New insights into the mechanisms of polymorphic light eruption: resistance to ultraviolet radiation-induced immune suppression as an aetiological factor

Eradication of skin microbiota restores cytokine production and release in polymorphic light eruption

Polymorphic light eruption (PLE) has been mechanistically linked to cytokine abnormalities. Emerging preclinical evidence posits the skin microbiome as a critical modulator of ultraviolet (UV)-induced cytokine expression, thereby influencing subsequent immune responses. This intricate relationship remains underexplored in the context of PLE. Hence, we investigated the differential responses between disinfected and non-disinfected skin following both single and repetitive exposures to solar-simulated UV radiation in patients with PLE. An experimental, half-body pilot study was conducted involving six PLE patients and 15 healthy controls. Participants' skin was exposed to single and multiple doses of solar-simulated UV radiation, both in disinfected and in non-disinfected skin areas. The co-primary outcomes were PLE score and cytokine expression in blister fluid analysed through OLINK proteomic profiling. Secondary outcomes were erythema, pigmentation, induction of apoptotic cells in vacuum-generated suction blisters, and density of infiltrate in skin biopsies of PLE patients. Among the 71 cytokines analysed, baseline expression levels of 20 specific cytokines-integral to processes such as apoptosis, inflammation, immune cell recruitment, cellular growth, and differentiation-were significantly impaired in PLE patients compared with healthy controls. Notably, skin disinfection reversed the observed cytokine imbalances following a single UV exposure at the minimal erythema dose (MED) level and exhibited even more pronounced effects after multiple UV exposures. However, no significant differences were evident in PLE score, erythema, pigmentation, or rates of apoptotic cell induction upon UV radiation. These findings provide evidence for UV-driven cytokine regulation by the skin microbiota and imply microbiome involvement in the PLE immune response.

A systematic review of natural products for skin applications: Targeting inflammation, wound healing, and photo-aging

BACKGROUND

Every day the skin is constantly exposed to several harmful factors that induce oxidative stress. When the cells are incapable to maintain the balance between antioxidant defenses and reactive oxygen species, the skin no longer can keep its integrity and homeostasis. Chronic inflammation, premature skin aging, tissue damage, and immunosuppression are possible consequences induced by sustained exposure to environmental and endogenous reactive oxygen species. Skin immune and non-immune cells together with the microbiome are essential to efficiently trigger skin immune responses to stress. For this reason, an ever-increasing demand for novel molecules capable of modulating immune functions in the skin has risen the level of their development, particularly in the field of natural product-derived molecules.

PURPOSE

In this review, we explore different classes of molecules that showed evidence in modulate skin immune responses, as well as their target receptors and signaling pathways. Moreover, we describe the role of polyphenols, polysaccharides, fatty acids, peptides, and probiotics as possible treatments for skin conditions, including wound healing, infection, inflammation, allergies, and premature skin aging.

METHODS

Literature was searched, analyzed, and collected using databases, including PubMed, Science Direct, and Google Scholar. The search terms used included "Skin", "wound healing", "natural products", "skin microbiome", "immunomodulation", "anti-inflammatory", "antioxidant", "infection", "UV radiation", "polyphenols", "polysaccharides", "fatty acids", "plant oils", "peptides", "antimicrobial peptides", "probiotics", "atopic dermatitis", "psoriasis", "auto-immunity", "dry skin", "aging", etc., and several combinations of these keywords.

RESULTS

Natural products offer different solutions as possible treatments for several skin conditions. Significant antioxidant and anti-inflammatory activities were reported, followed by the ability to modulate immune functions in the skin. Several membrane-bound immune receptors in the skin recognize diverse types of natural-derived molecules, promoting different immune responses that can improve skin conditions.

CONCLUSION

Despite the increasing progress in drug discovery, several limiting factors need future clarification. Understanding the safety, biological activities, and precise mechanisms of action is a priority as well as the characterization of the active compounds responsible for that. This review provides directions for future studies in the development of new molecules with important pharmaceutical and cosmeceutical value.

A postulated model for photoimmunopathogenesis of chronic actinic dermatitis around adaptive immunity, including Th17 cells, Tregs, TRMs, cytotoxic T cells, and/or common-γ chain receptor+ cells

BACKGROUND/PURPOSE

The pathogenesis of chronic actinic dermatitis (CAD) is more complicated than other photodermatoses. However, the relationship between the clinical severity of CAD and the offending photocontact or contact allergens or both, and the correlations of CAD immunopathogenesis with the immunoregulatory molecules involved in adaptive immunity are yet to be investigated.

METHODS

We performed phototesting with broad-spectrum ultraviolet (UV) B, UVA, and visible light to establish the presence of photosensitivity in 121 patients with CAD, together with photopatch and contact patch testing. Nine patients with CAD were selected according to their clinical severity score for CAD (CSS-CAD), and triple direct immunofluorescence analysis was performed with paraffin-embedded skin biopsy samples.

RESULTS

As CSS-CAD was closely correlated with the multiplicity of photo(contact) allergens, particularly photoallergens, three or more photoallergens were detected in the severe CAD group (52.5%); less in the moderate group (32.8%); and only one in the mild group (14.8%; P = .025). In the groups showing greater severity of disease, the absolute numbers of IFN-γ⁺ , IL-17⁺ , CD4+, CD8+, common-γ chain receptor (common-γCR)⁺ , and CD69⁺ tissue-resident memory cells increased on average; there was also an increase in the CD4+/CD8+ cell ratio, with the more severely affected groups. However, the levels of TNF-α⁺ and FoxP3⁺ regulatory T (Treg) cells and the mean IL-17/IFN-γ cell ratio decreased in the more severely affected CSS-CAD subgroups.

CONCLUSIONS

Based on the clinical analysis and immunopathogenic results, avoidance of excessive sun exposure, and topical and systemic blocking agents for photo(contact) allergens are recommended. Additionally, conventional immunomodulators and emerging agents including JAK-STAT inhibitors may be administered for CAD treatment in the future.

Clinical characteristics of patients with human immunodeficiency virus and immune-mediated photodermatoses: A retrospective study of 39 patients

BACKGROUND

HIV/AIDS patients are susceptible to various infectious and inflammatory dermatoses. No systemic work has been done on HIV/AIDS patients with immune-mediated photodermatoses in China. Here, we aim to determine the clinical features of immune-mediated photodermatoses in HIV/AIDS patients.

METHODS

A retrospective analysis of HIV/AIDS patients with immune-mediated photodermatoses was carried out with demographic data, clinical characteristics, laboratory data, and follow-up data at the First Affiliated Hospital of Kunming Medical University between 2012 and 2019. The data were subjected to statistical analysis.

RESULTS

A total of 39 HIV/AIDS patients with immune-mediated photodermatoses were enrolled, including 22 cases of polymorphic light eruption (PLE), 16 cases of chronic actinic dermatitis (CAD), and one actinic reticuloid. The CD4 count at the visit of the HIV-positive CAD group was lower than the PLE group (p = .049). The HIV-positive CAD group was more sensitive toward UVB than the PLE group (p = .020) and had a lower MED-UVB value (p = .044). There was no significant difference in UV tests among different categories of skin types.

CONCLUSION

Immune-mediated photodermatoses are a manifestation of the advanced symptom of HIV infection, and sometimes also the presenting feature of HIV infection. Compared with HIV-positive PLE patients, CAD patients showed higher sensitivity to UVB radiation and had a lower MED-UVB value. The primary treatment for immune-mediated photodermatoses in HIV/AIDS patients is HAART and sun avoidance.

Association of polymorphous light eruption with NOD-2 and TLR-5 gene polymorphisms

BACKGROUND

Polymorphous light eruption (PLE) is a common, immunologically mediated, photosensitive skin disease. After ultraviolet-B (UV-B) irradiation, patients with PLE show reduced Langerhans cell (LC) depletion in the epidermis, which results in a non-suppressive microenvironment in the skin. Interestingly, severe acute graft-versus-host-disease (aGvHD) occurred in stem cell transplanted patients that showed no or incomplete depletion of LCs after UVB-irradiation. Genetic variation in nucleotide-binding oligomerization domain 2 (NOD-2) and toll-like receptor 5 (TLR-5) genes also confers susceptibility to aGvHD.

OBJECTIVES

We hypothesized that PLE is associated with genetic variation in the NOD-2 and TLR-5 genes.

METHODS

We investigated single nucleotid polymorphisms (SNPs) of NOD-2 (R702W, G908R, 3020Cins) and TLR-5 (A592S, P616L, N392STOP) in skin biopsies of PLE-patients (n=143) and in healthy controls (n=104) using restriction fragment-length polymorphism analysis.

RESULTS

The frequency of NOD-2 alleles with the SNP R702W was significantly higher in PLE than in controls (31.8% vs 6.3%; p<0.0001), and homozygous carriers of this mutation were more common in PLE (27.9% vs 0%; p<0.0001). For SNP 3020Cins, the allele frequency (7.3% vs 0.7%; p=0.0025) and the number of heterozygotes (14.7% vs 1.3%; p=0.0019) were higher in PLE. The frequency of alleles with the N392STOP SNP of the TLR5 gene, which is associated with a truncated, non-functional receptor, was significantly higher in PLE (21% vs 5%; 7% vs 1% homozygotes, 28% vs 8% heterozygotes; p<0.0001). The other SNPs did not differ significantly.

CONCLUSIONS

This study yielded a high frequency of functional SNPs in the NOD-2 and TLR-5 genes in PLE. The same SNPs are associated with aGvHD and there are similarities in the reaction of LCs after UVB-irradiation between aGvHD and PLE. This leads to the hypothesis that PLE-patients may be more susceptible to developing GvHD after stem-cell transplantation, an assumption that needs to be investigated further.

Long-Term Course of Polymorphic Light Eruption: A Registry Analysis

Background: Little is known about the long-term course of polymorphic light eruption (PLE).

Objective: To predict disease course, a questionnaire was sent to patients whose PLE had been diagnosed between March 1990 and December 2018 and documented in the Austrian Cooperative Registry for Photodermatoses.

Methods: In January 2019, 205 PLE patients were contacted by mail and asked to complete a questionnaire on their disease course, including whether the skin's sun sensitivity had normalized (i.e., PLE symptoms had disappeared), improved, stayed the same, or worsened over time. Patients who reported normalization of sun sensitivity were asked to report when it had occurred.

Results: Ninety-seven patients (79 females, 18 males) returned a completed questionnaire. The mean (range) duration of follow-up from PLE onset was 29.6 (17–54) years for females and 29.4 (16–47) years for males. The disease disappeared in 32 (41%) females after 17.4 (2–41) years and in 4 (24%) males after 11.8 (5–26) years. Twenty-nine (37%) females and 6 (35%) males reported improvement of symptoms over time; 15 females (19%) and 7 males (41%) reported no change; and 3 females (4%) and no males reported worsening of symptoms. Kaplan-Meier analysis revealed that after 20 years 74% (95%CI, 64–82%) of patients still suffered from PLE. PLE lesion persistence (>1 week) tended to predict a prolonged course of PLE.

Conclusions: PLE usually takes a long-term course over many years though in most patients its symptoms improve or disappear over time. How improvement relates to the pathophysiology of the disease remains to be determined.

Polymorphous Light Eruption- An Indian Scenario

Polymorphous light eruption (PMLE) is the most common, idiopathic, acquired photodermatosis, characterized by abnormal, recurrent, and delayed reaction to sunlight. Polymorphous light eruption is common worldwide but the morphology, distribution, and pigmentary changes are unique in Indian skin which is discussed in this review. The prevalence of PMLE is around 10–20% in the general population. It commonly occurs in females between 20and 30 years of age. It is the most common photodermatosis in school-going children. Visible light sensitivity is an important phenomenon in PMLE. It typically presents as recurrent and chronic lesions over photoexposed sites. Initially, patchy erythema occurs with pruritus. Most of the Indians belong to type IV to type VI skin and pigmentary changes are commonly seen. The unique feature of PMLE in Indian skin is the pigmentary change which varies from hypopigmented to hyperpigmented lesions. These pigmentary changes may occur alone or in combination with erythematous or skin-colored lesions. The pigmentary lesions are seen in more than 50% of lesions. The histopathology of PMLE is characterized by the presence of hyperkeratosis, spongiosis with or without the presence of liquefactive degeneration in the epidermis. Dermal changes in the upper and mid dermis include the presence of dense perivascular lymphocytic infiltrate. The management of PMLE includes both preventive measures and medical management. Topical sunscreens, topical steroids, hydroxychloroquine and antioxidants play a very important role.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

Actinic prurigo in a dermatological reference center in Colombia: 108 cases

Introducción.

El prurigo actínico es una fotodermatosis crónica. Afecta con mayor frecuencia a la población latinoamericana, predomina en mujeres y compromete la piel expuesta al sol, las conjuntivas y los labios.

Objetivo.

Actualizar la información sobre las características clínico-epidemiológicas y el tratamiento de pacientes con prurigo actínico en Colombia.

Materiales y métodos.

Se hizo un estudio de corte transversal que incluyó los registros clínicos de pacientes con prurigo actínico atendidos en el Servicio de Fotodermatología del Hospital Universitario Centro Dermatológico Federico Lleras Acosta entre el 2011 y el 2016, y se describieron sus características demográficas, clínicas e histopatológicas, así como su tratamiento.

Resultados.

Se incluyeron 108 pacientes, el 71,3 % de ellos mujeres y el 28,7% hombres, con predominio de los fototipos III-IV (70 %). La enfermedad se había iniciado durante la primera década de vida en el 66,4% de los casos y el 25 % de los pacientes tenía antecedentes familiares de la enfermedad. Las lesiones predominaban en el rostro (93,5 %), los antebrazos (79,6 %) y el dorso de las manos (70,4 %). También, se documentó compromiso ocular (87,9 %) y de los labios (88,8 %). Se hizo la prueba de fotoprovocación con radiación ultravioleta A en el 25 % de los casos y biopsia cutánea en el 19,4 %. Todos los pacientes se trataron con protección solar química y física. En los casos leves a moderados, se formularon corticoides tópicos (91,7 %) e inhibidores de la calcineurina (65,7 %), y en los graves, talidomida (33,3 %) y pentoxifilina (14,8 %).

Conclusión.

Las características de los pacientes colombianos con prurigo actínico son similares a las reportadas en otros países latinoamericanos: inicio temprano de la enfermedad, predominio en mujeres, compromiso frecuente de conjuntivas y labios, y adecuada respuesta al tratamiento tópico y sistémico.

Recent Developments in the Diagnosis and Management of Photosensitive Disorders

Photodermatoses occur in males and females of all races and ages. Onset can be variable in timing and influenced by genetic and environmental factors. Photodermatoses are broadly classified as immunologically mediated, chemical- and drug-induced, photoaggravated, and genetic (defective DNA repair or chromosomal instability) diseases. Advances in the field have led to improved recognition and treatment of many photodermatoses. The purpose of this focused review is to provide an update on the diagnosis and management of a variety of photodermatoses, both common and less common, with review of recent updates in the literature pertaining to their diagnosis and management.

Unique profile of antimicrobial peptide expression in polymorphic light eruption lesions compared to healthy skin, atopic dermatitis, and psoriasis

Background

Polymorphic light eruption (PLE) has been attributed to type IV, most likely delayed‐type hypersensitivity response (adaptive immunity) but little is known on innate immunity, especially antimicrobial peptides (AMPs) in the disease. Abnormalities in AMP expression have been linked to pathological skin conditions such as atopic dermatitis (AD) and psoriasis.

Methods

Antimicrobial peptide profiling was carried out in PLE skin samples (n,12) compared with that of healthy (n,13), atopic (n,6), and psoriatic skin (n,6).

Results

Compared to healthy skin, we observed increased expression of psoriasin and RNAse7 (both mostly in stratum granulosum of the epidermis), HBD‐2 (in the cellular infiltrate of the dermis), and LL37 (mostly in and around blood vessels and glands) in PLE lesional skin, a similar expression profile as present in psoriatic skin and different to that of AD (with little or no expression of psoriasin, RNAse7, HBD‐2, and LL37). HBD‐3 was downregulated in PLE compared to its high expression in the epidermis and dermis of healthy skin, AD, and psoriasis.

Conclusion

The unique profile of differentially expressed AMPs in PLE implies a role in the pathophysiology of the disease, possibly directly or indirectly linked to the microbiome of the skin.

Photodermatitis for the Allergist

PURPOSE OF REVIEW

The photodermatoses represent a group of disorders of sensitivity to light that continue to pose difficulties in diagnosis and management. Photodermatoses are of interest to allergists because many photosensitive skin disorders have immunologic underpinnings, and patients often present to clinic complaining of "allergy" to the sun. We provide a concise reference for allergists on the clinical recognition and management of photodermatitis.

RECENT FINDINGS

New developments in the understanding of immunomodulatory effects of light have demonstrated normally immunosuppressive responses in the skin to light exposure, and a blunted immunosuppressive response in the pathogenesis of many photodermatoses. Vitamin D plays an important role in immunomodulation and itself may be affected by photodermatoses due to the impact of photoprotective treatment strategies on circulating vitamin D levels. The elucidation of the immunological basis of many photodermatoses may provide guidance for developing new treatment modalities. Further research is necessary to determine the optimal management of vitamin D metabolism in patients with photodermatoses.

Polymorphous Light Eruption

Polymorphous light eruption (PLE) is the commonest immuno-mediated photodermatosis. It occurs after solar or artificial UV-light exposure and affects only the sun-exposed areas with preference of the V-area of the chest, of arms and forearms, legs, upper part of the back, and rarely the face. The lesions are itching or burning, and vary morphologically from erythema to papules, vesico-papules and occasionally blisters, plaques, sometimes erythema multiforme-like, insect bite-like wheals and purpura. The clinical manifestations befall within a few hours to days from light exposure, last a few days, and subside in about a week without sequelae. Its diagnosis is based on history, morphology and phototests. PLE is considered as a delayed hypersensitivity response to newly UV induced, but still unidentified, antigen(s). Usually, MED is normal, but the provocative phototests with UVA or UVB reproduce the spontaneous lesions in about 50% of the patients. Broad spectrum sunscreens and antioxidants, photohardening with PUVA or narrow band UVB may be beneficial to prevent the disease. Therapy is based mainly on topical or systemic corticosteroids.

Levels and function of regulatory T cells in patients with polymorphic light eruption: relation to photohardening

Background

We hypothesized that regulatory T cells (Tregs) are involved in the immunological abnormalities seen in patients with polymorphic light eruption (PLE).

Objectives

To investigate the number and suppressive function of peripheral Tregs in patients with PLE compared with healthy controls.

Methods

Blood sampling was done in 30 patients with PLE [seeking or not seeking 311‐nm ultraviolet (UV)B photohardening] as well as 19 healthy controls at two time points: TP1, March to June (before phototherapy); and TP2, May to August (after phototherapy). We compared the number of CD4⁺CD25^highCD127⁻FoxP3⁺ Tregs by flow cytometry and their function by assessing FoxP3 mRNA levels and effector T cell/Treg suppression assays.

Results

Tregs isolated from healthy controls significantly suppressed the proliferation of effector T cells at TP1 by 68% (P = 0·0156). In contrast, Tregs from patients with PLE entirely lacked the capacity to suppress effector T‐cell proliferation at that time point. The medical photohardening seen in 23 patients with PLE resulted in a significant increase in the median percentage of circulating Tregs [both as a proportion of all lymphocytes; 65 6% increase (P = 0·0049), and as a proportion of CD4⁺ T cells; 32.5% increase (P = 0·0049)]. This was accompanied by an increase in the expression of FoxP3 mRNA (P = 0·0083) and relative immunosuppressive function of Tregs (P = 0·083) comparing the two time points in representative subsets of patients with healthy controls tested. Seven patients with PLE not receiving 311‐nm UVB also exhibited an increase in the number of Tregs but this was not statistically significant. No significant differences in Treg numbers were observed in healthy subjects between the two time points.

Conclusions

An impaired Treg function is likely to play a role in PLE pathogenesis. A UV‐induced increase in the number of Tregs (either naturally or therapeutically) may be a compensatory mechanism by which the immune system counteracts the susceptibility to PLE.

What's already known about this topic?

Patients with polymorphic light eruption (PLE) display immunological abnormalities.

Previous studies have shown that they are resistant to the immune suppressive effects of sunlight.

What does this study add?

We found that the number and suppressive function of regulatory T cells (Tregs) are crucial in the pathogenesis of PLE.

An increase in Treg levels (after photohardening) might be a compensatory mechanism by which the immune system intends to counteract the susceptibility to PLE formation.

Photohardening of polymorphic light eruption patients decreases baseline epidermal Langerhans cell density while increasing mast cell numbers in the papillary dermis

The pathogenesis of polymorphic light eruption (PLE) has been linked to a lack of UV-induced immune suppression. To determine the role of Langerhans cells (LC), mast cells and regulatory T cells, biopsies from PLE patients were taken from exposed sites in spring before and after photohardening with 311 nm or PUVA as well as again in summer. Skin sections were assessed for the presence of Langerin/CD1a+ LC and CD3+, CD4+, CD25+ or FoxP3+ T cells and mast cells. Photohardening transiently decreased the density of epidermal LC and significantly increased a low baseline mast cell density in the papillary dermis of PLE patients. Baseline T cell numbers in the skin were low, and there was no difference in PLE patients among any time point. This suggests that LC suppression together with recruitment of mast cells into photohardened skin may be a key cellular event underlying the mechanism by which phototherapy protects from PLE.

Actinic prurigo

Actinic prurigo is a chronic photodermatosis with onset in childhood or before 20 years of age. It is most prevalent in Amerindians and Latin American mestizos, although it has been reported worldwide. Patients present with photodistributed, erythematous excoriated papules, cheilitis, and conjunctivitis. There is strong association with human leukocyte antigen DR4, especially the DRB1*0407 subtype. Treatment consists of photoprotection and the use of thalidomide.

Polymorphous light eruption: clinic aspects and pathogenesis

Polymorphous light eruption is an immunologically mediated photodermatosis with high prevalence, particularly among young women in temperate climates, characterized by pruritic skin lesions of variable morphology, occurring in spring or early summer on sun-exposed body sites. A resistance to ultraviolet radiation (UVR)-induced immunosuppression and a subsequent delayed-type hypersensitivity response to a photoantigen have been suggested as key factors in the disease. Molecular and immunologic disturbances associated with disease pathogenesis include a failure of skin infiltration by neutrophils and other regulatory immune cells on UVR exposure linked to a disturbed cytokine microenvironment. Standard management is based on prevention.

Interleukin-17 mediated inflammatory responses are required for ultraviolet radiation-induced immune suppression

Ultraviolet radiation (UVR) induces immunosuppression and is a major factor for development of skin cancer. Numerous efforts have been made to determine mechanisms for UVR-induced immunosuppression and to develop strategies for prevention and treatment of UVR-induced cancers. In the current study, we use IL-17 receptor (IL-17R) deficient mice to examine whether IL-17 mediated responses have a role in UVB (290-320)-induced immunosuppression of contact hypersensitivity responses. Results demonstrate that IL-17 mediated responses are required for UVB-induced immunosuppression of contact hypersensitivity responses. The systemic immune suppression and development of regulatory T cells are inhibited in UVB-treated IL-17R deficient mice compared to wild-type animals. The deficiency in IL-17R inhibits the infiltration and development of a tolerogenic myeloid cell population in UVB-treated skin, which expresses CD11b and Gr-1 and produces reactive oxygen species. We speculate that the development of the tolerogenic myeloid cells is dependent on IL-17-induced chemokines and inflammatory mediators in UVB-treated skin. The inhibition of the tolerogenic myeloid cells may be attributed to the suppression of regulatory T cells in UVR-treated IL-17R(-/-) mice. The findings may be exploited to new strategies for prevention and treatment of UVR-induced skin diseases and cancers.

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.

T regulatory cells and related immunoregulatory factors in polymorphic light eruption following ultraviolet A1 challenge

BACKGROUND

Polymorphic light eruption (PLE) is considered to be an autoimmune-mediated skin condition in which the normal ultraviolet (UV)-induced local immunosuppression appears to be absent, leading to recognition of photoinduced autoantigens and subsequent inflammation.

OBJECTIVES

To investigate T regulatory cells (Tregs) and related immunoregulatory factors in PLE lesions and controls.

METHODS

Skin biopsies were performed in 13 patients with UVA1-challenged PLE, 12 female patients with chronic discoid lupus erythematosus (CDLE) and 11 healthy controls who had exposure to UVA1. Immunohistochemistry and four-colour immunofluorescence studies were performed.

RESULTS

Patients with CDLE and UVA1-exposed controls showed significantly decreased epidermal immunoreactivity for CD1a compared with patients with PLE (P = 0·0001). Four-colour immunofluorescence revealed a median percentage of CD4+CD25+FOXP3+ Tregs of 7·6% (range 3·7-13·6%) in PLE, a median of 11·7% (range 9·5-13·9%) in CDLE and a median of 3·4% (range 0-6·8%) in controls. Compared with UVA1-exposed controls, PLE and CDLE lesions showed significantly decreased transforming growth factor (TGF)-β1 immunoreactivity in the epidermis (P = 0·0003). In PLE lesions, we observed significantly decreased interleukin (IL)-10 expression compared with CDLE (P = 0·022). In the dermis, receptor activator of nuclear factor-κB ligand (RANKL) expression was increased in UVA1-exposed controls compared with PLE and CDLE (P = 0·018).

CONCLUSIONS

Similar to CDLE lesions, UVA1-challenged PLE lesions display an altered immunoregulatory network, as indicated by decreased epidermal or dermal expression of TGF-β1, IL-10 and RANKL, and a relatively low number of Tregs, particularly when compared with other inflammatory skin conditions reported in the literature.

Phototherapeutic hardening modulates systemic cytokine levels in patients with polymorphic light eruption

The etiopathogenesis of polymorphic light eruption (PLE) has been linked to impaired UV-immunosuppression, Langerhans cell (LC) retention, and an absence of neutrophil infiltration into UV-exposed PLE skin. We have previously shown that photohardening restores the impaired neutrophil responsiveness to the chemoattractants leucotriene B4 and formyl-methionyl-leucyl-phenylalanin in PLE patients. The aim of this study was to investigate whether photohardening modulates baseline chemokine and cytokine levels which would alter chemoresponsiveness and hence immune function in PLE patients. Sixteen PLE patients received photohardening therapy for 4-9 weeks by 311 nm UVB. Plasma samples were taken both before and within 48 h of the penultimate phototherapeutic exposure. Plasma from these 16 patients, 8 non-irradiated PLE patients, and 14 control subjects was analyzed for IL-1β, CXCL8 (IL-8), IL-10, IL-17, TNF, CCL2 (MCP-1), CCL5 (RANTES), CCL11 (eotaxin), and CCL22 (MDC). These cytokines and chemokines were measured in early spring (March to April) and again in late spring (April to June). PLE patients had a significantly elevated level of CCL11 (p = 0.003) and IL-1β (p = 0.002) in early spring (before phototherapy). In late spring, after phototherapy, PLE patients had significantly elevated CCL2 (p = 0.002) and TNF (p = 0.002) but a trend for lowered plasma levels of CXCL8 (p = 0.021). When comparing the cytokine shifts from early to late spring, while healthy controls and non-UV-irradiated PLE patients showed an increase, PLE patients undergoing photohardening exhibited a trend for decrease in IL-1β (p = 0.012). Taken together, our results indicate that photohardening may alter the complex cytokine milieu in PLE, in particular via IL-1β, helping to normalise the pathophysiologic response to subsequent UV exposure.

Patients with polymorphic light eruption have decreased serum levels of 25-hydroxyvitamin-D3 that increase upon 311 nm UVB photohardening

BACKGROUND

Polymorphic light eruption (PLE) is a very common condition whose pathogenesis may involve immunological abnormalities. Vitamin D sufficiency is thought to be important for normal immune function.

OBJECTIVE

To determine whether PLE patients are vitamin D deficient and to study how photohardening with 311 nm UVB affects the vitamin D status of PLE patients.

METHODS

The vitamin D status of 23 PLE patients (21 females and 2 males; age range, 18-55 years) was analysed at four different time points (early spring, late spring, summer, and winter) by measuring 25-hydroxyvitamin-D(3) (25(OH)D) serum levels through a standardised immunoassay. Fifteen of those patients received 311 nm UVB in early spring for prevention of PLE symptoms. 25(OH)D levels of the PLE patients were compared to that of 23 sex-, age-, and body-mass-index post hoc-matched control subjects.

RESULTS

PLE patients had low levels of 25(OH)D throughout the year compared to that of the control subjects. At baseline in early spring, the mean ± SD 25(OH)D level was 14.9 ± 3.0 ng ml(-1) in the PLE patients that would later receive 311 nm UVB and 14.4 ± 2.4 ng ml(-1) in the patients not receiving 311 nm UVB. Successful prophylactic treatment with 311 nm UVB significantly increased 25(OH)D levels to a mean of 21.0 ± 3.4 ng ml(-1) (p < 0.001; ANOVA, Tukey's test). Heading into summer, the 25(OH)D levels in treated patients decreased again, reaching their lowest levels in winter. In contrast, the 25(OH)D levels of untreated PLE patients stayed in the low range in early and late spring but increased by trend towards summer, reaching similar levels to that of the PLE patients who had received 311 nm UVB (17.1 ± 2.3 vs. 17.3 ± 6.0 ng ml(-1)). Like the treated PLE patients, 25(OH)D levels of untreated patients significantly decreased in winter to comparable levels (12.2 ± 1.9 vs. 13.8 ± 1.8 ng ml(-1)). Taken together, the 25(OH)D levels of PLE patients were significantly lower at all time points than that observed in the matched control population (34.4 ± 12.5 ng ml(-1)) (p < 0.000003).

CONCLUSIONS

PLE patients have low 25(OH)D serum levels. 311 nm UVB phototherapy that prevented PLE symptoms increased those levels. Thus, we speculate that boosting levels of vitamin D may be important in ameliorating PLE.

Dermal mast cells affect the development of sunlight-induced skin tumours

Ultraviolet (UV) radiation contained in sunlight is considered a major risk in the induction of skin cancer. While mast cells are best known for their role in allergic responses, they have also been shown to play a crucial role in suppressing the anti-tumour immune response following UV exposure. Evidence is now emerging that UV may also trigger mast cell release of cutaneous tissue remodelling and pro-angiogenic factors. In this review, we will focus on the cellular and molecular mechanisms by which UV recruits and then activates mast cells to initiate and promote skin cancer development.

The mechanisms and consequences of ultraviolet-induced immunosuppression in the skin and eye

Ultraviolet radiation (UVR) of the skin results in immune suppression to antigens encountered shortly after the exposure. The pathways leading to the downregulation in immunity are complex, initiated by chromophores located at the surface of the skin and ending with the generation of immunosuppressive mediators and regulatory cells. Ultraviolet-induced immunosuppression can be considered not only as beneficial, such as in preventing chronic inflammatory responses and allergic and automimmune reactions, but it can also be detrimental, such as in the lack of control of skin tumors and infectious diseases. The eye is an immune privileged site through a wide variety of mechanisms that allow selected immune responses without causing inflammation. The role of UVR in altering immune responses in the eye is not clear and is discussed in relation to photokeratitis, herpetic stromal keratitis, and pterygium.

The challenges of UV-induced immunomodulation for children's health

Exposure to solar ultraviolet radiation (UVR) is recognised to have both beneficial and harmful effects on human health. With regard to immune responses, it can lead to suppression of immunity and to the synthesis of vitamin D, a hormone that can alter both innate and adaptive immunity. The consequences in children of such UV-induced changes are considerable: first there are positive outcomes including protection against some photoallergic (for example polymorphic light eruption) and T cell-mediated autoimmune diseases (for example multiple sclerosis) and asthma, and secondly there are negative outcomes including an increased risk of skin cancer (squamous cell carcinoma, basal cell carcinoma and cutaneous malignant melanoma) and less effective control of several infectious diseases. Many uncertainties remain regarding the amount of sun exposure that would provide children with the most effective responses against the variety of immunological challenges that they are likely to experience.

The consequences of UV-induced immunosuppression for human health

Exposure to UV radiation can cause suppression of specific immune responses. The pathways leading to the down-regulation are complex, starting from the absorption of UV photons by chromophores in the skin and ending with local and systemic changes in immune mediators, the generation of T and B regulatory cells and inhibition of effector and memory T cell activation. The consequences for human health are thought to be both beneficial and adverse. The former are illustrated by protection against polymorphic light eruption, and possible protection against T cell-mediated autoimmune diseases and asthma. The latter are illustrated by skin cancer, cutaneous lupus erythematosus and infectious diseases including vaccination. Many outstanding questions remain in this rapidly developing and controversial area, not least what advice to give the general public regarding their sun exposure. While considerable advances have been made in the development of strategies that preserve the health benefits of sunlight exposure and decrease its detrimental effects, further research is required before optimal levels of protection are achieved.

Oral administration of a hydrophilic extract of Polypodium leucotomos for the prevention of polymorphic light eruption

BACKGROUND

Polymorphic light eruption (PLE) is the most common idiopathic photodermatosis. Reactive oxygen species have been implicated in the pathogenesis of PLE. Polypodium leucotomos (PL) is a natural extract from tropical fern leaves with potent antioxidant and anti-inflammatory properties.

OBJECTIVE

In this study we sought to evaluate whether a concentrated hydrophilic extract of PL might prevent or delay the photoinduction of typical PLE lesions by artificial ultraviolet (UV) radiation.

METHODS

A total of 35 patients with long-standing PLE were included in this open, uncontrolled bicenter study. PLE was induced by photoprovocation with artificial UVB and UVA light, thereafter oral treatment with PL was initiated. Two weeks later a second photoprovocation was performed while the patients were still taking PL.

RESULTS

Thirty patients developed PLE lesions after repeated irradiation with UVA. Of these, 18 patients also responded to UVB. After PL treatment, 9 (30%) and 5 (28%) patients, respectively, were unresponsive to repeated UVA and UVB exposure. In the remaining patients, the mean number of UVA and UVB irradiations required to elicit PLE increased significantly from 1.95 to 2.62 (P = .005) and from 2.38 to 2.92 (P = .047), respectively.

LIMITATIONS

The study was open and uncontrolled and included a relatively small number of patients.

CONCLUSION

Our data indicate that oral PL treatment might be beneficial for the prevention of PLE.

Photohardening restores the impaired neutrophil responsiveness to chemoattractants leukotriene B4 and formyl-methionyl-leucyl-phenylalanin in patients with polymorphic light eruption

A failure to induce immune suppression after UV exposure has been implicated in the pathogenesis of polymorphic light eruption (PLE). This immunological resistance has been linked to an impaired neutrophil infiltration into the skin following UV exposure. Therapeutic photohardening can restore this abnormal neutrophil infiltration in PLE skin and is thought to be responsible for the prophylactic efficacy. The aim of this study was to elucidate the pathogenic mechanism of the described neutrophil deficiency in PLE. Peripheral blood neutrophil responses to the chemoattractants leukotriene B4 (LTB(4)) and formyl-methionyl-leucyl-phenylalanin (fMLP) were investigated in vitro. Samples from 10 patients with PLE before and after 6 weeks of photohardening therapy were assessed. Flow cytometry was used to measure the changes associated with neutrophil activation. We found a significantly reduced neutrophil responsiveness to LTB(4) and fMLP in PLE patients, which was restored to normal levels after phototherapy. Indeed, PLE neutrophil responsiveness to these two chemoattractants after (but not before) phototherapy was similar to that of age- and sex-matched healthy control subjects. This indicates that an abnormal chemotactic potential to neutrophils is a crucial factor in the pathogenesis of PLE. Normalization following photohardening may therefore account for the therapeutic efficacy by restoring UV-induced neutrophil skin infiltration. Our results reveal a completely novel pathogenic mechanism involved in PLE and offer unique targets for therapy.

Randomized double-blinded placebo-controlled intra-individual trial on topical treatment with a 1,25-dihydroxyvitamin D₃ analogue in polymorphic light eruption

BACKGROUND

Polymorphic light eruption (PLE) is a very frequent photodermatosis whose pathogenesis may involve resistance to ultraviolet (UV)-induced immune suppression. Similar to UV radiation, calcitriol (1,25-dihydroxyvitamin D₃) and its analogues such as calcipotriol have been shown to exhibit immunosuppressive properties.

OBJECTIVES

We performed a randomized double-blinded placebo-controlled intraindividual half-body trial (NCT00871052) to investigate the preventive effect of a calcipotriol-containing cream in PLE.

METHODS

Thirteen patients with PLE (10 women, three men; mean age 37 years) pretreated their skin on two symmetrically located test fields with calcipotriol or placebo cream twice daily for 7 days before the start of photoprovocation testing with solar-simulated UV radiation. We established a specific PLE test score [AA + SI + 0·4 P (range 0-12), where AA is affected area score (range 0-4), SI is skin infiltration score (range 0-4) and P is pruritus score on a visual analogue scale (range 0-10)] to quantify PLE severity.

RESULTS

Photoprovocation led to PLE lesions in 12/13 (92%) patients. As shown by the PLE test score, compared with placebo calcipotrial pretreatment significantly reduced PLE symptoms in average by 32% (95% confidence interval 21-44%; P = 0·0022, exact Wilcoxon signed-rank test) throughout the observation period starting at 48 h until 144 h after the first photoprovocation exposure. At 48, 72 and 144 h calcipotriol pretreatment resulted in a lower PLE test score in 7 (58%), 9 (75%) and 10 (83%) of the 12 cases, respectively. Considering all time points together, calcipotriol diminished the PLE test score in all 12 photoprovocable patients (P = 0·0005; Wilcoxon signed-rank test).

CONCLUSIONS

These results suggest a potential therapeutic benefit of topical 1,25-dihydroxyvitamin D₃ analogues as prophylactic treatment in patients with PLE.

The immune-modulating cytokine and endogenous Alarmin interleukin-33 is upregulated in skin exposed to inflammatory UVB radiation

The cellular and molecular mechanisms by which UV radiation modulates inflammation and immunity while simultaneously maintaining skin homeostasis is complex and not completely understood. Similar to the effects of UV, IL-33 has potent immune-modulating properties that are mediated by the downstream induction of cytokines and chemokines. We have discovered that exposure of mice in vivo or human skin samples ex vivo to inflammatory doses of UVB induced IL-33 expression within the epidermal and dermal skin layers. Using a combination of murine cell lines and primary human cells, we demonstrate that both UV and the oxidized lipid platelet activating factor induce IL-33 expression in keratinocytes and dermal fibroblasts. Highlighting the significance of these results, we found that administering IL-33 to mice in vivo suppressed the induction of Th1-mediated contact hypersensitivity responses. This may have consequences for skin cancer growth because UV-induced squamous cell carcinomas that evade immunological destruction were found to express significantly higher levels of IL-33. Finally, we demonstrate that dermal mast cells and skin-infiltrating neutrophils closely associate with UV-induced IL-33-expressing fibroblasts. Our results therefore identify and support a role for IL-33 as an important early danger signal produced in response to inflammation-inducing UV radiation.

Topical liposomal DNA-repair enzymes in polymorphic light eruption

Polymorphic light eruption (PLE) is a very frequent photodermatosis in Europe whose pathogenesis may involve resistance to UV-induced immune suppression and simultaneous immune reactions against skin photoneoantigens. We performed a randomized, double-blind, placebo-controlled intra-individual half-body trial to investigate the protective effect of an after-sun (AS) lotion containing DNA-repair enzymes (photolyase from Anacystis nidulans and Micrococcus luteus extract with endonuclease activity). Fourteen PLE patients were exposed to suberythemal doses of solar-simulated UV radiation on 4 consecutive days at 4 symmetrically located PLE-prone test fields per patient. The test fields were treated with (i) active AS lotion or (ii) a placebo lotion immediately after each UV exposure, or (iii) an SPF30 sunscreen before UV exposure or left untreated. All test fields were exposed to photoactivating blue light 1 h after each UV exposure. As shown by a newly established specific PLE test score (AA + SI + 0.4P [range, 0-12], where AA is affected area score [range, 0-4], SI is skin infiltration score [range, 0-4], and P is pruritus score on a visual analogue scale [range, 0-10]), PLE symptoms were significantly fewer on test sites treated with active AS lotion than on untreated (P = 0.00049) or placebo-treated test sites (P = 0.024). At 144 h after first UV exposure (the time point of maximal PLE symptoms), the mean test scores for untreated, active AS lotion-treated, and placebo-treated test fields were 4.39, 1.73 (61% reduction; 95% confidence interval (CI), 36% to 85%), and 3.20 (27% reduction; 95% CI, 3% to 51%), respectively. Pretreatment with SPF30 sunscreen completely prevented PLE symptoms in all patients. The present results indicate that DNA damage may trigger PLE and that the application of topical liposomes containing DNA repair enzymes to increase DNA repair may effectively prevent PLE.

The human health effects of ozone depletion and interactions with climate change

Depletion of the stratospheric ozone layer has led to increased solar UV-B radiation (280-315 nm) at the surface of the Earth. This change is likely to have had an impact on human exposure to UV-B radiation with consequential detrimental and beneficial effects on health, although behavioural changes in society over the past 60 years or so with regard to sun exposure are of considerable importance. The present report concentrates on information published since our previous report in 2007. The adverse effects of UV radiation are primarily on the eye and the skin. While solar UV radiation is a recognised risk factor for some types of cataract and for pterygium, the evidence is less strong, although increasing, for ocular melanoma, and is equivocal at present for age-related macular degeneration. For the skin, the most common harmful outcome is skin cancer, including melanoma and the non-melanoma skin cancers, basal cell carcinoma and squamous cell carcinoma. The incidence of all three of these tumours has risen significantly over the past five decades, particularly in people with fair skin, and is projected to continue to increase, thus posing a significant world-wide health burden. Overexposure to the sun is the major identified environmental risk factor in skin cancer, in association with various genetic risk factors and immune effects. Suppression of some aspects of immunity follows exposure to UV radiation and the consequences of this modulation for the immune control of infectious diseases, for vaccination and for tumours, are additional concerns. In a common sun allergy (polymorphic light eruption), there is an imbalance in the immune response to UV radiation, resulting in a sun-evoked rash. The major health benefit of exposure to solar UV-B radiation is the production of vitamin D. Vitamin D plays a crucial role in bone metabolism and is also implicated in protection against a wide range of diseases. Although there is some evidence supporting protective effects for a range of internal cancers, this is not yet conclusive, but strongest for colorectal cancer, at present. A role for vitamin D in protection against several autoimmune diseases has been studied, with the most convincing results to date for multiple sclerosis. Vitamin D is starting to be assessed for its protective properties against several infectious and coronary diseases. Current methods for protecting the eye and the skin from the adverse effects of solar UV radiation are evaluated, including seeking shade, wearing protective clothing and sunglasses, and using sunscreens. Newer possibilities are considered such as creams that repair UV-induced DNA damage, and substances applied topically to the skin or eaten in the diet that protect against some of the detrimental effects of sun exposure. It is difficult to provide easily understandable public health messages regarding "safe" sun exposure, so that the positive effects of vitamin D production are balanced against the negative effects of excessive exposure. The international response to ozone depletion has included the development and deployment of replacement technologies and chemicals. To date, limited evidence suggests that substitutes for the ozone-depleting substances do not have significant effects on human health. In addition to stratospheric ozone depletion, climate change is predicted to affect human health, and potential interactions between these two parameters are considered. These include altering the risk of developing skin tumours, infectious diseases and various skin diseases, in addition to altering the efficiency by which pathogenic microorganisms are inactivated in the environment.

UV-induced tolerance to a contact allergen is impaired in polymorphic light eruption

Polymorphic light eruption (PLE) is a common skin disorder provoked by exposure to UVR. Its clinical symptoms resemble those of a contact allergic reaction. PLE is generally considered a T-cell-mediated autoimmune reaction toward a yet unidentified antigen formed in UVR-exposed skin. Predisposition to such an immune reaction may result from aberrant epitope formation, increased immune reactivity to a universal epitope, or diminished propensity to UVR-induced immunosuppression or to the induction of tolerance. In a study comprising a total of 24 PLE patients and 24 healthy sex- and age-matched controls, we found that both groups demonstrated similar immunosuppression of contact sensitization to diphenylcyclopropenone by earlier exposure to solar-simulating UVR. However, only 1 out of 13 PLE patients (8%) versus 6 out of 11 controls (55%) that had been immunosuppressed by UVR exhibited a state of immunotolerance toward the same allergen after 10-24 months (P=0.023). We conclude that the impaired propensity to UVR-induced allergen-specific immunotolerance may promote recurrent PLE.

8-methoxypsoralen plus ultraviolet A therapy acts via inhibition of the IL-23/Th17 axis and induction of Foxp3+ regulatory T cells involving CTLA4 signaling in a psoriasis-like skin disorder

To elucidate the molecular action of 8-methoxypsoralen plus UVA (PUVA), a standard dermatological therapy, we used K5.hTGF-beta1 transgenic mice exhibiting a skin phenotype and cytokine abnormalities with strong similarities to human psoriasis. We observed that impaired function of CD4+CD25+ regulatory T cells (Tregs) and increased cytokine levels of the IL-23/Th17 pathway were responsible for the psoriatic phenotype in this mouse model. Treatment of K5.hTGF-beta1 transgenic mice with PUVA suppressed the IL-23/Th17 pathway, Th1 milieu, as well as transcription factors STAT3 and orphan nuclear receptor RORgammat. PUVA induced the Th2 pathway and IL-10-producing CD4+CD25+Foxp3+Tregs with disease-suppressive activity that was abolished by anti-CTLA4 mAb treatment. These findings were paralleled by macroscopic and microscopic clearance of the diseased murine skin. Anti-IL-17 mAb treatment also diminished the psoriatic phenotype of the mice. This indicated that both induced Tregs involving CTLA4 signaling and inhibition of the IL-23/Th17 axis are central for the therapeutic action of PUVA.

[UV Filters. State of the art]

This article describes the basic principles of photoprotection with classic sunscreens containing chemical and/or physical UV filters and standard methods of sun protection factor (SPF) determination. In addition, the new governmental regulations and recommendations of the European Commission for photoprotection are presented and compared to regulations in other regions of the world. Finally, the efficacy of sunscreens in sunlight-induced non-sunburn effects, such as immune suppression and carcinogenesis are discussed.