Sunscreens Protect Epidermal Langerhans Cells and Thy-1+ Cells But Not Local Contact Sensitization from the Effects of Ultraviolet Light

Redefine photoprotection: Sun protection beyond sunburn

Excessive exposure to ultraviolet (UV) light leads to acute and chronic UV damage and is the main risk factor for the development of skin cancer. In most countries with western lifestyle, the topical application of sunscreens on UV-exposed skin areas is by far the most frequently used preventive measure against sunburn. Further than preventing sunburns, increasing numbers of consumers are appreciating sunscreens with a medium- to high-level sun protective factor (SPF) as basis for sustainable-skin ageing or skin cancer prevention programs. However, recent investigations indicate that clinically significant DNA damages as well as a lasting impairment of cutaneous immunosurveillance already occur far below the standard of one minimal erythema dose (MED) sunburn level, which contributes to the current discussion of the clinical value of high-protective SPF values. Ex vivo investigations on human skin showed that the application of SPF30 reduces DNA damage for a day long sun exposure (24 MED) drastically by about 53% but is significantly surpassed by SPF100 reducing DNA damage by approx. 73%. Further analysis on different SPF protection levels in UV-exposed cell culture assays focusing on IL-18, cell vitality and cis/trans-urocanic acid support these findings. Whereas SPF30 and SPF50+ sunscreens already offer a solid UVB cover for most indications, our results indicate that SPF100 provides significant additional protection against mutagenic (non-apoptotic-) DNA damage and functional impairment of the cutaneous immunosurveillance and therefore qualifies as an optimized sunscreen for specifically vulnerable patient groups such as immunosuppressed patients, or skin cancer patients.

Broad-spectrum sunscreens provide better protection from solar ultraviolet-simulated radiation and natural sunlight-induced immunosuppression in human beings

BACKGROUND

It is well established that ultraviolet (UV) radiation induces immunomodulatory effects that may be involved in skin cancer. Recent studies have shown that UVA (320-400 nm) and UVB (290-320 nm) radiation are immunosuppressive. As a result, sunscreens, which mainly absorb UVB, may be less effective in preventing UV radiation-induced immunosuppression than broad-spectrum products.

OBJECTIVE

We sought to study the effects of UVA exposure on human delayed-type hypersensitivity (DTH) response and compare the efficacy of sunscreens having different levels of sun-protection factor (SPF) and UVA protection against both solar-simulated radiation and outdoor real-life sunlight exposure conditions.

METHODS

DTH was assessed using a kit which includes 7 recall antigens that most of the participants encountered during childhood immunization. Evaluation of DTH test response was made 48 hours after test application before and after UV exposure with or without sunscreens.

RESULTS

In unprotected participants, the response to DTH tests was significantly reduced irrespective of UV types of exposure (full-spectrum UVA, long UVA, solar-simulated radiation). A UVB sunscreen failed to protect from solar-simulated radiation-induced immunosuppression. In contrast, a broad-spectrum sunscreen with the same SPF but providing a high protection in the UVA range significantly reduced local UV-induced immunosuppression and prevented the distant effects. In the outdoor study, as compared with DTH responses obtained before sun exposure, no alteration of immune response was detected when the skin was protected by a broad-spectrum sunscreen having a high protection level in the UVA (SPF 25, UVA protection factor 14). Conversely a broad-spectrum sunscreen with lower protection against UVA (SPF 25, UVA protection factor 6) failed to prevent UV-impaired response.

LIMITATIONS

These results have been obtained after repeated exposure. Additional experiments obtained under acute exposure are in progress.

CONCLUSION

These findings clearly demonstrated the role of UVA in the induction of photoimmunosuppression together with the need for sunscreen products providing efficient photoprotection throughout the entire UV spectrum.

Advantages of using hairless mice versus haired mice to test sunscreen efficacy against photoimmune suppressions

We tested the hypothesis that the strain of mice used in sunscreen protection experiments may influence immune protection. Ultraviolet (UV) dose-response curves were done in the presence or absence of a sun protection factor (SPF) 15 sunscreen using SKH1:hrBR or C3H/HeN mice. SKH1:hrBR mice showed a higher sensitivity to the suppressive effects of UV radiation (50% immune suppression equal to 5.2 kJ/m2 UVB in SKH1:hrBR mice versus 18.5 kJ/m2 in C3H mice). Immune protection factors (IPF) and an erythema protection factor (Ery-PF) for SKH1:hr mice were derived. The Ery-PF in hairless mice was 13.5, which was similar to the SPF of 15 measured in humans. When IPF were calculated as a ratio of minimal immune suppressive doses, the IPF for the SKH1:hrBR mice was 8.23 and the IFP for the C3H/HeN mice was 1.92. When IPF were estimated using the entire UV dose-response range, they were equal to 9.01 for SKH1:hrBR mice and 1.79 for the C3H/HeN mice. Because IPF and SPF can be measured directly in hairless mice, we suggest that the use of hairless mice may provide a better model to measure sunscreen efficacy, especially when the use of human volunteers is inappropriate, unethical or impossible.

Protection against UV-induced suppression of contact hypersensitivity responses by sunscreens in humans

Both in vivo skin immune responses and the skin's reaction to sun exposure integrate a complex interplay of biologic responses. The complexity and multiplicity of events that occur in the skin during an immune response make it a sensitive indication of both UVB and UVA-induced changes in the skin by sun damage, as well as those changes that are prevented by various sunscreens. Sunscreens are the most effective and widely available intervention for sun damage, other than sun avoidance or clothing. However, sunscreens vary widely in their relative ability to screen various UV waveband components, and their testing has been variably applied to outcomes other than for erythema to determine the sunburn protection factor (SPF), a measure primarily of UVB filtration only. Determination of an immune protection factor (IPF) has been proposed as an alternative or adjunctive measure to SPF, and recent studies show IPF can indeed detect added in vivo functionality of sunscreens, such as high levels of UVA protection, that SPF cannot. Clarification of the definition of IPF, however, is required. Excellent data are available on quantification of the IPF for restoring the afferent or induction arm of contact sensitivity, but other immune parameters have also been measured. Proposed here is nomenclature for whether the IPF is measured using contact sensitivity induction (IPF-CS-I), contact sensitivity elicitation (IPF-CS-E), delayed-type hypersensitivity elicitation (IPF-DTH-E), antigen-presenting cell function (IPF-APC-FXN) or numbers (IPF-APC-#), and cytokine modification such as IL-10 (i.e. IPF-cyto-IL-10). Similar nomenclatures could be used for other measures of skin function protection (i.e. DNA damage, p53 induction, oxidation products, etc.). A review of in vivo human studies, in which sunscreens are used to intervene in a UV-induced modulation of immune response, cells or cytokines, highlights the technical variables and statistical approaches which must also be standardized in the context of an IPF for regulatory or product claim purposes. Development of such IPF standards would allow the integration of both UVB and nonUVB (UVA, blue and possible IR) solar waveband effect-reversals, could be applied to integrate effects of other ingredients with protective function (i.e. antioxidants, retinoids, or other novel products), and would spur development of more advanced and complete protection products.

Effects of UVA radiation on an established immune response in humans and sunscreen efficacy

It is well established that ultraviolet radiation has immunomodulatory effects which may be involved in skin cancer. Recent studies have shown that UVA radiation (320-400 nm) as well as UVB (290-320 nm) is immunosuppressive. This means that sunscreens which mainly absorb UVB (protection against erythema) may be less effective in preventing UVR-induced immunosuppression than broad-spectrum products. We have studied the effects of UVA exposure on the human delayed-type hypersensitivity response (DTH) and compared the efficacy of sunscreens having different levels of UVA protection under both solar-simulated radiation (SSR) chronic exposures or acute exposure and outdoor real-life solar exposure conditions. DTH was assessed using recall antigens. Our studies clearly demonstrate the role of UVA in the induction of photoimmunosuppression together with the need for sunscreen products providing efficient photoprotection throughout the entire UV spectrum. These data suggest that sun protection factor may not be sufficient to predict the ability of sunscreens for protection from UV-induced immune suppression. Determining the level of UVA protection is particularly necessary, because UVA seems to have a relatively low contribution to erythema but is highly involved in immunosuppression.

A commercial sunscreen's protection against ultraviolet radiation-induced immunosuppression is more than 50% lower than protection against sunburn in humans

Ultraviolet radiation (280-400 nm)-induced suppression of cutaneous cell-mediated immunity plays an important part in the development of skin cancer. Sunscreens are widely advocated to protect against skin cancer but if they offer insufficient protection against immunosuppression they may inadvertently increase skin cancer risk. This human study evaluated immunoprotection afforded by a commercial sunscreen preparation (labeled sun protection factor 15) offering primarily ultraviolet B (280-320 nm) protection. Indirectly, it also investigated whether ultraviolet A (320-400 nm) plays a part in ultraviolet radiation-induced immunosuppression. Healthy white-skinned volunteers were used (n=119). Ultraviolet radiation exposures were on previously unexposed buttock skin with an ultraviolet radiation source that complied with European recommendations for sunscreen testing. Ultraviolet radiation dose-response curves for sunburn/erythema and suppression of the contact hypersensitivity response were generated either with or without sunscreen in vivo and protection factors were derived for both end-points. The ultraviolet radiation wavelengths transmitted by the sunscreen were determined in vitro and showed that the sunscreen was primarily an ultraviolet B absorber, with relatively poor absorption in the ultraviolet A region. The sun-screen protected against both erythema and immunosuppression but protection against immunosuppression (IPF=4.9, 95% confidence interval: 2.3-10.6) was less than half that for erythema (Ery-PFg=14.2, 95% confidence interval: 10.2-19.8). Failure of the sunscreen to afford comparable protection against both end-points was probably due to immunosuppression by ultraviolet A, a part of the solar spectrum that does not readily cause sunburn. The sunscreen protected against both end-points, which supports the use of sunscreens to reduce immunosuppression but protection against immunosuppression may be improved if sunscreens are formulated to offer equivalent protection against ultraviolet B and ultraviolet A.

Broad-spectrum sunscreens provide better protection from the suppression of the elicitation phase of delayed-type hypersensitivity response in humans

It is well established that ultraviolet radiation has immunomodulatory effects that may be involved in skin cancer. Recent studies have shown that ultraviolet A radiation (320-400 nm) as well as ultraviolet B (290-320 nm) is immunosuppressive. This means sunscreens that mainly absorb ultraviolet B (protection against erythema) may be less effective in preventing ultraviolet radiation-induced immunosuppression than broad-spectrum products. We have studied the effects of ultraviolet A exposure on the human delayed-type hypersensitivity response and compared the efficacy of sunscreens having different levels of ultraviolet A protection under both solar-simulated radiation and outdoor real-life solar exposure conditions. Delayed-type hypersensitivity was assessed using recall antigens. In a first study, two groups of volunteers were exposed to ultraviolet A (either full spectrum ultraviolet A or ultraviolet A1) without prior application of sunscreen and they were shown to exhibit significantly reduced delayed-type hypersensitivity responses. In order to compare the efficacy of sunscreens in preventing photoimmunosuppression, three groups of subjects received 10 cumulative exposures to solar-simulated radiation; one group was exposed unprotected and the other two were exposed after being applied either a ultraviolet B or a broad-spectrum sunscreen, each with the same sun protection factor 9, but with different ultraviolet A protection factors 9 and 2. Then, an outdoor study was conducted in which delayed-type hypersensitivity was assessed before and after six daily exposures. Two different groups of subjects were treated with one of two sunscreens having the same sun protection factor 25 but different ultraviolet A-protection factors. In unprotected volunteers, responses to delayed-type hypersensitivity tests were significantly reduced irrespective of ultraviolet exposure conditions (full spectrum ultraviolet A, ultraviolet A1, solar-simulated radiation). The ultraviolet B sunscreen failed to protect from solar- simulated radiation-induced immunosuppression. In contrast, the broad-spectrum sunscreen having the same sun protection factor but providing high protection in the ultraviolet A range significantly reduced local ultraviolet-induced immunosuppression and prevented the distal effects. In the outdoor study, as compared with delayed-type hypersensitivity responses obtained before sun exposure, no alteration of immune response was detected when the skin was protected by broad-spectrum sunscreen sun protection factor 25 and ultraviolet A-protection factor 14. Conversely, a broad-spectrum sunscreen sun protection factor 25 ultraviolet A-protection factor 6 failed to protect against the sun-impaired response. The above studies clearly demonstrate the role of ultraviolet A in the induction of photoimmunosuppression together with the need for sunscreen products providing efficient photoprotection throughout the entire ultraviolet spectrum.

Cytochrome P450 4A11 expression in human keratinocytes: effects of ultraviolet irradiation

BACKGROUND

The skin is the major interface between the body and its environment. Directly and continuously exposed to a large variety of foreign agents and stimuli such as ultraviolet radiation (UVR), cutaneous cells are active sites of intense metabolism. The cytochromes P450 (P450) are a group of enzymes that play an important part in the protective role of the skin; they are a family of microsomal membrane-bound mono-oxygenases. These haem-containing proteins catalyse the insertion of an atom of molecular oxygen into the substrate. Although generally present at low levels, a certain number of these enzymes have now been characterized in mammalian skin as constitutive or inducible isoforms.

OBJECTIVES

To test the effects of UVR, a source of oxidative stress, on the expression of mRNA coding for several P450 isoforms (CYP), with particular reference to the CYP2E1 and CYP4A11 isoforms, which might play a role in lipid metabolism in human keratinocytes.

METHODS

Human keratinocytes were cultured, irradiated and mRNA expression was analysed by gel electrophoresis after reverse transcriptase polymerase chain reactions. CYP proteins were determined from keratinocyte microsomal fractions by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoperoxidase staining. Thin layer chromatography was used to detect (omega-1)- and (omega)-hydroxylation of lauric acid in the microsomal fractions.

RESULTS

mRNAs for CYP2E1, CYP1A1 and CYP3A5 were expressed in all the keratinocyte preparations tested; however, neither CYP3A4 nor CYP3A7 were detected, either in the presence or absence of UVR treatment. CYP19Aro, CYP2C19 and CYP26 were not expressed constitutively, although some induction of CYP19Aro was seen after combined UVB and UVA irradiation. CYP4A11 mRNA was not detected in any keratinocyte preparations either under control conditions or after UVB treatment. Nevertheless, in non-irradiated keratinocyte microsomes, two protein bands were immunoreactive with anti-CYP4A11 enzyme antibodies, one of which corresponds to CYP4A11 protein. UVA treatment of cultured keratinocytes induced CYP4A11 mRNA expression after 24 h, as well as an increase in immunoreactivity of the two protein bands. Although (omega-1)- and (omega)-hydroxylation of fatty acids is attributed to CYP2E1 and CYP4A11, respectively, in the liver or kidney, no omega-hydroxylation of lauric acid was observed in microsomal preparations from cultured keratinocytes.

CONCLUSIONS

However, CYP4A11 may participate in the defence mechanism against UVA-induced oxidative damage.

Improved protection against solar-simulated radiation-induced immunosuppression by a sunscreen with enhanced ultraviolet A protection

Ultraviolet radiation-induced immunosuppression is thought to play a part in skin cancer. Several studies have indicated that sunscreens that are designed to protect against erythema failed to give comparable protection against ultraviolet radiation-induced immunosuppression. One possible reason for this discrepancy is inadequate ultraviolet A protection. This study evaluated the level of immunoprotection in mice afforded by two broad-spectrum sunscreens with the same sun protection factor, but with different ultraviolet A protection factors. Both sunscreens contained the same ultraviolet B and ultraviolet A filters, in the same vehicle, but at different concentrations. Solar simulated radiation dose-response curves for erythema, edema, and systemic suppression of contact hypersensitivity were generated and used to derive protection factors for each end-point. The results of three different techniques for determining immune protection factor were compared. A comparison of the two sunscreens showed that the protection factor for erythema in mice was similar to that determined in humans (sun protection factor) but the protection factor for edema in mice was lower. Both sunscreens protected against suppression of contact hypersensitivity but the product with the higher ultraviolet A-protection factor showed significantly greater protection. The three techniques for determining immunoprotection gave very similar results for a given sunscreen, but immune protection factor was always lower than sun protection factor. These data suggest that sun protection factor may not predict the ability of sunscreens to protect the immune system and that a measure of ultraviolet A protection may also be necessary.

Photoprotection

Protection from solar ultraviolet radiation is discussed. Methods of protection include avoiding outdoor activities during times of greatest ultraviolet radiation insolation, seeking shade while outdoors, and wearing appropriate clothing. Sunscreens are reviewed, including newer compounds that may also offer photoprotection.

Antioxidant protection from solar-simulated radiation-induced suppression of contact hypersensitivity to the recall antigen nickel sulfate in human skin

Solar radiation induces suppression of the local effector mechanisms involved in immune responses to recall antigens. By using a low-dose solar-simulated radiation protocol, we investigated whether oral supplementation of the antioxidants RRR-alpha-tocopherol combined with L-ascorbic acid prevented radiation-induced suppression of the contact hypersensitivity response to nickel sulfate. In a prospective, randomized study, nickel-sensitive individuals were given RRR-alpha-tocopherol 2 g/d oral supplements combined with L-ascorbic acid 3 g/d for 50 d (group 1). Individuals in the control group were given a placebo (group 2). The reaction to a standardized patch test with serial dilutions of nickel sulfate and the irritant skin reaction to sodium lauryl sulfate were assessed by visual grading and by reflectance spectrophotometry in radiation-exposed and nonexposed skin 50 days after supplementation. Results showed that the contact hypersensitivity response to the recall antigen nickel sulfate was significantly suppressed in the radiation-exposed skin of those who took the placebo. Supplementation with RRR-alpha-tocopherol combined with L-ascorbic acid significantly protected against the radiation-induced suppression of the contact hypersensitivity response to nickel sulfate. The irritant reaction to sodium lauryl sulfate was not suppressed by radiation, and antioxidant supplementation did not modulate this response. In conclusion, a combination therapy of systemic high-dose RRR-alpha-tocopherol combined with L-ascorbic acid prevented solar-simulated radiation-induced suppression of the local immune response to the recall antigen nickel sulfate in human skin. This immunoprotective effect of combined RRR-alpha-tocopherol and L-ascorbic acid could be exploited for the prevention of solar radiation-induced skin cancer in an antioxidant intervention study.

The health impact of solar radiation and prevention strategies: Report of the Environment Council, American Academy of Dermatology

It is well recognized that exposure to solar radiation is a major risk factor for the development of skin cancer, photoaged skin, and immune system alterations. However, major questions remain regarding the specific wavelengths and type of exposure that incur risk. The purpose of this article is to critically examine, on the basis of current knowledge, the impact of stratospheric ozone depletions, tanning bed skin cancer risk, the safety of sunscreens as an important element of our solar protection strategies, the wavelengths of solar radiation responsible for melanoma, and the incidence of melanoma. Recommendations are made on prevention strategies and public health messages.

An extract of Polypodium leucotomos appears to minimize certain photoaging changes in a hairless albino mouse animal model. A pilot study

Chronic ultraviolet B (UVB) exposure of human or murine skin is known to induce cutaneous photoaging and enhanced carcinogenic risk. An extract of Polypodium leucotomos (PL), a tropical fern plant, has been known to exhibit interesting antioxidant and photoprotective properties against acute exposure to ultraviolet radiation. The objective of this preliminary (or pilot) study was to determine the photoprotective role of topically applied Polypodium leucotomos extract in the prevention or amelioration of cutaneous changes of photoaging in hairless mice. PL-treated mice showed significant reduction of skinfold thickness than those observed in PL-untreated controls. Additionally, PL-treated mice showed a significantly lower degree of histologic parameters of photoaging damage, including dermal elastosis, compared with positive control mice. Interestingly, PL treatment also showed reduction in the number of mice showing skin tumors at 8 weeks after the cessation of the UVB exposure protocol. The results of this preliminary study illustrate that PL treatment helped to ameliorate and to partially inhibit some of the histologic damage associated with photoaging of skin and appeared to contribute to a decrease in the prevalence of UVB-induced skin tumors in mice.

Prevention of ultraviolet radiation-induced suppression of contact hypersensitivity by Aloe vera gel components

We have recently reported that Aloe vera gel contains small molecular weight immunomodulators, G1C2F1, that restore ultraviolet B (UVB)-suppressed accessory cell function of epidermal Langerhans cells (LC) in vitro. In the present study we evaluated the UVB-protective activity of G1C2F1 in vivo. Exposure of the shaved abdominal skin of mice to 2.4 KJ/m2 of UVB radiation resulted in suppression of contact sensitization through the skin to 41.1%, compared to normal unirradiated skin. Topical application of G1C2F1 immediately after irradiation reduced this suppression significantly. The percentage recovery of UVB-suppressed contact hypersensitivity (CHS) response was 52.3, 77.3, and 86.6% when the irradiated skin was treated once with 0.1, 0.5, and 2.5 mg/ml of G1C2F1-containing cream, respectively. G1C2F1 did not show nonspecific stimulatory activity on CHS response. The present study, together with the previous observation, show that Aloe vera gel contains small molecular weight immunomodulators that prevent UVB-induced immune suppression in the skin by restoration of UVB-induced damages on epidermal LC.

UVA-induced immune suppression through an oxidative pathway

Although ultraviolet B (UVB) irradiation induces local immune or systemic immune suppression, depending on the dose, the immune suppression by ultraviolet A (UVA) has not been fully investigated. In this study, we investigated the effect of UVA on the immune response in vitro and in vivo. The effect of UVA on the antigen-presenting function of epidermal cells was measured in terms of antigen-specific T cell proliferation. A murine epidermal cell suspension was exposed to UVA in vitro, pulsed with trinitrobenzenesulfonic acid, and cultured with T cells prepared from syngeneic mice previously sensitized with trinitrochlorobenzene. UVA (5-20 J per cm2) suppressed the antigen-presenting function of epidermal cells in a dose-dependent manner, accompanied with suppression of the expression of costimulatory molecules on Langerhans cells. In order to investigate the effect of an antioxidant on the immune suppression, an epidermal cell suspension was irradiated with UVA in the presence or absence of glutathione. The suppressions of antigen-presenting function and ICAM-1 expression were significantly prevented by glutathione in a dose-dependent manner. Further, the effect of UVA on the immune response at the induction phase of contact hypersensitivity was evaluated in terms of lymph node cell proliferation ex vivo. UVA irradiation suppressed the endogenous proliferation of lymph node cells in trinitrochlorobenzene-painted mice, and this suppression was significantly reversed by the application of glutathione to the skin during irradiation. These results suggest that UVA-induced immune suppression may be mediated by reactive oxygen species, at least in part.

Photoprotection: sunscreens and the immunomodulatory effects of UV irradiation

UV-B irradiation (UVR) of the host, in both humans and animal models, induces dose-related acute and chronic changes in skin which include erythema and photoageing, and induction of cancer. It can also induce modulation of immune responses of the host to antigens presented following irradiation. Commercially-available, broad-spectrum, high SPF (15, 15 + ) sunscreens protect against most effects of UV irradiation. An exception is the effects of UVR on immune responsiveness, with varying degrees of protection having been reported. We examined a system of UV-induced systemic suppression of contact hypersensitivity (CHS) responses in BALB/c mice. A range of commercially-available, broad spectrum, high SPF (15 + ) sunscreens demonstrated at best partial protection against systemic immunosuppression, yet were able to protect against two hallmarks of acute UVR-induced damage: skin oedema and keratinocyte proliferation. Two major models have been identified for the induction of immunosuppression following UVR, one identifying trans-urocanic acid (trans-UCA; deaminated histidine, located in the stratum corneum) as the critical photoreceptor, the other featuring DNA. UVR of trans-UCA produces cis-UCA, which itself is immunomodulatory. There was some abrogation of trans to cis isomerisation of urocanic acid in UV-irradiated, sunscreen-protected mice. However, the majority of the immunomodulation seen in these mice was abrogated by pretreatment with a monoclonal antibody to cis-urocanic acid. It is possible to induce formation of cis-urocanic acid in BALB/c skin in the absence of immunosuppression, using lower doses of UV radiation, indicating that formation of cis-urocanic acid in the stratum corneum is not necessarily sufficient to induce immunosuppression in the UV-irradiated host. The mechanisms of induction of the immunomodulated state in the UV-irradiated host are potentially diverse and the subject of ongoing debate. Our studies maintain a role for cis-UCA, and form the basis for further studies on its involvement in immunomodulation by UVR in sunscreen-protected hosts.

Commercial sunscreen lotions prevent ultraviolet radiation-induced depletion of epidermal Langerhans cells in Skh-1 and C3H mice

There is much controversy regarding the ability of sunscreens to prevent ultraviolet (UV)-induced immune suppression. Epidermal Langerhans cells (LC) play a key antigen-presenting role in the afferent limb of the immune system's response to antigens introduced through the skin. It has been suggested that depletion of LC in UV-exposed skin is a critical step toward the induction of immunosuppression by UV radiation. There are a number of disparate reports with inconsistent results concerning the ability of sunscreens to prevent UV-induced depletion of LC. The purpose of this study was to systematically evaluate the ability of sunscreens to prevent UV-induced LC depletion in mice. Epidermal sheets obtained from skin biopsies taken from mice exposed to UV radiation from Kodacel-filtered FS20 sunlamps, which do not emit UV power at wavelengths < 290 nm, were immunoperoxidase stained for LC using a rat monoclonal antibody against mouse Ia (major histocompatibility complex class II antigen). Time course and dose-response curves for LC depletion were generated for Skh-1 and C3H mice. Dose-response curves for acute UV exposure induced depletion of LC in Skh-1 and C3H mice were similar, but not identical. LC density in the skin of Skh-1 mice that received chronic UV exposure (3 days/week for 8 weeks) was reduced by 62% after 2 weeks of exposure, but returned to normal levels by 6 weeks. Five commercial sunscreen lotions with labeled sun protection factors (SPF) of 4, 8, 15, 30 and 45 were tested for their capacity to block UV-induced depletion of LC. LC were depleted approximately 75% in the skin of unprotected or placebo lotion treated Skh-1 mice exposed to UV given on two consecutive days. Conversely, LC depletion was prevented in similarly UV exposed Skh-1 mice protected with a SPF 30 sunscreen. In C3H mice the levels of protection against LC depletion provided by the five sunscreens were proportional to the level of protection predicted by their labeled SPF. Comparisons of dose-response curves showed that significantly higher doses of UV were required for LC depletion and induction of skin edema than for the induction of local suppression of contact hypersensitivity. Thus, at UV doses where sunscreens provide complete protection against immunosuppression of contact hypersensitivity, prevention of LC depletion and skin edema would be expected.

Sunscreens and vitamin E provide some protection to the skin immune system from solar-simulated UV radiation

Previous studies have indicated that sunscreens designed to protect from erythema do not adequately prevent immunosuppression. Mice were irradiated with suberythemal doses of solar-simulated ultraviolet radiation (ssUVR) to assess the immunoprotective ability of sunscreens. Whereas C3H/HeJ and BALB/c mice had similar sensitivities to ssUVR-induced inflammation, C3H/HeJ mice were more sensitive to ssUVR-induced immunosuppression. Octyl dimethyl-p-aminobenzoic acid did not protect from immunosuppression and, thus, had an immune protection factor (IPF) of 1. 2-Ethylhexyl-p-methoxycinnamate and microfine titanium dioxide provided limited protection, both having IPF values of 1.127. Immune protection by the sunscreens appeared to be dependent upon absorption of UVA as well as UVB, and was much less than predicted from the sun protection factor. Vitamin E, an inhibitor of lipid peroxidation, also protected the immune system, with an IPF of 1.2, indicating that oxidation of lipids is involved in UVR-induced immunosuppression, and that it should be possible to develop sunscreens which protect the immune system.

Sunscreens. Use and misuse

Although sunscreens are widely available and in common use, surveys show that an average of only half of the people on a beach on a given day wear sunscreens. Many people go to the beach to get or maintain a suntan, but many people also leave their skin unprotected. This article discusses the proper use of sunscreens, common misunderstandings, and how unprotected long-term exposure to the sun can effect your skin.

Sun exposure, sunscreen and their effects on epidermal Langerhans cells

This study examined the effects of chronic and current sun exposure on the number of Langerhans cells in epidermal sheets of UV-exposed and unexposed skin of the arms and assessed the effect of sunscreens. Participants were enrolled in a skin cancer prevention trial and had been using sunscreen daily for the previous 3 years. There were significantly fewer Langerhans cells on the exposed (463 cells/mm2) than on the unexposed forearm (528 cells/mm2) (P = 0.0001). High sun exposure in the previous 2 weeks and a history of predominantly outdoor occupations were both associated with a reduced number of Langerhans cells, although age and other biological indicators of chronic exposure were not associated. Sunscreen use was protective against the effects of current but not chronic sun exposure, with a suggestion of a greater effect at higher levels of exposure. Unexpectedly, people with a past history of nonmelanoma skin cancer had more Langerhans cells in both the exposed and the unexposed skin. These results emphasize the need for continued public health education to protect the immune system from the damaging effects of UV radiation.

Immunologic protection afforded by sunscreens in vitro

Several studies have suggested a lack of correlation between sunscreen sun protection factor and protection of the skin immune system, potentially allowing greater damage to the skin by removing the natural protective erythemal response to sun exposure. Despite this, routine testing of immune protection afforded by sunscreens is not performed by industry. Current laboratory methods for investigating the efficacy of sunscreen protection of epidermal immune function use the induction of contact hypersensitivity or epidermal cell alloantigen presentation. Animal models, cell culture systems, and in vivo human studies are commonly employed, but all these systems have significant drawbacks for use in routine testing. The purpose of this study was to develop an in vitro system for testing the immunologic protection afforded by sunscreens in human skin. Five test sunscreens plus a vehicle control were tested in a "blind" fashion for their in vitro level of immune protection. Creams were applied in a standard manner to human whole skin explants and were irradiated over a range of physiologic doses using an Oriel solar simulator. A mixed epidermal lymphocyte reaction was used to quantify epidermal alloantigen-presenting capacity, in the presence or absence of test cream, for five explants. Results consistently demonstrated that all the test sunscreens protected beyond their designated sun protection factors, whereas the vehicle conferred no protection. The explant-mixed epidermal lymphocyte reaction system gave consistent, reproducible results and may prove useful for the allocation of an immune protection factor to all sunscreens.

Sunscreens prevent local and systemic immunosuppression of contact hypersensitivity in mice exposed to solar-simulated ultraviolet radiation

Ultraviolet (UV) irradiation causes the immunosuppression of contact hypersensitivity (CH) responses in animals and humans. There are conflicting reports regarding the effectiveness of sunscreens in preventing UV-induced suppression of both local-type CH (induced by the application of the contact sensitizer directly to UV-exposed skin) and systemic-type CH (induced by the application of the contact sensitizer to an unirradiated skin site 3 days after UV exposure). The purposes of this study were as follows: 1. to derive solar simulator UV dose-response curves for the induction of local and systemic CH suppression in C3H mice; 2. to establish minimum immune suppression doses (MISDs) for local and systemic CH; 3. to determine the local and systemic immune protection capacity of two commercial sunscreen lotions with labeled sun protection factors (SPFs) of 4 and 8. Dose-response curves for the induction of local and systemic CH suppression were derived by exposing groups of mice to a range of full-spectrum UV doses (0.37-21.4 kJ m-2) on two consecutive days delivered from a filtered 1000 W xenon arc lamp solar simulator. The MISDs, defined as the lowest dose tested to cause approximately 50% suppression of the normal CH response, were obtained from the dose-response curves. Although the local and systemic immunosuppression dose-response curves were not statistically different, the MISD for local suppression of CH (1.35 kJ m-2) was about fivefold lower than that for systemic CH suppression (6.76 kJ m-2). The MISD was used as the endpoint to determine sunscreen immune protection levels. Both sunscreens, applied at 2 mg cm-2, provided immune protection against the induction of local and systemic CH suppression in mice exposed to an effective UV dose of 1 MISD given through the sunscreen, i.e. 4 MISD to SPF 4 sunscreen-protected mice and 8 MISD to SPF 8 sunscreen-protected mice mounted CH responses that were significantly greater than those elicited in unprotected mice exposed to 1 MISD of solar-simulated UV radiation. The calculated immune protection factors for these sunscreens exceeded the level of protection predicted by their labeled SPFs, i.e. the local immune protection factor of both sunscreens was 15 and the systemic immune protection factors were 8 for the SPF 4 sunscreen and 15 for the SPF 8 sunscreen. Our data show that these two sunscreens provide levels of immune protection which exceed the levels predicted by their labeled SPFs in immunoprotection tests conducted in mice exposed to a relevant MISD of UV radiation from a source emitting a UV power spectrum similar to that of sunlight.

Sunscreens offer the same UVB protection factors for inflammation and immunosuppression in the mouse

Many studies report that sunscreens effective against UVR-induced inflammation afford poor protection against immunosuppression. We have studied the relationship between photoprotection of inflammation and immunosuppression with monochromatic UVB (Philips TL01 tubes, lambda max = 311 nm) to remove possible confounding effects of differences in end point action spectra. Dose-response curves for edema and systemic suppression of contact hypersensitivity (CHS) in HRA.HRII-c/+/Skh mice showed that suppression of CHS was more sensitive to UVB irradiation by a factor of 2. The UVB dose-response curve for murine edema was similar to that for human erythema, with threshold doses of 773 mJ x cm(-2) and 632 mJ x cm(-2), respectively. The protection afforded by two UVB filters, octyl dimethyl para-aminobenzoic acid and 2-ethylhexyl-4'-methoxycinnamate, prepared in an identical vehicle, each with the same optical density at 311 nm, was tested in mice. We applied sunscreen to all exposed skin or to transpore tape above the irradiation cages, prior to exposure with 2.8 minimal edema doses. Topical or tape application of both sunscreens protected totally against edema but only partially against immunosuppression, with no significant difference in protection between the two application techniques (p > 0.4). A sunscreen protection factor of 4 in vivo was determined for 2-ethylhexyl-4'-methoxycinnamate for both edema and immunosuppression. Failure of the sunscreens to protect completely against immunosuppression was due to the ability of subedemal doses of UVB to induce substantial immunosuppression and not, as previously suggested, to any skin interaction.

Evaluation of an economical sunlamp that emits a near solar UV power spectrum for conducting photoimmunological and sunscreen immune protection studies

Expense and inconvenience have restricted the use of the filtered xenon are lamp (solar simulator) as a UV source for conducting large-scale animal studies. Because sunscreen immunoprotective levels are significantly affected by the UV power spectrum of the source it is imperative that a solar simulating source be used for accurate measurements of sunscreen protection levels that are relevant to human LV exposures from sunlight. However, relatively inexpensive sunlamps, e.g. the UVA-340, that emit a UV power spectrum similar to that of a solar simulator are available. Unlike FS-type UVB sunlamps, which have a significant amount of effective immunosuppressive non-solar UV energy at wavelengths below 295 nm, the immunosuppression effectiveness spectrum of UVA-340 sunlamps was nearly identical to that of a solar simulator. The purpose of this study was to evaluate this sunlamp for conducting photoimmunological and sunscreen immune protection studies. Groups of C3H mice were exposed to a range of UVA-340 sunlamp doses (0.25 kJ/m2 to 20.0 kJ/m2) to establish a dose-response curve and determine the minimum immune suppression dose (MISD) for iduction of local-type suppression of contact hypersensitivity (CH). The MISD, defined as the lowest UV dose given to produce approximately 50% suppression of the CH response in mice, was determined to be 1.0 kJ/m2 for UVA-340 sunlamps. Immune protection tests on four marketed sunscreen lotions (sun protection factors [SPF] 4, 8, 15 and 30) were then conducted with UVA-340 sunlamps using MISD as the endpoint. The immune protection factors for these sunscreens were equivalent to the level of protection predicted by their labeled SPF. These results are similar to those we have previously obtained using a solar simulator. We conclude from these data that the immunosuppressive effects of UVA-340 sunlamps are similar to those of a solar simulator; however, further studies are needed to determine if UVA-340, or similar, sunlamps are a viable alternative to the solar simulator for conducting large-scale animal experiments that require a relevant UV solar spectrum.

Sunscreens protect from UV-promoted squamous cell carcinoma in mice chronically irradiated with doses of UV radiation insufficient to cause edema

Previously we reported that the broad-spectrum sunscreen microfine titanium dioxide (MTD) could completely protect C3H/HeJ mice from UV radiation-induced immunosuppression to a contact sensitizer. In contrast, 2-ethylhexyl p-methoxycinnamate (2-EHMC), a UVB-absorbing sunscreen, only partially protected the skin immune system. In this study we investigated further this differential protection of the skin immune system by comparing the ability of 2-EHMC and MTD to protect these mice from the promotion phase of tumorigenesis. The mice were initiated using a single subcarcinogenic dose of 7,12-dimethylbenz(alpha)anthracene (DMBA) followed by promotion with chronic low-dose solar-simulated UV radiation for 32 weeks. We used doses of UV insufficient to cause edema in order to simulate daily human exposure to solar UV radiation. Mice were observed for the appearance of squamous cell carcinomas for 48 weeks. The DMBA-initiation alone and DMBA-initiated, sunscreen-treated groups did not develop tumors. Ultra-violet alone induced the appearance of tumors in 46% of mice at week 48 and therefore some tumors were initiated by UV. Initiation with DMBA prior to UV irradiation enhanced tumorigenesis such that 87% of mice at week 48 had tumors. Both 2-EHMC and MTD completely protected these mice from UV-induced promotion as well as from complete carcinogenesis despite the different UV-absorption spectra of the sunscreens and their differential abilities to protect from UV-induced immuno-suppression. Furthermore, we have shown that, if UV exposure is not increased to compensate for tolerance to edema, protection from tumorigenesis is afforded by sunscreens.

Ultraviolet spectral energy differences affect the ability of sunscreen lotions to prevent ultraviolet-radiation-induced immunosuppression

Acute exposure to UV radiation causes immunosuppression of contact hypersensitivity (CH) responses. Past studies conducted with unfiltered sunlamps emitting nonsolar spectrum UV power (wavelengths below 295 nm) or using excessive UV doses have suggested sunscreens may not prevent UV-induced immunosuppression in mice. This study was thus designed to evaluate critically the effects of different UV energy spectra on the immune protection capacity of sunscreen lotions. Minimum immune suppression doses (MISD), i.e. the lowest UV dose to cause approximately 50% suppression of the CH response to dinitrofluorobenzene in C3H mice, were established for three artificial UV sources. The MISD for each UV source was 0.25 kJ/m2 for unfiltered FS20 sunlamps (FS), 0.90 kJ/m2 for Kodacel-filtered FS20 sunlamps (KFS), which do not emit UV power at wavelengths < 290 nm, and 1.35 kJ/m2 for a 1000 W filtered xenon arc lamp solar simulator. Using MISD as baseline, sunscreens with labeled sun protection factors (SPF) of 4, 8, 15 and 30 were tested with each UV source to establish their relative immune protection factors. The immune protection factor of each sunscreen exceeded its labeled SPF in tests conducted with the solar simulator, which has a UV power spectrum (295-400 nm) similar to that of sunlight. Conversely, sunscreen immune protection factors were significantly less than the labeled SPF in tests conducted with FS and KFS. Comparison of the immunosuppression effectiveness spectra showed that relatively small amounts of nonsolar spectrum UV energy, i.e. UVC (200-290 nm) and/or shorter wavelength UVB (between 290 and 295 nm), produced by FS and KFS contributes significantly to the induction of immunosuppression. For example, 36.3% and 3.5% of the total immunosuppressive UV energy from FS and KFS, respectively, lies below 295 nm. Sunscreen absorption spectra showed that transmission of immunosuppressive UV energy below 295 nm for FS was at least eight-fold higher than that for KFS. Compared to the solar simulator UV spectrum the transmission of nonsolar immunosuppressive UV energy through sunscreens was > 15-fold higher for FS and > or = 1.5-fold higher for KFS. These data demonstrate that relevant evaluations of sunscreen immune protection can only be obtained when tests are conducted with UV sources that produce UV power spectra similar to that of sunlight and UV doses are employed that are based on established MISD.

Minimum doses of ultraviolet radiation required to induce murine skin edema and immunosuppression are different and depend on the ultraviolet emission spectrum of the source

Many photo immunological studies have used UV radiation sources that emit nonsolar UV spectral energy and UV doses based on nonimmunological endpoints, e.g. erythema and skin edema. Interpretation of these data has led to misunderstanding when extrapolated to hypothetical effects in humans exposed to solar UV. The purpose of this study was to: (1) establish UV dose response relationships for murine skin edema and immunosuppression, and (2) determine how different UV spectra affect these relationships. Back skin and ear minimum edema doses (MEdD) for Kodacel-filtered FS20 sunlamp UV (290-400 nm) were greater than two-fold higher than those for unfiltered FS20 sunlamp UV (250-400 nm). Xenon are solar simulator UV (295-400 nm) MEdD were > 10-fold higher than those for unfiltered sunlamp UV. Back skin and ear MEdD differed two- to five-fold between C3H/HeN, SWR/J and HRA/Skh-1 mice. The minimum immunosuppression doses (MISD) in C3H mice showed similar UV source spectrum dependence. The solar simulator UV MISD was 5.4- and 1.5-fold higher than for unfiltered and Kodacel-filtered sunlamp UV MISD, respectively. Furthermore, MISD were from 3- to 50-fold higher than the MEdD for the three UV sources. The UV bioeffectiveness spectra indicated that UVC energy (250-290 nm) contributed 12% and 18%, respectively, of the total skin edema and immunosuppression UV energy. These data demonstrate the variability in UV sensitivity among mouse strains, the significant differences between murine MEdD and MISD and how these differences are influenced by nonsolar regions (below 295 nm) of the UV spectrum.

Commercial sunscreen lotions prevent ultraviolet-radiation-induced immune suppression of contact hypersensitivity

Ultraviolet (UV) radiation suppresses certain immunologic responses, such as contact hypersensitivity (CH). Some previous studies, using sunlamps emitting nonsolar-spectrum UV or excessive UV doses, have questioned the ability of sunscreens to prevent UV-induced immune suppression. Our study evaluated the immune protection capacities of commercial sunscreen lotions in relation to the effects of UV spectrum and dose. C3H mice were exposed to a fixed UV dose from Kodacel-filtered FS sunlamps that caused maximum Langerhans cell depletion and suppression of CH. Kodacel film blocks UV energy below 290 nm, thus eliminating immune-suppressive effects of UVC (200-290 nm) not present in sunlight. CH was equally suppressed in unprotected and placebo-lotion-treated, UV-exposed mice. Mice protected with sun protection factor (SPF)-15 and SPF-30 sunscreens mounted normal CH responses. SPF-4 and SPF-8 sunscreen-protected mice had CH responses significantly greater than those of unprotected mice. Direct effects of UV spectral differences on the immune protection value of an SPF-15 sunscreen were determined by exposing mice to UV radiation from unfiltered and Kodacel-filtered sunlamps and a 1000-W xenon lamp solar simulator (UV spectrum nearly equivalent to sunlight). The sunscreen immune protection value was 30 times the minimum immune suppression dose for the solar simulator, while being 7.5 times this dose for Kodacel-filtered and 2 times the dose for unfiltered sunlamps. These results demonstrate that commercial sunscreen lotions prevent UV-induced immune suppression at a level exceeding the labeled SPF when tested with an environmentally relevant UV source.

Sunscreen protection of contact hypersensitivity responses from chronic solar-simulated ultraviolet irradiation correlates with the absorption spectrum of the sunscreen

This study compares the ability of two ultraviolet (UV) B-absorbing sunscreens, 2-ethylhexyl p-methoxycinnamate (2-EHMC) and 2-ethylhexyl p-aminobenzoate (Padimate O), and two physical sunscreens, microfine titanium dioxide (MTD) and zinc oxide, to protect the skin immune system from chronic (4 weeks) solar-simulated UV irradiation. Mice were exposed to suberythemal doses of UV before assessing local and systemic immunosuppression and tolerance to a contact sensitizer. Using a UV protocol that induced local but not systemic immunosuppression or tolerance in BALB/c mice, it was shown that Padimate O made the immunosuppression worse, whereas 2-EHMC and MTD protected the immune system. When the cumulative dose was increased by 12.7%, causing systemic immunosuppression and tolerance, none of the sunscreens protected from immunosuppression, but 2-EHMC provided partial, and MTD gave complete protection from tolerance. To examine this apparent lack of protection from systemic immunosuppression, C3H/HeJ mice were used. These mice had a minimal erythema dose similar to that of the BALB/c mice but were systemically immunosuppressed, with only 44% of the UV dose required to immunosuppress BALB/c mice. 2-EHMC provided some protection, whereas MTD provided complete protection from systemic immunosuppression in C3H/HeJ mice. Hence, sunscreens can protect from local and systemic immunosuppression, although this protection is limited and is not related to the sun protection factor of the sunscreens or the minimal erythema dose of the mouse strain. Instead, protection seems to be related to the sunscreens' having a broad absorption spectrum.

The effect of chronic low-dose UVB radiation on Langerhans cells, sunburn cells, urocanic acid isomers, contact hypersensitivity and serum immunoglobulins in mice

C3H mice were irradiated three times a week for up to 6 weeks with either 500 J/m2 or 1000 J/m2 broadband UVB (270-350 nm) or 3000 J/m2 narrowband UVB (311-312 nm; TL01 source). Each dose was suberythemal to the mouse strain used. The number of Langerhans cells (LC) in the epidermis was reduced by over 50% after 2 weeks of irradiation with the UVB source and by 20% following TL01 irradiation. Continued irradiation for up to 6 weeks resulted in no further decrease in LC numbers in the case of the UVB source but a steady decline to 40% in the case of the TL01 source. Sunburn cells were detected following irradiation with both sources but the numbers were very low in comparison with acute exposure. Ultraviolet-B exposure resulted in doubling of the thickness of the epidermis throughout the 6 weeks of irradiation while TL01 exposure did not alter epidermal thickness. Conversion of trans- to cis-urocanic acid (UCA) was observed with both UVB and TL01 sources. The percentage of cis-UCA started to return to normal after 4 weeks of TL01 exposure despite continued irradiation. As observed following a single exposure, the contact hypersensitivity (CH) response was significantly reduced following 6 weeks of UVB irradiation but was unaffected by TL01 exposure, indicating no correlation between cis-UCA levels and CH response. Total serum immunoglobulin levels remained unchanged throughout the 6 weeks of UVB or TL01 irradiation but IgE titers significantly increased in all cases in the first 2 weeks of irradiation, indicating a possible shift to a TH2 cytokine profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Sunscreens and T4N5 liposomes differ in their ability to protect against ultraviolet-induced sunburn cell formation, alterations of dendritic epidermal cells, and local suppression of contact hypersensitivity

Exposure of skin to ultraviolet (UV) radiation can lead to diverse biologic effects, including inflammation, sunburn cell formation, alterations of cutaneous immune cells, and impaired induction of contact hypersensitivity responses. The molecular mechanisms of these UV-induced effects are not completely understood. We investigated the ability of sunscreens and liposomes containing the DNA excision repair enzyme T4 endonuclease V to prevent these effects of UV radiation. The use of T4N5 liposomes, which increase the repair of cyclobutyl pyrimidine dimers, provides an approach for assessing the role of DNA damage in the effects of UV radiation on the skin. Exposing C3H mice to 500 mJ/cm2 UVB radiation from FS40 sunlamps resulted in skin edema, sunburn cell formation, and morphologic alterations and decreased numbers of Langerhans cells and Thy-1+ dendritic epidermal T cells. In addition, the induction of contact hypersensitivity after application of 2,4-dinitrofluorobenzene on UV-irradiated skin was diminished by 80%. Applying sunscreens containing octyl-N-dimethyl-p-aminobenzoate, 2-ethylhexyl-p-methoxycinnamate, or benzophenone-3 before this dose of UV irradiation gave nearly complete protection against all of these effects of UV irradiation. In contrast, topical application of T4N5 liposomes after UV irradiation had no effect on UV-induced skin edema and only partially protected against sunburn cell formation and local suppression of contact hypersensitivity, although its ability to protect against alterations in dendritic immune cells was comparable to that of the sunscreens. These results suggest that DNA damage is involved in only some of the local effects of UV radiation on the skin. In addition, T4N5 liposomes may be a useful adjunct to sunscreens because they can reduce some of the deleterious effects of UV radiation on skin even after a sunburn has been initiated.

Differential photoimmunoprotection by sunscreen ingredients is unrelated to epidermal cis urocanic acid formation in hairless mice

A series of experimental sunscreen preparations based on a common vehicle, containing increasing concentrations of either octyl-N-dimethyl-p-aminobenzoate (o-PABA) or 2-ethylhexyl-p-methoxycinnamate (2-EHMC) as the ultraviolet B (UVB) absorber, has been tested in the hairless mouse for the ability to protect from erythema, from the systemically suppressive effects of UVB (280-320 nm) radiation on contact hypersensitivity, and from photoisomerization of epidermal urocanic acid. All the preparations protected efficiently from the edema component of the erythema response when mice were exposed to UVB radiation equivalent to three times the minimal erythema dose (MED). However, when mice were exposed to UVB radiation equivalent to 15 x MED, protection from erythema was observed only at the higher concentrations of each UVB absorber (10% 2-EHMC and 10% or 15% o-PABA). Protection from the UVB-induced suppression of contact hypersensitivity was shown to be dependent on both the nature of the UVB absorber and its concentration. Photoimmunoprotection by the sunscreens containing 2-EHMC was evident at lower concentrations (5% and 10% 2-EHMC) than with o-PABA, following both 3 x MED and 15 x MED of UVB exposure. Photoimmunoprotection by o-PABA-containing sunscreens was observed only at 15% o-PABA following 3 x MED, and failed at all tested concentrations after 15 x MED of UVB exposure. Regardless of the photoimmunoprotective capacity, sunscreen preparations containing either of the UVB absorbers prevented the UVB-induced formation of cis urocanic acid in the mouse epidermis and in vitro under all conditions tested. Thus, there appeared to be a correlation between protection from edema and from cis urocanic acid formation at 3 x MED of UVB, but a dissociation of these variables at 15 x MED of UVB. There was no relation apparent at either UVB dose between either edema or cis urocanic acid formation and protection from suppression of contact hypersensitivity.

The effects of sunscreens on UVB erythema and Langerhans cell depression

Langerhans cells (LCs) are epidermal antigen-presenting cells capable of initiating a specific T lymphocyte-mediated immune response. It is a well known fact that ultraviolet light B (UVB) suppresses LC number and function. In this study, we confirmed that the sunscreens CITY BLOCK, and TOTAL SUN SHIELD 28 (Clinique Laboratories Tokyo, Japan) protected the epidermis against the depletion of LC number. We also investigated whether or not sunscreens could provide LC protection from ultraviolet ray (UVR) damage other than the prevention of the decrease in the total number of cells. Our data showed that the LC population was depressed after irradiation by 100 mJ/cm2 or 10 mJ/cm2 of UVB, but recovered to within normal levels after 16 days. Both sunscreens provided protection against erythema and LC depression due to UVB irradiation. However, despite the fact that these sunscreens had completely suppressed UVB erythema, shrinkage of LC dendrites was seen. Apparently, sunscreens prevent UVB erythema, but do not protect against functional changes in LC due to UVB. Recently, it has been reported that sunscreens are less effective in protecting against systemic immunosuppression that against inflammation. The shrinkage of LC dendrites despite sunscreen application may help explain this discrepancy.

Relationship between the ability of sunscreens containing 2-ethylhexyl-4'-methoxycinnamate to protect against UVR-induced inflammation, depletion of epidermal Langerhans (Ia+) cells and suppression of alloactivating capacity of murine skin in vivo

The UVB sunscreen 2-ethylhexyl-4'-methoxycinnamate was evaluated in hairless albino mouse skin for its ability to inhibit UVR-induced (i) oedema, (ii) epidermal Langerhans cell (Ia+) depletion and (iii) suppression of the alloactivating capacity of epidermal cells (mixed epidermal cell-lymphocyte reaction, MECLR). The sunscreen, prepared at 9% in ethanol or a cosmetic lotion, was applied prior to UVB/UVA irradiation. In some experiments there was a second application halfway through the irradiation. Single applications in both vehicles gave varying degrees of protection from oedema and Langerhans cell depletion but afforded no protection from suppression of MECLR. When the sunscreens were applied twice there was improved protection from oedema and Langerhans cell depletion and complete protection was afforded from suppression of MECLR. There was a clear linear relationship between Langerhans cell numbers and oedema with and without sunscreen application. The relationship between Langerhans cell numbers and MECLR was more complex. These data confirm published discrepancies between protection from oedema (a model for human erythema) and endpoints with immunological significance, but show that 2-ethylhexyl-4'-methoxycinnamate can afford complete immunoprotection, although protection is dependent on the application rate and vehicle.

Long-term ultraviolet B-induced impairment of Langerhans cell function: an immunoelectron microscopic study

The influence of low-dose, long-term ultraviolet B (UVB) light exposure on HLA class II-positive human epidermal Langerhans cells (LC) was studied using a sensitive immunoelectron microscopic technique for the ultrastructural assessment of HLA class II expression on LC and for quantification of these cells in situ. Six healthy Caucasian volunteers participated in the experiments and received thrice weekly UVB treatments for 4 weeks. The initial dose ranged from 30 to 50 mJ/cm2 and the total dose from 600 to 3500 mJ/cm2, depending on skin type. Suction blisters and biopsies were obtained before the start of the UVB protocol and 48 h after the last UVB irradiation, and processed for the mixed epidermal cell-lymphocyte reaction (MECLR) and electronmicroscopy, respectively. The MECLR was used as a measure of the immune response. The distribution of HLA class II molecules on LC was studied by incubating ultrathin cryosections of human skin tissue with an anti-HLA class II MoAb that was conjugated to 10 nm colloidal gold. Furthermore, the number of LC was assessed ultrastructurally, when they could be recognized by their unique cytoplasmic organelle, the Birbeck granule (BG). The UVB protocol that was employed caused a marked suppression of the MECLR responses. This UVB-induced reduction of the immune response was not paralleled by changes in HLA class II expression on LC, nor in the number of epidermal LC. These findings are further support for our hypothesis that UVB-induced immune suppression in the skin is not due to a depletion of local LC.

Effects of sunscreens and a DNA excision repair enzyme on ultraviolet radiation-induced inflammation, immune suppression, and cyclobutane pyrimidine dimer formation in mice

Exposure of skin to ultraviolet (UV) radiation inhibits the induction of delayed-type hypersensitivity (DTH) responses initiated at a distant, unirradiated site. Recent studies attributed this form of immune suppression to DNA damage in the form of cyclobutane pyrimidine dimers (CPD). In the present study, we investigated the protective defects of sunscreens on UV-induced systemic suppression of DTH to Candida albicans, inflammation, and DNA damage. The photoprotective effects of sunscreen preparations containing 8% octyl-N-dimethyl-p-aminobenzoate, 7.5% 2-ethylhexyl-p-methoxycinnamate, or 6% benzophenone-3 were studied in C3H mice exposed to a single dose of 500 mJ/cm2 UVB radiation from FS40 sunlamps. Inflammation was determined by the amount of skin edema at the site of UV irradiation, and DNA damage was assessed by measuring the frequency of endonuclease-sensitive sites in the epidermis. Application of the sunscreens before UV irradiation gave 75-97% protection against UV-induced edema, 67-91% protection against formation of CPD, but only 30-54% protection against suppression of DTH. In contrast, the topical application of liposomes containing a CPD-specific DNA repair enzyme immediately after UV irradiation resulted in 82% protection against suppression of DTH, but at best, 39% protection against skin edema. These findings demonstrate that sunscreens give less protection against UV-induced immune suppression than against skin edema and CPD formation. Furthermore, they suggest that less DNA damage is required to cause UV-induced immune suppression than to cause sunburn.

Autoimmunity and selected environmental factors of disease induction

Autoimmune diseases may be induced by physical and/or chemical environmental factors. A review of the available literature on mercuric chloride, iodine, silicone, anilides, L-tryptophan, vinyl chloride, and canavanine suggests three general mechanisms by which they may induce disease. First, oxidative damage probably is a frequent process involved in disease induction and pathogenesis. Second, certain compounds also may generate antigen-specific immune responses that could then cross-react with self-tissues. Other xenobiotics might bind to self-tissues and increase self-tissue immunogenicity. Third, physical and chemical agents may also modulate the immune system. Finally, in response to controversies surrounding the influence of human activities on global climate changes, the immunosuppressive effects of ozone and ultraviolet radiation are discussed.

Analysis of the protective effect of different sunscreens on ultraviolet radiation-induced local and systemic suppression of contact hypersensitivity and inflammatory responses in mice

We investigated the capacity of three sunscreen compounds to protect mice from the inflammatory and immunosuppressive effects of ultraviolet radiation (UVR). The sunscreen preparations contained 7.5% 2-ethylhexyl-p-methoxycinnamate, 8% octyl-N-dimethyl-p-aminobenzoate, or 6% benzophenone-3 in an oil-in-water emulsion. Skin swelling was used as the measure of their effect on UVR-induced inflammation, and immunosuppression was assessed by contact sensitization with 2,4-dinitrofluorobenzene applied to UV-irradiated skin (local suppression) or a distant site (systemic suppression). The sunscreens were applied to the shaved dorsal skin of C3H mice, which were then given a single dose of UVR ranging from 2 to 32 kJ/m2 within the UVB (280-320 nm) region. All three sunscreens gave complete protection against local suppression of contact hypersensitivity caused by a dose of 2 kJ/m2 UVB. They also protected against both inflammation and systemic immunosuppression caused by UVR; however, protection was highly dependent on the UVR dose. Furthermore, the sunscreens were less effective in protecting against systemic immunosuppression than against inflammation. These results indicate that immunosuppression is less sensitive to the protective effects of the sunscreens than inflammation and that protection against UVR-induced inflammation does not necessarily imply prevention of immunologic alterations. In addition, these studies suggest that UVR-induced immunosuppression and inflammation may involve different mechanisms.