Contrasting effects of ultraviolet A1 and ultraviolet B exposure on the induction of tumour necrosis factor-alpha in human skin

Molecular mechanisms of cis-urocanic acid and permethrin-induced alterations in cutaneous immunity

BACKGROUND/PURPOSE

Cutaneous cis-urocanic acid (cUCA) or ultraviolet B exposure has been shown to cause diminished cutaneous contact hypersensitivity (CH) and to induce systemic tolerance (increased regulatory T lymphocytes) in mice. Permethrin is also a known CH inhibitor, but the molecular mechanisms are currently poorly understood. In this study, CH was evaluated in four strains of mice: an immunosensitive strain (C57BL/6N), an immunoresistant strain (SvImJ), a strain developed from C57BL/6N mice but genetically altered at both the tumor necrosis factor-alpha receptors (TNFalphap55R and p75R), and a strain developed from C57BL/6N but genetically deleted at the interferon-gamma (IFNgamma) locus.

METHODS

CH was evaluated in each group via oxazolone challenge following a 5-day exposure to intradermal (ID) cUCA or a single exposure to topical permethrin, or co-exposure to both chemicals in 5-week-old female C57BL/6N, SvImJ, and C57BL/6N mice genetically altered at the TNFalpha or IFNgamma locus.

RESULTS

A 5-day exposure to ID cUCA or a single exposure to topical permethrin resulted in diminished CH response in C57BL/6N mice, and this effect was exacerbated with concurrent exposure to both chemicals. CH in SvImJ was both cUCA- and permethrin-resistant relative to C57BL/6N mice, as 5-day cUCA or a single exposure to permethrin did not diminish CH, nor did concurrent exposure to cUCA and permethrin. Mice deleted at both TNFalphaR loci displayed similar but somewhat blunted diminished CH responses to cUCA or permethrin. This trend became significant with combined chemical exposure. IFNgamma knockout mice displayed similar diminished CH responses to cUCA or permethrin alone. Unlike C57BL/6N mice, the IFNgamma knockout mice did not show a further reduction in CH with combined chemical exposure.

CONCLUSIONS

These results suggest the following: (1)Mouse strains show variable susceptibility to permethrin- and cUCA-induced immunomodulation. (2)TNFalpha may be involved in the immunomodulatory effects of cUCA and permethrin. (3)IFNgamma may be required for the more than additive depression of CH caused by cUCA+permethrin.

Pathogenesis of pterygia: role of cytokines, growth factors, and matrix metalloproteinases

Pterygium is a common ocular surface disease apparently only observed in humans. Chronic UV exposure is a widely accepted aetiological factor in the pathogenesis of this disease and this concept is supported by epidemiological data, ray tracing models and histopathological changes that share common features with UV damaged skin. The mechanism(s) of pterygium formation is incompletely understood. Recent data have provided evidence implicating a genetic component, anti-apoptotic mechanisms, cytokines, growth factors, extracellular matrix remodelling (through the actions of matrix metalloproteinases), immunological mechanisms and viral infections in the pathogenesis of this disease. In this review, the current knowledge on pterygium pathogenesis is summarised, highlighting recent developments. In addition, we provide novel data further demonstrating the complexity of this intriguing disease.

Photosensitivity in rheumatic diseases

There have been a number of recent advances in the genetic understanding of photosensitive rheumatic diseases, especially subacute cutaneous lupus erythematosus and dermatomyositis. These advances support the concept that increased numbers of ultraviolet light-induced apoptotic cells in skin lead to a supra-threshold concentration of antigenic peptides. The current genetic data suggest that increased keratinocyte apopotosis can result from increased amounts of TNF-alpha that induce apoptosis due to a ultraviolet light-sensitive TNF promoter polymorphism or to decreased clearance of apototic cells due to polymorphisms associated with decreased serum levels of collectins such as C1q and mannose-binding lectin. These diseases are frequently oligogenic, and other yet to be elucidated genes will, in individual patients, lead to increased numbers of apoptotic cells associated with these cutaneous autoimmune diseases. In the presence of specific MHC class I and II genes, antigen-presenting cells initiate a primary immune response that leads to cutaneous, and likely systemic, autoimmune disease.

Basal cell carcinoma is associated with high TNF-alpha release but not with TNF-alpha polymorphism at position - 308

The mechanisms underlying induction of UVB-induced immunosuppression are not fully understood, but tumor necrosis factor alpha (TNF-alpha) is suggested to play a central role. A single base pair polymorphism at position --308 in the promoter region of the TNF-alpha gene associated with an enhanced secretion of TNF-alpha has been identified in humans. We have therefore investigated the association of the --308 polymorphism with the risk of basal cell carcinoma (BCC) in humans. The frequency of TNF G and TNF A alleles among Caucasian patients with a previous BCC (n=191) and health adults (n-107) were compared. For the TNF--308 polymorphism there was significant association between the genotype or allele frequencies and having BCC. To determine whether patients with a previous BCC had an increased capacity to secrete TNF-alpha, mononuclear cells were stimulated with lipopolysaccharide. Mononuclear cells from patients with a previous BCC (n=15) demonstrated a significantly increased release of TNF-alpha upon stimulation with lipopolysaccharide (P<0.03) compared with mononuclear cells age-matched control subjects (n=16). Further studies of other polymorphisms of the TNF-alpha gene associated with increased TNF-alpha production and BCC and necessary.

Changes in the immune system of female sunbathers due to the effect of natural UV radiation

Exposure to UV radiation may cause health hazards and suppress immune responses. The aim of this study was to evaluate whether recurrent suberythemal doses of natural UV radiation can have a harmful effect on the lymphocyte subpopulations of local sunbathers. Sixteen healthy local female volunteers at the age of 23 to 44 recurrently sunbathed during the summer of 2000 in the Pärnu beach area (58 degrees 22'N, 24 degrees 31'E). They were informed of the actual UV index and encouraged to gather only suberythemal UV doses. Before and after the sunbathing period the CD3+, CD3+CD4+, CD3+CD8+, CD19+, CD3-CD16+ CD56+, CD4+CD25+, CD4+HLA-DR+ and CD3+HLA-DR+ cells were determined in the peripheral blood of the volunteers. A statistically significant increase in the CD4+CD25+ and CD3+HLA-DR+ cells and a decrease in the CD3-CD16+CD56+ cells were detected. However, all changes remained in the normal range and there were no serious deviations in the composition of lymphocyte subpopulations. It was concluded that suberythemal doses of UV radiation gathered by volunteers had apparently no harmful effect on the immune system.

Stress-related modulation of matrix metalloproteinase expression

Matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs), whose expression can be controlled by cytokines, play a role in extracellular matrix remodeling in physiological and pathological processes. Using a blister chamber wound model on UV-B-exposed human forearm skin, we examined whether stress or mood-associated neuroendocrine alteration is sufficient to modulate MMP and TIMP expression. We did not find evidence that depressive symptoms were reliably associated with modulation of either MMP or TIMP expression. However, we did find that activation of the hypothalamic-pituitary-adrenal (HPA) and sympathetic-adrenal medullary (SAM) axes can modulate levels of MMPs. A positive association between plasma norepinephrine levels and MMP-2 protein levels, and a negative correlation between plasma cortisol levels and MMP-2 levels were found. The data suggest that activation of the HPA and SAM axes, even in individuals within the normal range of depressive symptoms, could mediate MMP levels and wound healing in blister wounds.

Studies to determine the immunomodulating effects of cis-urocanic acid

Exposure to ultraviolet (UV) radiation, particularly the UVB wavelengths, leads not only to DNA damage but also to suppression of cell-mediated immunity to antigens encountered shortly after the irradiation. One initiator of this complex process is cis-urocanic acid (cis-UCA), which is formed from the naturally occurring trans isomer in the epidermis on absorption of UV. cis-UCA has been shown to have immunomodulating properties in a variety of in vivo and in vitro experimental systems, although its mechanism of action is not yet clear. This article covers methods of preparing cis-UCA and of analyzing UCA isomers in various human and mouse tissues. Experiments that demonstrate that cis-UCA is immunosuppressive are described. The final section deals with the preparation and characterization of a monoclonal antibody with specificity for cis-UCA.

Mechanisms underlying the suppression of established immune responses by ultraviolet radiation

The ultraviolet radiation present in sunlight is immune suppressive. Recently we showed that solar-simulated ultraviolet radiation (ultraviolet A + B; 295-400 nm), applied after immunization, suppressed immunologic memory and the elicitation of delayed-type hypersensitivity to the common opportunistic pathogen, Candida albicans. Further, we found that wavelengths in the ultraviolet A region of the solar spectrum (320-400 nm), devoid of ultraviolet B, were equally effective in activating immune suppression as ultraviolet A + B radiation. Here we report on the mechanisms involved. Maximal immune suppression was found when mice were exposed to solar-simulated ultraviolet radiation 7-9 d post immunization. No immune suppression was found in ultraviolet-irradiated mice injected with monoclonal anti-interleukin-10 antibody, or mice exposed to solar-simulated ultraviolet radiation and injected with recombinant interleukin-12. Suppressor lymphocytes were found in the spleens of mice exposed to ultraviolet A + B radiation. In addition, antigen-specific suppressor T cells (CD3+, CD4+, DX5+) were found in the spleens of mice exposed to ultraviolet A radiation. Applying liposomes containing bacteriophage T4N5 to the skin of mice exposed to solar-simulated ultraviolet A + B radiation, or mice exposed to ultraviolet A radiation, blocked immune suppression, demonstrating an essential role for ultraviolet-induced DNA damage in the suppression of established immune reactions. These findings indicate that overlapping immune suppressive mechanisms are activated by ultraviolet A and ultraviolet A + B radiation. Moreover, our findings demonstrate that ultraviolet radiation activates similar immunologic pathways to suppress the induction of, or the elicitation of, the immune response.

Indoor tanning facility density in eighty U.S. cities

The purpose of this study was to examine the number of tanning facilities in select U.S. cities. The twenty most populated cities from each of 4 U.S. regions were selected for the sample. For each city, data on the number of tanning facilities, climate, and general demographic profile were collected. Data for state tanning facility legislation also were collected. A tanning facility density variable was created by dividing the city's number of facilities by its population size. The 80 cities had an average of 50 facilities each. Results of linear regression analysis indicated that higher density was significantly associated with colder climate, lower median income, and higher proportion of Whites. These data indicate that indoor tanning facilities are prevalent in the environments of U.S. urban-dwellers. Cities having the higher density profile may be logical targets for interventions promoting less or safer use of these facilities.

Ultraviolet B radiation induces a transient appearance of IL-4+ neutrophils, which support the development of Th2 responses

UVB irradiation can cause considerable changes in the composition of cells in the skin and in cutaneous cytokine levels. We found that a single exposure of normal human skin to UVB induced an infiltration of numerous IL-4(+) cells. This recruitment was detectable in the papillary dermis already 5 h after irradiation, reaching a peak at 24 h and declining gradually thereafter. The IL-4(+) cells appeared in the epidermis at 24 h postradiation and reached a plateau at days 2 and 3. The number of IL-4(+) cells was markedly decreased in both dermis and epidermis at day 4, and at later time points, the IL-4 expression was absent. The IL-4(+) cells did not coexpress CD3 (T cells), tryptase (mast cells), CD56 (NK cells), and CD36 (macrophages). They did coexpress CD15 and CD11b, showed a clear association with elastase, and had a multilobed nucleus, indicating that UVB-induced infiltrating IL-4(+) cells are neutrophils. Blister fluid from irradiated skin, but not from control skin, contained IL-4 protein as well as increased levels of IL-6, IL-8, and TNF-alpha. In contrast to control cultures derived from nonirradiated skin, a predominant type 2 T cell response was detected in T cells present in primary dermal cell cultures derived from UVB-exposed skin. This type 2 shift was abolished when CD15(+) cells (i.e., neutrophils) were depleted from the dermal cell suspension before culturing, suggesting that neutrophils favor type 2 T cell responses in UVB-exposed skin.

Reduction of acute photodamage in skin by topical application of a novel PARP inhibitor

The ultraviolet (UV) components of sunlight induce damage to the DNA in skin cells, which is considered to be the initiating step in the harmful biological effects of UV radiation. Repair of DNA damage results in the formation of single-strand DNA breaks, which activate the nuclear poly(ADP-ribose) polymerase (PARP). Overactivation of PARP worsens the oxidative cell damage and impairs the energy metabolism, raising the possibility that moderation of PARP activation following DNA damage may protect skin cells from UV radiation. The topical effects of the novel PARP inhibitor O-(3-pyperidino-2-hydroxy-1-propyl) pyridine-3-carboxylic acid amidoxime monohydrochloride (BGP-15M) were investigated on UV-induced skin damage in a hairless mouse model. For evaluation of the UV-induced acute photodamage to the skin and the potential protective effect of BGP-15M, DNA injury was detected by measuring the formation of single-strand DNA breaks and counting the resulting sunburn (apoptotic) cells. The ADP-ribosylation of PARP was assessed by Western blot analysis and then quantified. In addition, the UV-induced immunosuppression was investigated by the immunostaining of tumor necrosis factor alpha and interleukin-10 expressions in epidermal cells. The signs of inflammation were examined clinically and histochemically. Besides its primary effect in decreasing the activity of nuclear PARP, topically applied BGP-15M proved to be protective against solar and artificial UV radiation-induced acute skin damage. The DNA injury was decreased (P<0.01). An inhibition of immunosuppression was observed by down-regulation of the epidermal production of cytokines IL-10 and TNFalpha. In the mouse skin, clinical or histological signs of UV-induced inflammation could not be observed. These data suggest that BGP-15M directly interferes with UV-induced cellular processes and modifies the activity of PARP. The effects provided by topical application of the new PARP-regulator BGP-15M indicate that it may be a novel type of agent in photoprotection of the skin.

Ultraviolet light induced injury: immunological and inflammatory effects

This article reviews many of the complex events that occur after cutaneous ultraviolet (UV) exposure. The inflammatory changes of acute exposure of the skin include erythema (sunburn), the production of inflammatory mediators, alteration of vascular responses and an inflammatory cell infiltrate. Damage to proteins and DNA accumulates within skin cells and characteristic morphological changes occur in keratinocytes and other skin cells. When a cell becomes damaged irreparably by UV exposure, cell death follows via apoptotic mechanisms. Alterations in cutaneous and systemic immunity occur as a result of the UV-induced inflammation and damage, including changes in the production of cytokines by keratinocytes and other skin-associated cells, alteration of adhesion molecule expression and the loss of APC function within the skin. These changes lead to the generation of suppressor T cells, the induction of antigen-specific immunosuppression and a lowering of cell-mediated immunity. These events impair the immune system's capacity to reject highly antigenic skin cancers. This review gives an overview of the acute inflammatory and immunological events associated with cutaneous UV exposure, which are important to consider before dealing with the complex interactions that occur with chronic UV exposure, leading to photocarcinogenesis.

Ultraviolet a radiation suppresses an established immune response: implications for sunscreen design

The ultraviolet radiation present in sunlight is the primary cause of nonmelanoma skin cancer and has been implicated in the development of cutaneous malignant melanoma. In addition, ultraviolet is immune suppressive and the suppression induced by ultraviolet radiation has been identified as a risk factor for skin cancer induction. Ultraviolet also suppresses the immune response to infectious agents. In most experimental models, ultraviolet is applied to immunologically naive animals prior to immunization. Of equal concern, however, is the ability of sunlight to suppress established immune reactions, such as the recall reaction in humans, which protects against microbial infections. Here we demonstrate that solar-simulated ultraviolet radiation, applied after immunization, suppresses immunologic memory and the elicitation of delayed-type hypersensitivity. Further, we found that wavelengths in the ultraviolet A region of the solar spectrum were critical for inducing immune suppression. Ultraviolet A (320-400 nm) radiation was as effective as solar-simulated ultraviolet A + B (290-400 nm) in suppressing the elicitation of an established immune response. Irradiation with ultraviolet AI (340-400 nm) had no effect. Supporting a critical role for ultraviolet A in ultraviolet-induced immune suppression was the observation that applying a sunscreen that contained an ultraviolet B only filter had no protective effect, whereas, a sunscreen containing both ultraviolet A and ultraviolet B filters totally blocked ultraviolet-induced immune suppression. These data suggest that sunlight may depress the protective effect of prior vaccination. In addition, the observation that ultraviolet A is immunosuppressive indicates the need for ultraviolet A protection when designing sun protection strategies.

Contrasting effects of an ultraviolet B and an ultraviolet A tanning lamp on interleukin-6, tumour necrosis factor-alpha and intercellular adhesion molecule-1 expression

BACKGROUND

Recent studies have demonstrated that a tanning lamp emitting predominantly ultraviolet (UV) A induces significant yields of the type of potentially mutagenic DNA damage that are associated with the onset of skin cancer (i.e. cyclobutane pyrimidine dimers). UV-induced immunosuppression is also an important event leading to skin cancer.

OBJECTIVES

To the modulation of key immunological molecules following exposure to a broad-spectrum UVB lamp and a predominantly UVA-emitting tanning lamp using model in vitro systems.

METHODS

We compared secretion and mRNA expression of interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in normal human epidermal keratinocytes, and interferon (IFN)-gamma-induced intracellular adhesion molecule (ICAM)-1 in normal human fibroblasts irradiated in vitro with a broad-spectrum UVB lamp or with a Philips 'Performance' tanning lamp.

RESULTS

With broad-spectrum UVB irradiation, upregulation of IL-6 and TNF-alpha mRNA was detected 6 h after irradiation, and a dose-dependent increase of cytokines in the supernatants of irradiated cells was found 24 h after irradiation. In contrast, there was no cytokine secretion and little evidence for mRNA upregulation following exposure to a tanning lamp. When cells were exposed first to broad-spectrum UVB, then the tanning lamp, UVB-induced cytokine secretion was inhibited, although mRNA levels were upregulated to a level close to that observed with UVB alone. By using a Schott WG 320 nm filter to attenuate the level of UVB relative to UVA emitted by the tanning lamp, the inhibition of cytokine secretion was shown to be associated with UVA exposure. Both UV sources inhibited IFN-gamma-induced ICAM-1 mRNA expression in a dose-dependent fashion. By using a Schott WG 335 nm filter, inhibition of ICAM-1 mRNA expression by the tanning lamp was shown to be associated with UVB exposure.

CONCLUSIONS

These results suggest that UV sources emitting different levels of UVA and UVB have differential effects on the modulation of different immunoregulatory molecules, and indicate that there are potential interactions between these wavelengths.

Higher sensitivity in induction of apoptosis in fibroblast cell lines derived from LEC strain rats to ultraviolet B radiation

When lung fibroblast cell lines from LEC and WKAH rats were irradiated with ultraviolet B (UVB) and assayed for colony formation, LEC rat cells showed a higher sensitivity than did WKAH rat cells. The LEC rat cells were approximately 1.5-fold more sensitive to UVB radiation than were the WKAH rat cells in terms of D37 values, which are the doses of UVB required to reduce cell survival to 37%. When the rat cells were irradiated with UVB in the presence of 0.5 M dimethyl sulfoxide (DMSO), which efficiently scavenges free radicals such as hydroxyl radicals, no significant difference was observed between the survival curves of either LEC or WKAH rat cells irradiated with UVB in the presence of 0.5 M DMSO and those irradiated with UVB in the absence of DMSO. Therefore, formation of free radicals may not be involved in cell death induced by UVB radiation. Flow cytometry showed that the percentage of apoptotic cells in the LEC rat cell population increased with post-incubation time after UVB radiation. The proportion of apoptotic cells in the UVB-irradiated LEC rat cell population increased as the dose of UVB was increased. In contrast, no significant proportion of apoptotic cells was observed in the UVB-irradiated WKAH rat cell population. These results showed a higher sensitivity in induction of apoptosis by UVB radiation in LEC rat cells than in WKAH rat cells.

Ultraviolet AI exposure of human skin results in Langerhans cell depletion and reduction of epidermal antigen-presenting cell function: partial protection by a broad-spectrum sunscreen

BACKGROUND

Ultraviolet (UV) B-induced effects on the skin immune system have been extensively investigated, but little is known regarding the immunological changes induced by UVA exposure of human skin. Recent data assessing the protection afforded by sunscreens against photoimmunosuppression stress the need for broad-spectrum sunscreens with an adequate UVA protection.

OBJECTIVES

The purpose of this study was first to determine the changes observed in epidermal Langerhans cells (ELC) density and epidermal antigen-presenting cell (APC) activity after exposure of human skin to UVAI (340-400 nm) radiation, and secondly to assess the immune protection afforded in vivo by a sunscreen formulation containing a long wavelength UVA filter with a low UVA protection factor (UVA-PF = 3).

METHODS

Epidermal cell (EC) suspensions were prepared from skin biopsies 3 days after exposure to a single dose of UVAI (either 30 or 60 J cm(-2)).

RESULTS

Flow-cytometric analysis of EC suspensions revealed that exposure to 60 J cm(-2) UVAI resulted in a decreased number of ELC without infiltration of CD36+ DR+ CD1a- antigen-presenting macrophages into the epidermis, and a significant reduction of HLA-DR expression on viable ELC. In vivo exposure to both 30 and 60 J cm(-2) resulted in a decreased allogeneic CD4+ T-cell proliferation induced by UVAI-irradiated ECs. The sunscreen application partially prevented (57 +/- 9%) the decrease in epidermal allogeneic APC activity induced by 60 J cm(-2) UVAI.

CONCLUSIONS

In vivo UVAI exposure of human skin results in a decreased number of ELC and in a downregulation of epidermal APC activity. This last effect is partially prevented by prior application of a sunscreen with a low UVAI-PF value. These results indicate that increasing the absorption of UV filters for long UVA wavelengths may lead to an improved immune protection.

UVA exposure affects UVB and cis-urocanic acid-induced systemic suppression of immune responses in Listeria monocytogenes-infected Balb/c mice

Ultraviolet radiation can inhibit immune responses locally as well as systemically. Such effects have been measured in animals and humans exposed to ultraviolet B (wavelength 280-315 nm) (UVB) and ultraviolet A (315-400 nm) (UVA). The precise wavelength dependence is important for the identification of possible molecular targets and for assessments of risk of different artificial UV sources and solar UV. In such analyses, it is commonly assumed that radiation energy from each wavelength contributes to the effect independent of the other wavelengths. Here we show that this assumption does not hold good. In the present study, it was investigated whether exposure to broadband UVA or longwave ultraviolet A 1 (340-400 nm) (UVA 1) prior to the standard immunosuppressive UVB protocol might modulate the immunosuppressive effects induced by UVB. Preexposure to broadband UVA or longwave UVA 1, 1 day prior to the standard immunosuppressive UVB protocol, inhibited the UVB-induced suppression of delayed type hypersensitivity (DTH) to Listeria monocytogenes significantly. This effect was not associated with restoring the number of interleukin (IL-12)-positive cells in the spleen. Since isomerization of trans-urocanic acid (UCA) into the immunosuppressive cis-UCA isomer plays a crucial role in UVB-induced immunomodulation, in a second set of experiments it was investigated whether immunosuppression induced by cis-UCA might also be downregulated by preexposure to UVA. Animals were exposed to broad-band UVA or longwave UVA 1 prior to application of an immunosuppressive dose of cis- or trans-UCA as a control. Both UVA and UVA 1 appear to inhibit the cis-UCA-induced systemic immunosuppression (DTH and IL-12) to L. monocytogenes. These studies clearly show that UVA radiation modulates both UVB and cis-UCA-induced immunomodulation. In general, our studies indicate that both broadband UVA and longwave UVA 1 could induce modulation of UVB and cis-UCA-induced immunomodulation. As sunlight contains both UVA and UVB radiation the balance between these two radiations apparently determines the net immunomodulatory effect.

Opposite regulation of the HPV 20-URR and HPV 27-URR promoters by ultraviolet irradiation and cytokines

Epidemiological evidence implicates ultraviolet radiation and genetic changes (e.g., p53 mutations) as important factors in the etiology of nonmelanoma skin cancer. Little is known about a possible role of cutaneous papillomaviruses in these tumors. We previously reported both positive and negative regulation of the promoter activity of a number of HPV types by UV irradiation. To determine the underlying mechanism, we examined the influence of pro-inflammatory cytokines and MAP-kinases induced by UV irradiation by transfecting the HPV 20-URR and the HPV 27-URR into the RKO, HaCaT and H1299 cell lines expressing wild-type or mutated p53 or lacking p53, respectively. IL-1alpha, IL-1beta, IL-6, IL-17, TNF-alpha, as well as interferon-alpha, -beta and -gamma activated the promoter in the HPV 20-URR but inhibited the HPV 27-URR promoter. The effect of IL-1alpha and UV light was abolished by the addition of IL-1 receptor antagonist. UV irradiation induced a prolonged activation of JNK in HaCaT and H1299 but not in RKO cells, and its dephosphorylation was enhanced in the presence of p53 and the HPV-URRs.

Long-wave UVA offers partial protection against UVB-induced immune suppression in human skin

Ultraviolet-B (UVB, 280-320 nm) interferes with the generation of cell-mediated immunity to contact allergens applied epicutaneously on the irradiated site. To investigate whether pretreatment with UVA-1 (340-400 nm) protects against the UVB-induced immune suppression we sensitized human volunteers with diphenylcyclopropenone (DPCP) on normal buttock skin (n= 12), on UVB-irradiated buttock skin (n=21), on buttock skin pretreated with UVA-1 (n= 12), and on buttock skin pretreated with UVA-1 and thereafter irradiated with UVB (n=22). Sensitization on UVB-irradiated skin reduced the immunization rate to DPCP compared with sensitization on non-irradiated skin (p<0.01) and skin pretreated with UVA-1 (p<0.01). In contrast, the immunization rate in the group of volunteers sensitized on skin pretreated with UVA-1 before UVB irradiation was significantly higher than the immunization rate in the group of volunteers sensitized on UVB-irradiated skin alone (p<0.05). These results indicate that pretreatment with UVA-1 under certain conditions offers partial protection against the UVB-induced reduction in the immunization rates to epicutaneous allergens.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Differential effects of UVA1 and UVB radiation on Langerhans cell migration in mice

The UVB (280-315 nm)- and UVA1 (340-400 nm)-induced migration of Langerhans cells (LC) from the epidermis and accumulation of dendritic cells (DC) in the lymph nodes draining the exposed skin site of C3H/HeN mice have been investigated. One minimum erythemal dose (MED) of UVB (1.5 kJ/m2) and of UVA1 (500 kJ/m2) were chosen, which have been shown previously to suppress delayed hypersensitivity (DTH). UVB irradiation resulted in a reduction in epidermal LC numbers, local to the site of the exposure, which was most apparent 12 h after exposure, but, in contrast, UVA1 had no significant effect even at 72 h after exposure. UVA1 did not exert any protection against the UVB-mediated depletion in LC numbers. The reduction in local LC following UVB exposure was prevented by systemic (intraperitoneal) treatment of mice with neutralising antibodies to either tumor necrosis factor (TNF)-alpha or interleukin (IL)-beta 2 h prior to the irradiation. It has been reported previously that UVB exposure caused an increase in the number of dendritic cells (DC) in the lymph nodes draining the irradiated skin site. In the present study we have shown that UVA1 had a similar effect. Pretreatment of the mice with neutralising antibodies to IL-1beta (by intraperitoneal injection) substantially inhibited DC accumulation induced by both UV regimens. However, anti-TNF-alpha antibodies affected only the UVB-induced increase, and did not alter the elevation in DC numbers observed following UVA1 exposure. These results indicate that UVB causes the migration of LC from the epidermis and an accumulation of DC in the draining lymph nodes by a mechanism that requires both TNF-alpha and IL-1beta. In contrast, UVAI does not cause LC migration from the epidermis and the accumulation of DC in the draining lymph nodes observed following UVA1 exposure requires IL-1beta, but not TNF-alpha. It is likely therefore that UVA1 acts through a different mechanism from UVB and may target a cutaneous antigen presenting cell other than LC, such as the dermal DC.

Modulation of IL-10, IL-12, and IFN-gamma in the epidermis of hairless mice by UVA (320-400 nm) and UVB (280-320 nm) radiation

We have observed recently that the suppression of contact hypersensitivity (CHS) induced in mice by UVB irradiation may be prevented by suberythemal exposure to UVA radiation. Because the UVB-immunosuppressed state is associated with an upregulation of the Th2-associated cytokines IL-10 and IL-4, and a deficiency in Th1-associated IL-2, IL-12, and IFN-gamma, and because UVA photoimmunoprotection appeared to be IFN-gamma- dependent, we tested the hypothesis that UVA immunoprotection results from an ability to prevent the UVB-induced cytokine disarray. This study describes changes in epidermal IL-10, IL-12 and IFN-gamma for 5 d following irradiation of hairless mice with the CHS-modulating doses of UVB, UVA, or UVA + UVB, using immuno-histochemical detection in paraffin embedded skin sections, followed by image analysis quantitation. We found that UVB, but not UVA exposure, caused an increase in epidermal IL-10 expression, peaking at 3 d. UVA irradiation, but not UVB, resulted in increased epidermal IL-12 expression, peaking at 3 d, and increased epidermal IFN-gamma expression peaking earlier at 1 d. Irradiation with UVA + UVB abrogated the UVB-enhanced expression of IL-10, and caused small but significant increases in IL-12 and IFN-gamma at 3 d and 1 d, respectively. These findings suggest that UVA photoimmunoprotection is mediated via prevention of IL-10 release, and thus the maintenance of the Th1/Th2 balance, probably by upregulation of IL-12 and IFN-gamma, which are known to antagonize IL-10 in numerous models. The time course suggests that IFN-gamma responds initially to UVA radiation, and may stimulate the increased expression of IL-12.

Wavelength-specific synergy between ultraviolet radiation and interleukin-1 alpha in the regulation of matrix-related genes: mechanistic role for tumor necrosis factor-alpha

Ultraviolet light causes both acute and chronic changes in extracellular matrix. We sought to examine the effects of different ultraviolet wavelengths on expression of matrix-related genes in fibroblasts. We previously reported that tropoelastin gene expression in vivo decreases with acute ultraviolet B exposure, and interleukin-1 alpha-mediated upregulation of tropoelastin is blocked in vitro after ultraviolet B radiation. In this study, we found that only ultraviolet B, but not ultraviolet A or ultraviolet A1, blocked the ability of interleukin-1 alpha to stimulate tropoelastin expression in vitro. Ultraviolet B and interleukin-1 alpha synergistically increased tumor necrosis factor-alpha secretion by fibroblasts, a finding not seen with ultraviolet B alone nor with ultraviolet A or ultraviolet A1 combined with interleukin-1 alpha. Keratinocytes showed a similar ultraviolet B-specific induction of tumor necrosis factor-alpha production. Addition of tumor necrosis factor-alpha to cultured fibroblasts blocked interleukin-1 alpha-induced stimulation of tropoelastin message, and addition of anti-tumor necrosis factor-alpha antibodies restored the responsiveness of tropoelastin and collagen messages to exogenous interleukin-1 alpha after ultraviolet B exposure. We conclude that interleukin-1 alpha in combination specifically with ultraviolet B induces fibroblasts to secrete tumor necrosis factor-alpha, and that this ultraviolet B-specific induction of tumor necrosis factor-alpha secretion is responsible for effects of ultraviolet B on the expression of matrix-related genes in the skin.

Interferon-gamma is involved in photoimmunoprotection by UVA (320-400 nm) radiation in mice

Ultraviolet B radiation not only inflicts tumor-initiating DNA damage, but also impairs T cell-mediated immunity relevant to survival of the initiated cells. We have reported, however, that ultraviolet A radiation, in contrast, is immunologically innocuous in hairless mice and opossums, but renders the animals resistant to the immunosuppression by ultraviolet B, or its mediator cis-urocanic acid. Ultraviolet B irradiation of skin causes abundant release of numerous cytokines (interleukin-1, interleukin-6, interleukin-10, tumor necrosis factor-alpha); notably interleukin-12 and interferon-gamma do not appear to be upregulated. A recent report has indicated that interleukin-12 protects from photoimmunosuppression in mice, but it remains unclear whether interleukin-12 acts directly or via interferon-gamma, which it is known to stimulate. Here we investigate the possible role of interferon-gamma in UVA photoimmunoprotection, using interferon-gamma gene knockout mice in comparison with control C57/BL6 mice, and the systemic contact hypersensitivity reaction (induced by sensitization through a nonirradiated skin site) to measure immunity. interferon-gamma-/- mice raised normal contact hypersensitivity responses, and were unaffected, as were C57BL control mice, by ultraviolet A exposure. In response to ultraviolet B irradiation or topical cis-urocanic acid treatment, control mice became immunosuppressed by 69% and 27%, respectively, and interferon-gamma-/- mice by 79% and 27%. When ultraviolet B exposure or cis-urocanic acid was followed by ultraviolet A irradiation, however, contact hypersensitivity was totally restored in control mice, but remained suppressed by 55% and 25%, respectively, in interferon-gamma-/- mice. Injection of recombinant interferon-gamma in the interferon-gamma-/- mice restored the ultraviolet A protective effect against cis-urocanic acid-induced immunosuppression. These observations suggest that interferon-gamma plays a part in ultraviolet A immunoprotection from the suppressive effect of ultraviolet B radiation and, and that the mechanism appears to be via antagonism by this cytokine of the cis-urocanic acid immunosuppressive action.

The effects of ultraviolet radiation on the human immune system

The adverse outcome of increased ultraviolet (UV) irradiation on human health is currently of concern. While many experiments have been carried out in rodent models, fewer have been designed to test the effects of UV exposure in human subjects. This review concentrates on the modulations induced in the human immune system by UV, and outlines changes in antigen presentation by Langerhans cells and macrophages, in the activities of natural killer cells and T cells, and in cytokine regulation. Precautionary measures which might be taken to help protect people against the immunosuppressive action of UV irradiation are considered.

The UV waveband dependencies in mice differ for the suppression of contact hypersensitivity, delayed-type hypersensitivity and cis-urocanic acid formation

Solar radiation contains ultraviolet B (280-315 nm) and ultraviolet A (ultraviolet AII, 315-340 nm; ultraviolet AI, 340-400 nm) wavebands. Ultraviolet B is known to suppress certain aspects of cell mediated immunity. Using three ultraviolet lamps (the broad-band ultraviolet B TL-12, the narrow-band ultraviolet B TL-01 and an ultraviolet AI source), we investigated the dose and waveband dependencies for the suppression of contact hypersensitivity to oxazolone and delayed-type hypersensitivity to herpes simplex virus, plus the formation of cis-urocanic acid in C3H/HeN mice. A single exposure of 1500 J/m2 TL-12 or 10,000 J/m2 TL-01 or 500,000 J/m2 ultraviolet AI corresponded to 1 minimum erythema dose in this mouse strain. The percentage of cis-urocanic acid of the total urocanic acid rose from a background level of 1.7% to 40% with 1000 J/m2 TL-12 or 10,000 J/m2 TL-01, but only 17% cis-urocanic acid was obtained with 500,000 J/m2 ultraviolet AI. The contact hypersensitivity response was significantly suppressed after a minimum dose of 5000 J/m2 TL-12 or 50,000 J/m2 TL-01 or 500,000 J/m2 ultraviolet AI. The delayed-type hypersensitivity response was suppressed by a minimum dose of 100 J/m2 TL-12 or 10,000 J/m2 TL-01 or 1000 J/m2 ultraviolet AI. So, whereas a low dose of ultraviolet AI reduced the delayed-type hypersensitivity response, a 500-fold higher dose was required to suppress contact hypersensitivity. There was no correlation between the suppression of these responses and the concentration of cis-urocanic acid in the skin. Thus different mediators may modulate the various immune responses affected by ultraviolet exposure, depending on the wavelength of the radiation.