and skin hemorrhage and lesion, the optimal ETSP supplementation levels in low protein diets were estimated to be 1.48%, 1.61% and 1.03%, respectively. In summary, ETSP supplementation in low protein diets improved immune function of head kidney, spleen and skin in on-growing grass carp.

CYP11A1-derived vitamin D3 products protect against UVB-induced inflammation and promote keratinocytes differentiation

UVB radiation mediates inflammatory responses causing skin damage and defects in epidermal differentiation. 1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) interacts with the vitamin D3 receptor (VDR) to regulate inflammatory responses. Additionally, 1,25(OH)2D3/VDR signaling represents a potential therapeutic target in the treatment of skin disorders associated with inflammation and poor differentiation of keratinocytes. Since the protective effect of 1,25(OH)2D3 against UVB-induced skin damage and inflammation is recognized, CYP11A1-derived vitamin D3-hydroxyderivatives including 20(OH)D3, 1,20(OH)2D3, 20,23(OH)2D3 and 1,20,23(OH)3D3 were tested for their anti-inflammatory and skin protection properties in UVB-irradiated human epidermal keratinocytes (HEKn). HEKn were treated with secosteroids for 24 h pre- and post-UVB (50 mJ/cm2) irradiation. Secosteroids modulated the expression of the inflammatory response genes (IL-17, NF-κB p65, and IκB-α), reducing nuclear-NF-κB-p65 activity and increasing cytosolic-IκB-α expression as well as that of pro-inflammatory mediators, IL-17, TNF-α, and IFN-γ. They stimulated the expression of involucrin (IVL) and cytokeratin 10 (CK10), the major markers of epidermal differentiation, in UVB-irradiated cells. We conclude that CYP11A1-derived hydroxyderivatives inhibit UVB-induced epidermal inflammatory responses through activation of IκB-α expression and suppression of NF-kB-p65 activity and its downstream signaling cytokines, TNF-α, and IFN-γ, as well as by inhibiting IL-17 production and activating epidermal differentiation.

Mast Cells as a Double-Edged Sword in Immunity: Their Function in Health and Disease. First of Two Parts

Mast cells (MCs) have recently been re-interpreted in the context of the immune scenario in the sense that their pro-allergic role is no longer exclusive. In fact, MCs even in steady state conditions maintain homeostatic functions, producing mediators and intensively cross-talking with other immune cells. Here, emphasis will be placed on the array of receptors expressed by MCs and the variety of cytokines they produce. Then, the bulk of data discussed will provide readers with a wealth of information on the dual ability of MCs not only to defend but also to offend the host. This double attitude of MCs relies on many variables, such as their subsets, tissues of residency and type of stimuli ranging from microbes to allergens and food antigens. Finally, the relationship between MCs with basophils and eosinophils will be discussed.

Are there differences in immune responses following delivery of vaccines through acutely or chronically sun-exposed compared with sun-unexposed skin?

The majority of human vaccines are administered above the deltoid muscle of the arm, a site that is chronically sun-exposed in many people. It is known that exposure of the skin to the UV wavelengths in sunlight stimulates systemic immunosuppression, an outcome that is associated with reduced immunity to microbial infections in animal models. Here we consider whether immunization of humans through a UV-irradiated skin site will lead to a less effective immune response compared with immunization through an unexposed site. Studies showing that the efficacy of vaccination can be reduced when surrogates of increased levels of sun exposure, such as latitude of residence and season of the year, are considered. Results from a limited number of intervention experiments in humans demonstrate a similar pattern. To provide an explanation for these findings, changes in the number and functional potential of immune cells in chronically sun-exposed compared with unexposed skin are outlined. UV radiation-induced changes to skin cells are also relevant when considering skin sites for administration of immune-tolerizing peptides. The review provides the basis for further research into the effects of acute and chronic UV radiation exposure on skin cells in the context of vaccination.

Meningeal Mast Cells as Key Effectors of Stroke Pathology

Stroke is the leading cause of adult disability in the United States. Because post-stroke inflammation is a critical determinant of damage and recovery after stroke, understanding the interplay between the immune system and the brain after stroke holds much promise for therapeutic intervention. An understudied, but important aspect of this interplay is the role of meninges that surround the brain. All blood vessels travel through the meningeal space before entering the brain parenchyma, making the meninges ideally located to act as an immune gatekeeper for the underlying parenchyma. Emerging evidence suggests that the actions of immune cells resident in the meninges are essential for executing this gatekeeper function. Mast cells (MCs), best known as proinflammatory effector cells, are one of the long-term resident immune cells in the meninges. Here, we discuss recent findings in the literature regarding the role of MCs located in the meningeal space and stroke pathology. We review the latest advances in mouse models to investigate the roles of MCs and MC-derived products in vivo, and the importance of using these mouse models. We examine the concept of the meninges playing a critical role in brain and immune interactions, reevaluate the perspectives on the key effectors of stroke pathology, and discuss the opportunities and challenges for therapeutic development.

Ultraviolet radiation-induced immunosuppression and its relevance for skin carcinogenesis

The realisation that UV radiation (UVR) exposure could induce a suppressed immune environment for the initiation of carcinogenesis in the skin was first described more than 40 years ago. Van der Leun and his colleagues contributed to this area in the 1980s and 90s by experiments in mice involving UV wavelength and dose-dependency in the formation of such tumours, in addition to illustrating both the local and systemic effect of the UVR on the immune system. Since these early days, many aspects of the complex pathways of UV-induced immunosuppression have been studied and are outlined in this review. Although most experimental work has involved mice, it is clear that UVR also causes reduced immune responses in humans. Evidence showing the importance of the immune system in determining the risk of human skin cancers is explained, and details of how UVR exposure can down-regulate immunity in the formation and progression of such tumours reviewed. With increasing knowledge of these links and the mechanisms of UVR-induced immunosuppression, novel approaches to enhance immunity to skin tumour antigens in humans are becoming apparent which, hopefully, will reduce the burden of UVR-induced skin cancers in the future.

ASTHMA - comparing the impact of vitamin D versus UVR on clinical and immune parameters

The incidence of asthma has increased markedly since the 1960s and is currently estimated to affect more than 300 million individuals worldwide. A number of environmental factors are implicated in asthma pathogenesis, one of which is vitamin D. Vitamin D deficiency is a global health concern and has increased in parallel with asthma incidence. Epidemiological studies report associations between low vitamin D status, assessed as circulating levels of 25-hydroxyvitamin D, with asthma incidence, severity, exacerbations and responses to treatment. This has led to clinical studies to test whether increasing the levels of vitamin D improves asthma management. Despite being highly variable in dosing regimens, design and outcomes, meta-analyses suggest overall positive outcomes with respect to reduced asthma exacerbations and steroid requirements. The primary mechanism for increasing vitamin D levels in the body is through exposure of the skin to the ultraviolet B (UVB) component of ultraviolet radiation (UVR), most commonly from sun exposure. However, only a limited number of studies investigating the impact of UVR on the asthmatic response have been performed; these generally report on the impact of latitude as a surrogate of sun exposure, or address this in animal models. To the best of our knowledge no comprehensive trials to assess the impact of UVB radiation on asthma outcomes have been performed. Within this review we discuss observational and clinical studies in this field, and innate and adaptive immune mechanisms through which UVR and vitamin D may impact respiratory health, and asthma. We highlight the heterogeneity of asthmatic disease, which is likely to impact upon the efficacy of interventional studies, and briefly overview more recent findings relating to the impact of vitamin D/UVR on the development of asthma.

Does sunlight protect us from cancer?

The Ultraviolet (UV) radiation contained in sunlight is a powerful mutagen and immune suppressant which partly explains why exposure to solar UV is the biggest risk factor for the development of cutaneous tumours. Evidence is building that sunlight may be protective against some internal malignancies. Because patients with these tumours are often vitamin D deficient, this has led some to propose that vitamin D supplementation will be beneficial in the treatment of these cancers. However, the results from already completed trials have been disappointing which has given weight to the argument that there must be something else about sunlight that explains its cancer-protecting properties.

Vitamin D in Asthma: Mechanisms of Action and Considerations for Clinical Trials

There is increasing interest in the therapeutic utility of vitamin D in asthma, which is supported by a significant body of evidence on epidemiologic associations between vitamin D insufficiency and worse asthma control. In support of a causal relationship, vitamin D beneficially modulates diverse immunologic pathways in heterogeneous asthma endotypes, regulating the actions of lymphocytes, mast cells, antigen-presenting cells, and structural cells to dampen excessive inflammatory responses. Allergic asthma is characterized by a failure of immune tolerance and the development of pathologic responses to inhaled aeroallergens, and vitamin D has been extensively shown to support immune regulation. Alarmin cytokines are increasingly implicated in nonallergic eosinophilic inflammation, which vitamin D also regulates. Steroid resistance and pathologic interleukin (IL)-17 responses are features of severe asthma, and vitamin D beneficially enhances the response to steroids in these individuals. Additionally, vitamin D enhances antimicrobial pathways, which is of relevance to infection-precipitated asthma exacerbations. These mechanisms support a role for vitamin D as secondary prevention to reduce exacerbations and inflammation in asthma. Similar mechanisms, and effects on fetal lung development, likely underlie a primary prevention therapeutic role in pregnancy for vitamin D to reduce the development of asthma in children. However, randomized controlled trials of variable design show inconsistent positive outcomes for vitamin D interventions in asthma. Increased understanding of the biological characteristics of vitamin D reveals methodological issues that might explain certain negative outcomes. Importantly, on systematic review of the trials to date, vitamin D is shown to be beneficial in asthma. The evidence discussed in this review supports the importance of optimizing vitamin D in holistic asthma care.

Ultraviolet radiation and skin mast cells: Effects, mechanisms and relevance for skin diseases

Mast cells (MCs) are well known as versatile effector cells in allergic reactions and several other immune responses. Skin MCs and cutaneous MC responses are subject to the effects of environmental factors including ultraviolet radiation (UVR). Numerous studies have assessed the effects of UVR on MCs, in vitro and in vivo. Interestingly, UVR seems to have variable effects on non-activated and activated mast cells. In general, UV therapy is beneficial in the treatment of urticaria and mastocytosis, but the effects are variable depending on treatment regimen and type of UVR. Here, we review and summarise key reports from the older and current literature on the crosstalk of UVR and skin MCs. Specifically, we present the literature and discuss published reports on the effects of UVR on skin MCs in rodents and humans. In addition, we review the role of MCs in UVR-driven skin diseases and the influence of UV light on MC-mediated skin diseases. This summary of our current understanding of the interplay of skin MCs and UVR may help to improve the management of patients with urticaria and other MC disorders, to identify current gaps of knowledge, and to guide further research.

Protective Role of Mast Cells in Primary Systemic Vasculitis: A Perspective

Mast cells are important cells of the immune system. Although traditionally considered as key players in allergic and hypersensitivity reactions, emerging evidence suggests that mast cells have many complex roles in vascular disease. These include regulation of vasodilation, angiogenesis, activation of matrix metalloproteinases, apoptosis of smooth muscle cells, and activation of the renin angiotensin system. Mast cells are also known to play an immunomodulatory role via modulation of regulatory T-cell (Treg), macrophage and endothelial cell functions. This dual role of the mast cells is evident in myeloperoxidase anti-neutrophil cytoplasmic antibodies-mouse model of glomerulonephritis in which mast cell deficiency worsens glomerulonephritis, whereas inhibition of mast cell degranulation is effective in abrogating the development of glomerulonephritis. Our previous work demonstrated that mast cell degranulation inhibits lipopolysaccharide-induced interleukin 6 (IL-6) production in mice. This effect was not seen in histamine-1-receptor knockout (H1R^-/-) mice suggesting a role for histamine in IL-6 homeostasis. In addition, mast cell degranulation-mediated decrease in IL-6 production was associated with an upregulation of suppressor of cytokine signaling-1 protein in the aorta. We propose that mast cells regulate large artery inflammation through T-cells, shifting a primarily Th1 and Th17 toward a Th2 response and leading to enhanced IL-10 production, activation Treg cells, and the inhibition of macrophage functions.

Skin Immunity

Skin is the largest organ of the body with a complex network of multitude of cell types that perform plastic and dynamic cellular communication to maintain several vital processes such as inflammation, immune response including induction of tolerance and disease prevention, wound healing, and angiogenesis. Of paramount importance are immunological functions of the skin that protect from harmful exposure coming from external and internal environments. Awareness of skin immunity can provide a better comprehension of inflammation, autoimmunity, cancer, graft-versus-host disease, vaccination, and immunotherapy approaches. This paper will update on what we currently know about immune sentinels contributing to skin immunity.

The Role of Vitamin D in the Immune System as a Pro-survival Molecule

PURPOSE

Vitamin D is a fascinating and attractive molecule that has gained particular attention in medicine in recent years. Its immunomodulatory and anti-inflammatory potential might resemble the activity of many nature-derived molecules (eg, flavonoids), but its role in biology was selected during a long evolutionary pathway to dampen the damaging effect of cell stress response and of the immune reaction. In this sense, this molecule can be considered an ancient hormone that serves, in its primary role, as a pro-survival agent. The goal of this review was to elucidate this topic.

METHODS

The article reviews current literature on the field, focusing on issues regarding the role of vitamin D in immunity.

FINDINGS

Vitamin D participates in the survival machinery used by the cell, and in particular it plays a major role in synchronizing calcium oscillatory signaling to allow cell autophagy or apoptosis during a stress response.

IMPLICATIONS

Vitamin D should be better highlighted in its molecular action and vitamin D receptor genomics to conceive a more suited therapeutic supplementation protocol in clinics.

Are low sun exposure and/or vitamin D risk factors for type 1 diabetes?

Ultraviolet radiation and vitamin D, with their known immunosuppressive effects, have the potential to delay or inhibit type 1 diabetes.

The Nedd4-2/Ndfip1 axis is a negative regulator of IgE-mediated mast cell activation

Cross-linkage of the high-affinity immunoglobulin E (IgE) receptor (FcɛRI) on mast cells by antigen ligation has a critical role in the pathology of IgE-dependent allergic disorders, such as anaphylaxis and asthma. Restraint of intracellular signal transduction pathways that promote release of mast cell-derived pro-inflammatory mediators is necessary to dampen activation and restore homoeostasis. Here we show that the ligase Nedd4-2 and the adaptor Ndfip1 (Nedd4 family interacting protein 1) limit the intensity and duration of IgE-FcɛRI-induced positive signal transduction by ubiquitinating phosphorylated Syk, a tyrosine kinase that is indispensable for downstream FcɛRI signalosome activity. Importantly, loss of Nedd4-2 or Ndfip1 in mast cells results in exacerbated and prolonged IgE-mediated cutaneous anaphylaxis in vivo. Our findings reveal an important negative regulatory function for Nedd4-2 and Ndfip1 in IgE-dependent mast cell activity.

Aberrant activation of the IgE receptor on mast cells leads to allergic responses. Here, the authors identify an E3 ligase and adaptor protein that can reduce IgE signalling by targeting phosphorylated-Syk for degradation.

Targeting mast cells: Uncovering prolific therapeutic role in myriad diseases

The mast cells are integral part of immune system and they have pleiotropic physiological functions in our body. Any type of abnormal stimuli causes the mast cells receptors to spur the otherwise innocuous mast cells to degranulate and release inflammatory mediators like histamine, cytokines, chemokines and prostaglandins. These mediators are involved in various diseases like allergy, asthma, mastocytosis, cardiovascular disorders, etc. Herein, we describe the receptors involved in degranulation of mast cells and are broadly divided into four categories: G-protein coupled receptors, ligand gated ion channels, immunoreceptors and pattern recognition receptors. Although, activation of pattern recognition receptors do not cause mast cell degranulation, but result in cytokines production. Degranulation itself is a complex process involving cascade of events like membrane fusion events and various proteins like VAMP, Syntaxins, DOCK5, SNAP-23, MARCKS. Furthermore, we described these mast cell receptors antagonists or agonists useful in treatment of myriad diseases. Like, omalizumab anti-IgE antibody is highly effective in asthma, allergic disorders treatment and recently mechanistic insight of IgE uncovered; matrix mettaloprotease inhibitor marimistat is under phase III trial for inflammation, muscular dystrophy diseases; ZPL-389 (H4 receptor antagonist) is in Phase 2a Clinical Trial for atopic dermatitis and psoriasis; JNJ3851868 an oral H4 receptor antagonist is in phase II clinical development for asthma, rheumatoid arthritis. Therefore, research is still in inchoate stage to uncover mast cell biology, mast cell receptors, their therapeutic role in myriad diseases.

Anti-trypanosome effects of nutritional supplements and vitamin D3: in vitro and in vivo efficacy against Trypanosoma brucei brucei

BACKGROUND

Previous publications suggest that nutritional supplements have anti-trypanosome activity in vitro, although apparent efficacy was not noted in vivo. This study was conducted by experimentally infecting mice with Trypanosoma brucei brucei to assess the anti-trypanosome activity of various nutritional supplements with the hope of finding possible application in the treatment of African trypanosomiasis.

METHODS

Activities of nutritional supplements were screened in vitro against bloodstream forms of T. b. brucei. To evaluate selectivity, we used two mammalian cells, Jurkat cells and Vero cells. The IC50 values and selectivity index values were calculated, and supplements with promising efficacy in vitro were selected for further testing in vivo. Mice were infected intraperitoneally with 1 × 10(3) T. b. brucei. We observed parameters for disease progression such as parasitemia, red blood cell count, white blood cell count, survivability, and splenomegaly. Morphological profiles after the treatment were analyzed by scanning electron microscopy.

RESULTS

Vitamin D3 showed anti-trypanosome efficacies both in vitro and in vivo. It seemed to have suppressive effects on parasitemia, and spleen weight was also significantly lower in vitamin D3-treated mice when compared to non-treated control mice. There was, however, no significant prolonged survivability of infected mice treated with vitamin D3. Among green tea extracts, polyphenon-60 and epigallocatechin gallate had suppressive effects against T. b. brucei in vitro, but in vivo efficacies were marginal.

CONCLUSIONS

Treatment with nutritional supplements, vitamin D3, and polyphenon-60 seemed to have anti-trypanosome activity in vitro and protective activity to some extent in vivo, respectively, although those supplements themselves did not have curable effects. The exact mechanisms of action are not clear, but the significant efficacy in vitro suggested direct effects of supplements against African trypanosome parasites.

Ultraviolet radiation, vitamin D and multiple sclerosis

There is compelling epidemiological evidence that the risk of developing multiple sclerosis is increased in association with low levels of sun exposure, possibly because this is associated with low vitamin D status. Recent work highlights both vitamin D and non-vitamin D effects on cellular immunity that suggests that higher levels of sun exposure and/or vitamin D status are beneficial for both MS risk and in ameliorating disease progression. Here we review this recent evidence, focusing on regulatory cells, dendritic cells, and chemokines and cytokines released from the skin following exposure to ultraviolet radiation.

Mast Cell Stabilization Ameliorates Autoimmune Anti-Myeloperoxidase Glomerulonephritis

Observations in experimental murine myeloperoxidase (MPO)-ANCA-associated vasculitis (AAV) show mast cells degranulate, thus enhancing injury as well as producing immunomodulatory IL-10. Here we report that, compared with biopsy specimens from control patients, renal biopsy specimens from 44 patients with acute AAV had more mast cells in the interstitium, which correlated with the severity of tubulointerstitial injury. Furthermore, most of the mast cells were degranulated and spindle-shaped in patients with acute AAV, indicating an activated phenotype. We hypothesized that the mast cell stabilizer disodium cromoglycate would attenuate mast cell degranulation without affecting IL-10 production. We induced anti-MPO GN by immunizing mice with MPO and a low dose of anti-glomerular basement membrane antibody. When administered before or after induction of MPO autoimmunity in these mice, disodium cromoglycate attenuated mast cell degranulation, development of autoimmunity, and development of GN, without diminishing IL-10 production. In contrast, administration of disodium cromoglycate to mast cell-deficient mice had no effect on the development of MPO autoimmunity or GN. MPO-specific CD4(+) effector T cell proliferation was enhanced by co-culture with mast cells, but in the presence of disodium cromoglycate, proliferation was inhibited and IL-10 production was enhanced. These results indicate that disodium cromoglycate blocks injurious mast cell degranulation specifically without affecting the immunomodulatory role of these cells. Thus as a therapeutic, disodium cromoglycate may substantially enhance the regulatory role of mast cells in MPO-AAV.

Immune Modulation by Vitamin D and Its Relevance to Food Allergy

Apart from its classical function in bone and calcium metabolism, vitamin D is also involved in immune regulation and has been linked to various cancers, immune disorders and allergic diseases. Within the innate and adaptive immune systems, the vitamin D receptor and enzymes in monocytes, dendritic cells, epithelial cells, T lymphocytes and B lymphocytes mediate the immune modulatory actions of vitamin D. Vitamin D insufficiency/deficiency early in life has been identified as one of the risk factors for food allergy. Several studies have observed an association between increasing latitude and food allergy prevalence, plausibly linked to lower ultraviolet radiation (UVR) exposure and vitamin D synthesis in the skin. Along with mounting epidemiological evidence of a link between vitamin D status and food allergy, mice and human studies have shed light on the modulatory properties of vitamin D on the innate and adaptive immune systems. This review will summarize the literature on the metabolism and immune modulatory properties of vitamin D, with particular reference to food allergy.

Vitamin D and the Development of Atopic Eczema

A “vitamin D hypothesis” has been proposed to explain the increased prevalence of eczema in regions with higher latitude. This review focuses on the current available evidence with regard to the possible effect of vitamin D on the development of atopic eczema. Observational studies have indicated a link between vitamin D status and eczema outcomes, including lower serum vitamin D levels associated with increased incidence and severity of eczema symptoms. Vitamin D is known to have a regulatory influence on both the immune system and skin barrier function, both critical in the pathogenesis of eczema. However heterogeneous results have been found in studies to date investigating the effect of vitamin D status during pregnancy and infancy on the prevention of eczema outcomes. Well-designed, adequately powered, randomised controlled trials are needed. The study design of any new intervention trials should measure vitamin D levels at multiple time points during the intervention, ultraviolet (UV) radiation exposure via the use of individual UV dosimeters, and investigate the role of individual genetic polymorphisms. In conclusion, the current available evidence does not allow firm conclusions to be made on whether vitamin D status affects the development of atopic eczema.

Photoimmunology and Multiple Sclerosis

The ultraviolet (UV) radiation contained in sunlight is a powerful immune suppressant. While exposure to UV is best known for its ability to cause skin cancer, it is also associated with protection against a range of autoimmune diseases, particularly multiple sclerosis (MS). Although the precise mechanism by which sunlight affords protection from MS remains to be determined, some have hypothesised that UV immunosuppression explains the "latitude-gradient effect" associated with MS. By stimulating the release of soluble factors in exposed skin, UV activates immune suppressive pathways that culminate in the induction of regulatory cells in distant tissues. Each and every one of the immune suppressive cells and molecules activated by UV exposure are potential targets for treating and preventing MS. A thorough understanding of the mechanisms involved is therefore required if we are to realise the therapeutic potential of photoimmunology.

Mast cell plasticity and sphingosine-1-phosphate in immunity, inflammation and cancer

Mast cells (MC) are found in all vascularized tissues at homeostasis and, until recently, were viewed only as effector cells of allergic reactions via degranulation, the canonical process through which MC release mediators, including histamine and pre-formed proteases and cytokines such as TNF. Cross-linking of IgE bound to surface high affinity receptors for IgE (FcɛRI) by a specific antigen (Ag) triggers signaling events leading to degranulation. We and others have reported the concomitant production and export of an influential multifaceted sphingolipid mediator, sphingosine-1-phosphate (S1P) transported outside of MC by ATP-binding cassettes (ABC) transporters, i.e., independently of degranulation. Indeed, the MC horizon expanded by the discovery of their unique ability to selectively release mediators depending upon the stimulus and receptors involved. Aside from degranulation and transporter usage, MC are also endowed with piecemeal degranulation, a slower process during which mediator release occurs with minor morphological changes. The broad spectrum of pro- and anti-inflammatory bioactive substances MC produce and release, their amounts and delivery pace render these cells bona fide fine-tuners of the immune response. In this viewpoint article, MC developmental, phenotypic and functional plasticity, its modulation by microRNAs and its relevance to immunity, inflammation and cancer will be discussed.

How much sunlight is enough?

Living on a sun-drenched planet has necessitated adaption to and protection from the harmful effects of solar ultraviolet (UV) radiation, particularly skin cancer. However, convincing epidemiological and recent empirical evidence also supports a protective effect of UV against a range of diseases including multiple sclerosis, asthma and cardiovascular disease. Despite years of research attention into the biological effects of sunlight exposure, we are still far from being able to fully answer the question: How much sunlight is enough? This is probably because the answer is dependent on many complex and interacting variables. Many talented researchers are focused on exploring whether UV-induced vitamin D explains some of these effects. This perspectives article proposes an alternative hypothesis, namely that targeting UV-induced immune suppression by affecting the activation of regulatory cells and molecules will be of therapeutic benefit.

Mechanisms of vitamin D₃ metabolite repression of IgE-dependent mast cell activation

BACKGROUND

Mast cells have gained notoriety based on their detrimental contributions to IgE-mediated allergic disorders. Although mast cells express the vitamin D receptor (VDR), it is not clear to what extent 1α,25-dihydroxyvitamin D3 (1α,25[OH]2D3) or its predominant inactive precursor metabolite in the circulation, 25-hydroxyvitamin D3 (25OHD3), can influence IgE-mediated mast cell activation and passive cutaneous anaphylaxis (PCA) in vivo.

OBJECTIVE

We sought to assess whether the vitamin D3 metabolites 25OHD3 and 1α,25(OH)2D3 can repress IgE-dependent mast cell activation through mast cell-25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and mast cell-VDR activity.

METHODS

We measured the extent of vitamin D3 suppression of IgE-mediated mast cell degranulation and mediator production in vitro, as well as the vitamin D3-induced curtailment of PCA responses in WBB6F1-Kit(W/W-v) or C57BL/6J-Kit(W-sh/W-sh) mice engrafted with mast cells that did or did not express VDR or CYP27B1.

RESULTS

Here we show that mouse and human mast cells can convert 25OHD3 to 1α,25(OH)2D3 through CYP27B1 activity and that both of these vitamin D3 metabolites suppressed IgE-induced mast cell-derived proinflammatory and vasodilatory mediator production in a VDR-dependent manner in vitro. Furthermore, epicutaneously applied vitamin D3 metabolites significantly reduced the magnitude of skin swelling associated with IgE-mediated PCA reactions in vivo; a response that required functional mast cell-VDRs and mast cell-CYP27B1.

CONCLUSION

Taken together, our findings provide a mechanistic explanation for the anti-inflammatory effects of vitamin D3 on mast cell function by demonstrating that mast cells can actively metabolize 25OHD3 to dampen IgE-mediated mast cell activation in vitro and in vivo.

The enzyme Cyp26b1 mediates inhibition of mast cell activation by fibroblasts to maintain skin-barrier homeostasis

Mast cells (MCs) mature locally, thus possessing tissue-dependent phenotypes for their critical roles in both protective immunity against pathogens and the development of allergy or inflammation. We previously reported that MCs highly express P2X7, a receptor for extracellular ATP, in the colon but not in the skin. The ATP-P2X7 pathway induces MC activation and consequently exacerbates the inflammation. Here, we identified the mechanisms by which P2X7 expression on MCs is reduced by fibroblasts in the skin, but not in the other tissues. The retinoic-acid-degrading enzyme Cyp26b1 is highly expressed in skin fibroblasts, and its inhibition resulted in the upregulation of P2X7 on MCs. We also noted the increased expression of P2X7 on skin MCs and consequent P2X7- and MC-dependent dermatitis (so-called retinoid dermatitis) in the presence of excessive amounts of retinoic acid. These results demonstrate a unique skin-barrier homeostatic network operating through Cyp26b1-mediated inhibition of ATP-dependent MC activation by fibroblasts.

Loss of epidermal p38α signaling prevents UVR-induced inflammation via acute and chronic mechanisms

Ultraviolet B radiation (UVB) is a component of solar radiation primarily responsible for causing damage and cancer in irradiated skin, and disrupting immune homeostasis. The immediate harm and long-term health risks of excessive sunlight exposure are impacting the lives of nearly all people worldwide. Inflammation is a key mechanism underlying UVB’s various detrimental effects. Here we show that activation of the protein kinase p38α is restricted to the epidermis in UVB-exposed skin, and p38α ablation targeted to the epithelial compartment is sufficient to suppress UVB-induced inflammation. Mechanistically, loss of epithelial p38α signaling attenuates the expression of genes required to induce vascular leakage and edema, and also increases the steady-state abundance of epidermal γδ T cells, which are known to promote the repair of damaged epidermis. These effects of p38α deficiency delineate a molecular network operating at the organism-environment interface, and reveal conditions crucial to preventing the pathology resulting from sun-damaged skin.

Targeting mast cells in inflammatory diseases

Although mast cells have long been known to play a critical role in anaphylaxis and other allergic diseases, they also participate in some innate immune responses and may even have some protective functions. Data from the study of mast cell-deficient mice have facilitated our understanding of some of the molecular mechanisms driving mast cell functions during both innate and adaptive immune responses. This review presents an overview of the biology of mast cells and their potential involvement in various inflammatory diseases. We then discuss some of the current pharmacological approaches used to target mast cells and their products in several diseases associated with mast cell activation.