CD11b+ cells and ultraviolet-B-resistant CD1a+ cells in skin of patients with polymorphous light eruption

Ultraviolet Radiation-Induced Tolerogenic Dendritic Cells in Skin: Insights and Mechanisms

Ultraviolet (UV) radiation has profound effects on the immune system, including the induction of tolerogenic dendritic cells (DCs), which contribute to immune suppression and tolerance. This review explores the roles of conventional CD11c⁺ DCs, as well as cutaneous Langerhans cells and CD11b⁺ myeloid cells, in UV-induced immune modulation. Two key mechanisms underlying the immunosuppressive relationship between UV and DCs are discussed: the inactivation of DCs and the induction of tolerogenic DCs. DCs serve as a critical link between the innate and adaptive immune systems, serving as professional antigen-presenting cells. In this context, we explore how UV-induced DCs influence the activity of specific T cell subsets, including regulatory T lymphocytes and T helper cells, and shape immune outcomes. Finally, we highlight the implications of UV-induced tolerogenic DCs in select dermatologic pathologies, including cutaneous lupus, polymorphic light eruption, and skin cancer. Understanding the mechanisms by which UV radiation alters DC function offers insights into the complex interplay between environmental factors and immune regulation, providing potential avenues for preventive and therapeutic intervention in UV-induced skin diseases.

Accumulation of Cytotoxic Skin Resident Memory T Cells and Increased Expression of IL-15 in Lesional Skin of Polymorphic Light Eruption

Patients with polymorphic light eruption (PLE) develop lesions upon the first exposure to sun in spring/summer, but lesions usually subside during season due to the natural (or medical) photohardening. However, these lesions tend to reappear the following year and continue to do so in most patients, suggesting the presence of a disease memory. To study the potential role of skin resident memory T cells (Trm), we investigated the functional phenotype of Trm and the expression of IL-15 in PLE. IL-15 is known to drive Trm proliferation and survival. Multiplex immunofluorescence was used to quantify the expression of CD3, CD4, CD8, CD69, CD103, CD49a, CD11b, CD11c, CD68, granzyme B (GzmB), interferon-gamma (IFN-γ), and IL-15 in formalin-fixed, paraffin-embedded lesional skin samples from PLE patients and healthy skin from control subjects. Unlike the constitutive T cell population in healthy skin, a massive infiltration of T cells in the dermis and epidermis was observed in PLE, and the majority of these belonged to CD8⁺ T cells which express Trm markers (CD69, CD103, CD49a) and produced cytotoxic effector molecules GzmB and IFN-γ. Higher numbers of CD3⁺ T cells and CD11b⁺CD68⁺ macrophages produced IL-15 in the dermis as compared to healthy skin. The dominant accumulation of cytotoxic Trm cells and increased expression of IL-15 in lesional skin of PLE patients strongly indicates the potential role of skin Trm cells in the disease manifestation and recurrence.

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.

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.

Epidermal Langerhans cells resistance to solar-simulated radiation in actinic prurigo patients with low minimal erythema dose

BACKGROUND

Actinic prurigo is a chronic photodermatosis of unclear pathogenesis. Epidermal Langerhans cell resistance to migration after ultraviolet radiation exposure has been proposed as a possible mechanism, as occurs in polymorphic light eruption patients. The purpose of this study was to evaluate the effect of solar-simulated radiation (SSR) on epidermal Langerhans cells in the uninvolved skin of actinic prurigo patients.

PATIENTS AND METHODS

Fifteen patients with actinic prurigo participated in the study. A biopsy from the uninvolved and unirradiated skin of the left buttock was performed, and another from the uninvolved skin of the right buttock, 72 hours after exposure to two MEDs of SSR. Immunohistochemistry staining was used to identify Langerhans cells (CD1a) in all samples.

RESULTS

In actinic prurigo patients with normal MED, there was a significant decrease in the number of epidermal Langerhans cells on the buttock skin exposed to two MED of SSR compared with the unirradiated buttock skin (P = .02 and .035 respectively). On the contrary, in patients with low MED there were no significant differences in the number of epidermal Langerhans cells between irradiated and unirradiated skin (P = .39).

CONCLUSION

Epidermal Langerhans cells migration after ultraviolet radiation exposure is decreased in actinic prurigo patients with low MED as has been reported in PLE patients, especially, those with low MED or positive UVB provocation tests. Langerhans cells resistance could be part of a common pathogenic mechanism in these two photodermatoses.

Polymorphic light eruption and IL-1 family members: any difference with allergic contact dermatitis?

Polymorphic light eruption (PLE) is described as a delayed-type hypersensitivity reaction (DTHR) toward a de novo light-induced antigen, yet to be identified. In effect, the inflammatory pathways of PLE and allergic contact dermatitis (ACD) share common patterns in terms of the mediators involved from the innate and adaptive immune system participating in the DTHR. As we have previously highlighted the role of interleukin (IL)-1 family members in ACD, we hypothesised that the same mediators could have similar functions in PLE. Our research aimed to assess the expression of certain IL-1family members in PLE patients vs. controls, and to compare it with ACD. The study population comprised 17 patients with PLE, 5 affected by ACD and 10 healthy controls in the same age range. Lesional and healthy skin samples were collected respectively from patients and donors. IL-36α, IL-36β, IL-36γ, IL-36 receptor antagonist (Ra), IL-1β, IL-33 gene and protein expressions were evaluated through RT-PCR and immunohistochemistry. Circulating proteins in the PLE patients were analysed by using western blot. The IL-36γ gene expression was significantly increased in PLE lesions compared to that in healthy controls and ACD lesions (***p < 0.001; ##p < 0.01 respectively), whereas the other analyzed ILs were more expressed in ACD. Immunohistochemical analysis revealed that IL-36α and IL-36γ protein levels were increased in PLE lesions compared to those of the healthy samples (***p < 0.001). Furthermore the IL-36γ plasma level was increased in PLE patients vs. controls (*p < 0.05). Our findings indicate that the IL-1 family pro-inflammatory members are increased in PLE with distinct differences from those in ACD, in particular with regard to IL-36γ mRNA regulation. Their role as activators of the local, and perhaps systemic, immune response, or as inhibitors of the immune tolerance machinery, needs further investigation.

Insight into immunocytes infiltrations in polymorphous light eruption

Polymorphous light eruption (PLE) which is one of the most common photodermatoses has been demonstrated to be immune-mediated disorder. Resistance to UV-induced immunosuppression resulting from differential immune cells infiltration and cytokines secretion has been highlighted in the pathogenesis of PLE. In this study, we reviewed differential patterns of immune cells infiltrations and cytokines secretion that may contribute to PLE occurrence and development.

Evidence and conjecture about mechanisms of cutaneous disease in photodermatology

Photosensitivity disorders are caused by a variety of mechanisms. Three common themes are as follows: excess chromophore allowing visible light energy to cause photodynamic damage, reduced DNA repair capacity to UV-induced DNA damage, and enhanced sensitivity to light-induced allergens mediated immunologically. Although the cause of each condition may be known, the precise pathogenesis underlying the photosensitivity has taken longer to understand. By focussing on three clinical disorders under each of these themes, we have explored the following: why erythropoietic protoporphyria differs so markedly from the other cutaneous porphyrias; how a DNA repair defect was eventually revealed to be the underlying cause of the vitamin B3 deficiency disorder of pellagra; an immunological explanation for the over reactivity to photoallergens in chronic actinic dermatitis.

Influence of the season on vitamin D levels and regulatory T cells in patients with polymorphic light eruption

The exact mechanisms of photohardening in polymorphic light eruption (PLE) are still unknown, but medical photohardening was shown to increase regulatory T cell (Treg) numbers in the blood of PLE patients, similar to natural hardening. Furthermore, oral vitamin D supplementation increased peripheral Tregs in healthy individuals. We herein report on a post hoc analysis of 26 screened PLE patients of a clinical trial (ClinicalTrials.gov No. NCT01595893), in which the influence of the progressing season was investigated on baseline CD4+CD25+FoxP3+CD127- Treg numbers by flow cytometry and Treg suppressive function by co-culture assays with T effector cells as a secondary endpoint, together with 25-hydroxy vitamin D (25(OH)D) serum levels at the study's screening visit, taking place in the period from January to June. The mean 25(OH)D serum level of all patients was 33.2 ng ml(-1). Ten of those patients (38.5%) were identified with low 25(OH)D levels (<30 ng ml(-1)). Significantly higher baseline 25(OH)D serum levels (plus 34.4%; P = 0.0182) as well as higher relative Treg percentages in CD4+ population (plus 62.8%; P = 0.0157) and in total lymphocyte population (plus 59.6%; P = 0.0372) and higher absolute Treg numbers (plus 100.2%; P = 0.0042) were observed in the late spring/early summer period (April to June) compared to the winter period (January to February). No significant relationship was observed when Treg numbers and function were correlated with 25(OH)D levels. These data indicate that in PLE patients Treg numbers and their suppressive function are independent of vitamin D serum levels and suggest that UV light and/or other seasonal factors may affect these cells via the non-vitamin D related pathway(s).

Mast cells are required for phototolerance induction and scratching abatement

Dermal mast cells protect the skin from inflammatory effects of ultraviolet (UV) radiation and are required for UV-induced immune suppression. We sought to determine a potential mechanistic role of mast cells in reducing the sensitivity to UV radiation (i.e. phototolerance induction) through photohardening. We administered single UV exposures as well as a chronic UV irradiation regime to mast cell-deficient Kit(W-Sh/W-Sh) mice and their controls. The chronic irradiation protocol was similar to that given for prophylaxis in certain photodermatoses in humans. Compared to controls, UV-exposed Kit(W-Sh/W-Sh) mice were more susceptible to epidermal hyperplasia and dermal oedema which was linked to blood vessel dilation. Unexpectedly, Kit(W-Sh/W-Sh) mice exhibited an excessive scratching behaviour following broadband UVB plus UVA or solar simulated UV irradiation at doses far below their minimal skin-swelling dose. Protection from this UV-induced scratching phenotype was dependent on mast cells, as engraftment of bone marrow-derived cultured mast cells abated it entirely. Kit(W-Sh/W-Sh) mice were entirely resistant to phototolerance induction by photohardening treatment. Compared to controls, these mice also showed reduced numbers of regulatory T cells and neutrophils in the skin 24 h after UV irradiation. While it is well known that mast cell-deficient mice are resistant to UV-induced immune suppression, we have discovered that they are prone to develop photo-itch and are more susceptible to UV-induced epidermal hyperplasia and skin oedema.

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.

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.

Photoimmunology

The discipline that investigates the biologic effects of ultraviolet radiation on the immune system is called photoimmunology. Photoimmunology evolved from an interest in understanding the role of the immune system in skin cancer development and why immunosuppressed organ transplant recipients are at a greatly increased risk for cutaneous neoplasms. In addition to contributing to an understanding of the pathogenesis of nonmelanoma skin cancer, the knowledge acquired about the immunologic effects of ultraviolet radiation exposure has provided an understanding of its role in the pathogenesis of other photodermatologic diseases.

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.

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.

A review of UVA-mediated photosensitivity disorders

A number of skin conditions are characterised by photosensitivity to UVA. Some of these are exclusively UVA-mediated conditions, while others include UVA in the action spectrum which also include UVB and/or visible light. This review aims to describe this diverse range of conditions for non-dermatologist scientists with an interest in this topic. As such, clinical details, including treatments, are brief and succinct. Recent advances in understanding the pathogenesis of these conditions is highlighted.

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.

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.

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.

Polymorphisms of the ITGAM gene confer higher risk of discoid cutaneous than of systemic lupus erythematosus

Background

Lupus erythematosus (LE) is a heterogeneous disease ranging from mainly skin-restricted manifestations (discoid LE [DLE] and subacute cutaneous LE) to a progressive multisystem disease (systemic LE [SLE]). Genetic association studies have recently identified several strong susceptibility genes for SLE, including integrin alpha M (ITGAM), also known as CD11b, whereas the genetic background of DLE is less clear.

Principal Findings

To specifically investigate whether ITGAM is a susceptibility gene not only for SLE, but also for cutaneous DLE, we genotyped 177 patients with DLE, 85 patients with sporadic SLE, 190 index cases from SLE families and 395 population control individuals from Finland for nine genetic markers at the ITGAM locus. SLE patients were further subdivided by the presence or absence of discoid rash and renal involvement. In addition, 235 Finnish and Swedish patients positive for Ro/SSA-autoantibodies were included in a subphenotype analysis. Analysis of the ITGAM coding variant rs1143679 showed highly significant association to DLE in patients without signs of systemic disease (P-value  = 4.73×10⁻¹¹, OR  = 3.20, 95% CI  = 2.23–4.57). Significant association was also detected to SLE patients (P-value  = 8.29×10⁻⁶, OR  = 2.14, 95% CI  = 1.52–3.00), and even stronger association was found when stratifying SLE patients by presence of discoid rash (P-value  = 3.59×10⁻⁸, OR  = 3.76, 95% CI  = 2.29–6.18).

Significance

We propose ITGAM as a novel susceptibility gene for cutaneous DLE. The risk effect is independent of systemic involvement and has an even stronger genetic influence on the risk of DLE than of SLE.

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.

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

An abnormal immune response has long been thought responsible for the patho-aetiology of polymorphic light eruption, the most common photodermatosis. Recent evidence indicates that polymorphic light eruption patients are resistant to the immune suppressive effects of sunlight, a phenomenon that leads to the formation of skin lesions upon seasonal sun exposure. This immunological abnormality in polymorphic light eruption supports the concept of the biological significance and evolutionary logic of sunlight-induced immune suppression, i.e. the prevention of immune responses to photo-induced neo-antigens in the skin, thereby preventing autoimmunity and skin rashes. This article focuses on the immunological alterations in polymorphic light eruption and the pathogenic significance to the disease state and skin carcinogenesis.

Polymorphous light eruption

Polymorphous light eruption is the most common photodermatosis, with a prevalence of as high as 10-20% in Western Europe and in the USA. It starts during the second and third decades of life. Although not life-threatening it can severely impair the quality of life, in particular during leisure activities and in outdoors workers. Polymorphous light eruption belongs to the group of so-called idiopathic photodermatoses. This term denotes dermatoses that occur in otherwise healthy individuals from exposure to sunlight or artificial light without the intervention of an exogenous photosensitizing agent. These diseases have two factors in common: they are precipitated by ultraviolet or visible radiation; and their exact pathomechanism remains obscure but is presumably immunologic in nature.

UV-induced immunosuppression in the balance

Around 1980, experiments with hairless mice showed us that UV-induced actinic keratoses (AK) and ensuing skin carcinomas did not arise independently: the rate of occurrence in one skin area was increased considerably if AKs had already been induced separately in another distant skin area, i.e. a systemic effect. The ground laying work of Margaret Kripke in the 1970s provided a fitting explanation: UV-induced immunosuppression and tolerance toward the UV-induced tumors. From Kripke's work a new discipline arose: "Photoimmunology." Enormous strides were made in exploring and expanding the effects from UV carcinogenesis to infectious diseases, and in elucidating the mechanisms involved. Stemming from concerns about a depletion of the ozone layer and the general impact of ambient UV radiation, the groups I worked in and closely collaborated with explored the anticipated adverse effects of UV-induced immunosuppression on healthy individuals. An important turning point was brought about in 1992 when the group of Kevin Cooper reported that immunosuppression could be induced by UV exposure in virtually all human subjects tested, suggesting that this is a normal and sound physiological reaction to UV exposure. This reaction could actually protect us from illicit immune responses against our UV-exposed skin, such as observed in idiopathic polymorphic light eruption. This premise has fruitfully rekindled the research on this common "sun allergy," affecting to widely varying degrees about one in five Europeans with indoor professions.

Photoimmunology--illuminating the immune system through photobiology

We review the field of photoimmunology with emphasis on immunosuppression induced by ultraviolet B radiation. Recent studies have focused on UVB-induced alterations in epidermal Langerhans cell function, resulting in a shift from Th1 to Th2 phenotype and the activation of regulatory T cells as the source of IL-10 that is central to this form of immunosuppression.

Plasmacytoid dendritic cells are absent in skin lesions of polymorphic light eruption

BACKGROUND/PURPOSE

Polymorphic light eruption (PLE) is a common photodermatosis of potential autoimmune origin, and an overlap with lupus erythematosus (LE) has been described. Plasmacytoid dendritic cell (PDC)-induced expression of interferon (IFN)-alpha has been found to be present in LE skin lesions and plays a pivotal role in the pathogenesis of LE by promoting autoimmunity. We therefore asked whether PDCs may also be involved in the pathogenesis of PLE and searched for those cells [which can be identified by their high levels of interleukin (IL)-3 receptor alpha chain (CD123), combined with other cell markers such as CD68] in skin lesions.

METHODS

Paraffin-embedded biopsy specimens from a total of 27 patients with clinically and histologically confirmed PLE (nine women, mean age 32.7 years, age range 18-43), LE (seven women, four men, CCLE: n=4, SCLE: n=2, lupus tumidus: n=5, mean age 48.5 years, age range 41-65) or psoriasis (four women, three men, mean age 43.3 years, age range 19-54) (as control group) were analyzed by immunohistochemical CD68/CD123 double staining. Quantification of the immunohistochemical staining was performed by visual cell counting of CD68-/CD123+, CD68+/123-, and CD68+/CD123+ cells separately in the epidermis and dermis of the samples in at least 10 random fields per sample at x 400 microscopic magnification by two of the investigators in a blinded fashion.

RESULTS

Microscopic examination of the immunohistochemically stained sections revealed that CD68+/CD123+ cells were present in most specimens obtained from LE [10/11 (91%)] and psoriasis [6/7 (86%)] patients but not at all in those obtained from PLE patients. Quantification and statistical analysis of the dermal infiltrate revealed that CD68+/CD123+ cells were present at a mean+/-SEM field density of 5.6+/-1.3 in LE, 1.6+/-0.6 in psoriasis but totally absent in PLE (P=0.0010 vs. LE, P=0.0135 vs. psoriasis by an unpaired Student's t-test).

CONCLUSION

The results confirm the potential significance of PDCs in LE and psoriasis, however the absence of PDCs in PLE contradicts the hypothesis that these cells might play a role in the latter disease.

Lucite estivale bénigne : prévention par un topique associant des filtres anti-UVA et des antioxydants

BACKGROUND

In a recent randomized, double-blind, placebo-controlled clinical study, the efficacy of a combination consisting of 0.25% alpha-glucosyl-rutin, 1% vitamin E and a broad-spectrum, highly UVA-protective sunscreen (sun protector factor 15 - persistent pigmentation darkening 6) regarding prevention of polymorphous light eruption was well demonstrated. We evaluated this combination under real solar exposure conditions.

PATIENTS AND METHODS

Patients with three previous typical polymorphous light eruptions (including one in the last year) were included in an open prospective multicenter study. The preparation was applied every two hours after the first summer exposure. No topical or systemic treatments presumed to be effective against polymorphous light eruption were given concomitantly. Evaluation was performed after the summer by a dermatologist.

RESULTS

Two of the 54 patients dropped out of the study, one for an adverse effect (contact dermatitis). At the end of the study following application of the test preparation, no eruption was seen for 35 patients (67%), with minor eruption for 10 patients (19%) and an marked eruption for 7 patients (13%). Pruritus (present in all patients the year before) was not seen in 36 patients (69%), was considered bearable for 36 patients and unbearable for only 3 patients compared to 27 before inclusion. For the dermatologists, efficacy was excellent for 35 patients and good for 7 patients, giving global efficacy of around 80%, with inadequate results in 10% of cases (5 patients). Concerning protection against erythema, the test product reduced sunburn by 60% compared with the previous year.

DISCUSSION

Because of the high clinical efficacy of the product noted after UVA challenge tests and verified by this clinical study under actual conditions of exposure, it may be proposed as a new prophylactic treatment for polymorphous light eruption.

Normalized ultraviolet (UV) induction of Langerhans cell depletion and neutrophil infiltrates after artificial UVB hardening of patients with polymorphic light eruption

BACKGROUND

Ultraviolet (UV) B hardening has been widely used as a prophylactic treatment in patients with polymorphic light eruption (PLE). Recent investigations have shown that in patients with PLE Langerhans cells (LCs) and neutrophils display less migration from and to the epidermis after an intense UVB irradiation compared with controls.

OBJECTIVES

To investigate the effect of UVB hardening of patients with PLE on their cell migratory responses after intense UVB exposure.

METHODS

Thirteen patients with PLE were recruited and UVB provocation testing was performed before entering the study. Among these patients, seven developed PLE rash upon UVB provocation ('UVB-P') and the other six did not respond ('UVB-NP'). Eleven age/sex-matched controls were included. Buttock skin of all included individuals was exposed to 6 minimal erythema doses (MED) of UVB (TL-12 lamps). Biopsies were taken after 24 h and 48 h, together with one control biopsy of unirradiated skin. Patients received total-body UVB hardening therapy consisting of 12 irradiations, on average rising from 10% to 140% of the initial MED in 6 weeks. Subsequently, MEDs were reassessed and biopsies were taken from newly irradiated (6 MED UVB) and unirradiated buttock skin. Skin sections were stained for the presence of LCs, macrophages and neutrophils. The cross-sectional area (in percentage) of positively stained cells within the epidermis was assessed from patients before and after hardening and compared with controls.

RESULTS

Before therapy, epidermal LC depletion and neutrophil influx at 48 h after 6 MED were most significantly reduced in 'UVB-P' patients (P = 0.025 and P =0.006, respectively) when compared with controls. 'UVB-NP' patients did not differ significantly from controls. After therapy, there were no longer any significant differences in the cell numbers among these three groups.

CONCLUSIONS

UVB hardening significantly improves UV-induced cell migratory responses in patients with PLE. UVB provokability of PLE appears to be most strongly linked to reduced UVB-induced trafficking of LCs and neutrophils, and 'UVB-P' patients show normalization of these responses after UVB hardening.

The Effect of Solar-Simulated Radiation on the Elicitation Phase of Contact Hypersensitivity does not Differ Between Controls and Patients with Polymorphic Light Eruption

It has been suggested that polymorphic light eruption (PLE) is characterized by a failure of ultraviolet radiation (UVR)-induced immunosuppression, resulting in a type-IV hypersensitivity response to photoinduced antigens. We measured the effect of solar-simulated radiation (SSR) on the elicitation phase of contact hypersensitivity to 2,4-dinitrochlorobenzene (DNCB), in ten PLE patients and 11 controls. Subjects were given a sensitizing dose of DNCB, and 3 wk later were exposed to 0.75 and 2 minimum erythema doses (MED) of SSR on the upper inner arm. Immediately and 24 h later these sites, and a non-irradiated control site, were challenged with DNCB. The resulting increase in skin thickness was measured with high-frequency ultrasound. Overall, 2 MED caused 17%-20% suppression of elicitation responses (compared with 93% suppression of sensitization reported previously), but the effect of SSR varied greatly between subjects, with some subjects showing potentiated responses, which may be of relevance to false-positive reactions in photopatch testing. In a repeated measures general linear model, SSR overall caused significant suppression of responses (p<0.001); there was less suppression in older subjects (p=0.009) but there was no significant difference between PLE patients and age-matched normal controls. These results contrast with our previous finding of a resistance to UVR-induced suppression of sensitization to DNCB in PLE. This difference may reflect the greater importance of Langerhans cells in the sensitization phase, and is consistent with the hypothesis that PLE arises from impaired suppression of Langerhans cell activation or migration.

UVB-induced leucocyte trafficking in the epidermis of photosensitive lupus erythematosus patients: Normal depletion of Langerhans cells

BACKGROUND

The pathogenic mechanisms of UV-induced skin lesions of lupus erythematosus (LE) are unknown. In a recent study of pathogenic mechanisms of polymorphic light eruption (PLE), significantly more Langerhans cells (LCs) persisted in the epidermis after UVB overexposure than in healthy individuals. Interestingly, the same phenomenon was observed in one subacute cutaneous lupus erythematosus (SCLE) patient. It could therefore be hypothesized that both photodermatoses share a common pathogenic mechanism of photosensitivity. In the present study, we tested this hypothesis by investigating leucocyte trafficking in the initial phase of cutaneous LE after intense UVB exposure.

METHODS

In 22 photosensitive LE patients (12 chronic discoid lupus erythematosus, seven systemic lupus erythematosus and three SCLE) and nine age/sex-matched controls, uninvolved buttock skin was exposed to six minimal erythemal dose (MED) UVB radiation. Subsequently, biopsies were taken after 24, 48 and 72 h, and one control biopsy was taken from unirradiated skin. Skin sections were stained for the presence of LCs, neutrophils and macrophages. Areal percentages of positively stained cells within the epidermis were quantified and compared between the patients and controls.

RESULTS

A gradual decrease of epidermal LCs and a gradual increase of epidermal neutrophils and macrophages at several timepoints after six MED irradiation was observed equally in both LE patients and controls.

CONCLUSION

Immunohistopathology of irradiated uninvolved skin of photosensitive LE patients did not reveal the same pathologic trafficking of LCs and neutrophils as described for PLE patients. We conclude that different mechanisms are operative in the pathogenesis of PLE and photosensitive LE.

Why is polymorphous light eruption so common in young women?

Despite the fact that polymorphous light eruption (PLE) is the most common photodermatosis, affecting 15% of healthy people in the UK, its pathogeny remains unclear. The condition is more frequent in females and begins often in young adults and in mid-adult life. The mechanism of PLE is under active research as shown by recent results, and it is hypothesized that in PLE patients, there is a partial failure of ultraviolet radiation-induced immunosuppression, causing an abnormal response to autologous antigens generated by ultraviolet radiation (UVR). The recent demonstration that the female hormone, 17beta-estradiol prevents UVR-induced suppression of the contact hypersensitivity response caused by the release of immunosuppressive cytokines (IL-10) from keratinocytes might thus explain why the risk of PLE is higher in females than in males and why the risk decreases in women after the menopause.

Polymorphous light eruption (PLE) and a new potent antioxidant and UVA-protective formulation as prophylaxis

BACKGROUND

Polymorphous light eruption (PLE) is the most common photodermatosis. While its etiology still remains elusive, pathogenesis seems to involve UVA-induced oxidative stress and subsequent deregulation of antioxidative immune responses. Only few and often ineffective prophylactic and therapeutic measures exist to date.

METHODS

In our randomized, double-blind, placebo-controlled clinical study, we compared the efficacy of a new topical formulation, consisting of 0.25%alpha-glucosylrutin (AGR) (a natural, modified flavonoid), 1% tocopheryl acetate (vitamin E) and a broad-spectrum, highly UVA-protective sunscreen (SPF 15) in a hydrodispersion gel vehicle, to a sunscreen-only gel and vehicle. Thirty patients with a history of PLE were pretreated with either the above formulation, a similar preparation (with the same concentration for vitamin E and AGR, but a different UV filter system), placebo or a SPF 15 sunscreen-only gel, 30 min prior to daily photoprovocation with UVA irradiations of 60-100 J/cm(2) to 5 x 5 cm(2) areas on the upper arms.

RESULTS

After 4 days, results revealed a statistically highly significant difference (P<0.001) between the antioxidant containing formulations and placebo, and sunscreen-only formulation, respectively, in experimentally eliciting PLE. While only one patient developed clinical signs of PLE with accompanying itch in the area treated with the new antioxidant UV-protective gel formulation, 62.1% of the placebo-treated areas and 41.3% of the sunscreen-only treated areas showed mild to moderate signs of PLE.

CONCLUSION

Combining a potent antioxidant with a broad-spectrum, highly UVA-protective sunscreen is far more effective in preventing PLE than sunscreen alone or placebo and should thus be employed as the prophylaxis of choice for PLE.