Mechanisms of ultraviolet (UV) B and UVA phototherapy

Efficacy of UVA1 phototherapy in 230 patients with various skin diseases

OBJECTIVE

Investigation of the efficacy of ultraviolet (UV) A1 phototherapy on atopic eczema, scleroderma, granuloma annulare, urticaria pigmentosa, prurigo nodularis, lichen sclerosus et atrophicus, T-cell lymphoma, keratosis lichenoides chronica, chronic urticaria and some rare, sclerosing skin diseases.

METHODS

The data of 230 patients treated with low-dose, medium-dose and high-dose UVA1 therapy during 6 years were retrospectively analysed. The mean single dose (J/cm(2)), the mean number of irradiations and the mean total dose (J/cm(2)) were evaluated. The efficacy of phototherapy was assessed by a grading scale and the number of patients was given in percentage for each group.

RESULTS

Good therapeutic effects of UVA1 therapy were shown in patients with atopic eczema, scleroderma, lichen sclerosus et atrophicus, keratosis lichenoides chronica, prurigo nodularis and with cutaneous T-cell lymphoma. Positive effects in some patients were seen in the urticaria pigmentosa and granuloma annulare group, no change to slight improvement was seen in most of the patients with rare, sclerosing skin diseases and no effect was seen in the chronic urticaria group.

CONCLUSION

Besides topical and systemic therapy, UVA1 radiation is a good option of treatment in various skin diseases. It is one of the first-line treatments for several sclerotic diseases and it often improves pruritus considerably.

Autoimmunity as an aetiological factor in vitiligo

Vitiligo is a common dermatological disorder characterized by the presence on the skin of depigmented macules resulting from the destruction of cutaneous melanocytes. Autoimmunity is an important hypothesis with regard to vitiligo aetiology and the evidence for autoimmune responses being involved in the pathogenesis of this disorder will be discussed in the present review. All immune system compartments, including innate and adaptive immunity have been implicated in vitiligo development. Particularly relevant are autoantibodies and autoreactive T cells in vitiligo patients that have cytotoxic effects upon pigment cells. Furthermore, predisposition to vitiligo appears to be associated with certain alleles of the major histocompatibility complex class II antigens as well as with other autoimmune-susceptibility genes. Moreover, the association of vitiligo with autoimmune disorders, the animal models of the disease, and the positive response to immunosuppressive therapeutic agents emphasize the role of autoimmunity in the development of this disorder.

Ultraviolet B light stimulates interleukin-20 expression by human epithelial keratinocytes

The proinflammatory cytokine interleukin-20 (IL-20) may exert the majority of its activity in the skin. We examined the effect of various treatments including several forms of phototherapy on IL-20 expression using cultured normal human epithelial keratinocytes (NHEK). Broadband UVB light, recombinant (r) IL-1 and rIL-8 increased, while hydrocortisone reduced, NHEK supernatant IL-20 levels. Elevation of NHEK IL-20 mRNA and maximal supernatant IL-20 levels occurred with a UVB light dose (40 mJ cm(-2)) that reduced cell viability by approximately 50%. While this UVB light dose also elevated supernatant IL-1 alpha and IL-8 levels, antibody neutralization studies indicated that neither of these cytokines was directly responsible for this increase in IL-20 expression. However, the elevation in IL-20 levels was fully inhibited by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB-203580, suggesting involvement of this stress signaling pathway in this UVB light response. Photodynamic therapy (PDT) with the photosensitizer lemuteporfin, UVA light, cisplatin, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) or recombinant interferon-gamma (rIFN-gamma) either had little effect or decreased NHEK supernatant IL-20 levels. Reduced IL-20 levels paralleled the cytotoxic actions of PDT, UVA light or cisplatin and the antiproliferative effect of rIFN-gamma. Neither rIL-20 supplementation nor anti-IL-20 antibody treatments affected cell viability indicating that soluble IL-20 did not affect the short-term survival of UVB light-irradiated NHEK. Stimulation of IL-20 expression in keratinocytes by UVB light suggests that this cytokine might participate in skin responses to this ever-present environmental factor and potentially has a role in UV light-associated dermatoses.

Local narrowband UVB phototherapy vs. local PUVA in the treatment of chronic hand eczema

BACKGROUND

Hand eczema is a chronic skin disorder characterized by a poor response to conventional therapies. Although local PUVA has been proven to be effective in the treatment of chronic hand eczema, little is known about the efficacy and safety of local narrowband UVB (TL-01) for this condition. The aim of our study was to compare the efficacy and safety of local narrowband UVB phototherapy with paint-PUVA in patients with chronic hand eczema of dry and dyshidrotic types unresponsive to conventional therapies.

PATIENTS/METHODS

Fifteen patients (nine men and six women) with chronic hand eczema of dry and dyshidrotic types was included in this prospective, comparative study based on a left to right comparison pattern. The treatments were administered with local narrowband UVB irradiation on one hand and local paint-PUVA using 0.1% 8-methoxypsoralen gel on the other hand three times a week over a 9-week period. The NB-UVB irradiation was administered using a local NB-UVB system equipped with TL-01 lamps. The initial dose was 150 mJ/cm(2) for each patient. An increasing percentile dose schedule based on an increase of 20% was used in every session, until a final dose of 2000 mJ/cm(2) was reached. Evaluation of clinical scores was carried out every 3 weeks during the treatment period.

RESULTS

Twelve of the 15 recruited patients completed the study. There was a statistically significant decrease in the mean clinical score at the third, sixth and nineth week in both groups. The difference in clinical response between the two treatment modalities was not statistically significant at the end of the 9-week treatment period. In the narrowband UVB-treated side, the tolerance of all the patients to the treatment was good all patients well-tolerated the treatment with the exception of mild xerosis that responded to topical emollients.

CONCLUSION

Local narrowband UVB phototherapy regimen is as effective as paint-PUVA therapy in patients with chronic hand eczema of dry and dyshidrotic types.

UVB therapy of pityriasis lichenoides - our experience with 29 patients

BACKGROUND

Pityriasis lichenoides comprises a clinical and pathological spectrum of disorders. So far no highly effective treatment has been reported. Previous small studies have suggested that ultraviolet B (UVB) is a good alternative.

METHODS

This is a retrospective analysis of 29 pityriasis lichenoides patients treated in our institution with broad- or narrow-band UVB during the period 1996-2002. Twenty-one of these patients had one or more previous unsuccessful treatments.

RESULTS

Complete response was achieved in 93.1% in both treatment groups, with 73% of them still relapse free after a mean follow-up of 58 and 38 months in broad- and narrow-band UVB treatment groups, respectively. Mild side-effects were observed in about one-third of the patients.

CONCLUSION

We believe both forms of UVB are a good option for pityriasis lichenoides and should be considered as the first line in generalized cases interested in treatment.

Ultraviolet phototherapy for pruritus

Ultraviolet-based therapy has been used to treat various pruritic conditions including pruritus in chronic renal failure, atopic dermatitis, HIV, aquagenic pruritus and urticaria, solar, chronic, and idiopathic urticaria, urticaria pigmentosa, polycythemia vera, pruritic folliculitis of pregnancy, breast carcinoma skin infiltration, Hodgkin's lymphoma, chronic liver disease, and acquired perforating dermatosis, among others. Various mechanisms of action for phototherapy have been posited. Treatment limitations, side effects, and common dosing protocols are reviewed.

Effects of ultraviolet B irradiation on the production of regulated upon activation normal T-cell expressed and secreted protein in cultured human epidermal keratinocytes

The modulatory effects of ultraviolet B (UVB) irradiation on cutaneous inflammatory responses are well known but their mechanism remains obscure. It has been proposed that regulated upon activation normal T-cell expressed and secreted protein (RANTES), which is one of the chemokines produced by epidermal keratinocytes, might play an important role in the pathogenesis of cutaneous inflammatory disorders, such as atopic dermatitis and psoriasis vulgaris. This study was designed to determine whether UVB irradiation could affect the production of RANTES that is induced in cultured normal human epidermal keratinocytes upon stimulation by inflammatory cytokines. We measured levels of the transcript of the gene for RANTES in cultured keratinocytes and of RANTES itself in culture supernatants by semiquantitative reverse transcription and the polymerase chain reaction and by an enzyme-linked immunosorbant assay (ELISA), respectively. Neither the transcript nor RANTES itself was detected without prior stimulation of cells by tumor necrosis factor alpha (TNF-alpha) and/or interferon gamma (IFN-gamma) and production of RANTES was not induced by UVB (100 J/m2) irradiation alone. Cells were irradiated with UVB just before addition of TNF-alpha and IFN-gamma to the medium and then cells and culture supernatants were harvested 12, 24, and 36 h later. In both irradiated and non-irradiated cells, RANTES mRNA was first detected at 12 h and the level increased subsequently. RANTES itself was detected at 24 h, with a higher level at 36 h. At all time points examined, UVB irradiation inhibited the production of RANTES mRNA and of the protein itself. These results suggest that suppression of the production of RANTES by epidermal keratinocytes might be involved in the modulatory effects of UVB irradiation on cutaneous inflammation.

Bivalent effect of UV light on human skin mast cells-low-level mediator release at baseline but potent suppression upon mast cell triggering

Ultraviolet (UV) irradiation is an established treatment for inflammatory skin diseases, although the precise mode of action is still unclear. Activating and suppressive effects on mast cell (MC) mediator release have been described. The aim of this study was to investigate systematically the effects of UVB, UVA-1, and psoralen plus UVA-1 at therapeutic doses on skin-derived human MC. Baseline and stimulated release of histamine, tryptase, and of interleukin (IL)-6, IL-8 and tumor necrosis factor-alpha (TNF-alpha) were examined. In resting MC, UV light induced a slight, yet significant histamine release corresponding to enhanced surface levels of lysosome-associated membrane proteins (LAMP). In contrast, UV pre-treatment caused a marked suppression of the anti-IgE-induced histamine release, accompanied by a diminished, anti-IgE-mediated increase in LAMP expression. The secretion of IL-6, IL-8, and TNF-alpha was inhibited in resting and activated MC, suggesting a different mode of action. Regarding the importance of MC in a variety of allergic and inflammatory processes, our data show a high susceptibility of this cell type towards UV light, which seems to partially depend on the state of cellular activation. Immunosuppressive effects predominate in activated MC, thus corresponding with the beneficial effects in inflammatory diseases, whereas in resting MC, both stimulatory and inhibitory effects are observed.

Seasonality in Symptom Severity Influenced by Temperature or Grass Pollen: Results of a Panel Study in Children with Eczema

Although seasonal variations are well known in many patients with eczema, no systematic population-based panel study evaluating seasonality and quantifying the influence of factors like climate and pollen on symptom variations has been conducted so far. Thirty-nine children with eczema, who had been identified in 1996 in a cross-sectional study on 1673 6-y-olds in Augsburg (Germany), participated in the study. Between March and September 1999, they daily recorded itch, extent, and possibly triggering factors on quantitative scales. Daily temperature, humidity, radiation, and pollen concentration were measured. Mixed linear models, taking the time series structure and confounding into account, were used for analysis. Seasonal patterns were significantly different between children: twenty-one had symptoms mainly in winter. They were affected by changes in outdoor temperature: itch was reduced by 22% (95% confidence interval (CI): 16%-27%) and extent by 65% (CI: 54%-72%) per 15 degrees C temperature increase. Eighteen children exhibited more symptoms in summer and especially during days with high grass-pollen exposure when itch was 16% higher (CI: 8%-24%) and extent 19% (CI: 2%-39%). This effect was stronger for children sensitized against pollen. Consideration of the individual type of eczema may help to arrange appropriate preventive and therapeutic measures.

An update and guidance on narrowband ultraviolet B phototherapy: a British Photodermatology Group Workshop Report

Summary These guidelines for use of narrowband (TL-01) ultraviolet B have been prepared for dermatologists by the British Photodermatology Group on behalf of the British Association of Dermatologists. They present evidence-based guidance for treatment of patients with a variety of dermatoses and photodermatoses, with identification of the strength of evidence available at the time of preparation of the guidelines, and a brief overview of background photobiology.

Phototherapy for cutaneous T-cell lymphoma

Phototherapy has been utilized for decades in the treatment of various dermatologic conditions, including cutaneous T-cell lymphoma (CTCL). Currently, a number of light sources are available, and selection of the specific modality is based on a number of factors, the most important of which is disease stage. The efficacy of broadband ultraviolet B (UVB) is limited to the patch stage, while psoralen and ultraviolet A (PUVA) is capable of clearing plaques and, sometimes, early tumors. Narrowband UVB is also effective for early stages and has practical advantages over PUVA, but more studies are needed to more fully evaluate its role in CTCL. Long-wave ultraviolet A (UVA1) has likewise shown efficacy, supported by findings of apoptosis induction in UVA1-treated cells. Long-term remissions have been reported for PUVA, but in the majority of cases, maintenance therapy was necessary. Although beneficial as monotherapy for early stages of the disease, phototherapy is also a useful adjunct to other modalities such as interferons, retinoids and electron beam therapy. Studies are ongoing to refine protocols for combination therapy, with the goal of improving efficacy, while minimizing adverse effects.

Treatment of polymorphic light eruption

Polymorphic light eruption (PLE) is a highly prevalent photosensitivity disorder, estimated to affect 11-21% people in temperate countries. Typically, PLE appears as a recurrent pruritic eruption comprising papules and/or vesicles and/or plaques, which occurs on photo-exposed skin sites following sun exposure, and which heals without scarring. Commoner in females, the aetiology is uncertain, although there is evidence of an immune basis. We perform a review of the prophylaxis and treatment of this condition. While sun protection, corticosteroids and desensitization phototherapy are the mainstays of management, a range of anti-inflammatory and immunomodulatory agents are reported.

Global surface ultraviolet radiation intensity may modulate the clinical and immunologic expression of autoimmune muscle disease

OBJECTIVE

To determine if geoclimatic factors may influence the nature and frequency of dermatomyositis (DM), polymyositis, and associated autoantibodies around the world.

METHODS

We assessed, in the first global evaluation of these conditions, the relationship between 13 geoclimatic variables that may modulate disease and the relative proportion of DM and its associated autoantibody anti-Mi-2, directed against an SNF2-superfamily helicase associated with the nucleosome remodeling and histone acetylation and deacetylation complex, in a global myositis population. Altogether, 919 consecutive patients from populations at 15 locations were studied.

RESULTS

Univariate and multivariate analyses demonstrated that of the variables evaluated, surface ultraviolet (UV) radiation intensity (irradiance) most strongly contributed to the relative proportion of DM and was strongly related to the proportion of anti-Mi-2 autoantibodies (weighted r = 0.939, P < 4 x 10(-7) and weighted r = 0.69, P = 0.02, respectively). Published ethnogeographic immunogenetic allele frequencies imply that the striking differences in the proportion of DM- and DM-specific autoantibodies observed around the world are not the result of inherent global variations in known genetic risk factors.

CONCLUSION

These data suggest that UV radiation exposure may modulate the clinical and immunologic expression of an autoimmune disease in different populations around the world.

Ultraviolet A radiation induces rapid apoptosis of human leukemia cells by Fas ligand-independent activation of the Fas death pathways

Endogenous cellular chromophores absorb ultraviolet A radiation (UVA, 290-320 nm), the major UV component of terrestrial solar radiation, leading to the formation of reactive oxidizing species that initiate apoptosis, gene expression and mutagenesis. UVA-induced apoptosis of T helper cells is believed to underlie the UVA phototherapy for atopic dermatitis and other T cell-mediated inflammatory skin diseases. We have evaluated the involvement of the Fas-Fas ligand (FasL) pathway in rapid UVA-induced apoptosis in human leukemia HL-60 cells. UVA-induced apoptosis was not inhibited by pretreatment with a neutralizing anti-Fas antibody, although the same UVA treatment initiated cleavage of caspase-8 and subsequent processing of Bid and caspase-3-like proteases. Inhibition of caspase-8 by Lle-Glu (OMe)-Thr-Asp(OMe)-fluoromethyl ketone completely blocked caspase-3 cleavage and apoptosis in UVA-treated cells, suggesting that apoptosis was initiated by the Fas pathway. This inference was supported by demonstrating that immunoprecipitates obtained from UVA-treated cells using anti-Fas antibody contained caspase-8 and Fas-associating protein with death domain (FADD). In addition, Fas clustering in response to UVA treatment was observed by immunofluorescence microscopy. These data support a mechanism for rapid, UVA-induced apoptosis in HL-60 cells involving initial formation of the Fas-FADD-caspase-8 death complex in an FasL-independent manner.

Influence of UVB, UVA and UVA1 irradiation on histamine release from human basophils and mast cells in vitro in the presence and absence of antioxidants

UV irradiation is widely used for the treatment of atopic eczema. In recent years, UVA1 phototherapy has gained increasing attention. This study analyzed the influence of different UV wavelengths--especially UVA1--on histamine release from human basophils and mast cells. The modulation of this parameter might be responsible for some of the therapeutic effects of UV irradiation. Enriched human basophils and human mast cells (HMC1 cell line) were irradiated with increasing doses of UVB, UVA and UVA1 in vitro. After irradiation, different stimulants were added to induce histamine release. In additional experiments, basophils were preincubated with superoxide dismutase, ascorbate or trolox to study the role of antioxidants in the modulation of histamine release after UV irradiation. UVA and UVA1 significantly inhibited histamine release from basophils and mast cells. UVB only had an inhibitory effect on mast cells. Preincubation with superoxide dismutase and ascorbate did not influence the inhibitory effect of UVA1 on basophil histamine release, whereas trolox decreased significantly the histamine release from nonirradiated basophils.

Evidence for an autoimmune pathogenesis of vitiligo

Vitiligo is a depigmenting disorder characterized by the development of white patches in various distributions, which are due to the loss of melanocytes from the epidermis. A variety of arguments from clinical observations to research findings in human and animal models support the hypothesis of autoimmunity and are reviewed in this article. The association with autoimmune diseases and organ-specific autoantibodies is well known. Various effective treatment options have an immunosuppressive effect. Today the autoimmune pathogenesis of the disease has become a rapidly evolving field of research. Detection of circulating melanocyte antibodies in human and animal models implicates a possible role of humoral immunity. Histological and immunohistochemical studies in perilesional skin suggest the involvement of cellular immunity in vitiligo. Recently, T-cell analyses in peripheral blood further support this hypothesis. Interestingly, new insights in the association of vitiligo and melanoma may help to clarify the role of autoimmunity in the development of vitiligo.

Occupational exposures and autoimmune diseases

Autoimmune diseases are pathologic conditions defined by abnormal autoimmune responses and characterized by immune system reactivity in the form of autoantibodies and T cell responses to self-structures. Here we review the limited but growing epidemiologic and experimental literature pertaining to the association between autoimmune diseases and occupational exposure to silica, solvents, pesticides, and ultraviolet radiation. The strongest associations (i.e., relative risks of 3.0 and higher) have been documented in investigations of silica dust and rheumatoid arthritis, lupus, scleroderma and glomerulonephritis. Weaker associations are seen, however, for solvent exposures (in scleroderma, undifferentiated connective tissue disease, and multiple sclerosis) and for farming or pesticide exposures (in rheumatoid arthritis). Experimental studies suggest two different effects of these exposures: an enhanced proinflammatory (TH1) response (e.g., TNF-alpha and IL-1 cytokine production with T cell activation), and increased apoptosis of lymphocytes leading to exposure to or modification of endogenous proteins and subsequent autoantibody formation. The former is a general mechanism that may be relevant across a spectrum of autoimmune diseases, whereas the latter may be a mechanism more specific to particular diseases (e.g., ultraviolet radiation, Ro autoantibodies, and lupus). Occupational exposures are important risk factors for some autoimmune diseases, but improved exposure assessment methods and better coordination between experimental/animal models and epidemiologic studies are needed to define these risks more precisely.

Ultraviolet B induces mast cell apoptosis: a hypothetical mechanism of ultraviolet B treatment for uraemic pruritus

The pathogenesis of uraemic pruritus is unclear, although there is some evidence that an increased number of skin-infiltrating mast cells may play a role. Ultraviolet B reduces itchy sensation of uraemic patients by leading to depletion of cutaneous mast cells. This study presents data that both broad-band and narrow-band ultraviolet B irradiation are able to induce apoptosis in transformed mast cells (murine mastocytoma cell line P815) in a dose-dependent manner at a time point of 24 hours. The positive apoptotic rates were as follows: sham-exposed cells (controls) -- 13.3% +/- 0.6%; with broad-band ultraviolet B irradiation -24.5% +/- 1.1% with 10mJ/cm(2), 57.9% +/- 4.6% with 20mJ/cm(2) and 70.9% +/- 4.5% with 30mJ/cm(2); with narrow-band ultraviolet B irradiation -- 29.6% +/- 2.3% with 100mJ/cm(2), 57.3% +/- 4.1% with 200mJ/cm(2) and 81.5% +/- 1.9% with 300mJ/cm(2). The difference between the number of apoptotic cells in all groups of ultraviolet B-irradiated cells and sham-exposed cells was highly significant (P<0.001). Based on these findings, it is hypothesized that ultraviolet B induced mast cell apoptosis could be an important factor in phototherapy for the diseases dependent on increased number of cutaneous mast cells, including uraemic pruritus.

Narrow-band ultraviolet B and broad-band ultraviolet A phototherapy in adult atopic eczema: a randomised controlled trial

BACKGROUND

Narrow-band ultraviolet B (UVB) is an effective treatment for psoriasis, and open studies suggest that this phototherapy might improve atopic eczema. We did a randomised controlled trial to compare narrow-band UVB, UVA, and visible light phototherapy as second-line, adjunctive treatments in adult patients with moderate to severe atopic eczema.

METHODS

Phototherapy was administered twice a week for 12 weeks. 26 patients were randomly assigned narrow-band UVB, 24 were assigned UVA, and 23 visible fluorescent light. The primary endpoints were change in total disease activity (sum of scores at six body sites) and change in extent of disease after 24 treatments compared with baseline. Data were analysed by the method of summary measures.

FINDINGS

13 patients withdrew or were excluded from analysis. Mean reductions in total disease activity over 24 treatments in patients who received narrow-band UVB and UVA, respectively, were 9.4 points (95% CI 3.6 to 15.2) and 4.4 points (-1.0 to 9.8) more than in patients who received visible light. Mean reductions in extent of disease after 24 treatments with narrow-band UVB and UVA were 6.7% (1.5 to 11.9) and -1.0% (-5.3 to 3.3) compared with visible light. A small proportion of patients developed erythema after phototherapy or had a flare in their eczema sufficient to withdraw from treatment.

INTERPRETATION

Narrow-band UVB is an effective adjunctive treatment for moderate to severe atopic eczema, and the treatment is well tolerated by most patients.

Simultaneous determination of reduced and oxidized glutathione in peripheral blood mononuclear cells by liquid chromatography-electrospray mass spectrometry

We developed a sensitive and specific liquid chromatography-electrospray mass spectrometric (HPLC-ESI-MS) assay for the simultaneous determination of reduced and oxidized glutathione (GSH and GSSG) in peripheral blood mononuclear cells (PBMC). Following derivatization with N-ethylmaleimide to prevent GSH auto-oxidation, addition of thiosalicylic acid as internal standard, and protein precipitation with cold acetonitrile, the samples were injected into a diol column, eluted with acetonitrile-1% aqueous acetic acid (25:75) and detected by the ESI-MS system. The optimized method exhibited a good detection limit for both analytes (0.01 and 0.05 microM for GSH and GSSG, respectively). Good linearity was reached in the 0.01-20 microM range for GSH and 0.05-20 microM for GSSG. The mean recoveries of GSH and GSSG were 98.5-100.6% and 105.8-111.5%, respectively. The run-to-run repeatability for retention time and peak area was RSD% 0.06 and 1.75 for GSH and 0.18 and 2.50 for GSSG. The optimized method was applied to GSH and GSSG assay in PBMC analyzing 20 healthy individuals.

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.

Sunlight, immunosuppression and skin cancer: role of histamine and mast cells

1. The development into tumours of skin cells transformed by ultraviolet (UV) B radiation of wavelengths 290-320 nm is enhanced by the ability of UVB to suppress an immune response that would otherwise destroy them. Ultraviolet B-induced immunomodulation may be by multiple mechanisms, but generally manifests in an antigen-presenting cell defect and an altered cytokine environment in the draining lymph nodes. 2. Immune responses to microbial or self-antigens may be dysfunctional by similar mechanisms following UVB exposure. 3. Earliest-acting intermediates in the initiation of UVB-induced immunosuppression are the UVB absorbers (photoreceptors) of the skin, notably DNA resulting in immunoregulatory cytokine production, and trans-urocanic acid (UCA), which, upon isomerization to its cis isomer, signals downstream immunosuppressive events. 4. In mice, dermal mast cells are critical to UVB-induced systemic immunomodulation. In mice, there is a functional link as well as a linear relationship between the prevalence of histamine-staining dermal mast cells and the log of the dose of UVB required for 50% immunosuppression. Studies with histamine receptor antagonists support histamine as the main' product of mast cells involved. Histamine acts in large part via a prostanoid-dependent pathway. 5. Approximately 50% of humans and greater than 90% of patients with non-melanoma skin cancer are UVB susceptible for suppression of a contact hypersensitivity response. Neither cytokine polymorphisms nor UVB-induced levels of cis-UCA in irradiated skin have been linked to UVB susceptibility. Patients with basal cell carcinomas (BCC) have an increased dermal mast cell prevalence in non-sun-exposed buttock skin. We propose that mast cells function in humans, as in mice, by initiating immunosuppression and, thereby, allowing a permissive environment for BCC development.