Evidence that ultraviolet B radiation transiently inhibits emigration of Langerhans cells from exposed epidermis, thwarting contact hypersensitivity induction

Causal association between skin cancer and immune cells: mendelian randomization (MR) study

BACKGROUND

Numerous meta-analyses and clinical studies have shown that subtypes of immune cells are associated with the development of skin cancer, but it is not clear whether this association is causal or biased. Mendelian randomization (MR) analysis reduces the effect of confounding factors and improves the accuracy of the results when compared to traditional studies. Thus, in order to examine the causal relationship between various immune cell and skin cancer, this study employs two-sample MR.

METHODS

This study assesses the causal association between 731 immune cell characteristics and skin cancer using a two-sample Mendel randomization (MR) methodology. Multiple MR methods were used to bias and to derive reliable estimates of causality between instrumental variables and outcomes. Comprehensive sensitivity analyses were used to validate the stability, heterogeneity and horizontal multiplicity of the results.

RESULTS

We discovered that potential causal relationships between different types of immune cells and skin cancer disease. Specifically, one type of immune cell as potentially causal to malignant melanoma of skin (MM), eight different types of immune cells as potentially causal to basal cell carcinoma (BCC), four different types of immune cells as potentially causal to actinic keratosis (AK), and no different types of immune cells were found to have a potential causal association with squamous cell carcinoma(SCC), with stability in all of the results.

CONCLUSION

This study demonstrates the close connection between immune cells and skin cancer disease by genetic means, which enriches the current knowledge about the role of immune cells in skin cancer and also contributes to the design of therapeutic strategies from an immunological perspective.

Inhibition of UVB radiation-induced tissue swelling and immune suppression by nicotinamide riboside and pterostilbene

BACKGROUND

Environmental ultraviolet radiation has deleterious effects on humans, including sunburn and immune perturbations. These immune changes are involved in skin carcinogenesis.

OBJECTIVES

To determine whether nicotinamide riboside and/or pterostilbene administered systemically inhibits inflammatory and immune effects of exposure to mid-range ultraviolet radiation.

METHODS

To examine UVB radiation-induced inflammatory effects, mice were fed standard chow/water, 0.04% pterostilbene in chow and 0.2% nicotinamide riboside in drinking water, diet with nicotinamide riboside alone, or diet with pterostilbene alone. After 4 weeks, mice were exposed to UVB radiation (3500 J/m2), and 24-/48-h ear swelling was assessed. We also asked if each agent or the combination inhibits UVB radiation suppression of contact hypersensitivity in two models. Mice were fed standard diet/water or chow containing 0.08% pterostilbene, water with 0.4% nicotinamide riboside, or both for 4 weeks. Low-dose: Half the mice in each group were exposed on the depilated dorsum to UVB radiation (1700 J/m2) daily for 4 days, whereas half were mock-irradiated. Mice were immunized on the exposed dorsum to dinitrofluorobenzene 4 h after the last irradiation, challenged 7 days later on the ears with dinitrofluorobenzene, and 24-h ear swelling assessed. High dose: Mice were treated similarly except that a single dose of 10,000 J/m2 of radiation was administered and immunization was performed on the unirradiated shaved abdomen 3 days later.

RESULTS

Nicotinamide riboside and pterostilbene together inhibited UVB-induced skin swelling more than either alone. Pterostilbene alone and both given together could inhibit UVB-induced immune suppression in both the low-dose and high-dose models while nicotinamide riboside alone was more effective in the low-dose model than the high-dose model.

CONCLUSION

Nicotinamide riboside and pterostilbene have protective effects against UVB radiation-induced tissue swelling and immune suppression.

UV-Induced Molecular Signaling Differences in Melanoma and Non-melanoma Skin Cancer

There are three major types of skin cancer: melanoma, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). BCC and SCC are often referred to as non-melanoma skin cancer (NMSC). NMSCs are relatively non-lethal and curable by surgery, hence are not reportable in most cancer registries all over the world. Melanoma is the deadliest skin cancer. Its incidence rate (case number) is about 1/10th of that for NMSC, yet its death toll is ~8 fold higher than NMSC.Melanomas arise from melanocytes which are normally located on the basement membrane with dendrites extending into the epidermal keratinocytes. A major known function of melanocytes is to produce pigments which are enclosed by lipid membrane (termed melanosomes) and distribute them into keratinocytes, thus give different shade of skin colors. BCCs arise from basal cells, which are a layer of cells located at the deepest part of epidermis. Basal cells are recently considered to be skin stem cells as they are constantly proliferating and generating keratinocytes which are continuously pushed to the surface and eventually become a dead layer of stratum corneum. Squamous cells are the keratinocytes which resembles fish scale shape, ie, those initiated from basal cells and differentiated into squamous cells. Both basal cells and squamous cells belong to keratinocytes, therefore sometimes BCC and SCC are termed keratinocyte cancer.These three types of cancer share many characteristics, yet they are very different from etiology to progression. One shared characteristic of skin cancer is that, according to the current views, they all are caused by solar or artificial ultraviolet radiation (UVR). UVA and UVB from solar UVR are the major UV bands reaching the earth surface. Both UV types cause DNA damage and immune suppression which play crucial roles in skin carcinogenesis. UVB can be directly absorbed by DNA molecules and thus causes UV-signature DNA damages; UVA, on the other hand, may function through inducing cellular ROS which then causes oxidative DNA damages [1-4]. This chapter will discuss the molecular signaling differences of UVR in melanoma and NMSC.

Skin cancer and immunosuppression

All immunosuppressive treatments, either pharmacological or physical, have the potential to impair the skin immune system network of cells and cytokines, thus leading to an increased incidence of skin cancer. Since skin cancer in transplant recipients may show uncommon clinical features and have an unusually aggressive course, transplant patients should be strictly followed up by experienced dermatologists in order to diagnose and treat properly any skin cancer in an early phase. Importantly, due to the fact that sun exposure increases immunosuppression in the skin, patients should be clearly informed about the additional risk of sun exposure and the preventive measures to be taken.

Ultraviolet radiation downregulates allergy in BALB/c mice

The immunosuppressive effects of exposure to ultraviolet radiation (UVR) are well known and the underlying mechanisms extensively studied. The suppression of Th1 appears to account for UVR suppression of contact hypersensitivity and delayed-type hypersensitivity responses and increased susceptibility to certain infections and tumor development. The underlying mechanisms suggest Th2-mediated responses associated with immediate-type hypersensitivity and allergic lung disease should be unchanged or possibly enhanced by UVR. The hypothesis that UVR exposure enhances allergic lung disease in BALB/c mice was tested. Effects of UVR on sensitization and elicitation of respiratory hypersensitivity were assessed using a fungal extract, Metarhizium anisopliae (MACA), as the allergen. BALB/c mice were sham or UVR (8 KJ/m(2)) exposed 3d before involuntary aspiration (IA) of MACA or vehicle. The mice received UVR exposures before the first and second of three IAs in the sensitization protocol and 3 d before the fourth IA in the elicitation protocol. Serum and bronchoalveolar lavage fluid (BALF) were harvested before (d 21, sensitization/d 24, elicitation) and at 1 (d 22/d 28), 3 (d 24/d 29), and 7 (d 28/d 35) d following the last IA. UVR exposure prior to sensitization suppressed two hallmarks of allergic disease, immune-mediated inflammation (eosinophil influx) and total immunoglobulin (Ig)E compared to the sham-UVR controls. There were no differences attributable to UVR exposure in previously sensitized mice. These data suggest that UVR exposure prior to sensitization suppresses allergic responses but has no effect on the elicitation of allergic responses in previously sensitized individuals. Consequently, there is no evidence that exposure to UVR enhances the induction or expression of allergic lung disease.