Photoimmunoprotection by UVA (320-400 nm) radiation is determined by UVA dose and is associated with cutaneous cyclic guanosine monophosphate

Photoaging: UV radiation-induced inflammation and immunosuppression accelerate the aging process in the skin

Background

Excessive exposure of the skin to UV radiation (UVR) triggers a remodeling of the immune system and leads to the photoaging state which is reminiscent of chronological aging. Over 30 years ago, it was observed that UVR induced an immunosuppressive state which inhibited skin contact hypersensitivity.

Methods

Original and review articles encompassing inflammation and immunosuppression in the photoaging and chronological aging processes were examined from major databases including PubMed, Scopus, and Google Scholar.

Results

Currently it is known that UVR treatment can trigger a cellular senescence and inflammatory state in the skin. Chronic low-grade inflammation stimulates a counteracting immunosuppression involving an expansion of immunosuppressive cells, e.g., regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC), and regulatory dendritic cells (DCreg). This increased immunosuppressive activity not only suppresses the function of effector immune cells, a state called immunosenescence, but it also induces bystander degeneration of neighboring cells. Interestingly, the chronological aging process also involves an accumulation of pro-inflammatory senescent cells and signs of chronic low-grade inflammation, called inflammaging. There is also clear evidence that inflammaging is associated with an increase in anti-inflammatory and immunosuppressive activities which promote immunosenescence.

Conclusion

It seems that photoaging and normal aging evoke similar processes driven by the remodeling of the immune system. However, it is likely that there are different molecular mechanisms inducing inflammation and immunosuppression in the accelerated photoaging and the chronological aging processes.

The dual effects of riboflavin and kelp polyphenol extracts on the gel properties of myofibrillar protein from Scomberomorus Niphonius under UVA irradiation

In the present study, effects of riboflavin (RF) and kelp polyphenol extracts (KPE) on mackerel (Scomberomorus Niphonius) myofibrillar protein (MP) gel were studied with or without ultraviolet A (UVA) irradiation treatment. The gel strength was increased with the addition of RF and KPE under UVA irradiation. Analysis of the proteins in the gel indicated that the carbonyl content increased, while the contents of total sulfhydryl and amino groups decreased. The proteins appeared to have no α-helix structures, and the endogenous tryptophan content appeared to decrease. The results of SDS-PAGE indicated that the RF and KPE treated samples under UVA irradiation showed massive MP cross-linking by covalent bonds. Electron spin resonance (ESR) results indicated that UVA irradiation generated free radicals in RF and KPE, which ultimately led to an improvement in MP gel properties. It also indicated that KPE could prevent the occurrence of peroxidation to improve the gel properties.

Melanopsin and rhodopsin mediate UVA-induced immediate pigment darkening: Unravelling the photosensitive system of the skin

The mammalian skin has a photosensitive system comprised by several opsins, including rhodopsin (OPN2) and melanopsin (OPN4). Recently, our group showed that UVA (4.4 kJ/m²) leads to immediate pigment darkening (IPD) in murine normal and malignant melanocytes. We show the role of OPN2 and OPN4 as UVA sensors: UVA-induced IPD was fully abolished when OPN4 was pharmacologically inhibited by AA9253 or when OPN2 and OPN4 were knocked down by siRNA in both cell lines. Our data, however, demonstrate that phospholipase C/protein kinase C pathway, a classical OPN4 pathway, is not involved in UVA-induced IPD in either cell line. Nonetheless, in both cell types we have shown that: a) intracellular calcium signal is necessary for UVA-induced IPD; b) the involvement of CaMK II, whose inhibition, abolished the UVA-induced IPD; c) the role of CAMK II/NOS/sGC/cGMP pathway in the process since inhibition of either NOS or sGC abolished the UVA-induced IPD. Taken altogether, we show that OPN2 and OPN4 participate in IPD induced by UVA in murine normal and malignant melanocytes through a conserved common pathway. Interestingly, upon knockdown of OPN2 or OPN4, the UVA-driven IPD is completely lost, which suggests that both opsins are required and cooperatively signal in murine both cell lines. The participation of OPN2 and OPN4 system in UVA radiation-induced response, if proven to take place in human skin, may represent an interesting pharmacological target for the treatment of depigmentary disorders and skin-related cancer.

Ultraviolet-A1 irradiation therapy for systemic lupus erythematosus

Systemic lupus erythematosus (lupus, SLE) is a chronic autoimmune disease characterized by the production of autoantibodies, which bind to antigens and are deposited within tissues to fix complement, resulting in widespread systemic inflammation. The studies presented herein are consistent with hyperpolarized, adenosine triphosphate (ATP)-deficient mitochondria being central to the disease process. These hyperpolarized mitochondria resist the depolarization required for activation-induced apoptosis. The mitochondrial ATP deficits add to this resistance to apoptosis and also reduce the macrophage energy that is needed to clear apoptotic bodies. In both cases, necrosis, the alternative pathway of cell death, results. Intracellular constituents spill into the blood and tissues, eliciting inflammatory responses directed at their removal. What results is “autoimmunity.” Ultraviolet (UV)-A1 photons have the capacity to remediate this aberrancy. Exogenous exposure to low-dose, full-body, UV-A1 radiation generates singlet oxygen. Singlet oxygen has two major palliative actions in patients with lupus and the UV-A1 photons themselves have several more. Singlet oxygen depolarizes the hyperpolarized mitochondrion, triggering non-ATP-dependent apoptosis that deters necrosis. Next, singlet oxygen activates the gene encoding heme oxygenase (HO-1), a major governor of systemic homeostasis. HO-1 catalyzes the degradation of the oxidant heme into biliverdin (converted to bilirubin), Fe, and carbon monoxide (CO), the first three of these exerting powerful antioxidant effects, and in conjunction with a fourth, CO, protecting against injury to the coronary arteries, the central nervous system, and the lungs. The UV-A1 photons themselves directly attenuate disease in lupus by reducing B cell activity, preventing the suppression of cell-mediated immunity, slowing an epigenetic progression toward SLE, and ameliorating discoid and subacute cutaneous lupus. Finally, a combination of these mechanisms reduces levels of anticardiolipin antibodies and protects during lupus pregnancy. Capping all of this is that UV-A1 irradiation is an essentially innocuous, highly manageable, and comfortable therapeutic agency.

UVA-induced protection of skin through the induction of heme oxygenase-1

UVA (320-400 nm) and UVB (290-320 nm) are the major components of solar UV irradiation, which is associated with various pathological conditions. UVB causes direct damage to DNA of epidermal cells and is mainly responsible for erythema, immunosuppression, photoaging, and skin cancer. UVA has oxidizing properties that can cause damage or enhance UVB damaging effects on skin. On the other hand, UVA can also lead to high levels of heme oxygenase-1 (HO-1) expression of cells that can provide an antioxidant effect on skin as well as anti-inflammatory properties in mammals and rodents. Therefore, this review focuses on the potential protection of UVA wavebands for the skin immune response, instead of mechanisms that underlie UVA-induced damage. Also, the role of HO-1 in UVA-mediated protection against UVB-induced immunosuppression in skin will be summarized. Thus, this review facilitates further understanding of potential beneficial mechanisms of UVA irradiation, and using the longer UVA (UVA1, 340-400 nm) in combination with HO-1 for phototherapy and skin protection against sunlight exposure.

Hypoxia inducible factor-1α contributes to UV radiation-induced inflammation, epidermal hyperplasia and immunosuppression in mice

Hypoxia inducible factor-1α (HIF-1α), a ubiquitous inducible oxygen-sensing transcription factor, promotes cell survival under hypoxic conditions, including the early pre-angiogenic period of tumorigenesis, and is known to contribute to many malignancies. However HIF-1α can also be activated by inflammatory mediators, and can activate inflammation-modulating proteins itself, including heme oxygenase-1 (HO-1) and the cytokine IL-6. Recently HIF-1α was reported to be induced by UVB (290-320 nm) radiation in cultured human keratinocytes, acting as a stress protein associated with the release of reactive oxygen species. In this in vivo murine study we demonstrate that HIF-1α protein is an early responder to UV radiation in the skin, and its activation can be attenuated by treating mice with its post-translational inhibitor, YC-1. Treatment with YC-1 following UV-irradiation of mice has revealed the involvement of HIF-1α in UV-induced inflammation, IL-6 production, and epidermal hyperplasia. In addition, upregulated cutaneous HIF-1α was found to be an important factor in the UV-suppression of T cell-mediated immunity, measured by contact hypersensitivity (CHS). The mechanism remains unclear, however it did not appear to involve the immunosuppressive cutaneous photoproduct cis-urocanic acid, but HIF-1α induction was inhibited by irradiation with photoimmune protective UVA (320-400 nm), implicating a negative correlation between the two stress proteins, HIF-1α and the photoimmune protective UVA responder HO-1.

Gender differences in UV-induced inflammation and immunosuppression in mice reveal male unresponsiveness to UVA radiation

Immunosuppression attributed mainly to the UVB (290-320 nm) waveband is a prerequisite for skin cancer development in mice and humans. The contribution of UVA (320-400 nm) is controversial, but in mice UVA irradiation has been found to antagonise immunosuppression by UVB. In other studies of photoimmune regulation, protection mediated via oestrogen receptor-β signalling was identified as a normal endogenous defence in mice, and was shown to depend on UVA irradiation. A gender bias in photoimmune responsiveness was thus suggested, and is tested in this study by comparing the UV-induced inflammatory and immune responses in male and female hairless mice. We report that male mice, which show greater skin thickness than females, developed a less intense but slower resolving sunburn inflammatory oedema, correlated with reduced epidermal expression of pro-inflammatory IL-6 than females following solar simulated UV (SSUV, 290-400 nm) exposure. On the other hand, the contact hypersensitivity reaction (CHS) was more severely suppressed by SSUV in males, correlated with increased epidermal expression of immunosuppressive IL-10. Exposure to the UVB waveband alone, or to cis-urocanic acid, suppressed CHS equally in males and females. However, whereas UVA irradiation induced immunoprotection against either UVB or cis-urocanic acid in females, this protection was significantly reduced or abrogated in males. The results indicate that males are compromised by a relative unresponsiveness to the photoimmune protective effects of UVA, alone or as a component of SSUV. This could explain the known gender bias in skin cancer development in both mice and humans.

UVA1 radiation inhibits calcineurin through oxidative damage mediated by photosensitization

The protein phosphatase calcineurin has been gradually revealing itself as the central controller of our immune response, although it is involved in a wide array of signaling pathways related to cellular development and cell cycle progression. As such, calcineurin is an attractive, yet delicate, therapeutic target for the prevention of allograft rejection and treatment of several inflammatory skin conditions. However, calcineurin activity is not only sensitive to immunosuppressants such as cyclosporin A and tacrolimus, but also subject to modulation by reactive oxygen species. We have recently shown, both in vivo and in vitro, that UVA1 radiation suppresses calcineurin activity. In this paper, we present evidence that this activity loss is due to singlet oxygen and superoxide generated by photosensitization and show that a closely related phosphatase, PP2A, is not affected. Furthermore, a survey of this damage reveals oxidation of several Met and Cys residues as well as an overall conformational change. These findings provide a mechanistic basis for the hypothesis that UVA1 and calcineurin inhibitors both affect the same signal transduction pathway in skin.

UV exposure and protection against allergic airways disease

Asthma is a chronic inflammatory disease of the small and large conducting airway mucosa characterised by Th2 cell immunity. Allergen-specific IgE levels control the immediate response whilst the interplay between airway mucosal antigen presenting cells, Th2 effector cells and CD4+CD25+ regulatory T cells control the late phase, cell-mediated response. Using two experimental systems in mice with ovalbumin and papain, respectively, as the allergens, UV irradiation of skin prior to allergen sensitisation reduced the expression of allergic airways disease, particularly the late phase response. In this review, the reduced Th2-driven, asthma-like responses in respiratory tissues of UV-irradiated mice are detailed. Possible mechanisms of UV regulation are debated. The potential beneficial effects of UV irradiation of skin in controlling allergic airways disease are discussed. This review gives some scientific understanding to century-old anecdotal reports that beach and mountain resort holidays associated with increased UV exposure are beneficial in asthma treatment.

Diffuse reflectance spectroscopy for ultraviolet A protection factor measurement: correlation studies between in vitro and in vivo measurements

BACKGROUND/PURPOSE

Assessing the ultraviolet (UVA) protection factor of sunscreen formulations has been discussed for the past 20 years. The purpose of this study is to correlate the measurements of the UVA protection factor value (PFA value) via in vivo diffuse reflectance spectroscopy (DRS) and to compare this method with the in vitro method of measuring the PFA value, as well as with the in vivo persistent pigment darkening (PPD) and PFA methodologies.

METHODS

The UVA protection factor via DRS technique was assessed in two clinical studies. The first study was performed in 12 subjects and the second one consisting of 10 subjects. All subjects in these studies had Fitzpatrick skin phototypes II-IV. DRS measurements were performed using a SkinScan spectrofluorimeter (Spex SkinScan, Yvon Horiba). The in vitro PFA measurements were performed using Labsphere UV-1000s UV Transmission Analyzer.

RESULTS

The results obtained from the non-invasive DRS studies were used to correlate with the in vitro testing and with the in vivo PFA/PPD multicenter study. A positive relationship (regression coefficient r(2)=0.90) of PFA values was found between in vitro PFA testing and the in vivo DRS testing. There was also a very good correlation (regression coefficient r(2)=0.99) between the in vivo PFA/PPD values and UVA protection factor obtained from the DRS method.

CONCLUSION

This paper presents studies using the DRS technique to assess the UVA protection factor in different sunscreen formulae correlating with in vitro and in vivo PFA/PPD values. It is a fast method, non-invasive and does not involve any subject irradiation. The technique is a good estimator for the in vivo UVA protection factor as well as a way to assess, in vivo, the photostability of sunscreen formulation in the UVA.

Interdependence between heme oxygenase-1 induction and estrogen-receptor-beta signaling mediates photoimmune protection by UVA radiation in mice

Previous studies have found that signaling by the estrogen receptor-beta (Er-beta) attenuated solar-simulated UV radiation (SSUV)-induced immunosuppression. This study seeks evidence for a common mechanism for this immunoprotection for both Er-beta signaling and irradiation with the UVA waveband. In Skh:hr-1 hairless mice, the immunoprotection afforded by UVA exposure against subsequent UVB or cis-urocanic acid suppression of contact hypersensitivity (CHS) was abrogated by treatment with the antiestrogen, ICI 182,780. Furthermore, in normal C57BL mice, UVA enrichment of UVA/UVB sources provided protection against UVB-suppressed CHS and upregulated epidermal IL-10 expression, but this protection was inhibited in Er-beta-/- mice. These observations indicated that the immunoprotective response to UVA was dependent on Er-beta signaling. As earlier studies have established that UVA photoimmune protection depends on the induction of the stress enzyme, heme oxygenase (HO)-1, its activity was examined relative to Er-beta. Immunoprotection against SSUV by 17-beta-estradiol was prevented by inhibiting HO enzyme activity; immunoprotection against cis-urocanic acid by carbon monoxide (HO product) was prevented by ICI 182,780. In addition, the HO-1 gene was unresponsive to UVA induction in Er-beta-/- mice. Therefore, HO-1 inducibility and Er-beta signaling are interdependent requisite responses to the UVA waveband for its immunoprotective action against UVB exposure.

UVA-induced calcium oscillations in rat mast cells

UVA is a major bio-active component in solar irradiation, and is shown to have immunomodulatory and anti-inflammatory effects. The detailed molecular mechanism of UVA action in regard to calcium signaling in mast cells, however, is not fully understood. In this study, it was found that UVA induced ROS formation and cytosolic calcium oscillations in individual rat mast cells. Exogenously added H2O2 and hypoxanthine/xanthine oxidase (HX/XOD) mimicked UVA effects on cytosolic calcium increases. Regular calcium oscillation induced by UVA irradiation was inhibited completely by the phosphatidylinositol-specific phospholipase C inhibitor U73122, but U73343 was without effect. Tetrandrine, a calcium entry blocker, or calcium-free buffer abolished UVA-induced calcium oscillations. L-type calcium channel blocker nifedipine and stores-operated calcium channel blocker SK&F96365 had no such inhibitory effect. ROS induction by UVA was abolished after pre-incubation with anti-oxidant NAC or with NAD(P)H oxidase inhibitor DPI; such treatment also made UVA-induced calcium oscillation to disappear. UVA irradiation did not increase mast cell diameter, but it made mast cell structure more granular. Spectral confocal imaging revealed that the emission spectrum of the endogenous fluorophore in single mast cell contained a sizable peak which corresponded to that of NAD(P)H. Taken together, these data suggest that UVA in rat mast cells could activate NAD(P)H oxidase, to produce ROS, which in turn activates phospholipase C signaling, to trigger regular cytosolic calcium oscillation.

The role of interleukin-6 in UVA protection against UVB-induced immunosuppression

The proinflammatory cytokine IL-6 is released in the skin following UVB irradiation, but its potential for photoimmune modulation remains unclear. This study utilizes IL-6-deficient mice to demonstrate that IL-6 does not contribute to the normal contact hypersensitivity response, nor to its systemic suppression by UVB radiation or cis-urocanic acid. In contrast, IL-6 was required for the attenuation of UVB- or cis-urocanic acid-induced immunosuppression by sequential or concomitant UVA irradiation. The IL-6 was essential for several reactions previously established to be relevant for UVA photoimmune protection, namely the induction of heme oxygenase-1 (HO-1), the activity of its product carbon monoxide in activating guanylyl cyclase, and the consequent elevation of cutaneous cyclic guanosine monophosphate concentration. In addition, IL-6-deficient mouse skin had an elevated constitutive overexpression of HO activity, apparently not associated with photoimmune protection. This suggested that both the cutaneous level of HO activity, and the receptiveness of the HO-1 gene to stressors like UVA, normally controlled by promoter-binding repressor proteins, may also be under IL-6 control. Thus IL-6 has an important photoimmune protective function through interaction at several levels in the pathway determining the immunologically advantageous actions of UVA radiation. This may constitute a valuable endogenous antiphotocarcinogenic regulatory mechanism.

Redox regulation of cellular stress response by ferulic acid ethyl ester in human dermal fibroblasts: role of vitagenes

Skin is one of the main targets for reactive oxygen species; thus, reactive oxygen species-induced damage and protein and lipid modifications occur, and skin can undergo a wide array of diseases, from photosensitivity to cancer. In this study, human dermal fibroblasts exposed to hydrogen peroxide (0-1000 micromol/L) exhibited a marked increase in both protein carbonyls and 4-hydroxy-2-nonenal, which are indices of protein and lipid oxidation, respectively. An amount of 25 micromol/L ferulic acid ethyl ester, a well-known nutritional antioxidant, significantly counteracted both protein and lipid oxidation and reduced the loss in cell viability elicited by 500 micromol/L of hydrogen peroxide. A common way for cells to react to oxidative stress is up-regulation of vitagenes. To the vitagene family belong the heat shock proteins heme oxygenase-1 and heat shock protein-70, which are involved in the cellular defense against oxidative stress by different mechanisms. The administration of 25 micromol/L ferulic acid ethyl ester significantly decreased hydrogen peroxide-induced protein and lipid oxidation. Dermal fibroblasts exposed to 25 micromol/L ferulic acid ethyl ester in the presence of 500 micromol/L hydrogen peroxide showed an increased level of both heme oxygenase-1 and heat shock protein-70 compared with dermal fibroblasts treated with hydrogen peroxide alone. These findings provide evidence for the protective role of vitagenes in free radical-induced skin damage and highlight the potential protective use of nutritional antioxidants, such as ferulic acid and its derivatives.

Waveband and dose dependency of sunlight-induced immunomodulation and cellular changes

Both the UVB and UVA wavebands within sunlight are immunosuppressive. This article reviews the relationship between wavebands and dose in UV-induced immunosuppression mainly concentrating on responses in humans. It also contrasts the effects of UVB and UVA on cellular changes involved in immunosuppression. Over physiological sunlight doses to which humans can be exposed during routine daily living or recreational pursuits, both UVA and UVB suppress immunity. While there is a linear dose relationship with UVB commencing at doses less than half of what is required to cause sunburn, UVA has a bell-shaped dose response over the range to which humans can be realistically exposed. At doses too low for either waveband to be suppressive, interactions between UVA and UVB augment each other, enabling immunosuppression to occur. At doses beyond where UVA is immunosuppressive, it still contributes to sunlight-induced immunosuppression via this interaction with UVB. While there is little research comparing the mechanisms by which UVB, UVA and their interactions can cause immunosuppression, it is likely that different chromophores and early molecular events are involved. There is evidence that both wavebands disrupt antigen presentation and effect T cell responses. Different individuals are likely to have different immunomodulatory responses to sunlight.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.

Radiation Sources Providing Increased UVA/UVB Ratios Attenuate the Apoptotic Effects of the UVB Waveband UVA-Dose-Dependently in Hairless Mouse Skin

UV radiation-induced epidermal apoptotic sunburn cells provide a mechanism for eliminating cells with irreparable DNA damage. The UVB (290-320 nm) waveband is mainly responsible, but the role of UVA (320-400 nm) is less clear, and possible waveband interactions have not been examined. Recent studies in mice reveal a protective role for UVA against UVB-induced inflammation and immunosuppression, mediated via cutaneous heme oxygenase (HO). As HO has antiapoptotic properties in other tissues, this study examines the effect of UVA/UVB waveband interaction on apoptosis in the Skh:hr-1 hairless mouse epidermis. Apoptosis was assessed by sunburn cell number, caspase-3-positive cell number, and degree of DNA fragmentation, in mice exposed to radiation sources providing a constant UVB dose with increasing proportions of UVA. The results indicated that as the UVA/UVB ratio was increased, both the sunburn cell and caspase-3-positive cell number decreased, and the degree of DNA fragmentation was reduced. Treatment of mice with the HO inhibitor, tin protoporphyrin-IX, markedly reduced the UVA antiapoptotic effect, confirming a major role for HO. The observations suggest that UVA reduces UVB-induced DNA damage, and may therefore have anti-photocarcinogenic properties that could be harnessed for better photoprotection in humans.

Nox1-based NADPH oxidase is the major source of UVA-induced reactive oxygen species in human keratinocytes

UVA radiation is a major environmental stress on skin, causing acute and chronic photodamage. These responses are mediated by reactive oxygen species (ROS), although the cellular source of these ROS is unknown. We tested the hypotheses that UVA-induced activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is required for ROS generation in human keratinocytes (HK) and that these ROS initiate rapid prostaglandin E2 (PGE2) synthesis. Treatment of HK with a non-toxic dose of UVA rapidly increased NADPH oxidase activity and intracellular ROS, which were partially blocked by an inhibitor of NADPH oxidase and by a mitochondria-selective antioxidant. Depleting the Nox1 isoform of the catalytic subunit of NADPH oxidase using small interfering RNA (siRNA) blocked the UVA-induced ROS increase, indicating that ROS produced by mitochondria or other sources are downstream from Nox1. Nox1 siRNA also blocked UVA-initiated PGE2 synthesis. The mechanism for activation of Nox1 is mediated by an increase in intracellular calcium. Ceramide, which has been proposed to mediate responses to UVA in HK, also activated NADPH oxidase. These results indicate that UVA activates Nox1-based NADPH oxidase to produce ROS that stimulate PGE2 synthesis, and that Nox1 may be an appropriate target for agents designed to block UVA-induced skin injury.

Decreased human epidermal antigen-presenting cell activity after ultraviolet A exposure: dose–response effects and protection by sunscreens

BACKGROUND

Ultraviolet (UV) exposure of human skin causes immunosuppression that contributes to the growth of skin cancer. The contribution of UVA in these processes is still a matter of debate.

OBJECTIVES

The purpose of our study was first to find a dose-response effect of UVA exposure on human epidermal antigen-presenting cell (APC) activity and to evaluate the protective capacity of two sunscreen formulations against a high level of acute UVA exposure. We also tried to evaluate the protective capacity afforded by the same sunscreens against UVA-induced clinical changes such as redness and pigmentation.

METHODS

The functional assessment of the alloantigen-presenting capacity of epidermal cells prepared from skin keratotome samples 3 days after UVA exposure was measured with a mixed epidermal cell-lymphocyte reaction (MECLR) in each healthy volunteer (n = 16). Redness and pigmentation were assessed by chromametry 24 h after exposure to a single UVA dose.

RESULTS

In vivo UVA exposure to 15, 30 and 60 J cm(-2) resulted in a dose-dependent decrease in purified allogeneic T cell (CD4+ T cells) proliferation induced by UVA-irradiated epidermal cells. The epidermal APC function was significantly decreased with a suberythemal exposure corresponding to 15 J cm(-2). The decrease, partial and not statistically different between 30 and 60 J cm(-2), exhibits a plateau-response effect. There was no correlation between the decrease of the epidermal APC function and the intensity of erythema and persistent pigment darkening. Both sunscreen formulations strongly inhibited the UVA-induced reduction of MECLR at 90 J cm(-2).

CONCLUSION

Our results clearly demonstrate that UVA impairs the APC activity of the epidermal cells and thus may contribute to UV-induced immunosuppression in humans. They also indicate that erythema and immunosuppression have different dose-response curves in the UVA range. The two sunscreen formulations afforded a significant protection against the decrease in epidermal APC activity induced by exposure to a high UVA dose (90 J cm(-2)).

Sun exposure and malignant lymphoma: A population-based case–control study in Germany

Although some causes for malignant lymphoma are known their etiology is not well understood so far. We analyze the relationship between sun exposure and malignant lymphoma in a multicenter, population-based case-control study. Patients with malignant lymphoma (n = 710, 18-80 years) were prospectively recruited in 6 study regions in Germany. For each case, a gender, region and age-matched control was drawn from population-registers. In personal interviews, lifetime holidays spent in sunny climate, outdoor leisure activities and sunbed or sunlamp use were recorded. On basis of job task-specific supplementary questionnaires, an occupational physician assessed the cumulative working time outside. Odds ratios (OR) and 95%-confidence-intervals (CI) were calculated using conditional logistic regression analysis, adjusted for smoking and alcohol consumption. To increase statistical power, patients with specific lymphoma subentities were additionally compared with the entire control group using unconditional logistic regression. We observed a reduced overall lymphoma risk among subjects having spent vacations at sunny climates or frequently used sunbeds or sunlamps. The analysis of lymphoma subentities revealed similar results with the exception of T-NHL and follicular lymphoma which were positively associated with outdoor leisure activities. While cumulative working time outside appeared unrelated to NHL overall and most subentities, it was negatively associated with follicular lymphoma and weakly positively to HL. This data suggest that exposure to natural and artificial ultraviolet radiation may reduce the OR for lymphoma in this study population.

Potential protection of skin by acute UVA irradiation—From cellular to animal models

The UVA (320-380 nm) component of sunlight has oxidizing properties which may be deleterious to skin cells and tissue but can also lead to the strong up-regulation of the heme-catabolizing enzyme, heme oxygenase-1. This enzyme has well-established antioxidant actions in cells as well as anti-inflammatory properties in mammals. There is also evidence from rodent models that this enzyme is responsible for the UVA-mediated protection against UVB-induced immunosuppression that occurs in skin. The relevance of these findings to acute and chronic effects of sunlight including skin carcinogenesis is currently under investigation as are the potential implications for sunlight protection in humans.