Ultraviolet B-induced local immunosuppression of contact hypersensitivity is modulated by ultraviolet irradiation and hapten application

UV-based therapy

UV phototherapy has a long history of use for the treatment of select diseases in dermatology. Its use has evolved into more effective and targeted modalities, including psoralen + UV-A photochemotherapy, narrowband UV-B, excimer laser, and UV-A1 phototherapy. With its proven record of efficacy and safety, UV phototherapy is an excellent option in the treatment of an ever-growing number of skin conditions.

Phototherapy in psoriasis: a review of mechanisms of action

BACKGROUND

Phototherapy is one of the most efficacious treatment options for psoriasis. New, emerging studies are beginning to define the biologic mechanisms by which phototherapy improves psoriasis.

METHODS

To provide an overview of the mechanisms thought to be responsible for the therapeutic effects of phototherapy, a review was performed on all relevant published studies in the Medline database from January 1, 1985, to August 15, 2011.

FINDINGS

Four categories of action were proposed in the literature to describe the effects of phototherapy in psoriasis: (1) alteration of the cytokine profile, (2) induction of apoptosis, (3) promotion of immunosuppression, and (4) all other mechanisms.

CONCLUSIONS

Phototherapy acts through a combination of pathways to confer therapeutic benefits in psoriasis, and these different modalities may help explain its particular usefulness in treating this cutaneous disease.

Acute erythemal ultraviolet radiation causes systemic immunosuppression in the absence of increased 25-hydroxyvitamin D3 levels in male mice

Vitamin D is synthesised by ultraviolet (UV) irradiation of skin and is hypothesized to be a direct mediator of the immunosuppression that occurs following UV radiation (UVR) exposure. Both UVR and vitamin D drive immune responses towards tolerance by ultimately increasing the suppressive activities of regulatory T cells. To examine a role for UVR-induced vitamin D, vitamin D₃-deficient mice were established by dietary vitamin D₃ restriction. In comparison to vitamin D₃-replete mice, vitamin D₃-deficient mice had significantly reduced serum levels of 25-hydroxyvitamin D₃ (25(OH)D₃, <20 nmol.L⁻¹) and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃, <20 pmol.L⁻¹). Following either acute erythemal UVR, or chronic sub-erythemal UVR (8 exposures over 4 weeks) treatment, serum 25(OH)D₃ levels significantly increased in vitamin D₃-deficient female but not male mice. To determine if UVR-induced vitamin D was a mediator of UVR-induced systemic immunosuppression, responses were measured in mice that were able (female) or unable (male) to increase systemic levels of 25(OH)D₃ after UVR. Erythemal UVR (≥4 kJ/m²) suppressed contact hypersensitivity responses (T helper type-1 or -17), aspects of allergic airway disease (T helper type-2) and also the in vivo priming capacity of bone marrow-derived dendritic cells to a similar degree in female and male vitamin D₃-deficient mice. Thus, in male mice, UVR-induced 25(OH)D₃ is not essential for mediating the immunosuppressive effects of erythemal UVR.

Langerhans cells serve as immunoregulatory cells by activating NKT cells

Ultraviolet exposure alters the morphology and function of epidermal Langerhans cells (LCs), which play a role in UV-induced immune suppression. It is generally believed that UV exposure triggers the migration of immature LCs from the skin to the draining lymph nodes (LNs), where they induce tolerance. However, because most of the previous studies employed in vitro UV-irradiated LCs, the data generated may not adequately reflect what is happening in vivo. In this study, we isolated migrating LCs from the LNs of UV-irradiated mice and studied their function. We found prolonged LC survival in the LNs of UV-irradiated mice. LCs were necessary for UV-induced immune suppression because no immune suppression was observed in LC-deficient mice. Transferring LCs from UV-irradiated mice into normal recipient animals transferred immune suppression and induced tolerance. We found that LCs colocalized with LN NKT cells. No immune suppression was observed when LCs were transferred from UV-irradiated mice into NKT cell-deficient mice. NKT cells isolated from the LNs of UV-irradiated mice secreted significantly more IL-4 than NKT cells isolated from nonirradiated controls. Injecting the wild-type mice with anti-IL-4 blocked the induction of immune suppression. Our findings indicate that UV exposure activates the migration of mature LC to the skin draining LNs, where they induce immune regulation in vivo by activating NKT cells.

Narrowband ultraviolet B radiation suppresses contact hypersensitivity

BACKGROUND/PURPOSE

A main mechanism responsible for the efficacy of narrowband ultraviolet (UV)B is thought to be the induction of apoptosis in pathogenetically relevant cells. Narrowband UVB therapy, however, generally induces a relatively long remission period. Recently, evidence that UVB radiation induces regulatory T (Treg) cells was reported. Based on these findings, we examined whether narrowband UVB suppresses contact hypersensitivity (CHS) by inducing Treg cells.

METHODS

The shaved abdomens of C3H/HeN mice were irradiated with broadband or narrowband UVB. CHS was defined as an ear-swelling response. To examine whether tolerance can be induced by adoptive transfer, lymph node cells from UVB-irradiated mice were injected into naïve mice before sensitization and CHS challenge.

RESULTS

Narrowband UVB exposure dose dependently suppressed CHS. Significant suppression was observed at doses between 1000 and 3000 mJ/cm(2) (P<0.05). The suppressive effect achieved with 1000 mJ/cm(2) narrowband UVB was very similar to the effect achieved with 100 mJ/cm(2) broadband UVB. The suppressive effects on CHS were transferred to naïve mice by the injection of lymph node cells from tolerant mice.

CONCLUSION

Narrowband UVB induced local and systemic suppression of CHS. In addition, narrowband UVB induces tolerance to CHS and the suppressive effects were transferable to naïve mice.

Ultraviolet Radiation-Induced Impairment of Tumor Rejection Is Enhanced in Xeroderma Pigmentosum A Gene-Deficient Mice

Xeroderma pigmentosum (XP)A gene-deficient mice display dermatologic abnormalities similar to human XP, such as enhanced ultraviolet (UV)-induced acute inflammation and high incidence of UVB-induced skin cancer. We have previously reported that UVB-induced immunosuppression of contact hypersensitivity was greatly enhanced in XPA mice. In the present study, we examined the effects of UVB radiation on tumor rejection in XPA mice. Tumor cells established from UVB-induced squamous cell carcinoma in XPA mice were injected subcutaneously. No difference in the development of tumors was observed between the non-irradiated XPA and wild-type mice. Tumors developed, grew in size, and reached the maximum at 7-10 d after the inoculation. Thereafter, all tumors decreased in size and were completely rejected by 4 wk in both strains of mice. When tumor cells were inoculated into the skin that had been irradiated with 50-150 mJ per cm2 of UVB, tumor grew in 60% (12 of 20) of the XPA mice, but only in 4% (one of 23) of wild-type mice. Phenotyping of tumor-infiltrating cells revealed that the migration of natural killer cells and CD8+ T cells was inhibited in UVB-irradiated XPA mice. These data suggest that enhanced UVB-induced impairment of tumor rejection could be partially involved in the cancer development of XP patients.

Suppression of contact hypersensitivity after repeated exposures of humans to low doses of solar simulated radiation

Although it is generally recognised that UV radiation (UVR) can induce suppression of contact hypersensitivity (CHS) in human subjects, most protocols to date have not tested the effect of low daily doses of solar simulated radiation (SSR). In the present study, healthy individuals, divided into four groups each consisting of approximately 34 subjects, were whole-body irradiated with 1.2 standard erythema doses of SSR for 2, 10 or 30 consecutive days, or were unirradiated. They were sensitised with diphenylocyclopropenone (DPCP) on one exposed body site 24 h after the final UVR. The occurrence and severity of the primary allergic response were noted, and both parameters were shown to be significantly lowered in the group irradiated for 30 days compared with the unirradiated group. Elicitation of CHS was undertaken 3 weeks after the sensitisation, using a range of concentrations of DPCP on a UV-protected body site. The extent of the CHS at 48 h was assessed by the clinical score, by an erythema meter and by histological examination of a biopsy taken from the site challenged with one selected concentration of DPCP. Although erythema and pigmentation did not differ between the groups, a significant negative correlation was found between the clinical CHS score and the number of days of UV exposure, at the lowest challenge dose of DPCP. In addition a significant negative correlation was revealed between the intensity of spongiosis (intraepidermal oedema and vesicles, as evaluated by histology) and the number of days of UV exposure. Thus small daily doses of SSR induce suppression of CHS in human subjects and the effect is cumulative, indicating that there is no adaptation to the immunomodulating effects of UVR, at least over the test period of 30 days.

Divergence of contact hypersensitivity in vivo compared with hapten-specific lymphocyte proliferation and interferon-gamma production in vitro following ultraviolet B irradiation: the possibility that UVB does not affect the sensitizing phase of contact hypersensitivity

A hapten-specific lymphocyte proliferation assay, which measures the in vitro stimulation of DNA synthesis (as assessed by [3H]thymidine incorporation), was used to determine systemic immunization induced by an epicutaneously applied hapten in addition to the more commonly used method which measures ear (or footpad) swelling. 2,4-Dinitrofluorobenzene (DNFB) was painted on the shaved backs of C57BL/6 mice for two consecutive days after ultraviolet B (UVB) irradiation (at 1000 J/m2), and DNFB-sensitized lymph node cells (LNC) were obtained from the regional lymph nodes 4 days later. Although the ear swelling response (ESR) was suppressed by UVB radiation, as previously reported, analysis of LNC culture supernatants showed that the production of interferon-gamma, a Tc1-type cytokine, was not inhibited by the UVB irradiation. In addition, contact dermatitis was induced (at levels similar to those of non-irradiated mice) by painting DNFB on the abdomen as a secondary response. We then examined the effect of UVB exposure alone on the ESR by injecting a mast cell degranulator, compound 48/80, 7 days after irradiation. Both the ESR and the percentage of degranulated mast cells were significantly reduced in UVB-irradiated mice. These results demonstrate that UVB irradiation does not affect the sensitizing phase of contact hypersensitivity, but modulates the elicitation phase and reduces the ESR primarily by suppressing the degranulation of mast cells. Therefore, suppression of the ESR alone cannot always be considered as hapten-specific immunotolerance.

Ultraviolet radiation, resistance to infectious diseases, and vaccination responses

Exposure to ultraviolet (UV) radiation, as in sunlight, can modulate immune responses in animals and humans. This immunomodulation can lead to positive health effects especially with respect to certain autoimmune diseases and allergies. However, UV-induced immunomodulation has also been shown to be deleterious. Experimental animal studies have revealed that UV exposure can impair resistance to many infectious agents, such as bacteria, parasites, viruses, and fungi. Importantly, these effects are not restricted to skin-associated infections, but also concern systemic infections. The real consequences of UV-induced immunomodulation on resistance to infectious diseases are not known for humans. Risk estimations have been performed through extrapolation of animal data, obtained from infection models, to the human situation. This estimation indicated that UV doses relevant to outdoor exposure can impair the human immune system sufficiently to have effects on resistance to infections. To further quantify and validate this risk estimation, data, e.g., from human volunteer studies, are necessary. Infection models in humans are not allowed for ethical reasons. However, vaccination against an infectious disease evokes a similar immune response as the pathogen and thereby provides an opportunity to measure the effect of UV radiation on the immune system and an estimate of the possible consequences of altered resistance to infectious agents. Effects of controlled UVB exposure on immune responses after hepatitis B vaccination have been established in mice and human volunteers. In mice, cellular and Th1-associated humoral immune responses to hepatitis B were significantly impaired, whereas in human volunteers no significant effect of UVB on these responses could be found. Preliminary data indicate that cytokine polymorphisms might be, at least in part, responsible for interindividual differences in immune responses and in susceptibility to UVB-induced immunomodulation. In addition, adaptation to UV exposure needs to be considered as a possible explanation for the difference between mice and humans that was observed in the hepatitis B vaccination model.

Low-dose UVB contributes to host resistance against Leishmania amazonensis infection in mice through induction of gamma interferon and tumor necrosis factor alpha cytokines

UV radiation suppresses the immune response, a fact which raises the question of whether the phenomenon may find practical applications in the outcome of infectious diseases. In this study, BALB/c mice were exposed to low-dose UVB (250 J/m(2)) from Dermaray M-DMR-100 for 4 consecutive days. Twelve hours after the last UV exposure, groups of mice were injected with 2 x 10(6) Leishmania amazonensis promastigotes. The development of skin lesions, as assessed by measurement of visible cutaneous lesions, was significantly suppressed in low-dose UVB-irradiated mice compared to nonirradiated controls. In order to characterize the cytokines involved in this phenomenon, BALB/c mice were irradiated with identical doses of UVB, and gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and interleukin 4 cytokine levels in blood serum and skin were examined at different times by a sandwich enzyme-linked immunosorbent assay, immunohistochemical analysis, and reverse transcription (RT)-PCR. Upregulated expression of serum IFN-gamma and TNF-alpha was observed from 6 to 24 h. Positive results for IFN-gamma and TNF-alpha in UVB-irradiated mice were obtained by immunohistochemical analysis. By RT-PCR, the mRNA expression of both IFN-gamma and TNF-alpha cytokines was detected in a time-dependent manner only in UVB-irradiated mice. Histopathological analysis and electron microscopy revealed that cellular infiltration, tissue parasitism, and parasitophorus vacuoles in irradiated mice were markedly less noticeable than those in nonirradiated controls. These results suggested that low-dose UVB irradiation played a pathogen-suppressing role in Leishmania-susceptible BALB/c mice via systemic and local upregulation of Th1 (IFN-gamma and TNF-alpha) cytokines.

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.

Effects of low-dose ultraviolet radiation on in vivo human cutaneous recall responses

Relatively few studies have examined the effects of low-dose ultraviolet (UV) radiation on in vivo human cutaneous immunity, or the ability of sunscreens to prevent UV-induced immunosuppression. We have studied the effects of solar-simulated UV radiation on nickel contact hypersensitivity (CHS) in nickel-allergic volunteers, and on delayed type hypersensitivity responses in Mantoux-positive volunteers. Nickel CHS and Mantoux responses were significantly suppressed by acute, suberythemal UV exposures equivalent to less than 8 min summer sunlight. Both UVA and UVB wavebands were immunosuppressive, but UVA-induced immunosuppression was transient, whereas UVB had a more sustained effect. Dose-responses for UV immunosuppression were determined using the nickel method, enabling calculation of in vivo sunscreen immune protection factors in a manner analogous with sun protection factor measurement. Sunscreens were found to confer significantly less protection against UV-induced immunosuppression than against UV-induced erythema.

Indications and action mechanisms of phototherapy

Recently phototherapy has become one of the most commonly used modalities for the treatment of a variety of skin diseases, although the action mechanisms have not been fully understood. The inhibitory effect of UVR on DNA synthesis may be one of the actions for proliferating skin diseases. However, phototherapy is also used for the treatment of allergic or autoimmune diseases. It has been confirmed that the skin is an important immunologic organ whose constitutive cells are all involved in immunologic reactions. We have investigated the effects of PUVA and UVB radiation on the immunocompetent cells, including Langerhans cells, T lymphocytes, mast cells, endothelial cells and natural killer cells. Exposure to UVR inhibits contact sensitization to haptens applied not only to the irradiated skin area but also to the non-irradiated distant skin when the exposure dose is relatively high and/or the application skin area is large. In addition, hapten-specific tolerance develops by the generation of suppressor T cells. Phototherapy is also useful for immediate type hypersensitivity such as urticaria. Action mode in the case may be the inhibitory effects of UVR on histamine release from mast cells. The results obtained from these experiments suggest that phototherapy exerts its anti-allergic and anti-inflammatory effects through immunosuppression.

Sensitivity to sunburn is associated with susceptibility to ultraviolet radiation-induced suppression of cutaneous cell-mediated immunity

Skin cancer incidence is highest in white-skinned people. Within this group, skin types I/II (sun sensitive/tan poorly) are at greater risk than skin types III/IV (sun tolerant/tan well). Studies in mice demonstrate that ultraviolet radiation (UVR)-induced suppression of cell-mediated immune function plays an important role in the development of skin cancer and induces a susceptibility to infectious disease. A similar role is suspected in humans, but we lack quantitative human data to make risk assessments of ambient solar exposure on human health. This study demonstrates that ambient levels of solar UVR, typically experienced within 1 h of exposure to noonday summer sunlight, can suppress contact hypersensitivity (CHS) responses in healthy white-skinned humans in vivo (n = 93). There was a linear relationship between increase in erythema and suppression of CHS (P < 0.001), and a moderate sunburn (two minimal erythema doses [2 MED]) was sufficient to suppress CHS in all volunteers by 93%. However, a single suberythemal exposure of either 0.25 or 0.5 MED suppressed CHS responses by 50 and 80%, respectively, in skin types I/II, whereas 1 MED only suppressed CHS by 40% in skin types III/IV. The two- to threefold greater sensitivity of skin types I/II for a given level of sunburn may play a role in their greater sensitivity to skin cancer.

Genetic variation in low-dose UV-induced suppression of contact hypersensitivity and in the skin photocarcinogenesis response

Two of the major cutaneous consequences of ultraviolet (UV) radiation exposure are immunosuppression and the development of skin cancer. This study examined whether these effects are genetically determined. Suppression of contact hypersensitivity by local, low-dose UV radiation was examined in what have been termed "UV-susceptible" and "UV-resistant" strains of mice. C3H/HeJ mice ("UV resistant") were resistant to the adverse effects of low-dose UV radiation when normal doses of hapten were applied to UV-irradiated skin; however, they were sensitive when the amount of hapten used for sensitization was reduced. A similar effect was observed in BALB/c mice ("UV resistant") and when the hapten was dimethylbenz(a)anthracene, thus indicating that the genetic variation was not strain or hapten specific. Despite the fact that some strains were sensitive and some were resistant to low-dose UV radiation when high doses of hapten were employed, all strains initially sensitized to hapten through UV-irradiated skin were found to be unresponsive when rechallenged on normal skin, no matter what the initial sensitizing dose of hapten was. To determine whether other biologic effects of UV also exhibited genetic variation, C3H/HeN and C3H/HeJ mice were compared for susceptibility to UVB-induced skin cancer formation. C3H/HeJ mice developed significantly more tumors than C3H/HeN mice when subjected to a single dose of UV radiation followed by repeated exposure to the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. These studies provide strong evidence that genetic factors influence individual susceptibility to the biologic effects of UV radiation.

Immunosuppression induced by acute solar-simulated ultraviolet exposure in humans: prevention by a sunscreen with a sun protection factor of 15 and high UVA protection

BACKGROUND

Cutaneous exposure to UVB radiation impairs the induction of contact hypersensitivity (CHS). Variable results have been found among studies examining the use of sunscreens to prevent UV-induced immunosuppression.

OBJECTIVE

Our purpose was to determine whether solar-simulated exposure of human skin resulted in an impairment of CHS responses and whether the preapplication of an intermediate sun protection factor (SPF) sunscreen could prevent this locally UV-induced immunosuppression.

METHODS

Irritant and CHS responses to dinitrochlorobenzene (DNCB) were randomly assessed in 160 human volunteers with or without UV exposure and with or without prior application of an SPF 15 sunscreen with high UVA protection. DNCB sensitization was performed 3 days after acute UV irradiation corresponding to 3 minimal erythema doses.

RESULTS

After solar-simulated UV exposure, the percentage of positive responses to DNCB sensitization dropped from 95% to 50% (p = 0.003). Prior application of the sunscreen formulation did not modify the percentage of positive responses (90%) and maintained the immunization rate at 85% among volunteers exposed to UV.

CONCLUSION

A localized sunburn can impair the afferent arm of CHS reactions in humans. The use of intermediate SPF sunscreens with high UVA protection adequately protects from the suppression of CHS responses that occurs after acute solar-simulated UV exposure.

Suppressive effect of ultraviolet B radiation on contact sensitization in mice. II. Systemic immunosuppression is modulated by ultraviolet irradiation and hapten application

Irradiation of mice with ultraviolet-B (UVB) can suppress contact hypersensitivity "systemically", even if hapten is applied to the non-irradiated skin site. We previously reported the factors influencing UVB-induced "local" immunosuppression. To obtain the most effective systemic immunosuppression, we further investigated the effect of the following factors on contact hypersensitivity to dinitrofluorobenzene (DNFB): UVB dose, dividing exposure, timing of sensitization after irradiation, area of exposure, hapten concentration, age, and genetic basis. The suppression was enhanced by increasing UVB dose. When 1 J/cm2 of UVB was exposed, 4 daily divided exposures (0.25 J/cm2 x 4) was more suppressive than a single (1 J/cm2 x 1) or double divided (0.5 J/cm2 x 2) exposure. Five or 10 day intervals between irradiation and sensitization induced stronger suppression than 1 or 3 day intervals. When the total energy (Joule, J) was kept constant, the exposure of low dose-UVB to a large area (0.5 J/ cm2 x 16.45 cm2) suppressed contact hypersensitivity more strongly than did high dose-UVB to a small area (2 J/cm2 x 4.11 cm2). When 25 ml of DNFB solution was applied, high concentration induced lower suppression. The stronger suppression was most prominent in the young (7 week) than in the old (22 week) mice. No difference was found in the systemic immunosuppression between C3H/HeN and Balb/c mice. These results suggest that not only UVB dose but also various factors should be taken into consideration to effectively induce systemic immunosuppression.

Keratinocyte-derived cytokines and UVB-induced immunosuppression

Ultraviolet radiation (UVB) in sunlight is known to have multiple effects on the immune system. Evidence suggests that UVB-induced immunosuppression is mediated in part by immunosuppressive and immunoregulatory cytokines. Our studies have utilized gene-targeted mutant mice to determine key molecular requirements essential for the development of UVB-induced immunosuppression. Preliminary results from our laboratory suggest that TNF-alpha plays a regulatory role in contact hypersensitivity, but is not a crucial factor for UVB-induced immunosuppression, and that multiple factors are involved in the induction of UVB mediated immunosuppression.