Effect of phototherapy and urocanic acid isomers on natural killer cell function

More Than Effects in Skin: Ultraviolet Radiation-Induced Changes in Immune Cells in Human Blood

Cells of the skin and circulation are in constant two-way communication. Following exposure of humans to sunlight or to phototherapy, there are alterations in the number, phenotype and function of circulating blood cells. In this review, only data obtained from human studies are considered, with changes induced by UV radiation (UVR) exposure described for phagocytic leukocytes and peripheral blood mononuclear cells plus their component T and B cells, natural killer cells and dendritic cells. These immune modulations illustrate the potential of UVR to have therapeutic effects beyond the skin, and that sunlight exposure is an important environmental influence on human health.

Short-term changes in frequencies of circulating leukocytes associated with narrowband UVB phototherapy in people with clinically isolated syndrome

Clinically isolated syndrome (CIS) is the earliest clinical episode in multiple sclerosis (MS). Low environmental exposure to UV radiation is implicated in risk of developing MS, and therefore, narrowband UVB phototherapy might delay progression to MS in people with CIS. Twenty individuals with CIS were recruited, and half were randomised to receive 24 sessions of narrowband UVB phototherapy over a period of 8 weeks. Here, the effects of narrowband UVB phototherapy on the frequencies of circulating immune cells and immunoglobulin levels after phototherapy are reported. Peripheral blood samples for all participants were collected at baseline, and 1, 2, 3, 6 and 12 months after enrolment. An extensive panel of leukocyte populations, including subsets of T cells, B cells, monocytes, dendritic cells, and natural killer cells were examined in phototherapy-treated and control participants, and immunoglobulin levels measured in serum. There were significant short-term increases in the frequency of naïve B cells, intermediate monocytes, and fraction III FoxP3+ T regulatory cells, and decreases in switched memory B cells and classical monocytes in phototherapy-treated individuals. Since B cells are increasingly targeted by MS therapies, the effects of narrowband UVB phototherapy in people with MS should be investigated further.

Disseminated Superficial Actinic Porokeratosis in a Patient with Psoriasis, after Long-Term Narrowband Ultraviolet B Phototherapy

Porokeratosis is a rare epidermal disorder characterized by annular or linear hyperkeratotic plaques with slightly raised thread-like borders, and in most cases, atrophic centers. Disseminated superficial porokeratosis and disseminated superficial actinic porokeratosis (DSAP), which primarily involve sun-exposed areas, are common types of porokeratoses. Histologically, a column of parakeratotic cells, a so-called cornoid lamella, is a hallmark of porokeratosis. Porokeratosis is considered to result from the inability to eliminate an abnormal keratinocyte clone induced by genetic factors and various stimuli, including sunlight, artificial ultraviolet light, viral infections, immunosuppressive conditions (hematologic malignancies, organ transplants, or autoimmune disease), and immunosuppressive therapies. Here, we report a 59-year-old Korean woman with DSAP that developed after narrowband ultraviolet B (NB-UVB) therapy for psoriasis. Our case emphasizes the occurrence of DSAP due to NB-UVB that is able to induce local immunosuppression at the irradiated site; the pathogenesis of DSAP remains unclear.

Final Report on the Safety Assessment of Urocanic Acid

Urocanic Acid is a naturally occurring metabolite of histidine. The trans-Urocanic Acid isomer is found as a normal constituent of the epidermis, where it accumulates because there are only very low levels of the enzyme urocanase available to break it down; the accumulation causes trans-Urocanic Acid excretion in sweat. On exposure to UV radiation present in sunlight, the trans-Urocanic Acid isomer converts to the cis-Urocanic Acid isomer. In cosmetic formulations, Urocanic Acid is used as a skin-conditioning agent and as a sunscreen. Several questions were specifically considered in this safety assessment, including the extent to which applied Urocanic Acid is absorbed by the skin and, if absorbed, what the effect is on endogenous levels. Recognizing that photoisomerization is likely to occur in the skin, what is the resultant ability of cis-Urocanic Acid to act as an immunosuppressant? If the ingredient does cause immunosuppression, is there concomitant enhancement of photo-carcinogenesis? The available data indicate that Urocanic Acid is absorbed in mouse and human skin, although at a faster rate in mouse skin. Limited human data suggest that there is no increase in the total level (endogenous + applied) of Urocanic Acid in the skin over a 16-week period. Extensive animal data indicate that cis-Urocanic Acid is an immunosuppressant, but the clinical data are inconclusive as to the immunosuppressant effect of Urocanic Acid in humans (it may be problematic that Urocanic Acid was not exposed to UV radiation in the clinical tests). To directly assess the question of enhanced photocarcinogenesis, the results of two studies were considered. In one study of hairless mice, no neoplasms were found in the group exposed only to trans-Urocanic Acid, carcinomas were found in the group that received UV exposure and no trans-Urocanic Acid, and a significantly greater number of carcinomas was found in the group exposed to trans-Urocanic Acid followed by UV exposure. In a second study, using three similar groups of hairless mice (Urocanic Acid alone, UV alone, and UV plus varying concentrations of Urocanic Acid), all groups showed comparable numbers of carcinomas, papillomas, and other tumors. While there was concern about the influence of the methodologies on the interpretation of results in these two studies, the results from neither study could be discounted. Only further study, therefore, can resolve the questions of the immunosuppressive effect of Urocanic Acid in humans and whether the immunosuppressive effect in animals is linked to the incidence of cancer in those animals. The additional information needed includes human photoimmunosuppression data, data on the modulation of photocarcinogenicity using specified procedures, and a DNA adduct study in vivo and in vitro. Until these data are available, it cannot be concluded that Urocanic Acid is safe for use in cosmetic formulations.

Phototherapy and photochemotherapy for psoriasis

Phototherapy is a first-line option for the treatment of moderate to severe psoriasis. Systematic reviews indicate near comparable efficacy of the different forms of phototherapy. Localized phototherapy can be an adjunctive treatment of recalcitrant plaques during systemic treatment of psoriasis. More than 200 psoralen-UV-A therapy treatment sessions is associated with an increased risk of keratinocytic cancers, whereas no increased risk has been demonstrated for narrow-band UV-B therapy. The mechanism of action of phototherapy in psoriasis is via inhibition of keratinocyte proliferation; induction of apoptosis in keratinocytes, dendritic, and T cells; and inhibition of Th1 and Th17 pathways, but activation of Th2.

From the outside-in: Epidermal targeting as a paradigm for atopic disease therapy

Atopic dermatitis (AD) is a chronic inflammatory skin disorder which can precede asthma and allergic rhinitis in a disease trajectory known as the atopic march. The pathophysiology of AD includes cutaneous inflammation, disrupted epidermal barrier function, xerosis and propensity to secondary infections. AD had previously been thought to arise from the systemic atopic immune response and therapies are therefore directed towards ameliorating Th2-mediated inflammation. However in recent years the focus has shifted towards primary defects in the skin barrier as an initiating event in AD. Links between loss-of-function variants in the gene encoding filaggrin and disrupted activity of epidermal serine proteases and AD have been reported. Based on these observations, a mechanism has been described by which epidermal barrier dysfunction may lead to inflammation and allergic sensitization. Exogenous and endogenous stressors can further exacerbate inherited barrier abnormalities to promote disease activity. Pathways underlying progression of the atopic march remain unclear, but recent findings implicate thymic stromal lymphopoietin as a factor linking AD to subsequent airway inflammation in asthma. This new appreciation of the epidermis in the development of AD should lead to deployment of more specific strategies to restore barrier function in atopic patients and potentially halt the atopic march.

A consideration of biomarkers to be used for evaluation of inflammation in human nutritional studies

To monitor inflammation in a meaningful way, the markers used must be valid: they must reflect the inflammatory process under study and they must be predictive of future health status. In 2009, the Nutrition and Immunity Task Force of the International Life Sciences Institute, European Branch, organized an expert group to attempt to identify robust and predictive markers, or patterns or clusters of markers, which can be used to assess inflammation in human nutrition studies in the general population. Inflammation is a normal process and there are a number of cells and mediators involved. These markers are involved in, or are produced as a result of, the inflammatory process irrespective of its trigger and its location and are common to all inflammatory situations. Currently, there is no consensus as to which markers of inflammation best represent low-grade inflammation or differentiate between acute and chronic inflammation or between the various phases of inflammatory responses. There are a number of modifying factors that affect the concentration of an inflammatory marker at a given time, including age, diet and body fatness, among others. Measuring the concentration of inflammatory markers in the bloodstream under basal conditions is probably less informative compared with data related to the concentration change in response to a challenge. A number of inflammatory challenges have been described. However, many of these challenges are poorly standardised. Patterns and clusters may be important as robust biomarkers of inflammation. Therefore, it is likely that a combination of multiple inflammatory markers and integrated readouts based upon kinetic analysis following defined challenges will be the most informative biomarker of inflammation.

One remarkable molecule: filaggrin

The discovery, in 2006, that loss-of-function mutations in the filaggrin (FLG) gene are the cause of ichthyosis vulgaris-the most common disorder of keratinization-and also a strong genetic risk factor for atopic eczema, marked a significant breakthrough in the understanding of eczema pathogenesis. Subsequent investigations of the role of FLG-null mutations have identified a series of significant associations with atopic disease phenotypes, including atopic asthma, allergic rhinitis, and peanut allergy. However, many questions remain to be answered in relation to the precise mechanisms by which deficiency of an intracellular protein expressed primarily in the differentiating epidermis may contribute to the development of cutaneous and systemic pathology. This review aims to highlight the key milestones in filaggrin research over the past 25 years, to discuss the mechanistic, clinical, and therapeutic implications, and to consider possible future directions for ongoing investigation.

Effects of intramammary infusion of cis-urocanic acid on mastitis-associated inflammation and tissue injury in dairy cows

OBJECTIVE

To evaluate the effects of cis-urocanic acid (cis-UCA) on mammary gland (MG) inflammation and injury associated with Escherichia coli-induced mastitis in dairy cows.

ANIMALS

12 lactating dairy cows (36 MGs).

PROCEDURES

At 7-week intervals, a different MG in each cow was experimentally inoculated with E coli. At 6-hour intervals from 6 to 36 hours after inoculation, the inoculated MG in each cow was infused with 40 mL of saline (0.9% NaCl) solution, 12.5mM cis-UCA, or 25mM cis-UCA (4 cows/group); ultimately, each cow received each treatment. Immediately prior to and at various time points after inoculation and treatment, milk samples were collected. Bacterial CFUs, somatic cell counts (SCCs), N-acetyl-beta-D-glucosaminidase (NAGase) and lactate dehydrogenase (LDH) activities, and concentrations of bovine serum albumin, tumor necrosis factor-alpha, and cis-UCA were quantified in each milk sample. Results-Compared with findings in saline solution-treated MGs, NAGase and LDH activities in milk samples from cis-UCA-treated MGs were lower. Cis-UCA had no effect on milk SCCs and milk concentrations of bovine serum albumin and tumor necrosis factor-alpha. Furthermore, cis-UCA had no adverse effect on bacterial clearance; CFUs of E coli in MGs treated with saline solution or cis-UCA were equivalent.

CONCLUSIONS AND CLINICAL RELEVANCE

In cows, milk NAGase and LDH activities were both lower in E coli-infected MGs infused with cis-UCA than in those infused with saline solution, which suggests that cis-UCA reduced mastitis-associated tissue damage. Furthermore, these data indicated that therapeutic concentrations of cis-UCA in milk can be achieved via intramammary infusion.

Effect of cis-urocanic acid on bovine neutrophil generation of reactive oxygen species

Neutrophils play a fundamental role in the host innate immune response during mastitis and other bacterial-mediated diseases of cattle. One of the critical mechanisms by which neutrophils contribute to host innate immune defenses is through their ability to phagocytose and kill bacteria. The ability of neutrophils to kill bacteria is mediated through the generation of reactive oxygen species (ROS). However, the extracellular release of ROS can be deleterious to the host because ROS induce tissue injury. Thus, in diseases such as mastitis that are accompanied by the influx of neutrophils, the generation of large quantities of ROS may result in significant injury to the mammary epithelium. cis-Urocanic acid (cis-UCA), which is formed from the UV photoisomerization of the trans isoform found naturally in human and animal skin, is an immunosuppressive molecule with anti-inflammatory properties. Little is known about the effect of cis-UCA on neutrophils, although one report demonstrated that it inhibits human neutrophil respiratory burst activity. However, the nature of this inhibition remains unknown. Because of the potential therapeutic use that a molecule such as cis-UCA may have in blocking excessive respiratory burst activity that may be deleterious to the host, the ability of cis-UCA to inhibit bovine neutrophil production of ROS was studied. Further, because neutrophil generation of ROS is necessary for optimal neutrophil bactericidal activity, a response which is critical for the host innate immune defense against infection, the effects of cis-UCA on bovine neutrophil phagocytosis and bacterial killing were assayed. cis-Urocanic acid dose-dependently inhibited the respiratory burst activity of bovine neutrophils as measured by luminol chemiluminescence. Subsequently, the effect of cis-UCA on the production of specific oxygen radicals was investigated using more selective assays. Using 2 distinct assays, we established that cis-UCA inhibited the generation of extracellular superoxide. In contrast, cis-UCA had no effect on the generation of intracellular levels of superoxide or other ROS. At concentrations that inhibited generation of extracellular superoxide, bovine neutrophil phagocytosis and bacterial activity remained intact. Together, these data suggest that cis-UCA inhibits the tissue-damaging generation of extracellular ROS while preserving neutrophil bactericidal activity.

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.

Circulating leukocyte and cytokine responses to measles and poliovirus vaccination in children after ultraviolet radiation exposures

Suberythemal ultraviolet radiation (UVR) exposures of children are used routinely in Russia to prevent rickets and to strengthen general health. The aim of the present study was to re-evaluate the effects of such a regime on immune responses as UVR is now recognised to suppress cell-mediated immunity in many animal models. Seventeen infants were immunised with attenuated measles and recall polio vaccines of whom 10 had been given a course of prophylactic UV exposures before the vaccinations. All the infants in the study developed an acute infectious conjunctivitis one week prior to the vaccinations and were convalescent at the time of the vaccination. They were bled on the day of the vaccinations and at several times thereafter to assess leukocyte percentages and plasma cytokine levels. On the day of the vaccinations, an active immune response was apparent. The UV-exposed children differed from the unexposed children by having a smaller percentage of natural killer cells and a higher percentage of CD25-positive cells. In the days following the vaccinations, the UV-exposed infants had a lowered percentage of total lymphocytes with increased percentages of monocytes, eosinophils, neutrophils and HLA-DR-positive cells as well as higher concentrations of plasma IL-1beta and IL-10 compared with the unexposed infants. There were no local or systemic clinical reactions to the vaccines in the UV-group while a moderate rise in temperature of three children in the unexposed group occurred. Thus the UV irradiations modulated leukocyte percentages and plasma cytokine levels following the vaccinations, perhaps through the activation of a T helper 2-like response.

An Action Spectrum for the Production of cis-Urocanic Acid in Human Skin In Vivo

Urocanic acid (UCA) is present at millimolar concentrations in mammalian epidermis and undergoes photoisomerization from the naturally occurring trans-isomer to the cis-isomer on exposure to ultraviolet radiation (UVR). Cis-UCA causes downregulation of various immune responses in mouse and human experimental models and has been proposed as both a chromophore and a mediator of UV-induced immune suppression. In this study, the wavelength dependence from 260-340 nm for trans to cis-UCA photoisomerization in human skin was analyzed in five healthy volunteers. The resulting action spectrum demonstrated maximal cis-UCA production in the UVB spectral region of 280-310 nm. This spectral peak is red-shifted to longer wavelengths compared with the erythemal action spectrum. The cis-UCA action spectrum can be used to predict the ability of sunscreens to protect against UVR-induced cis-UCA formation and may assist in explaining discrepancies between sunscreens' abilities to protect against erythema and photoimmunosuppression.

Whole-body UVB (TL-01) or UVA-1 irradiation does not alter the levels of immunomodulatory cytokines in the serum of human volunteers

BACKGROUND/PURPOSE

Ultraviolet (UV) exposure of mammalian skin induces local and systemic immunosuppression. In mice it has been proposed that systemic immunosuppression is mediated by an UV-induced cytokine cascade involving systemic interleukin (IL)-4 and IL-10 and a reduction in IL-12 activity. To investigate whether there was a parallel mechanism in humans we examined the effect of whole-body narrowband ultraviolet B (UVB) (311-313 nm; TL-01) and ultraviolet A (UVA)-1 (340-400 nm) on serum cytokine levels.

METHODS/RESULTS

In a first study, five male psoriatic subjects were whole-body irradiated with three sessions of a standard UVB (TL-01) phototherapy regimen previously shown to cause downregulation of natural killer cell activity and T helper 1 (Th1) and Th2 cytokine production by peripheral blood mononuclear cells. Enzyme-linked immunoabsorbent assay (ELISA) of sera taken before and after the third session showed no effect of phototherapy on IL-10 and tumour necrosis factor-alpha (TNF-alpha). In a second study, five healthy subjects received three whole-body exposures of UVB (TL-01) and five other healthy subjects received three exposures of UVA-1 on alternate days (total 22 J/cm(2)). Blood samples were taken before the first irradiation and at 0, 4, 8, 12, 14, 24 and 48 h after the third irradiation. The sera were subsequently analysed for IL-10, IL-12, IL-8, IL-1beta and TNF-alpha, by ELISA. The levels of IL-1beta and TNF-alpha were below detection limits (<5 pg/ml), while no significant change in the levels of IL-10, IL-12 or IL-8 was detected as a result of either TL-01 or UVA-1.

CONCLUSIONS

It seems unlikely that a modulation in these circulating cytokines assessed in this study accounts for systemic UV-induced immunosuppression in human subjects.

Immunotoxic effects of cis-urocanic acid exposure in C57BL/6N and C3H/HeN mice

Exposure to ultraviolet radiation results in increased levels of intradermal cis-urocanic acid (cUCA) and alters cutaneous immunity by interfering with processing and presentation of antigen by Langerhans cells. Reports on effects of systemic immunotoxicity with 30 day cUCA exposure in laboratory rodents include thymic atrophy, thymic hypocellularity and decreased T-cell-mediated immunity; however, immune effects of single exposure or 5 day cUCA administration, which may better mimic human exposures, are poorly defined. The present study initially evaluated immune effects of single, 5 day, and 4 week cUCA exposure in C57BL/6N mice. Single administration of intradermal cUCA resulted in decreased splenocyte phagocytosis that persisted for 30 days after cUCA exposure. Five day consecutive cUCA exposure decreased numbers of phenotypically mature CD4(+)CD8(-) and CD4(-)CD8(+) (single positive) thymocytes, increased CD4(+)CD8(+) (double positive) immature thymocytes and increased splenocyte proliferation. Prolonged cUCA exposure (4 weeks) caused profound thymic hypocellularity and splenic hypercellularity and increased splenic macrophage chemiluminescence. Because of this apparent sensitivity of C57BL/6N mice to cUCA, thymic hypocellularity was compared between C57BL/6N and C3H/HeN mice dosed with cUCA, and was found to be more pronounced in the C57BL/6N strain. These results are an extension of previous conclusions on immune modulation caused by cUCA in the spleen and thymus. Further, the observed variation in sensitivity between the mouse strains is consistent with known genetic susceptibility of these strains to the immunomodulatory effects of exposure to sunlight.

Epidermal cis-urocanic acid levels correlate with lower specific cellular immune responses after hepatitis B vaccination of ultraviolet B-exposed humans

Urocanic acid (UCA) is a major UV-absorbing chromophore in the epidermis and has been suggested to act as one of the initiators of UV-induced immunosuppression. cis-UCA, the isomer from UCA that is formed upon UV exposure, has been shown to impair some cellular immune responses. cis-UCA levels were determined in a study in which the influence of ultraviolet B (UVB) exposure on immune responses after hepatitis B vaccination in human volunteers was established. A significant increase in cis-UCA levels was found in the skin of UVB-exposed volunteers compared with controls. cis-UCA levels, calculated as the percentage of the total UCA amount, in UVB-exposed volunteers correlated significantly with the cumulative UVB dose received in 5 consecutive days, i.e. the higher the UVB dose (J/m2), the higher the cis-UCA levels (until a cis-UCA plateau was reached in the so-called photostationary state). Correlations between skin cis-UCA levels and immune responses were determined, and they revealed no statistically significant correlations among lymphocyte proliferation responses after either mitogenic stimulation or stimulation with recall antigens. No correlation was found between cis-UCA levels and hepatitis B-specific antibody titers. However, we found a statistically significant negative correlation between cis-UCA levels and hepatitis B-specific lymphocyte proliferation responses when volunteers were irradiated with UVB before hepatitis B vaccination. In other words, volunteers with high cis-UCA levels caused by UVB exposure showed lower cellular immune responses against hepatitis B antigen after hepatitis B vaccination.

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.

Influence of ultraviolet B exposure on immune responses following hepatitis B vaccination in human volunteers

Exposure to ultraviolet radiation can modulate immune responses in animal and humans. Remarkably, the ultraviolet-induced immunosuppression is not restricted to the exposed skin but is also found at other body sites, i.e., systemic immunosuppression. Effects of ultraviolet radiation on infections cannot be determined by experimentation on humans, but the effects of ultraviolet on vaccination may serve as a model. Moreover, it is important in its own right to assess whether ultraviolet radiation affects vaccination responses. In this study the effect of ultraviolet B exposure on the development of immune responses after hepatitis B vaccination in human volunteers was investigated. To this end, 191 human volunteers were vaccinated against hepatitis B with the Engerix-B vaccine. Ninety-seven of them were prior to the first vaccination exposed to ultraviolet B on 5 consecutive days with one personal minimal erythema dose per day. At several time-points before and after the ultraviolet B exposure regimen and the vaccination, blood samples were taken. Parameters for specific as well as nonspecific cellular and humoral immunity were analyzed. It was demonstrated that ultraviolet B exposure prior to hepatitis B vaccination did not alter the cellular (lymphocyte stimulation test) nor the humoral (antibody titers) immune response against hepatitis B surface antigen significantly. In contrast, contact hypersensitivity to diphenylcyclopropenone was significantly suppressed after ultraviolet B exposure, as was natural killer cell activity. These latter results confirm earlier findings and demonstrate immunosuppressive effectiveness of the ultraviolet regimen. In summary, although natural killer cell activity and contact hypersensitivity responses were suppressed, the ultraviolet B radiation protocol did not alter the humoral nor the cellular immune responses against hepatitis B surface antigen after vaccination.

cis-Urocanic acid stimulates neuropeptide release from peripheral sensory nerves

Previous studies using an antibody to cis-urocanic acid and mast-cell-depleted mice implicated both cis-urocanic acid and mast cells in the mechanisms by which ultraviolet B light suppresses systemic contact hypersensitivity responses in mice. In the absence of a direct stimulatory effect of cis-urocanic acid on connective tissue mast cells, an indirect association was investigated. A blister induced in the rat hind footpad was used to examine the effects of slowly perfused cis-urocanic acid on cutaneous blood flow. cis-Urocanic acid but not trans-urocanic acid increased microvascular flow by a mechanism largely dependent on the combined activity of the neuropeptides, substance P and calcitonin gene-related peptide. Perfusion of cis-urocanic acid over the base of blisters induced in sensory-neuropeptide-depleted rats did not have any stimulatory effect above that seen with perfusion of cis-urocanic acid together with neuropeptide receptor antagonists in control rats. There was a small direct effect of cis-urocanic acid on microvascular blood flow. As both substance P and calcitonin gene-related peptide could directly degranulate connective tissue mast cells, this study suggests that cis-urocanic acid indirectly activates mast cells via its effects on peripheral terminals of unmyelinated primary afferent sensory nerves. cis-Urocanic-acid-induced neuropeptides may also contribute to ultraviolet-B-induced cutaneous inflammation and alterations to Langerhans cell activity.

Natural killer cell activity, serum immunoglobulins, complement proteins, and zinc levels in patients with psoriasis vulgaris

The role of the immune system in patients with psoriasis vulgaris (PV) was investigated. The genetic and immunological basis for psoriasis is still unknown. Because of the reports of immunological defects in this disease, we investigated serum levels of immunoglobulins IgG, IgM, IgA, complement proteins C3, C4, serum zinc (Zn) levels and natural killer (NK) cell activities. Skin lesions of the psoriatic patients involved in the study comprised less than 10 % of the total body and the disease was in a stationary period. Zn levels were measured by atomic absorption spectrophotometry. NK cell activity was measured by 51Cr (Na2 51CrO4). IgG, IgA, IgM, C3 and C4 assays were done by liquid-phase immunoprecipitation assay with nephelometric endpoint detection. IgG, IgA, C3 and C4 levels were significanty higher in patients with PV than in healty controls (p < 0.05). However, NK cell activity, serum Zn and IgM levels did not show significant differences between these two groups. There are changed immunological responses, which may play an important role in the pathogenesis of the disease. Many controversial results have been related to immunological parameters in psoriatic patients. Therefore, more detailed studies in this field need to be done to determine the relationship between psoriasis and the immune system.

Effects of UV irradiation on skin and nonskin-associated herpes simplex virus infections in rats

Herpes simplex virus (HSV) normally causes vescular lesions on mucocutaneous surfaces but can also cause encephalitis. The virus can reactivate from the latent state in neurons to form recrudescent lesions. One common stimulus for reactivation is exposure to sunlight. In the present study, the effects of irradiating rats with suberythemal ultraviolet (UV) before or after infecting them epidermally with HSV was investigated. Preexposure to UV impaired HSV-specific cellular immune responses, as indicated by delayed type hypersensitivity (DTH) and in vitro lymphoproliferation assays. However, the number and severity of the skin lesions were not altered. In contrast, exposure after infection did not affect cellular immunity but resulted in a large increase in the severity and number of lesions. In a second series of experiments, the effects of preirradiating with UV on HSV infection was examined using a route of inoculation which was not skin-associated, namely intranasal, allowing direct non-invasive access to the nervous system. It was found that suppressed DTH resulted, together with an increase in the incidence and severity of neurological symptoms and an increased viral load in the brain. Therefore, unlike the situation in the skin, irradiation of rats before intranasal inoculation led to a suppressed immune response to HSV which correlated with increased viral load and symptoms. These results indicate that the effects of UV may be dependent on whether the animal is exposed before or after the infection, and whether the infection is skin-associated or systemic.

Ultraviolet B irradiation modulates the immune system of fish (Rutilus rutilus, Cyprinidae). II: Blood

The effects of a single dose of ultraviolet B (UVB) radiation (0.4 J/cm2) on immunological functions by blood leukocytes and on hematological parameters was studied in roach (Rutilus rutilus), a teleostean fish. The respiratory burst of phorbol 12-myristate 13-acetate stimulated whole blood phagocytes increased significantly after UVB irradiation but spontaneous cytotoxicity of blood leukocytes toward 51chromium-labeled K562 target cells was not markedly altered. Differential cell counting revealed that UVB exposure significantly increased the proportion of granulocytes and significantly decreased the proportion of lymphocytes in the peripheral blood, whereas hematocrit and the total number of white and red blood cells were unchanged. Plasma cortisol concentration increased in UVB-exposed fish. Severe handling stress caused similar, although not as potent, effects on the measured parameters of fish blood as UVB irradiation. These observations suggest that in fish UVB brings about a stress response, which may account for the observed alterations in the immune parameters and leukocyte composition of blood. Exposure of fish to strong visible light induced no alterations in immunological or hematological parameters, making it unlikely that ultraviolet radiation mediates its effects through visual perception.

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.

Ultraviolet radiation-induced suppression of natural killer cell activity is enhanced in xeroderma pigmentosum group A (XPA) model mice

Xeroderma pigmentosum group A gene-deficient mice easily develop skin cancers by ultraviolet radiation. Natural killer cells play an important part in tumor surveillance. To study whether ultraviolet radiation-induced suppression of natural killer cell function is involved in the high incidence of skin tumors in patients with xeroderma pigmentosum, we analyzed the number and activity of natural killer cells in ultraviolet B-irradiated xeroderma pigmentosum A model mice. The number of natural killer cells in peripheral blood significantly decreased after ultraviolet B-irradiation only in xeroderma pigmentosum A mice, but those in the spleen were not affected. As compared with the wild-type mice, the xeroderma pigmentosum A mice displayed a higher level of spontaneous splenic natural killer cell activity (10%-15% vs 3%) and inducible natural killer activity (30%-50% vs 20%-25%) after injection of polyinosinic:polycytidylic acid. At 24 h after the last irradiation of three and five daily consecutive exposures to 500 mJ per cm2-ultraviolet B, however, the natural killer activity in xeroderma pigmentosum A mice decreased to 60 and 30% of the preirradiated level, respectively, but it did not in the wild-type mice. The depression of natural killer activity in xeroderma pigmentosum A mice recovered to a normal level at 10 and 15 d after the last irradiation, respectively. The high incidence of skin cancers in xeroderma pigmentosum patients may be mainly due to a defect in the repair of ultraviolet-damaged DNA of cutaneous cells, and possibly also due to an intensified ultraviolet-induced immunosuppression. Moreover, the present study suggests that the enhanced ultraviolet-induced impairment of natural killer function could be partially involved in cancer development.

Differential effect of phototherapy on the activities of human natural killer cells and cytotoxic T cells

Exposure to ultraviolet B (UV-B) light is recognized to induce suppression of certain immune responses, particularly delayed hypersensitivity. However, its effect on cytotoxic T lymphocyte (CTL) activity, of major importance in the resistance to viruses and tumours, has not been assessed to the same extent. In this study five normal subjects, seropositive for herpes simplex virus (HSV), underwent a standard course of broadband UV-B therapy, as used in the treatment of psoriasis. They received whole-body irradiation thrice weekly for four weeks with incremental doses dependent on skin type. Blood samples were taken immediately before, at two time points during, and at the end of the therapy. An HSV-specific CTL assay was performed using autologous B cells transformed with Epstein-Barr virus as targets. No consistent modulation in CTL activity was obtained as a result of the therapy. The CTLs were separated into CD4 and CD8 subsets by positive selection and, again, no effect of irradiation on CTL activity within each of these two populations was observed. In contrast, the natural killer (NK) cell activity, assessed by the lysis of K562 cells, was significantly reduced at the first time point after the initiation of the phototherapy in all five subjects, and it continued to decline as the treatment progressed. Thus a differential effect of UV-B exposure on cytotoxic activity has been demonstrated: the HSV-specific CTL response is unchanged, while the NK response is suppressed.

Comparative immunotoxicology of ultraviolet B exposure I. Effects of in vitro and in situ ultraviolet B exposure on the functional activity and morphology of Langerhans cells in the skin of different species

Ultraviolet (UV) B-induced morphological and functional changes in the skin of mice, rats and humans were investigated. Changes in the morphological structure of Langerhans cells (LC), the major antigen-presenting cells in the skin, using confocal laser scanning microscopy, were found in mouse and rat skin after in situ exposure to high doses of UVB radiation (FS40) (3-9 kJ/m2). Similar UVB doses failed to induce alterations in the morphological structure of human LC. Alterations in the function of epidermal cells (especially LC) were studied, using the mixed skin lymphocyte response (MSLR). In vitro UVB exposure of epidermal cells (EC), derived from the skin of the different species, revealed that low doses of UVB radiation impaired the stimulatory capacity of these cells dose-dependently; mouse epidermal cells were most UVB-susceptible, while human cells were least UVB susceptible. For suppression of the stimulatory capacity of EC after in situ UVB exposure of skin tissue, higher doses of UVB radiation than the in vitro UVB exposure were needed in all species tested. Also in this in situ set-up mouse epidermal cells were most UVB-susceptible, and human epidermal cells were least UVB-susceptible. The magnitude of differences in susceptibility for UVB-induced changes in the stimulatory capacity of EC after in situ and after in vitro exposure experiments was similar. Firstly, it may be concluded that UVB impairs the functional activity of LC at a lower dose than that which alters the morphology of these cells. Secondly, it is clear that epidermal cells, especially LC, from the skin of rodents are more susceptible to UVB than epidermal cells derived from human skin. It is important to account for these differences in susceptibility when data on the effects of UVB radiation on the immune system in rodents are extrapolated to humans.

Urocanic acid and cutaneous antigen presentation

Exposure to UVB results in the isomerization of trans-urocanic acid (UCA), localized in the stratum corneum, to cis-UCA. Cis-UCA can mediate at least some of the immunosuppressive effects of UVB, though the mechanism of cis-UCA action remains incompletely defined. Here, we review the evidence that cis-UCA acts through alterations in cutaneous antigen presentation.

Estimation of the effect of increasing UVB exposure on the human immune system and related resistance to infectious diseases and tumours

Exposure to UV light has, besides some beneficial effects (vitamin D production), many harmful effects on human health. UVB irradiation has been shown to suppress both systemic and local immune responses to a variety of antigens, including some microorganisms. However, it is still not known whether such immunomodulating effects may lead to an increase in the number and severity of certain tumours and/or infections in humans. We report herein the data provided by a project that was funded by the European Union (Programme Environment), and that was aimed at the estimation of the risk associated with increased UVB exposure due to ozone depletion regarding the deleterious effects on the immune system and related resistance to tumours and infections in humans. The data, obtained by the different research groups involved, were assembled and used to calculate for the first time a risk assessment for increased environmental exposure to UVB in human subjects.

Systemic treatment of severe psoriasis

Severe psoriasis presents a difficult therapeutic challenge. Some modalities such as synthetic retinoids, phototherapy and methotrexate have been available for many years and need reappraisal, cyclosporin has only recently become available and requires careful administration. In this article we focus on the therapeutic modalities available to the dermatologist in Australia.

Physiologic doses of urocanic acid do not alter the allostimulatory function or the development of murine dendritic cells in vitro

Exposure to UVB results in the isomerization of trans-urocanic acid (UCA), localized in the stratum corneum, to cis-UCA. Cis-UCA can mediate at least some of the immunosuppressive effects of UVB, though the mechanism of cis-UCA action remains incompletely defined. Alterations in Langerhans cells, and other dendritic antigen presenting cell populations in the skin, may contribute to the loss of skin immune function following UVB exposure. Hence, this study was designed to investigate whether cis-UCA directly can induce changes in the immunostimulatory capacity of dendritic cells (DC) and the development of DC from precursor cells. Murine DC were generated from C57BL/6 bone marrow (BM) using granulocyte-macrophage colony-stimulating factor (GM-CSF), and were used as stimulator cells in mixed lymphocyte reactions (MLR) using BALB/c lymph node cells (LNC) as responders. The addition of cis- and trans-UCA at concentrations ranging from 0.1-500 micrograms/ml to the MLR did not affect proliferative responses. Cis- or trans-UCA (100 micrograms/ml) was added to GM-CSF stimulated mouse BM cells on day 0, day 3 or day 5 of culture, and the phenotype and allo-stimulatory function of the DC were analysed on day 7. Treatment with cis- or trans-UCA did not affect the numbers or the viability of cells in the BM cultures. In addition, the expression on DC of Iab, CD11c or the costimulatory molecules ICAM-1, B7-1, B7-2 and CD40 was not altered by the addition of cis-UCA to BM cultures. The inability of cis-UCA to alter the development of DC in vitro was confirmed by analysing the functional capacity of DC in MLR. DC generated in the presence of cis-UCA were equally efficient in the induction of allo-stimulation, when compared with control DC. These results suggest that cis-UCA does not exert its immunosuppressive activity through direct effects on DC. Such activity may be independent of DC, or alternatively, cis-UCA may influence DC function indirectly, through the induction of secondary mediators.

High-performance liquid chromatographic measurement of urocanic acid isomers and their ratios in naturally light-exposed skin and naturally shielded skin

We have developed methods for sampling and extraction of trans-urocanic acid and cis-urocanic acid from human skin, and subsequent high-performance liquid chromatographic measurement of these isomers. Sampling involves applying cellophane adhesive tape to the skin for 10 s. Urocanic acid isomers were completely extracted by immersing the tape in KOH solution. The HPLC column was a Tosoh ODS 80TS (250x4.6 mm I.D., 7 microm average particle size) eluted with 20 mM potassium dihydrogenphosphate containing 1 g/l sodium heptanesulphonate (pH 3.7)-acetonitrile (93:7, v/v) at a flow-rate of 1.0 ml/min. The isomers were detected by UV absorbance at 264 nm. This technique was used to analyze the ratio of trans-urocanic acid/cis-urocanic acid on human skin at various sites on the body. It was found that the ratio was low in naturally light-exposed skin and high in naturally shielded skin.

Biological effects of narrow-band (311 nm TL01) UVB irradiation: a review

The narrow-band UVB (TL01) lamp (311 nm emission) was developed for use in phototherapy, as an alternative to a broad-band UVB source and to photochemotherapy, both of which have significant side effects and carry a risk of carcinogenesis. This new lamp has proved to be particularly effective at clearing psoriasis. It is now acknowledged that the TL01 lamp is probably 2-3 times more carcinogenic per minimum erythema dose than broad-band UVB, but the cumulative dose required in therapy is considerably less than when using broad-band UVB sources. In terms of irradiation dose, the TL01 lamp is about 5-10-fold less potent than broad-band UVB for erythema induction, hyperplasia, oedema, sunburn cell formation and Langerhans cell depletion from skin. However, the broad-band UVB to TL01 potency ratio for cis-urocanic acid formation in the skin is approximately unity. In addition, the TL01 lamp, as used in phototherapy, has relatively more suppressive effects than broad-band UVB on systemic immune responses as judged by natural killer cell activity, lymphoproliferation and cytokine responses. However, the TL01 lamp is less effective at reducing epidermal antigen presentation, inducing dendritic cell migration to lymph nodes draining irradiated sites and suppressing contact hypersensitivity at the doses tested. Therefore the use of the TL01 lamp in phototherapy should be considered carefully after weighing up its diverse effects on the skin and immune system.

Differential suppression of the human mixed epidermal cell lymphocyte reaction (MECLR) and mixed lymphocyte reaction (MLR) by cis-urocanic acid

Cis-urocanic acid (UCA), formed in the stratum corneum by UV irradiation of trans-UCA has been proposed as a mediator of UV-induced immunosuppression in the skin. In this study, we examined the in vitro effect of cis-UCA (6-100 micrograms/mL) on the human mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR). Addition of cis-UCA (purified or in a mixture with trans-UCA) did not affect the MLR but was able to induce a 20% suppression of the MECLR responses. Because this effect of cis-UCA on the MECLR was not as strong as could be expected from previous in vivo results, we designed a set of experiments in order to enhance the in vitro immunosuppressive capacity of cis-UCA. Firstly, we preincubated epidermal cells with UCA (50 micrograms/mL). for 3 or 6 days before culture in the MECLR because in vivo repeated UV exposure can lead to a photostationary state, where cis-UCA may be present for several weeks. This pretreatment with cis-UCA resulted in a maximal decrease of the MECLR response of 27%, whereas trans-UCA had no effect. Secondly, we investigated whether UVB irradiation of epidermal cells could make cells more sensitive to cis-UCA. However, addition of trans- or cis-UCA did not potentiate the reduced alloactivating capacity of UVB-irradiated cells. Finally, we examined the possibility of a synergistic effect of cis-UCA with histamine. Addition of histamine suppressed the MLR and MECLR responses, but neither cis- nor trans-UCA were able to modulate this decrease. We conclude that cis-UCA can partly downregulate the human MECLR but not the MLR. The mechanism involved in this differential downregulation is not known. In this respect it is striking that cis-UCA dose not potentiate the UVB- or histamine-induced suppression of the MECLR.