Ultraviolet light depletes surface markers of Langerhans cells

Basal Cell Carcinoma in Xeroderma Pigmentosa: Reduced CD1a Expression as a Sensitive Predictor of Recurrence

Xeroderma pigmentosa (XP) is a rare genetic disorder that is characterized by defective DNA repair after ultraviolet induced damage with a great tendency for recurrent cutaneous malignancies including basal cell carcinoma (BCC). BCC is frequently linked to impaired local immune response with a major role played by Langerhans cells (LCs). The current study aims at investigating LCs in BCC specimens of XP and non-XP patients, in a trial to study its possible impact on tumor recurrence. It included 48 retrospective cases of primary facial BCC (18 for XP patients and 30 for non-XP controls). Each group was subdivided, based on the 5 years follow-up data, into recurrent and non-recurrent BCC groups. LCs were assessed immunohistochemically using the sensitive marker; CD1a. Results showed significantly reduced LCs count (intratumoral, peritumoral, and in perilesional epidermis) in XP patients compared with non-XP controls ( P ˂0.001 for all). Intratumoral ( P =0.008), peritumoral ( P =0.005), and perilesional epidermal ( P =0.02) LCs mean values were significantly lower in recurrent versus non-recurrent BCC specimens. Also, within each group (XP and controls), LCs were of significantly lower means in recurrent versus non-recurrent cases ( P ≤0.001 for all). Regarding recurrent BCC cases, peritumoral LCs showed a significant positive correlation with 1ry BCC duration ( P =0.05). Also, intratumoral and peritumoral LCs correlated positively with BCC relapse interval ( P =0.04 for both). Among non-XP controls, periocular tumors had the least LCs count (22.00±3.56), whereas tumors located in the rest of the face had the greatest count (29.00±0.00) ( P =0.02). Sensitivity and specificity of LCs to predict BCC recurrence in XP patients reached 100% in intartumoral area and perilesional epidermis when cutoff points were less than 9.5 and 20.5, respectively. In conclusion; reduced LC count in primary BCC specimens of XP patients and also in normal subjects could help to predict its recurrence. Thus, it might be identified as a risk factor for relapse to apply new strict therapeutic and preventive measures. This presents new avenue for the immunosurveillance against skin cancer relapse. However, being the first study to investigate that link in XP patients recommends further research to confirm.

The CaSR Modulator NPS-2143 Reduced UV-Induced DNA Damage in Skh:hr1 Hairless Mice but Minimally Inhibited Skin Tumours

The calcium-sensing receptor (CaSR) is an important regulator of epidermal function. We previously reported that knockdown of the CaSR or treatment with its negative allosteric modulator, NPS-2143, significantly reduced UV-induced DNA damage, a key factor in skin cancer development. We subsequently wanted to test whether topical NPS-2143 could also reduce UV-DNA damage, immune suppression, or skin tumour development in mice. In this study, topical application of NPS-2143 (228 or 2280 pmol/cm²) to Skh:hr1 female mice reduced UV-induced cyclobutane pyrimidine dimers (CPD) (p < 0.05) and oxidative DNA damage (8-OHdG) (p < 0.05) to a similar extent as the known photoprotective agent 1,25(OH)₂ vitamin D3 (calcitriol, 1,25D). Topical NPS-2143 failed to rescue UV-induced immunosuppression in a contact hypersensitivity study. In a chronic UV photocarcinogenesis protocol, topical NPS-2143 reduced squamous cell carcinomas for only up to 24 weeks (p < 0.02) but had no other effect on skin tumour development. In human keratinocytes, 1,25D, which protected mice from UV-induced skin tumours, significantly reduced UV-upregulated p-CREB expression (p < 0.01), a potential early anti-tumour marker, while NPS-2143 had no effect. This result, together with the failure to reduce UV-induced immunosuppression, may explain why the reduction in UV-DNA damage in mice with NPS-2143 was not sufficient to inhibit skin tumour formation.

Antiviral therapy for COVID-19: Derivation of optimal strategy based on past antiviral and favipiravir experiences

Favipiravir, a broad-spectrum RNA-dependent RNA polymerase inhibitor, inhibits the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at significantly lower concentrations than the plasma trough levels achieved by the dosage adopted for influenza treatment and exhibits efficacy against coronavirus disease 2019 (COVID-19) pneumonia. Although high doses of favipiravir are required due to the molecule being a purine analog, its conversion into the active form in infected cells with active viral RNA synthesis enhances the antiviral specificity and selectivity as a chain terminator with lethal mutagenesis. Another characteristic feature is the lack of generation of favipiravir-resistant virus. COVID-19 pneumonia is caused by strong cell-mediated immunity against virus-infected cells, and the inflammatory response induced by adaptive immunity continues to peak for 3 to 5 days despite antiviral treatment. This has also been observed in herpes zoster (HZ) and cytomegalovirus (CMV) pneumonia. Inflammation due to an immune response may mask the effectiveness of favipiravir against COVID-19 pneumonia. Favipiravir significantly shortened the recovery time in patients with mild COVID-19 pneumonia by 3 days with the start of treatment by the 5th day of symptom onset. Since both CMV and COVID-19 pneumonia are caused by adaptive immunity and prevention of cytomegalovirus pneumonia is the standard treatment due to difficulties in treating refractory CMV pneumonia, COVID-19 pneumonia should be prevented with early treatment as well. In the present study, we have comprehensively reviewed the optimal antiviral therapy for COVID-19 based on clinical trials of favipiravir for the treatment of COVID-19 pneumonia and the concurrently established therapies for other viral infections, particularly HZ and CMV pneumonia. Optimally, antivirals should be administered immediately after COVID-19 diagnosis, similar to that after influenza diagnosis, to prevent COVID-19 pneumonia and complications resulting from microangiopathy.

Amenamevir, a Helicase-Primase Inhibitor, for the Optimal Treatment of Herpes Zoster

Acyclovir, valacyclovir, and famciclovir are used for the treatment of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. Helicase-primase inhibitors (HPIs) inhibit replication fork progression that separates double DNA strands into two single strands during DNA synthesis. The HPIs amenamevir and pritelivir have novel mechanisms of anti-herpetic action, and their once-daily administration has clinical efficacy for genital herpes. Among HPIs, amenamevir has anti-VZV activity. The concentrations of HSV-1 and VZV required for the 50% plaque reduction of amenamevir were 0.036 and 0.047 μM, respectively. We characterized the features of amenamevir regarding its mechanism, resistance, and synergism with acyclovir. Its antiviral activity was not influenced by the viral replication cycle, in contrast to acyclovir. A clinical trial of amenamevir for herpes zoster demonstrated its non-inferiority to valacyclovir. To date, amenamevir has been successfully used in over 1,240,000 patients with herpes zoster in Japan. Post-marketing surveillance of amenamevir in Japan reported side effects with significant potential risk identified by the Japanese Risk Management Plan, including thrombocytopenia, gingival bleeding, and palpitations, although none of these were serious. The clinical efficacy and safety profiles of amenamevir were established in patients with herpes zoster. Therefore, amenamevir as an HPI opens a new era of anti-herpes therapy.

Keratinocyte Carcinoma and Photoprevention: The Protective Actions of Repurposed Pharmaceuticals, Phytochemicals and Vitamins

Simple Summary

Keratinocyte carcinoma is the most common type of cancer. Sun exposure and ultraviolet radiation are significant contributors to the development of carcinogenesis, mediated by DNA damage, increased oxidative stress, inflammation, immunosuppression and dysregulated signal transduction. Photoprevention involves using different compounds to delay or prevent ultraviolet radiation-induced skin cancer. In this review, we look at new avenues for systemic photoprevention that are based on pharmaceuticals, plant-derived phytochemicals and vitamins. We also investigate the mechanisms underlying these strategies for preventing the onset of carcinogenesis.

Abstract

Ultraviolet radiation (UVR) arising from sun exposure represents a major risk factor in the development of keratinocyte carcinomas (KCs). UVR exposure induces dysregulated signal transduction, oxidative stress, inflammation, immunosuppression and DNA damage, all of which promote the induction and development of photocarcinogenesis. Because the incidence of KCs is increasing, better prevention strategies are necessary. In the concept of photoprevention, protective compounds are administered either topically or systemically to prevent the effects of UVR and the development of skin cancer. In this review, we provide descriptions of the pathways underlying photocarcinogenesis and an overview of selected photoprotective compounds, such as repurposed pharmaceuticals, plant-derived phytochemicals and vitamins. We discuss the protective potential of these compounds and their effects in pre-clinical and human trials, summarising the mechanisms of action involved in preventing photocarcinogenesis.

Protection from Ultraviolet Damage and Photocarcinogenesis by Vitamin D Compounds

Exposure of skin cells to UV radiation results in DNA damage, which if inadequately repaired, may cause mutations. UV-induced DNA damage and reactive oxygen and nitrogen species also cause local and systemic suppression of the adaptive immune system. Together, these changes underpin the development of skin tumours. The hormone derived from vitamin D, calcitriol (1,25-dihydroxyvitamin D₃) and other related compounds, working via the vitamin D receptor and at least in part through endoplasmic reticulum protein 57 (ERp57), reduce cyclobutane pyrimidine dimers and oxidative DNA damage in keratinocytes and other skin cell types after UV. Calcitriol and related compounds enhance DNA repair in keratinocytes, in part through decreased reactive oxygen species, increased p53 expression and/or activation, increased repair proteins and increased energy availability in the cell when calcitriol is present after UV exposure. There is mitochondrial damage in keratinocytes after UV. In the presence of calcitriol, but not vehicle, glycolysis is increased after UV, along with increased energy-conserving autophagy and changes consistent with enhanced mitophagy. Reduced DNA damage and reduced ROS/RNS should help reduce UV-induced immune suppression. Reduced UV immune suppression is observed after topical treatment with calcitriol and related compounds in hairless mice. These protective effects of calcitriol and related compounds presumably contribute to the observed reduction in skin tumour formation in mice after chronic exposure to UV followed by topical post-irradiation treatment with calcitriol and some, though not all, related compounds.

A case of Langerhans cell sarcoma on the scalp: Whole-exome sequencing reveals a role of ultraviolet in the pathogenesis

Langerhans cell sarcoma (LCS) is a high-grade neoplasm with overtly malignant cytological features and a Langerhans cell phenotype. The underlying genetic features are poorly understood, and only a few alterations, such as those of the MARK pathway-related genes, CDKN2A and TP53 have been reported. Here we present a 70-year-old male with LCS on the scalp and pulmonary metastasis. The multinodular tumor, 3.0 cm in diameter, consisted of diffusely proliferated pleomorphic cells with numerous mitoses (53/10 HPFs). Immunohistochemically, the tumor cells were positive for CD1a, Langerin and PD-L1, and the Ki-67 labeling index was 50%. These pathological features were consistent with LCS, and were also observed in the metastatic tumor. Whole-exome sequencing revealed that both the primary and metastatic tumors harbored a large number of mutations (>20 mutations/megabase), with deletion of CDKN2A and TP53 mutation, and highlighted that the mutational signature was predominantly characteristic of ultraviolet (UV) exposure (W = 0.828). Our results suggest, for the first time, that DNA damage by UV could accumulate in Langerhans cells and play a role in the pathogenesis of LCS. The high mutational burden and PD-L1 expression in the tumor would provide a rationale for the use of immune checkpoint inhibitors for treatment of unresectable LCS.

Density of Langerhans Cells in Nonmelanoma Skin Cancers: A Systematic Review

Langerhans cells (LCs) are bone marrow-derived dendritic cells (DCs) that represent 2-3% of the entire cell population of the human skin, known to have an ability to present antigens to T lymphocytes. Moreover, there is evidence that LCs are probably capable of inducing the local cytotoxic type T-cell-mediated response against the tumour-associated antigens. In the past two decades, a dramatic increase has been noted in the incidence of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). The purpose of this study was to critically assess the results of available studies quantitatively assessing the LCs in nonmelanoma skin cancers and try to establish a conclusion of its possible impact on their future treatment. The PubMed, EMBASE, and the Web of Science databases were searched, which returned 948 citations. After a thorough analysis of full article texts, 30 studies have been chosen, including 11 of the BCC, 12 of the SCC specimens, and 7 analysing both tumour types. There was an overall trend towards slightly higher numbers of LCs in BCC than in SCC; however, these tendencies were discrepant between the studies. We presume that such differences could be caused by various staining techniques with a broad spectrum of specificity, including anti-S100, anti-CD1a, and ATPase activity staining used for LCs identification. We hypothesise that as there is a high inconsistency between the results of the studies, as far as the densities of LCs observed in the specimens are concerned, it seems that the mechanism of the influence of LCs on the antitumoural immune response is complicated. Finally, as at present, there is a paucity of available risk scores for the recurrence or progression of BCC or SCC, the creation of classification stratifying that risk including the density of LCs could bring additional information both for the physician and the patient.

Oral administration of lipoteichoic acid from Lactobacillus rhamnosus GG overcomes UVB-induced immunosuppression and impairs skin tumor growth in mice

There is increasing evidence of the relevant connection and regulation between the gut and skin immune axis. In fact, oral administration of lipoteichoic acid (LTA) from Lactobacillus rhamnosus GG (LGG) prevents the development of UV-induced skin tumors in chronically exposed mice. Here we aim to evaluate whether this LTA is able to revert UV-induced immunosuppression as a mechanism involved in its anti-tumor effect and whether it has an immunotherapeutic effect against cutaneous squamous cell carcinoma. Using a mouse model of contact hypersensitivity, we demonstrate that LTA overcomes UV-induced skin immunosuppression. This effect was in part achieved by modulating the phenotype of lymph node resident dendritic cells (DC) and the homing of skin migratory DC. Importantly, oral LTA reduced significantly the growth of established skin tumors once UV radiation was discontinued, demonstrating that it has a therapeutic, besides the already demonstrated preventive antitumor effect. The data presented here strongly indicates that oral administration of LTA represents a promising immunotherapeutic approach for different conditions in which the skin immune system is compromised.

Macroenvironment-gene-microenvironment interactions in ultraviolet radiation-induced melanomagenesis

Cutaneous malignant melanoma is one of the few major cancers that continue to exhibit a positive rate of increase in the developed world. A wealth of epidemiological data has undisputedly implicated ultraviolet radiation (UVR) from sunlight and artificial sources as the major risk factor for melanomagenesis. However, the molecular mechanisms of this cause-and-effect relationship remain murky and understudied. Recent efforts on multiple fronts have brought unprecedented expansion of our knowledge base on this subject and it is now clear that melanoma is caused by a complex interaction between genetic predisposition and environmental exposure, primarily to UVR. Here we provide an overview of the effects of the macroenvironment (UVR) on the skin microenvironment and melanocyte-specific intrinsic (mostly genetic) landscape, which conspire to produce one of the deadliest malignancies.

Disruption of the Sensory System Affects Sterile Cutaneous Inflammation In Vivo

Increasing evidence suggests that nerve fibers responding to noxious stimuli (nociceptors) modulate immunity in a variety of tissues, including the skin. Yet, the role of nociceptors in regulating sterile cutaneous inflammation remains unexplored. To address this question, we have developed a detailed description of the sterile inflammation caused by overexposure to UVB irradiation (i.e., sunburn) in the mouse plantar skin. Using this model, we observed that chemical depletion of nociceptor terminals did not alter the early phase of the inflammatory response to UVB, but it caused a significant increase in the number of dendritic cells and αβ⁺ T cells as well as enhanced extravasation during the later stages of inflammation. Finally, we showed that such regulation was driven by the nociceptive neuropeptide calcitonin gene-related peptide. In conclusion, we propose that nociceptors not only play a crucial role in inflammation through avoidance reflexes and behaviors, but can also regulate sterile cutaneous immunity in vivo.

The skin as an immune organ: Tolerance versus effector responses and applications to food allergy and hypersensitivity reactions

Skin is replete with immunocompetent cells that modulate signaling pathways to maintain a salubrious immunogenic/tolerogenic balance. This fertile immune environment plays a significant role in the development of allergic responses and sensitivities, but the mechanisms underlying these pathways have been underappreciated and underused with respect to developing therapeutics. Among the complex repertoire of cells that promote tolerogenic pathways in the periphery, 2 key classes include dendritic cells and regulatory T (Treg) cells. Immature dendritic cells are the first line of defense, patrolling the periphery, sampling antigens, and secreting cytokines that suppress immune cells and promote the survival of Treg cells. Skin-homing Treg cells also play a critical role in mitigating the reactivity of immune cells, secreting high levels of cytokines that promote tolerance. Therapeutic approaches that capitalize on our knowledge of the rich cellular and molecular environment are emerging and show great promise. We will discuss the advantages and challenges of 5 such strategies and how these therapies might mitigate the atopic march by facilitating tolerance. We conclude that skin is a multifaceted structure that provides a fertile ground for therapeutic discovery. Accordingly, ongoing work in this domain will no doubt continue to deliver exciting progress for improved health outcomes.

Human skin explants an in vitro approach for assessing UVB induced damage

Lifestyle changes involving frequent outdoor activities are contributing to higher exposure to harmful ultraviolet light (UVB). The acute effects of UVB irradiation on human skin was evaluated in this study using freshly excised human skin from elective surgery subjected to UVB doses (0-3.76 J/cm²). The assessment of UVB induced cellular and skin damages was undertaken at two time points immediately and 24 h post exposure using in vitro, and immunohistochemical staining techniques. The results indicated no significant loss of skin integrity or significant acute mitochondrial cellular damages in UVB exposed skin sections as measured by the MTS cytotoxicity assay. The other key markers of damage showed significant extracellular LDH membrane leakages and upregulation of inflammatory cytokines such as IL-1β. Skin integrity analysis was also undertaken using H&E, HLADR, and anti-cytokeratin antibodies. The results showed significant epidermal changes, basal cell activation and Langerhans cells depletion. The research proved the usefulness of freshly excised human skin explant model in measuring UVB damage. Furthermore, freshly excised human skin maintains the natural layering and therefore does not pose the same challenges faced by commercially available reconstructed skin in terms of higher costs and accurate mimicking of all the complex interactions observed in human skin.

Differential Induction of IL-12 p40 and IL-10 mRNA in Human Langerhans' Cells and Keratinocytes by in Vivo Occlusion, Vehicle, and All-TRANS Retinoic Acid

Background:

Hydration and pharmacologic manipulation of the skin may have immunomodulatory effects. For instance, retinoic acid (RA) in vivo upregulates antigen-presenting cell (APC) activity of Langerhans' cells (LC).

Objective:

Our study was to determine whether RA increases LC APC activity via alteration of the potent immunoregulatory and reciprocally acting cytokines, IL-12 and IL-10.

Methods:

0.1% RA and vehicle solvent only (V) as a control were applied under occlusion on the skin of normal volunteers. Freshly selected CD1a+ LC and keratinocytes from keratome were subject to semiquantitative determination of IL-12 p40 and IL-10 mRNA levels. IL-12 p40 protein was measured by radioimmunoassay.

Results:

Occlusion alone and open vehicle alone did not induce LC immunoregulatory cytokines; LCs demonstrated significant induction of IL-12 p40 mRNA, when the vehicle was occluded for 48 hours and, to a lesser extent, IL-10 as well. IL-12 p40 mRNA could be further induced by RA-LC at the 20-hour time point; however, IL-10 mRNA was induced at the 48-hour time point. Neither occlusion nor RA significantly induced IL-12 p40 or IL-10 mRNA in CD1a keratinocytes at any time points.

Conclusion:

A tight reciprocal regulation of IL-10 and IL-12 is present in LCs and is consistent with the initial, but self-limited, inflammatory effect of occlusion and topical retinoids.

Nonredundant roles of keratinocyte-derived IL-34 and neutrophil-derived CSF1 in Langerhans cell renewal in the steady state and during inflammation

IL-34 and colony-stimulating factor 1 (CSF1) are two alternative ligands for the CSF1 receptor that play nonredundant roles in the development, survival, and function of tissue macrophages and Langerhans cells (LCs). In this study, we investigated the spatio-temporal production of IL-34 and its impact on skin LCs in the developing embryo and adult mice in the steady state and during inflammation using Il34(LacZ) reporter mice and newly generated inducible Il34-knockout mice. We found that IL-34 is produced in the developing skin epidermis of the embryo, where it promotes the final differentiation of LC precursors. In adult life, LCs required IL-34 to continually self-renew in the steady state. However, during UV-induced skin damage, LC regeneration depended on neutrophils infiltrating the skin, which produced large amounts of CSF1. We conclude that LCs require IL-34 when residing in fully differentiated and anatomically intact skin epidermis, but rely on neutrophil-derived CSF1 during inflammation. Our demonstration that neutrophils are an important source of CSF1 during skin inflammation may exemplify a mechanism through which neutrophils promote their subsequent replacement with mononuclear phagocytes.

The immune microenvironment in cutaneous leishmaniasis

BACKGROUND

Cutaneous leishmaniasis is an infection that has spread to non-endemic regions, stimulating recent interest for the enhanced understanding of this disease. Downregulation of the CD1a receptor on Langerhans cells has been described in various cutaneous infections.

OBJECTIVE

In this study, the immune response across different Ridley patterns and parasitic indices is outlined in a case series of cutaneous leishmaniasis.

METHODS

Skin punch biopsies from the interface of normal and lesional cutaneous leishmaniasis were collected from 33 patients with molecularly confirmed Leishmania tropica or L. major infection. Ridley patterns (2-5) were assessed for various clinicopathological features including age, gender, disease duration, parasitic index and constituents of the inflammatory infiltrate. CD1a, CD68, CD3, CD4, CD8, CD20 and CD138 stains were performed on normal skin tissue, cutaneous leishmaniasis biopsies and cytospin/cell block cytology preparations of cultured leishmania promastigotes. CD1a was quantified per mm2 in the epidermis and dermis. The remaining stains were graded according to a 4-tiered grading system [0 (0-4%); 1 (5-24%); 2 (25-49%); 3 (50-74%) and 4 (75-100%).

RESULTS

Total CD1a expression significantly decreased (14-fold) from parasitic indices (0-2) to (5-6); (ρ < 0.001). CD1a expression in the epidermis was at least 5-fold lower than normal skin (58 vs. 400 cells/mm2), inversely correlating with the parasitic index. There was an increase in dermal CD1a Langerhans cells (33 vs. 0 cells/mm² in the dermis). CD1a and CD68 staining of amastigotes was strong and diffuse, whereas promastigotes were negative. The major inflammatory infiltrate, in all Ridley patterns, consisted of macrophages and double-negative CD3(+) CD4(-) CD8(-) T lymphocytes. The double-negative CD3 T cells formed a ring around the parasitic laden macrophages. Apart from CD1a, there was no significant difference in inflammatory markers between the various Ridley patterns and parasitic indices. Disease duration did not correlate with Ridley pattern.

CONCLUSION

The significant decrease in CD1a expression is postulated by two mechanisms; either via direct CD1a receptor uptake by leishmania amastigotes and/or negative feedback inhibition of CD1a Langerhans cells by double-negative CD3 T-regulatory cells. Modulation of the immune microenvironment in cutaneous leishmaniasis represents a potential therapeutic and prophylactic target.

Human in vitro skin organ culture as a model system for evaluating DNA repair

BACKGROUND

UV-exposures result in accumulation of genetic lesions that facilitate the development of skin cancer. Numerous pharmacologic agents are currently under development to both inhibit formation of DNA lesions and enhance repair. Drugs must be evaluated in vitro, currently performed in cell culture systems, before being tested on humans. Current systems do not account for the architecture and diverse cellularity of intact human skin.

OBJECTIVE

To establish a novel, functionally viable, and reproducible in vitro skin organ culture system for studying the effects of various pharmacologic agents on DNA repair.

METHODS

Human skin was obtained from neonatal foreskins. Intact skin punches derived from foreskins were cultured in vitro prior to exposure to UV-irradiation, and evaluated for DNA-damage using a DNA dot blot. Serial skin biopsies were obtained from patients with actinic keratoses treated with topical imiquimod. Expression of immune-stimulating and DNA repair genes was evaluated in ex vivo and in vitro samples.

RESULTS

DNA dot blots revealed active repair of UV induced lesions in our in vitro skin organ culture. The photo-protective effect of sunscreen was detected, while imiquimod treatment did not enhance DNA repair in vitro. The DNA repair molecules XPA and XPF were up-regulated in the skin of imiquimod treated patients with actinic keratoses and imiquimod treated bone marrow-derived cell lines, but not keratinocytes.

CONCLUSION

Our in vitro human skin organ culture model detected repair of UV-induced DNA lesions, and may be easily adapted to investigate various photo-protective drugs intended to prevent or treat skin cancer.

Quantification of quantum dot murine skin penetration with UVR barrier impairment

Ultraviolet radiation (UVR) skin exposure is a common exogenous insult that can alter skin barrier and immune functions. With the growing presence of nanoparticles (NPs) in consumer goods and technological applications the potential for NPs to contact UVR-exposed skin is increasing. Therefore it is important to understand the effect of UVR on NP skin penetration and the potential for systemic translocation. Previous studies qualitatively showed that UVR skin exposure can increase the penetration of NPs below the stratum corneum. In this work, an in vivo mouse model was used to quantitatively examine the skin penetration of carboxylated (CdSe/ZnS, core/shell) quantum dots (QDs) through intact and UVR barrier-disrupted murine skin by organ Cd mass analysis. Transepidermal water loss was used to measure the magnitude of the skin barrier defect as a function of UVR dose and time post-UVR exposure. QDs were applied to mice 3-4 days post-UVR exposure at the peak of the skin barrier disruption. Our results reveal unexpected trends that suggest these negative-charged QDs can penetrate barrier intact skin and that penetration and systemic transport depends on the QD application time post-UVR exposure. The effect of UVR on skin-resident dendritic cells and their role in the systemic translocation of these QDs are described. Our results suggest that NP skin penetration and translocation may depend on the specific barrier insult and the inflammatory status of the skin.

Understanding engineered nanomaterial skin interactions and the modulatory effects of ultraviolet radiation skin exposure

The study of engineered nanomaterials for the development of technological applications, nanomedicine, and nano-enabled consumer products is an ever-expanding discipline as is the concern over the impact of nanotechnology on human environmental health and safety. In this review, we discuss the current state of understanding of nanomaterial skin interactions with a specific emphasis on the effects of ultraviolet radiation (UVR) skin exposure. Skin is the largest organ of the body and is typically exposed to UVR on a daily basis. This necessitates the need to understand how UVR skin exposure can influence nanomaterial skin penetration, alter nanomaterial systemic trafficking, toxicity, and skin immune function. We explore the unique dichotomy that UVR has on inducing both deleterious and therapeutic effects in skin. The subject matter covered in this review is broadly informative and will raise awareness of potential increased risks from nanomaterial skin exposure associated with specific occupational and life style choices. The UVR-induced immunosuppressive response in skin raises intriguing questions that motivate future research directions in the nanotoxicology and nanomedicine fields.

Effects of topical pimecrolimus 1% on high-dose ultraviolet B-irradiated epidermal Langerhans cells

Some studies reported no changes in the number of epidermal Langerhans cells (LC) that were observed in mice treated with pimecrolimus, and low-dose stimulated solar radiation (once)-induced changers in LC are minimally affected by pimecrolimus. This study is to investigate the effects of topical pimecrolimus 1% on high-dose ultraviolet B (UVB)-irradiated epidermal LC. Forty human foreskin tissues were randomly divided into 4 groups of 10 tissues each: Group A, control; Group B, pimecrolimus 1% (once)-only; Group C, 180 mJ/cm(2) UVB (once)-only; Group D, UVB+pimecrolimus. Each tissue was cut into 4 pieces corresponding to 4 time points. All the tissues were cultured at 37 °C. After being treated, the tissues were collected respectively and processed for immunohistochemical staining and immunofluorescence staining. For UVB-only group, epidermal CD1a(+) LC number at 18h decreased from 39.6 ± 8.30 to 22.3 ± 2.26/5 high magnification, compared to CD1a(+) LC number at 0 h (P<0.01). The CD1a(+) LC number of UVB-only group was significantly less than other groups at 18 h, 24h and 48 h (P<0.05, respectively). Similar results were obtained with immunofluorescence staining for CD 1a and immunohistochemical staining for Langerin. The numbers of epidermal HLA-DR(+) LC had no significant differences among all groups at different time points. Our study found a single 180 mJ/cm(2) UVB irradiation significantly reduced epidermal LC numbers at 18 h, 24h and 48 h, however, topical pimecrolimus could reverse these changes. UVB plus pimecrolimus treatment did not affect human LC maturation.

Induction of regulatory T cells by a murine β-defensin

β-Defensins are antimicrobial peptides of the innate immune system produced in the skin by various stimuli, including proinflammatory cytokines, bacterial infection, and exposure to UV radiation (UVR). In this study we demonstrate that the UVR-inducible antimicrobial peptide murine β-defensin-14 (mBD-14) switches CD4(+)CD25(-) T cells into a regulatory phenotype by inducing the expression of specific markers like Foxp3 and CTLA-4. This is functionally relevant because mBD-14-treated T cells inhibit sensitization upon adoptive transfer into naive C57BL/6 mice. Accordingly, injection of mBD-14, comparable to UVR, suppresses the induction of contact hypersensitivity and induces Ag-specific regulatory T cells (Tregs). Further evidence for the ability of mBD-14 to induce Foxp3(+) T cells is provided using DEREG (depletion of Tregs) mice in which Foxp3-expressing cells can be depleted by injecting diphtheria toxin. mBD-14 does not suppress sensitization in IL-10 knockout mice, suggesting involvement of IL-10 in mBD-14-mediated immunosuppression. However, unlike UVR, mBD-14 does not appear to mediate its immunosuppressive effects by affecting dendritic cells. Accordingly, UVR-induced immunosuppression is not abrogated in mBD-14 knockout mice. Together, these data suggest that mBD-14, like UVR, has the capacity to induce Tregs but does not appear to play a major role in UVR-induced immunosuppression. Through this capacity, mBD-14 may protect the host from microbial attacks on the one hand, but tame T cell-driven reactions on the other hand, thereby enabling an antimicrobial defense without collateral damage by the adaptive immune system.

Langerhans cells and melanocytes share similar morphologic features under in vivo reflectance confocal microscopy: a challenge for melanoma diagnosis

BACKGROUND

Intraepidermal Langerhans cells (ILC) are difficult to differentiate from melanocytes under reflectance confocal microscopy (RCM) and their presence may simulate pagetoid spread of melanocytes on RCM images.

OBJECTIVE

We sought to correlate bright round and dendritic cells in a pagetoid pattern identified on RCM with findings of conventional histopathology and immunohistochemistry for lesions that were falsely diagnosed as melanoma by RCM.

METHODS

This retrospective study included histopathologically proven nevi, imaged by RCM, which displayed bright cells in a pagetoid pattern (BCPP) under RCM, resulting in the incorrect RCM diagnosis of melanoma. Morphological comparisons were made between RCM images of nevi showing BCPP, histopathologically proven melanomas displaying BCPP, and biopsy-proven nevi without BCPP.

RESULTS

We identified 24 nevi that were falsely diagnosed as melanoma by RCM because of the presence of BCPP. These pagetoid cells on RCM corresponded on histopathology to ILC with a high density in 23 of the 24 nevi (95%) and to melanocytes in 7 of the 24 nevi (29%). Among 6 melanomas displaying BCPP on RCM, ILC with high density were observed histopathologically in 5 of the 6 cases (83%) and pagetoid melanocytes were seen in all 6 cases (100%).

LIMITATIONS

The results cannot be generalized to clinically banal-appearing nevi.

CONCLUSIONS

Although the finding of BCPP is a useful RCM feature for the diagnosis of melanoma, it does not always imply the presence of pagetoid melanocytes but may at times represent ILC.

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.

Leishmaniasis, contact hypersensitivity and graft-versus-host disease: understanding the role of dendritic cell subsets in balancing skin immunity and tolerance

Dendritic cells (DC) are key elements of the immune system. In peripheral tissues, they function as sentinels taking up and processing antigens. After migration to the draining lymph nodes, the DC either present antigenic peptides by themselves or transfer them to lymph node-resident DC. The skin is the primary interface between the body and the environment and host's various DC subsets, including dermal DC (dDC) and Langerhans cells (LC). Because of their anatomical position in the epidermis, LC are believed to be responsible for induction of adaptive cutaneous immune responses. The functions of LC and dDC in the skin immune system in vivo are manifold, and it is still discussed controversially whether the differentiation of T-cell subtypes (e.g. effector T cells and regulatory T cells) may be initiated by distinct DC subtypes. As skin DC are able to promote or downmodulate immune responses, we chose different skin diseases (cutaneous leishmaniasis, contact hypersensitivity, UV radiation-induced suppression, and graft-versus-host disease) to describe the biological interactions between different DC subtypes and T cells that lead to the development of efficient or unwanted immune responses. A detailed knowledge about the immune modulatory capacity of different cutaneous DC subsets might be helpful to specifically target these cells through the skin during therapeutic interventions.

Endonasal phototherapy significantly alleviates symptoms of allergic rhinitis, but has a limited impact on the nasal mucosal immune cells

The literature documents the fact that UV irradiation of cutaneous Langerhans cells (LC) in vivo prevents the development of contact allergy and produces long-lasting immunosuppression. However, not much is known about the effect of UV irradiation on the LC of the nasal mucosa and their connection with clinical scores. Local antigen presentation may be necessary for both primary and recall T cell responses to birch pollen in patients with hay fever. Endonasal phototherapy combination of UVB (5%), UVA (25%) and visible light (70%) utilises the immunosuppressive effects of UV irradiation. The aim of this study was to correlate clinical symptom scores with possible changes in the LC of the nasal mucosa induced by UV radiation. The clinical effectiveness of this form of treatment is discussed. Nasal biopsies were obtained from ten birch pollen-sensitive patients with seasonal rhinitis before and after endonasal phototherapy. All patients showed a significant clinical benefit post-treatment as assessed by standardised instruments, including total nasal symptom score, nasal congestion score, nasal itching score, sneezing score, nasal secretion score and impairment-to-health score. However, we found no significant morphological changes, to, or quantitative differences in, the CD1a+, CD4, CD8 or CD31 cells before and 14 days after treatment. Despite the positive clinical effect, the study revealed no effect of UV irradiation on the LC and other analysed cells of the nasal mucosa immune system. Possible reasons for this are discussed.

Immunohistochemical study of Langerhans cells in cutaneous lesions of the Jorge Lobo's disease

Jorge Lobo's disease is a chronic infection caused by the fungus Lacazia loboi endemic in South America. The infection is characterized by the appearance of parakeloidal, ulcerated or verrucous nodular or plaque-like cutaneous lesions. The histopathological aspect is characterized by poorly organized granulomas with histiocytes and multinucleated giant cells. Little is known about local immune response in lobomycosis skin lesions. Thirty-three skin biopsies from patients with Jorge Lobo's disease were selected from Ambulatory of Dermatology, UFPA. The control group was constituted by ten biopsies from normal skin. Langerhans cells were identified by immunohistochemistry using anti-CD1a antibody (Serotec). The number of positive cells was statistically analyzed. Langerhans cells were visualized along the epidermis in biopsies from Jorge Lobo's disease and the morphology and the number of Langerhans cells did not differ from normal skin (p>0.05). In Jorge Lobo's disease, this cell population probably presents some escape mechanism of the local immune system to evade the antigen presentation by those cells.

Langerhans cells: critical regulators of skin immunity?

Langerhans cells (LC) are members of the heterogenous family of professional antigen presenting dendritic cells (DC). They are identified by the C-type lectin receptor Langerin and form a contiguous network in the epidermis. Consequently, LC are an integral part of the skin barrier to the environment and were considered to be critical inducers of skin immunity, whereas dermal DC were largely overlooked. However, with the identification of a distinct subset of Langerin expressing dermal DC, the situation in the skin has become more complex and the relative contribution of the different cutaneous DC populations in balancing immunity and tolerance has become a matter of active debate. Here, we briefly review the classical paradigm and recent challenges of LC function, before focusing on advances concerning their role in contact hypersensitivity and ultraviolet radiation-induced immunosuppression obtained with in vivo LC ablation models. We then discuss novel LC/DC-specific gene targeting approaches currently used to dissect the role of the regulatory cytokines transforming growth factor-beta and interleukin-10 to govern LC and DC function in vivo. This second generation of LC-specific genetically engineered mice will considerably extend our understanding of the molecular control of LC function in regulating skin immunity and tolerance in the near future.

Langerhans cells are required for UVR-induced immunosuppression

Painting of haptens onto UVR-exposed skin does not result in sensitization but induces regulatory T cells (Treg). This was explained by UVR-mediated depletion of Langerhans cells (LCs). Furthermore, migration of UVR-damaged but still viable LCs into lymph nodes appears to be essential to induce Treg. Accordingly, the steroid mometasone, which kills LCs, inhibited sensitization but did not induce Treg. In Langerin-diphtheria toxin receptor knock-in (DTR) mice, LCs can be depleted by injection of diphtheria toxin (DT). LC-depleted mice could be sensitized though less pronounced than wild-type mice, but sensitization was not suppressed by UVR. Similarly, Treg did not develop. Langerin is not only expressed in LCs but also in some dermal dendritic cells (dDCs). Langerin-positive dDCs repopulate within 10 days after depletion, whereas LCs are still absent. Langerin-DTR mice treated with DT 10 days before UVR and sensitization were still resistant to UVR-induced inhibition of contact hypersensitivity (CHS). Similarly, Treg did not arise. As in this setting only LCs but not Langerin-positive dDCs are absent, LCs appear to be essential for both the suppression of CHS and the induction of Treg by UVR. This supports the concept that LCs are more important for the downregulation than the induction of immune responses in the skin.

Light, including ultraviolet

Ultraviolet (UV) light is intricately linked to the functional status of the cutaneous immune system. In susceptible individuals, UV radiation can ignite pathogenic inflammatory pathways leading to allergy or autoimmunity. In others, this same UV radiation can be used as a phototherapy to suppress pathogenic cutaneous immune responses. These vastly different properties are a direct result of UV light's ability to ionize molecules in the skin and thereby chemically alter them. Sometimes these UV-induced chemical reactions are essential, the formation of pre-vitamin D(3) from 7-dehydrocholesterol, for example. In other instances they can be potentially detrimental. UV radiation can ionize a cell's DNA causing adjacent pyrimidine bases to chemically bond to each other. To prevent malignant transformation, a cell may respond to this UV-induced DNA damage by undergoing apoptosis. Although this pathway prevents skin cancer it also has the potential of inducing or exacerbating autoreactive immune responses by exposing the cell's nuclear antigens. Ultraviolet-induced chemical reactions can activate the immune system by a variety of other mechanisms as well. In response to UV irradiation keratinocytes secrete cytokines and chemokines, which activate and recruit leukocytes to the skin. In some individuals UV-induced chemical reactions can synthesize novel antigens resulting in a photoallergy. Alternatively, photosensitizing molecules can damage cells by initiating sunburn-like phototoxic reactions. Herein we review all types of UV-induced skin reactions, especially those involving the immune system.

Epidermal Langerhans cells are not required for UV-induced immunosuppression

UV light can be highly beneficial in the treatment of skin disorders such as psoriasis. It is thought to cause immunosuppression by depleting or altering the function of epidermal Langerhans cells (LC). Our previous studies identified a novel langerin(+) dendritic cell in the dermis, distinct from LC in phenotype, circulation, and function. In this study, we determined the role of LC and dermal langerin(+) cells in UV suppression. UV light suppressed the CD8 T cell response to both contact hypersensitivity and epicutaneous protein immunization, and resulted in a dramatically altered phenotype of LC. UV light did not alter early CD8 T cell activation in the lymph nodes, but rather reduced CD8 T cell expansion at later time points. We found that dermal langerin(+) cells, but not LC, were essential for the CD8 T cell response. Furthermore, in the selective absence of LC, UV light still caused suppression of both CD8 T cell expansion and contact hypersensitivity.

25 years of UV-induced immunosuppression mediated by T cells-from disregarded T suppressor cells to highly respected regulatory T cells

For more than 25 years it is known that UV radiation, in particular the UVB range suppresses the immune system. In contrast to conventional immunosuppression by immunosuppressive drugs, UV radiation does not compromise the immune system in a general but rather in an antigen-specific fashion via induction of immunotolerance. This effect is mostly mediated via regulatory T cells (Treg) induced by UV. Several subtypes of UV-induced Treg may exist, the best characterized are those which inhibit contact hypersensitivity. Induction of these Tregs by UV radiation is an active process which requires antigen presentation by UV-damaged but still alive Langerhans cells (LC) in the lymph nodes. UV-induced Treg have recently been characterized as expressing CD4 and CD25 and as releasing upon activation the immunosuppressive cytokine interleukin (IL)-10. Once activated in an antigen-specific manner, they suppress immune responses in a general fashion via the release of IL-10, a phenomenon called bystander suppression. The further phenotypic and functional characterization of these cells will not only contribute to a better understanding of the impact of UV radiation on the immune system but will also determine whether they can be applied in the future therapeutically with the final aim of achieving specific immunosuppression.

Increased Langerhans cell accumulation after mycobacterial stimuli

Aims:

To evaluate the role of Langerhans cells (LCs) in the local activation of leprosy lesions. LCs, acting as tolerance inducers and immune stimuli, are dendritic cells recently implicated in cutaneous homeostasis. The role of LCs in the defence against mycobacterial infection remains poorly understood.

Methods and results:

The number and distribution of CD1a+ skin cells and HLA-DR and intercellular adhesion molecule (ICAM)-1 expression were analysed in leprosy skin lesions and in delayed-type hypersensitivity (DTH) tests. The results showed a high number of LCs in tuberculin and lepromin tests, in tuberculoid lesions and in the epidermis and dermis during type I and II reactions. In multibacillary lesions, however, the number of LCs was consistently low in comparison with other groups. Increased numbers of LCs were accompanied by marked HLA-DR and ICAM-1 expression, suggesting a strong relationship between these immunological events.

Conclusions:

CD1a+ cells are implicated in the local immunological events taking place after mycobacterial stimuli and may account for the local activation of all types of reactional episodes in leprosy.

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.

UV-induced immune suppression and photocarcinogenesis: chemoprevention by dietary botanical agents

Studies of immune-suppressed transplant recipients and patients with biopsy-proven skin cancer have confirmed that ultraviolet (UV) radiation-induced immune suppression is a risk factor for the development of skin cancer in humans. UV radiation suppresses the immune system in several ways. The UVB spectrum inhibits antigen presentation, induces the release of immunosuppressive cytokines, and elicits DNA damage that is a molecular trigger of UV-mediated immunosuppression. It is therefore important to elucidate the mechanisms underlying UV-induced immunosuppression as a basis for developing strategies to protect individuals from this effect and subsequent development of skin cancer. Dietary botanicals are of particular interest as they have been shown to inhibit UV-induced immune suppression and photocarcinogenesis. In this review, we summarize the most recent investigations and mechanistic studies regarding the photoprotective efficacy of selected dietary agents, including, green tea polyphenols, grape seed proanthocyanidins and silymarin. We present evidence that these chemopreventive agents prevent UVB-induced immunosuppression and photocarcinogenesis through: (i) the induction of immunoregulatory cytokine interleukin (IL)-12; (ii) IL-12-dependent DNA repair; and (iii) stimulation of cytotoxic T cells in the tumor microenvironment. The new information regarding the mechanisms of action of these agents supports their potential use as adjuncts in the prevention of photocarcinogenesis.

"Multi Light and Drugs": a new technique to treat face photoaging. Comparative study with photorejuvenation

Nonablative skin rejuvenation using laser, intense pulsed lights (IPLs), or radiofrequency techniques are becoming increasingly popular. In this paper, a novel protocol that integrates IPL sessions, low intense light and vitamin C, low-weight hyaluronic acid, betaglucan dermal injection versus IPL photorejuvenation as monotherapy is compared. A group of 100 patients, all women, with ages ranging from 35 to 65 years old (median age 56.3) with different degrees of photodamage was considered. A blinded control study was done. The patients were divided not randomly into two groups. These groups are similar for ages, skin types, and degrees of photoaging distribution. A first group of 40 patients had monotherapy consisting of seven sessions of IPL only. A second group of 60 patients had triple therapy consisting of seven sessions of IPL as well as nine sessions of low intense diode light and also biostimulation by drugs. Considering only the improvement in hyperpigmentations and teleangectasias, the monotherapy and the triple therapy show good results with no significant statistical difference between the two groups. Considering the improvement in skin texture and firmness in the group treated only with monotherapy, 30% (12 patients) had positive results, and 70% (28 patients) had poor results. In the group treated with triple therapy, 70% (42 patients) had positive results, and 30% (18 patients) had poor results, with the main differences in skin silicone negative imprints. On the basis of the data presented, the new technique of IPL, low intensity diode light, and multidrugs biostimulation seems to be a safe and effective method for skin rejuvenation and upgrades the effects of IPL in the fibroblasts' stimulation.

Immunosuppressive effects of photodynamic therapy by topical aminolevulinic acid

Photodynamic therapy (PDT) has been used for inflammatory skin disorders as well as superficial skin cancers such as solar keratosis and Bowen's disease. Whether PDT with topical application of aminolevulinic acid (ALA) and exposure to visible light has a similar immunosuppressive action to ultraviolet phototherapy was investigated using a murine contact hypersensitivity (CHS) model. The number of epidermal Langerhans cells (LC) was decreased with their morphological changes 1 day after PDT with the minimal level at 5 days and gradual recovery thereafter. Conversely, the number of CD11c(+) I-A(+) cells was significantly increased in the draining lymph nodes after PDT. This suggests that LC moved from PDT-treated skin, resulting in the decrement of epidermal LC and migration to lymph nodes. CHS response to DNFB applied on the PDT-treated skin with 20% ALA and 40 J/cm(2) visible light was significantly suppressed (local immunosuppression). When mice were treated with 80 J/cm(2) of PDT, CHS response to the antigen applied on untreated distant skin was also significantly suppressed (systemic immunosuppression). The locally or systemically immunosuppressed mice by PDT were attempted to sensitize again with DNFB on non-treated skin, but elicitation responses were significantly suppressed. However, these mice were able to be sensitized with another hapten, oxasolone. Thus, a hapten-specific immunological unresponsiveness (tolerance) was induced in mice by topical ALA-PDT. These findings suggest that PDT has a potential immunological contribution to clinical efficacy for inflammatory diseases identical to ultraviolet phototherapies.

Oxidative stress-related markers and langerhans cells in a hairless rat model exposed to UV radiation

Biomarkers related to the oxidative stress in blood and epidermis and the number of Langerhans cells were determined in hairless rats after acute irradiation with 1.54, 1.93, or 2.41 J/cm2 of ultraviolet (UV) light and chronic exposure to 13 suberythemal UV doses of 1.1 J/cm2 for 2 mo. After acute UV irradiation, in epidermis, the thiobarbituric acid-reactive substances (TBARS) content increased at the highest UV dose, whereas the activities of glutathione S-transferase and catalase rose and the oxidized glutathione (GSSG) content diminished at all UV doses. In erythrocytes, glutathione S-transferase activity increased at the two lowest UV doses, glutathione peroxidase activity rose at all UV doses, and catalase activity increased after the highest UV dose. In plasma, the TBARS content and the reduced glutathione (GSH)/GSSG ratio increased at the highest UV dose; the number of Langerhans cells decreased at all UV doses. Linear Pearson correlation analysis revealed many relationships between different biomarkers, and multiple linear regression analysis indicated that the number of Langerhans cells was predicted by epidermal GSSG and catalase (R2 = .64) and by erythrocytic glutathione peroxidase and GSSG (R2 = .72). After suberythemal UV radiation, in epidermis, the GST activity and the content of GSH and GSSG increased; in erythrocytes, the GST activity decreased and the GSH/GSSG ratio increased. Thus, the hairless rat appears to be a useful model for studying the oxidative stress-related mechanisms after UV radiation, which are involved in the loss of the immune capacity mediated by Langerhans cells, even at suberythemal doses.

Ultraviolet B radiation suppresses Langerhans cell migration in the dermis by down-regulation of alpha4 integrin

BACKGROUND/PURPOSE

Ultraviolet B (UVB) radiation affects the migration and function of epidermal Langerhans cells (LC) and causes immunosuppression of contact hypersensitivity. It is known that LC leaves the epidermis after exposure to UVB. To know the behavior of LC in the dermis after UVB radiation, we studied the effect of UVB radiation on the expression of integrin families on freshly isolated or cultured murine LC. We also examined whether UVB radiation affects the migration of LC to secondary lymphoid tissue chemokine (SLC/6Ckine).

METHODS

Integrin expressions of murine LC cultured in epidermal cell suspension were analyzed using flowcytometry. We used murine LC sorted flowcytometrically for binding assay to extracellular matrix and for migration assay to chemokine. Skin explant assay and immnohistochemical staining for 'cords formation' were performed as previously described.

RESULTS

Twenty and 40 mJ/cm2 of UVB radiation down-regulated the expression of alpha4 integrin on 24 h-cultured LC, but not that of alpha6, beta1, or beta4 integrin. The number of cultured LC adhered to fibronectin, a ligand for alpha4 integrin, was decreased after UVB irradiation, while that to laminin, a ligand for alpha6 integrin, was not influenced. UVB radiation reduced the number of migrating LC to SLC. Furthermore, skin sheet explant experiments showed that UVB radiation inhibited the 'cords' formation in dermal vessels of the 48 h-cultured skin.

CONCLUSIONS

These data suggest that UVB radiation may suppress the migration of LC from the dermis to lymphatic vessels. UVB radiation may downregulate the adherence of LC to dermal fibronectin and migration to SLC, and consequently suppress the migration of LC from the UVB-irradiated dermis to lymphatics.

Topical Imiquimod Treatment Prevents UV-Light Induced Loss of Contact Hypersensitivity and Immune Tolerance

Imiquimod (1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine) is a TLR7 agonist that induces cytokine production in TLR7 bearing antigen-presenting cells (APCs), including IL-12, a cytokine that has been demonstrated to be a critical effector molecule for contact hypersensitivity (CHS). To test our hypothesis that topical applications of imiquimod may protect the skin immune system against the deleterious effects of UV light exposures, we treated animals with this agent, or its vehicle or nothing before UV exposures. Although topical imiquimod exposures before UV light did not prevent the depletion of epidermal Langerhans cells, it did prevent the loss of CHS. IL-12 was important in the protective role of imiquimod in preventing UV-induced loss of CHS, as systemic treatment of mice with an anti-IL-12 p70 monoclonal antibody blocked the protective effects of imiquimod. Additionally, only imiquimod-treated mice were resistant to hapten-specific tolerance induction after UV irradiation at the site of the initial sensitization with the hapten 2,4 dinitro-1-fluorobenzene. To model for the effects of TLR7 activation on the UV effect on antigen-APCs, XS52 cell line was used to study this interaction in an in vitro model system. This cell line expressed mRNA for TLR7, downregulated IkappaB, phosphorylated c-Jun N-terminal kinase, and secreted cytokines after exposure to imiquimod or lipopolysaccharide. Activation of the TLR7 signaling pathway on XS52 before UV-light exposures enhanced IL-12p70 secretion by this cell line. Similarly, activation of TLR7 on XS52 before UV-light exposure also prevented the UV-induced loss of IFN-gamma triggering in T cells during an allogeneic mixed lymphocyte reaction. Imiquimod-treated, UV-irradiated XS52 triggered a more vigorous IFN-gamma production than did either imiquimod-treated XS52 or UV-irradiated XS52, again suggesting a synergy between the two treatments. Lastly, enriched lymph node CD11c+ APCs from mice treated with UV irradiation, imiquimod alone or the combination of UV irradiation and imiquimod indicated the same in vivo synergy between imiquimod irradiation and UV irradiation in enhancing IL-12p70 production. These data suggest that topical imiquimod applications may play a role in preventing UV-induced impairment of the skin immune system, which is thought to be one of the critical events that allow the development of UV-induced skin cancers.