Modulation of immunity to Borrelia burgdorferi by ultraviolet irradiation: differential effect on Th1 and Th2 immune responses

Effect of immunosuppression by UV-B radiation on components of the innate immune response in skin lesions with Leishmania mexicana: Effect of UVB on the innate immune response in cutaneous infection by L. mexicana

Cutaneous leishmaniasis is the most common form of leishmaniasis in humans, factors such as poverty, poor housing, inadequate domestic hygiene, malnutrition, mobility, and occupational exposure are risk factors associated with the condition, however, there are few studies focused on determining the immune mechanism involved in the resolution of cutaneous leishmaniasis caused by the species Leishmania mexicana, as well as possible environmental factors such as solar radiation, which could contribute to its establishment. through mechanisms immunosuppressants, of which to date is unknown. In this study, the effect of UV-B light was evaluated as a risk factor affecting components of the innate immune response 3 days after infection with L. mexicana. A delayed-type hypersensitivity reaction (DTH) was used to evaluate immunosuppression induced by UV-B light. Through a histological analysis, the skin lesions of the mice (Hematoxylin & Eosin) were evaluated, the presence of mast cells and their level of degranulation (toluidine blue staining), the presence of IL-10⁺ and MOMA2⁺ cells were analyzed by immunohistochemistry and finally, the cytokine profile was evaluated by qPCR in the skin lesions tissue. An alteration in the architecture of the tissue was observed, as well as a greater number of mast cells, both complete and degranulated, as well as an increase in IL-10⁺ and MOMA2⁺ cells in the skin lesions of the mice that were irradiated and subsequently infected, when compared with the lesions of infected mice (P> 0.0001), immunomodulation was also observed in the profile of cytokines expressed between both groups analyzed. This is the first study to demonstrate the effects of UV-B radiation on components of the innate immune response at short times of infection by L. mexicana.

Immunosuppression by UVB radiation exacerbates Leishmania mexicana skin lesions in mice

Cutaneous leishmaniasis is the most common form of leishmaniasis in humans. The disease is caused by several species, such as Leishmania mexicana, a protozoa parasite. Several major risk factors are associated with this disease, including poverty, poor housing, inadequate domestic hygiene, malnutrition, mobility, and occupational exposure. Solar radiation (UVB) has not been considered a risk factor because there is no scientific evidence demonstrating a correlation with increased susceptibility to cutaneous leishmaniasis. In this study, the shaved skin of the back of C57BL/6 mice was irradiated with 24.2 mJ/cm² of UVB. A delayed-type hypersensitivity (DTH) reaction was used to assess UV-induced immune suppression. Skin lesions were quantitated, and parasite burden and the presence of anti-Leishmania mexicana antibodies in serum and germinal centers in draining lymph nodes were determined. We found an increased in the lesion size and parasitic load in UVB-irradiated mice compared to the WT mice and B lymphocyte activation in draining lymph nodes and increased IgG1 production. Our results show an important role of UVB-induced suppression in cutaneous leishmaniasis through local production of IL-10 and systemic IgG1antibodies. This is the first study that demonstrates the effects of UVB radiation on cutaneous leishmaniasis by Leishmania mexicana.

Two polysaccharides from Porphyra modulate immune homeostasis by NF-κB-dependent immunocyte differentiation

Porphyra polysaccharides possess multiple pharmacological activities, such as immunoregulatory, anti-tumor and anti-inflammatory effects, but the specific underlying mechanisms are not fully understood.

B cells are required for sunlight protection of mice from a CNS-targeted autoimmune attack

The ultraviolet (UV) radiation contained in sunlight is a powerful immune suppressant. While exposure to UV is associated with protection from the development of autoimmune diseases, particularly multiple sclerosis, the precise mechanism by which UV achieves this protection is not currently well understood. Regulatory B cells play an important role in preventing autoimmunity and activation of B cells is a major way in which UV suppresses adaptive immune responses. Whether UV-protection from autoimmunity is mediated by the activation of regulatory B cells has never been considered before. When C57BL/6 mice were exposed to low, physiologically relevant doses of UV, a unique population of B cells was activated in the skin draining lymph nodes. As determined by flow cytometry, CD1d(low)CD5(-)MHC-II(hi)B220(hi) UV-activated B cells expressed significantly higher levels of CD19, CD21/35, CD25, CD210 and CD268 as well as the co-stimulatory molecules CD80, CD86, CD274 and CD275. Experimental autoimmune encephalomyelitis (EAE) in mice immunized with MOG/CFA was reduced by exposure to UV. UV significantly inhibited demyelination and infiltration of inflammatory cells into the spinal cord. Consequently, UV-exposed groups showed elevated IL-10 levels in secondary lymphoid organs, delayed EAE onset, reduced peak EAE score and significantly suppressed overall disease incidence and burden. Importantly, protection from EAE could be adoptively transferred using B cells isolated from UV-exposed, but not unirradiated hosts. Indeed, UV-protection from EAE was dependent on UV activation of lymph node B cells because UV could not protect mice from EAE who were pharmacologically depleted of B cells using antibodies. Thus, UV maintenance of a pool of unique regulatory B cells in peripheral lymph nodes appears to be essential to prevent an autoimmune attack on the central nervous system.

Understanding the connection between platelet-activating factor, a UV-induced lipid mediator of inflammation, immune suppression and skin cancer

Lipid mediators of inflammation play important roles in several diseases including skin cancer, the most prevalent type of cancer found in the industrialized world. Ultraviolet (UV) radiation is a complete carcinogen and is the primary cause of skin cancer. UV radiation is also a potent immunosuppressive agent, and UV-induced immunosuppression is a well-known risk factor for skin cancer induction. An essential mediator in this process is the glyercophosphocholine 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine commonly referred to as platelet-activating factor (PAF). PAF is produced by keratinocytes in response to diverse stimuli and exerts its biological effects by binding to a single specific G-protein-coupled receptor (PAF-R) expressed on a variety of cells. This review will attempt to describe how this lipid mediator is involved in transmitting the immunosuppressive signal from the skin to the immune system, starting from its production by keratinocytes, to its role in activating mast cell migration in vivo, and to the mechanisms involved that ultimately lead to immune suppression. Recent findings related to its role in regulating DNA repair and activating epigenetic mechanisms, further pinpoint the importance of this bioactive lipid, which may serve as a critical molecular mediator that links the environment (UVB radiation) to the immune system and the epigenome.

Photoimmunology and Multiple Sclerosis

The ultraviolet (UV) radiation contained in sunlight is a powerful immune suppressant. While exposure to UV is best known for its ability to cause skin cancer, it is also associated with protection against a range of autoimmune diseases, particularly multiple sclerosis (MS). Although the precise mechanism by which sunlight affords protection from MS remains to be determined, some have hypothesised that UV immunosuppression explains the "latitude-gradient effect" associated with MS. By stimulating the release of soluble factors in exposed skin, UV activates immune suppressive pathways that culminate in the induction of regulatory cells in distant tissues. Each and every one of the immune suppressive cells and molecules activated by UV exposure are potential targets for treating and preventing MS. A thorough understanding of the mechanisms involved is therefore required if we are to realise the therapeutic potential of photoimmunology.

Ultraviolet light and resistance to infectious diseases

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 the 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. UV radiation induces a multistep process, locally in the skin as well as systemically, that ultimately leads to immunosuppression. The first event is the absorption of "UV" photons by chromophores, or so-called photoreceptors, such as DNA and urocanic acid (UCA) in the upper cell layers of the skin. Upon absorption of UV radiation, trans-UCA isomerizes to the cis-isomer. Cis-UCA is likely the most important mediator of UV-induced immunosuppression, as this compound has been shown to modulate the induction of contact type hypersensitivity and delayed type hypersensitivity, allograft rejection, and the functions of monocytes and T-lymphocytes as well as natural killer cells. The real consequences of UV-induced immunomodulation on resistance to infectious diseases for humans are not fully known. 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, but also indicated that human data are necessary to further quantify and validate this risk estimation. Further information has been obtained from vaccination studies in human volunteers as ethical reasons prohibit studies with infectious agents. Studies in mice and human volunteers on the effects of prior UVB exposure on hepatitis B vaccination responses revealed suppressed cellular and humoral immune responses in mice but not in human volunteers. However, subgroups within the performed human volunteer study made by determination of cytokine polymorphisms or UVB-induced mediators, revealed that some individuals have suppressed hepatitis B vaccination responses after UVB exposure. Thus, it might be concluded that the human immune system can be affected by UVB exposure, and decreased resistance to infectious diseases can be expected after sun exposure.

The immunologic revolution: photoimmunology

UV radiation targets the skin and is a primary cause of skin cancer (both melanoma and nonmelanoma skin cancer). Exposure to UV radiation also suppresses the immune response, and UV-induced immune suppression is a major risk factor for skin cancer induction. The efforts of dermatologists and cancer biologists to understand how UV radiation exposure suppresses the immune response and contributes to skin cancer induction led to the development of the subdiscipline we call photoimmunology. Advances in photoimmunology have generally paralleled advances in immunology. However, there are a number of examples in which investigations into the mechanisms underlying UV-induced immune suppression reshaped our understanding of basic immunological concepts. Unconventional immune regulatory roles for Langerhans cells, mast cells, and natural killer T (NKT) cells, as well as the immune-suppressive function of lipid mediators of inflammation and alarmins, are just some examples of how advances in immunodermatology have altered our understanding of basic immunology. In this anniversary issue celebrating 75 years of cutaneous science, we provide examples of how concepts that grew out of efforts by immunologists and dermatologists to understand immune regulation by UV radiation affected immunology in general.

Circulating human B lymphocytes are deficient in nucleotide excision repair and accumulate mutations upon proliferation

Faithful repair of DNA lesions is a crucial task that dividing cells must actively perform to maintain genome integrity. Strikingly, nucleotide excision repair (NER), the most versatile DNA repair system, is specifically down-regulated in terminally differentiated cells. This prompted us to examine whether NER attenuation might be a common feature of all G0-arrested cells, and in particular of those that retain the capacity to reenter cell cycle and might thus convert unrepaired DNA lesions into mutations, a prerequisite for malignant transformation. Here we report that quiescent primary human B lymphocytes down-regulate NER at the global genome level while maintaining proficient repair of constitutively expressed genes. Quiescent B cells exposed to an environment that causes both DNA damage and proliferation accumulate point mutations in silent and inducible genes crucial for cell replication and differentiation, such as BCL6 and Cyclin D2. Similar to differentiated cells, NER attenuation in quiescent cells is associated with incomplete phosphorylation of the ubiquitin activating enzyme Ube1, which is required for proficient NER. Our data establish a mechanistic link between NER attenuation during quiescence and cell mutagenesis and also support the concept that oncogenic events targeting cell cycle- or activation-induced genes might initiate genomic instability and lymphomagenesis.

Mast cell-derived IL-10 suppresses germinal center formation by affecting T follicular helper cell function

The most prevalent cancer diagnosed in the world is sunlight-induced skin cancer. In addition to being a complete carcinogen, UV radiation, the causative agent of skin cancer, induces immune suppression. Because UV-induced immune suppression is a well-recognized risk factor for skin cancer induction, it is crucial to understand the mechanisms underlying UV-induced immune suppression. Mast cells, which have recently emerged as immune regulatory cells, are particularly important in UV-induced immune suppression. UV exposure does not induce immune suppression in mast cell-deficient mice. We report that UV irradiation blocks germinal center (GC) formation, Ab secretion, and T follicular helper (Tfh) cell function, in part by altering the expression of transcription factors BCL-6 and BLIMP-1. No suppression of GC formation, Tfh cell IL-21 expression, or Ab secretion was observed in UV-irradiated mast cell-deficient (Kit(W-sh/W-sh)) mice. When mast cell-deficient mice were reconstituted with wild type mast cells, immune suppression was restored. Reconstituting the mast cell-deficient mice with bone marrow-derived mast cells from IL-10-deficient mice failed to restore the ability of UV radiation to suppress GC formation. Our findings demonstrate a function for mast cells, suppression of Tfh cell production, GC formation, and Ab production in vivo.

Alloantigen-specific prolongation of allograft survival in recipient mice treated by alloantigen immunization following ultraviolet-B irradiation

It is well documented that ultraviolet (UV) radiation present in sunlight suppresses immune responses. However, the majority of studies documenting the immunosuppressive effects of UV irradiation have been carried out in animals exposed to UV irradiation before immunization. Here, we report that recipient mice exposed to UV irradiation 7 days after immunization with a donor alloantigen exhibited prolongation of allograft survival in an alloantigen-specific manner. Recipient mice (H-2(b)) intravenously immunized with 2 x 10(7) allogeneic spleen cells (H-2(b/d)) 7 days before UV irradiation (40 kJ/m(2)) showed prolonged survival of allografts presenting the alloantigen used for sensitization (H-2(b/d)), but not third-party allografts (H-2(b/k)). Adoptive transfer experiments revealed that CD4(+) T cells in UV-irradiated recipients were responsible for this prolongation. CD4(+) T cells that could transfer the suppression produced large amounts of interleukin (IL)-10, but not IL-4. The effect of UV irradiation on alloantigen-specific immunosuppression was cancelled by administration of an anti-IL-10 monoclonal antibody. These results indicate that UV irradiation given after alloantigen immunization induces alloantigen-specific type 1 regulatory T cell-like regulatory T cells that prolong allograft survival and imply that the difficulties associated with predicting donor-related organ availability in transplantation can be dealt with, given the effectiveness of UV irradiation after immunization.

Post-immune UV irradiation induces Tr1-like regulatory T cells that suppress humoral immune responses

It is well documented that UV radiation present in sunlight suppresses immune responses, especially T(h)1-driven cellular immune responses, resulting in the exacerbation of skin cancer and infectious diseases. However, the effects of UV irradiation on humoral immune responses remain less clearly defined. In addition, the majority of studies documenting immunosuppressive effects of UV irradiation has been demonstrated in animals exposed to UV radiation before immunization. In the present study, therefore, we examined the effects of UV irradiation on humoral immune responses in mice that had been immunized before UV irradiation. Both T(h)1- and T(h)2-associated Ig responses were significantly suppressed by UV irradiation given 7 days after immunization in an antigen-specific manner. Adoptive transfer experiments revealed that CD4(+) T cells from UV-irradiated mice are responsible for the UV-induced suppression of antibody responses. These CD4(+) regulatory T cells suppressed proliferation of conventional CD4(+) T cells in vivo and in vitro and contained IL-10-producing cells that did not express Foxp3. Mice depleted of CD25(+) cells also exhibited reduced antibody responses by UV irradiation. Finally, we showed that CD4(+) T cells from UV-irradiated mice treated with anti-IL-10 mAb failed to suppress antibody responses upon transfer. These results indicate that UV irradiation after immunization suppresses T(h)1- and T(h)2-mediated humoral immunity via the generation of Tr1-like regulatory T cells, in the process of which IL-10 appears to be important. Possible detrimental effects of UV irradiation after vaccination are also discussed.

Effect of Both Ultraviolet B Irradiation and Histamine Receptor Function on Allergic Responses to an Inhaled Antigen

Exposure of skin to UVB radiation (290-320 nm) modulates the immune system, with most studies showing a suppression of Th1-driven immune responses. This study investigated the effects of UVB on Th2-associated immune responses using a murine model of allergic respiratory inflammation. C57BL/6, histamine receptor-1 knockout (H1RKO), and histamine receptor-2 knockout (H2RKO) mice were exposed to a single 4 kJ/m(2) dose of UVB (twice a minimal edemal dose) on shaved dorsal skin 3 days before intranasal sensitization with papain, a cysteine protease homologue of the dust mite allergen Der p 1. H1RKO mice demonstrated enhanced papain-specific inflammatory responses in the lung-draining lymph nodes (LDLNs), whereas the responses of H2RKO mice closely mimicked those of C57BL/6 mice. UVB irradiation 3 days before sensitization reduced in vitro papain-specific proliferation of LDLN cells of C57BL/6 and H1RKO mice but not H2RKO mice 24 h after challenge. The regulatory effect of UVB was transferred by adoptive transfer of unfractionated LDLN cells from UVB-irradiated, papain-sensitized C57BL/6 and H1RKO donor mice in naive recipients of the corresponding strain that were subsequently sensitized and challenged with papain. Additionally, UVB exposure suppressed papain-induced IL-5 and IL-10 production in vitro by LDLN cells from H1RKO mice but not from C57BL/6 mice or H2RKO mice. The results of this study demonstrate systemic immunomodulation of responses to intranasally delivered Ag by UVB irradiation and implicate a role for the H2 receptor in UVB-induced suppression of Ag-specific responses in the draining lymph nodes.

The impact of immunosuppression on erythema migrans. A retrospective study of clinical presentation, response to treatment and production of Borrelia antibodies in 33 patients

BACKGROUND

Little is known about the potential influence of immunosuppression on erythema migrans, the hallmark of early Lyme borreliosis.

METHODS

We performed a retrospective study to assess the impact of immunosuppression on erythema migrans in 33 patients with a malignant or autoimmune disease, chronic infection, or immunosuppressive therapy for organ transplantation. Only patients with active disease status and/or current immunosuppressive therapy were included. Pre-treatment clinical parameters, such as presentation of the skin lesion and presence of extracutaneous signs and symptoms, the disease course during a median follow-up of 9 months after therapy and serum anti-Borrelia burgdorferi antibodies before therapy and by the end of follow-up in the 33 immunosuppressed patients were statistically compared with 75 otherwise healthy patients with erythema migrans. The 75 control patients were matched for sex, age and antibiotic therapy.

RESULTS

With the exception of the site of erythema migrans lesions, which were found more often on the trunk than on the legs in the immunosuppressed patients (vice versa in immunocompetent patients), we found no significant differences for all investigated parameters between the two groups.

CONCLUSIONS

It appears that immunosuppression does not influence clinical presentation, response to therapy, or production of anti-B. burgdorferi antibodies of patients with erythema migrans. It is thus not necessary to treat immunosuppressed patients with erythema migrans differently from immunocompetent patients.

Ultraviolet Irradiation Suppresses T Cell Activation via Blocking TCR-Mediated ERK and NF-κB Signaling Pathways

UV irradiation is carcinogenic and immunosuppressive. Previous studies indicate that UV-mediated alteration of APCs and induction of suppressor T cells play a critical role in UV-induced immune suppression. In this study, we show that UV irradiation can directly (independently of APCs and suppressor T cells) inhibit T cell activation by blocking TCR-mediated phosphorylation of ERK and IkappaB via overactivation of the p38 and JNK pathways. These events lead to the down-modulation of c-Jun, c-Fos, Egr-1, and NF-kappaB transcription factors and thereby inhibit production of cytokines, e.g., IL-2, IL-4, IFN-gamma, and TNF-alpha, upon TCR stimulation. We also show that UV irradiation can suppress preactivated T cells, indicating that UV irradiation does not only impair T cell function in response to T cell activation, but can also have systemic effects that influence ongoing immune responses. Thus, our data provide an additional mechanism by which UV irradiation directly suppresses immune responses.

The emergence of Lyme disease

Since its identification nearly 30 years ago, Lyme disease has continued to spread, and there have been increasing numbers of cases in the northeastern and north central US. The Lyme disease agent, Borrelia burgdorferi, causes infection by migration through tissues, adhesion to host cells, and evasion of immune clearance. Both innate and adaptive immune responses, especially macrophage- and antibody-mediated killing, are required for optimal control of the infection and spirochetal eradication. Ecological conditions favorable to the disease, and the challenge of prevention, predict that Lyme disease will be a continuing public health concern.

Ultraviolet radiation downregulates allergy in BALB/c mice

The immunosuppressive effects of exposure to ultraviolet radiation (UVR) are well known and the underlying mechanisms extensively studied. The suppression of Th1 appears to account for UVR suppression of contact hypersensitivity and delayed-type hypersensitivity responses and increased susceptibility to certain infections and tumor development. The underlying mechanisms suggest Th2-mediated responses associated with immediate-type hypersensitivity and allergic lung disease should be unchanged or possibly enhanced by UVR. The hypothesis that UVR exposure enhances allergic lung disease in BALB/c mice was tested. Effects of UVR on sensitization and elicitation of respiratory hypersensitivity were assessed using a fungal extract, Metarhizium anisopliae (MACA), as the allergen. BALB/c mice were sham or UVR (8 KJ/m(2)) exposed 3d before involuntary aspiration (IA) of MACA or vehicle. The mice received UVR exposures before the first and second of three IAs in the sensitization protocol and 3 d before the fourth IA in the elicitation protocol. Serum and bronchoalveolar lavage fluid (BALF) were harvested before (d 21, sensitization/d 24, elicitation) and at 1 (d 22/d 28), 3 (d 24/d 29), and 7 (d 28/d 35) d following the last IA. UVR exposure prior to sensitization suppressed two hallmarks of allergic disease, immune-mediated inflammation (eosinophil influx) and total immunoglobulin (Ig)E compared to the sham-UVR controls. There were no differences attributable to UVR exposure in previously sensitized mice. These data suggest that UVR exposure prior to sensitization suppresses allergic responses but has no effect on the elicitation of allergic responses in previously sensitized individuals. Consequently, there is no evidence that exposure to UVR enhances the induction or expression of allergic lung disease.

Biological and health effects of exposure to kerosene-based jet fuels and performance additives

Over 2 million military and civilian personnel per year (over 1 million in the United States) are occupationally exposed, respectively, to jet propulsion fuel-8 (JP-8), JP-8 +100 or JP-5, or to the civil aviation equivalents Jet A or Jet A-1. Approximately 60 billion gallon of these kerosene-based jet fuels are annually consumed worldwide (26 billion gallon in the United States), including over 5 billion gallon of JP-8 by the militaries of the United States and other NATO countries. JP-8, for example, represents the largest single chemical exposure in the U.S. military (2.53 billion gallon in 2000), while Jet A and A-1 are among the most common sources of nonmilitary occupational chemical exposure. Although more recent figures were not available, approximately 4.06 billion gallon of kerosene per se were consumed in the United States in 1990 (IARC, 1992). These exposures may occur repeatedly to raw fuel, vapor phase, aerosol phase, or fuel combustion exhaust by dermal absorption, pulmonary inhalation, or oral ingestion routes. Additionally, the public may be repeatedly exposed to lower levels of jet fuel vapor/aerosol or to fuel combustion products through atmospheric contamination, or to raw fuel constituents by contact with contaminated groundwater or soil. Kerosene-based hydrocarbon fuels are complex mixtures of up to 260+ aliphatic and aromatic hydrocarbon compounds (C(6) -C(17+); possibly 2000+ isomeric forms), including varying concentrations of potential toxicants such as benzene, n-hexane, toluene, xylenes, trimethylpentane, methoxyethanol, naphthalenes (including polycyclic aromatic hydrocarbons [PAHs], and certain other C(9)-C(12) fractions (i.e., n-propylbenzene, trimethylbenzene isomers). While hydrocarbon fuel exposures occur typically at concentrations below current permissible exposure limits (PELs) for the parent fuel or its constituent chemicals, it is unknown whether additive or synergistic interactions among hydrocarbon constituents, up to six performance additives, and other environmental exposure factors may result in unpredicted toxicity. While there is little epidemiological evidence for fuel-induced death, cancer, or other serious organic disease in fuel-exposed workers, large numbers of self-reported health complaints in this cohort appear to justify study of more subtle health consequences. A number of recently published studies reported acute or persisting biological or health effects from acute, subchronic, or chronic exposure of humans or animals to kerosene-based hydrocarbon fuels, to constituent chemicals of these fuels, or to fuel combustion products. This review provides an in-depth summary of human, animal, and in vitro studies of biological or health effects from exposure to JP-8, JP-8 +100, JP-5, Jet A, Jet A-1, or kerosene.

IL-12 completely blocks ultraviolet-induced secretion of tumor necrosis factor alpha from cultured skin fibroblasts and keratinocytes

Interleukin-12 is an important regulator of other cytokines. Although interleukin-12 is considered to act primarily on lymphocytes, provoking a shift from T helper 2 to T helper 1 cells and an increase in lymphocyte-derived tumor necrosis factor alpha, we hypothesized that interleukin-12 might also affect tumor necrosis factor alpha secretion from skin cells. In this study, keratinocytes were treated with ultraviolet-B, ultraviolet-A, or sham irradiation, without or with exogenous interleukin-12. Remarkably, the exogenous interleukin-12 totally blocked ultraviolet-B-induced tumor necrosis factor alpha production. Both ultraviolet-A and ultraviolet-B were capable of inducing interleukin-12 production. To determine the molecular mechanism of this effect, we used a chloramphenicol acetyl transferase reporter under the control of a 1.2 kb fragment of the wild-type (-308G) human tumor necrosis factor alpha promoter and found significant suppression of promoter activity with interleukin-12. Studies using the -308A variant of the human tumor necrosis factor alpha promoter showed much higher promoter activity overall, but also a greater sensitivity to suppression by interleukin-12. The mechanism did not involve blockage of the interleukin-1 receptor, because interleukin-12 did not suppress interleukin-1-mediated induction of collagenase mRNA. To determine the role of endogenous interleukin-12, we found that anti-interleukin-12 antibodies enhanced ultraviolet-B-induced tumor necrosis factor alpha secretion. Thus, interleukin-12 strongly inhibits tumor necrosis factor alpha production by noninflammatory skin cells, mostly or entirely through inhibition of gene transcription via an element within the first 1.2 kb of the tumor necrosis factor alpha promoter. The result is a shift in tumor necrosis factor alpha production from noninflammatory cells to T helper 1 cells. Because tumor necrosis factor alpha is central to the pathogenesis of several photosensitive skin diseases and certain forms of immune suppression, interleukin-12 may have important physiologic, pathophysiologic, and therapeutic roles.

Viability of the Antigen Determines Whether DNA or Urocanic Acid Act as Initiator Molecules for UV-induced Suppression of Delayed-type Hypersensitivity¶

UV radiation suppresses the immune response, and UV-induced immune suppression contributes to UV-induced photocarcinogenesis. For UV-induced immune suppression to occur, electromagnetic energy (i.e. UV radiation) must be converted to a biological signal. Two photoreceptors have been identified in the skin that serves this purpose, epidermal DNA and trans-urocanic acid (UCA). Although compelling evidence exists to support a role for each pathway (UV-induced DNA damage or photoisomerization of UCA) in UV-induced immune suppression, it is not clear what determines which photoreceptor pathway is activated. To address this question, we injected UV-irradiated mice with a monoclonal antibody with specificity for cis-UCA or applied liposomes containing DNA repair enzymes to the skin of UV-irradiated mice. The effect that each had on UV-induced suppression of delayed-type hypersensitivity was measured. We asked whether the light source used (FS-40 sunlamps vs solar-simulated UV radiation) altered whichever pathway of immune suppression was activated. Different doses of UV radiation and the viability of the antigen were also considered. Neither the dose of UV nor the light source had any influence on determining which pathway was activated. Rather, we found that the viability of the antigen was the critical determinant. When live antigens were used, UV-induced immune suppression was blocked with monoclonal anti-cis-UCA but not with T4 endonuclease V-containing liposomes. The reverse was observed when formalin-fixed or killed antigens were used. Our findings indicate that antigen viability dictates which photoreceptor pathway predominates after UV exposure.

The Staphylococcus aureus Map protein is an immunomodulator that interferes with T cell-mediated responses

Staphylococcus aureus (SA) is an opportunistic pathogen that affects a variety of organ systems and is responsible for many diseases worldwide. SA express an MHC class II analog protein (Map), which may potentiate SA survival by modulating host immunity. We tested this hypothesis in mice by generating Map-deficient SA (Map(-)SA) and comparing disease outcome to wild-type Map(+)SA-infected mice. Map(-)SA-infected mice presented with significantly reduced levels of arthritis, osteomyelitis, and abscess formation compared with control animals. Furthermore, Map(-)SA-infected nude mice developed arthritis and osteomyelitis to a severity similar to Map(+)SA-infected controls, suggesting that T cells can affect disease outcome following SA infection and Map may attenuate cellular immunity against SA. The capacity of Map to alter T cell function was tested more specifically in vitro and in vivo using native and recombinant forms of Map. T cells or mice treated with recombinant Map had reduced T cell proliferative responses and a significantly reduced delayed-type hypersensitivity response to challenge antigen, respectively. These data suggest a role for Map as an immunomodulatory protein that may play a role in persistent SA infections by affecting protective cellular immunity.

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.

The induction of systemic and mucosal immunity to protein vaccines delivered through skin sites exposed to UVB

It has been reported that common mucosal immunity can be efficiently induced in mice following immunization through the skin with vaccine formulations containing either the active form of vitamin D, or chemical agents capable of locally enhancing cyclic adenosine monophosphate levels. Herein, we report that exposure of skin to ultraviolet radiation B (UVB) can be employed as a means to alter systemic humoral immune responses and to promote the induction of mucosal immunity to protein antigens delivered into UVB-exposed skin sites. Our data indicates that the skin, as a vaccination site, can be manipulated to allow efficient induction of common mucosal and systemic immune responses.

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.

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

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

Ultraviolet light induced injury: immunological and inflammatory effects

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

Dose response for UV-induced immune suppression in people of color: differences based on erythemal reactivity rather than skin pigmentation

Ultraviolet radiation (UVR) is known to suppress immune responses in human subjects. The purpose of this study was to develop dose responses across a broad range of skin pigmentation in order to facilitate risk assessment. UVR was administered using FS 20 bulbs. Skin pigmentation and UVR sensitivity were evaluated using Fitzpatrick classifications, minimal erythemal dose (MED), slope of the erythemal dose response curve (sED), baseline pigmentation and tanning response. To assess immune responses dinitrochlorobenzene (DNCB) was applied to irradiated buttock skin 72 h after irradiation. Two weeks later DNCB was applied to the inside upper arm. Skin thickness was measured before and after challenge. Dose response was modeled (to obtain a regression line) for the entire group of 185 subjects. With the exception of sED none of the above-mentioned pigmentation indicators contributed significantly to variability around the regression line. Thus, differences in sensitivity for multiple skin types based on Fitzpatrick classification or MED were not observed. However, differences in immune sensitivity to UVR were detected between subjects with steep erythemal dose response curves and those with moderate or flat responses. For subjects with steep erythemal responses the dose calculated to suppress the immune response by 50% was 114 mJ/cm2. This group included individuals with Fitzpatrick skin types I-V, MED for these subjects ranged from 30 to 80 mJ/cm2. The 50% suppression dose for subjects with weak or no erythemal response could not be computed (the dose response was flat). This resistant group included subjects with skin types IV-VI and MED for these subjects ranged from 41 to > 105 mJ/cm2. This study provides a human dose response for UVR suppression of contact sensitivity that will be useful in risk assessment. It is the first study to provide this information using the FS sun lamp and is the first study to include people of color. The sED appears to be a new variable for identifying sensitive subjects at risk of UVR-induced immune suppression.

The Effect of UV Irradiation on Infection of Mice with Borrelia burgdorferi¶

These studies addressed the hypothesis that UV radiation (UVR) could affect immune responses in mice infected with Borrelia burgdorferi. Immunity against the Lyme spirochete B. burgdorferi was studied in a murine model of UV-induced immune suppression. Borrelia-specific cellular and humoral responses were examined following immunosuppressive doses of UVR. Low-passage Borrelia were injected intradermally at the base of the tail following irradiation. At various time points after infection the blood was cultured for the presence of Borrelia and the serum analyzed for Borrelia-specific antibodies. Two weeks after infection one hind-limb joint was cultured for the presence of spirochetes and the contralateral joint was examined histologically for arthritis formation. The results demonstrated that UV irradiation, administered at the site of infection or at a distant site, suppressed Borrelia-specific cellular and humoral responses in infected mice. Suppression of delayed-type hypersensitivity and antibody responses to UV was abrogated by administration of anti-interleukin (IL)-10 after UV irradiation. In addition, UV irradiation altered the dissemination pattern of the bacteria from the skin into the blood and exacerbated arthritis when compared with unirradiated controls. From these studies we concluded that UV irradiation can modulate the immune response to Borrelia and exacerbate the subsequent arthritic component of Lyme disease in mice. Furthermore, our studies suggest that IL-10 is in part responsible for the suppression of both cellular and humoral responses in addition to playing a role in the development of Lyme arthritis.

Early induction of gamma interferon and interleukin-10 production in draining lymph nodes from mice infected with Borrelia burgdorferi

Lymph node (LN) cells from C3H/HeJ mice (Lyme disease susceptible) infected for 1 week with Borrelia burgdorferi strain JD1 produced higher levels of gamma interferon (IFN-gamma) when stimulated in vitro with B. burgdorferi spirochetes than equivalent cells from B. burgdorferi-infected C57BL/6J mice (disease resistant). The interleukin-10 (IL-10) levels were comparable in the two strains, whereas the IL-4 levels were below detection limits. B. burgdorferi-stimulated LN cells from C57BL/6J mice produced significantly higher levels of IFN-gamma in the presence of neutralizing anti-IL-10 antibody than cells cultured with B. burgdorferi alone. No effect of IL-10 neutralization on IFN-gamma production by LN cells from C3H/HeJ mice was observed. Neutralizing antibody to IFN-gamma had no effect on the production of IL-10 by LN cells from C57BL/6J mice. A slight decrease in IL-10 production was detected in culture supernatants of equivalent cells from C3H/HeJ mice. The differential effect of IL-10 on IFN-gamma production in C57BL/6J and C3H/HeJ mice suggests that IL-10 is probably involved in the regulation of IFN-gamma production by LN cells during infection and may be at the root of the differential susceptibility to Lyme arthritis in these two strains of mice.

Differential expression of cytokine mRNA in skin specimens from patients with erythema migrans or acrodermatitis chronica atrophicans

Erythema migrans, the characteristic skin manifestation of acute Lyme borreliosis, is a self-limited lesion. In contrast, acrodermatitis chronica atrophicans, the typical cutaneous manifestation of late Lyme borreliosis, is a chronic skin condition. In an effort to understand pathogenic factors that lead to different outcomes in dermatoborrelioses, skin biopsy samples from 42 patients with erythema migrans and 27 patients with acrodermatitis chronica atrophicans were analyzed for mRNA expression of five pro-inflammatory cytokines (tumor necrosis factor alpha, interleukin-1 beta, interleukin-6, interferon-gamma, and interleukin-2) and two anti-inflammatory cytokines (interleukin-4 and interleukin-10) by in situ hybridization with cytokine-specific riboprobes. Among the 27 patients who had erythema migrans alone with no associated signs or symptoms, the major cytokines expressed in perivascular infiltrates of T cells and macrophages were the pro-inflammatory cytokine interferon-gamma and the anti-inflammatory cytokine interleukin-10. In the 15 erythema migrans patients who had associated signs and symptoms, including headache, elevated temperature, arthralgias, myalgias, or fatigue, a larger number of macrophages and greater expression of macrophage-derived pro-inflammatory cytokines, tumor necrosis factor alpha, interleukin-1 beta, and interleukin-6, were also found. In comparison, infiltrates of T cells and macrophages in the skin lesions of acrodermatitis chronica atrophicans patients had very little or no interferon-gamma expression. Instead, they usually expressed only the pro-inflammatory cytokine tumor necrosis factor alpha and the anti-inflammatory cytokine interleukin-4. Thus, the activation of pro-inflammatory cytokines in erythema migrans lesions, particularly interferon-gamma, seems to be important in the control of the spirochetal infection. In contrast, the restricted pattern of cytokine expression in acrodermatitis chronica atrophicans, including the lack of interferon-gamma, may be less effective in spirochetal killing, resulting in the chronicity of this skin lesion. J Invest Dermatol 115:1115-1123 2000

Exposure to ultraviolet radiation enhances mortality and pathology associated with influenza virus infection in mice

Ultraviolet radiation (UVR) causes systemic immune suppression, decreasing the delayed type and contact hypersensitivity responses in animals and humans and enhancing certain mycobacterial, parasitic and viral infections in mice. This study tests the hypothesis that prior exposure to UVR enhances influenza infections in mice. BALB/c female mice were exposed to 0-8.2 kJ/m2 of UVR. Exposed and unexposed mice were infected intranasally three days later with 150-300 plaque-forming units/mouse (lethal dose (LD)20-LD40) of mouse-adapted Hong Kong Influenza A/68 (H3N2) virus or sham infected with 50 microL Hanks' balanced salt solution/mouse. Mortality from viral infection ranged from 25-50%. UVR exposure increased virus-associated mortality in a dose-dependent manner (up to a two-fold increase at 8.2 kJ/m2). The increased mortality was not associated with bacterial pneumonia. The highest dose of UVR also accelerated the body weight loss and increased the severity and incidence of thymic atrophy associated with influenza infection. However, UVR treatment had little effect on the increase in lung wet weight seen with viral infection, and, to our surprise, did not cause an increase in virus titers in the lung or dissemination of virus. The mice died 5-6 days after infection, too early for adaptive immune responses to have much impact. Also, UVR did not interfere with the development of protective immunity to influenza, as measured by reinfection with a lethal challenge of virus. Also, cells adoptively transferred from UVR or untreated mice were equally protective of recipient mice challenged with a lethal dose of virus. The mice resemble mice succumbing to endotoxin, and influenza infection increased the levels of tumor necrosis factor alpha (TNF-alpha) in bronchoalveolar lavage fluid and serum cortisol levels; however, UVR preexposure did not increase either of these responses to the virus. The results show that UVR increased the morbidity, mortality and pathogenesis of influenza virus in mice without affecting protective immunity to the virus, as measured by resistance to reinfection. The mechanism of enhanced mortality is uncertain, but the data raises concerns that UVR may exacerbate early responses that contribute to the pathogenesis of a primary viral infection.

Exposure to ultraviolet radiation causes dendritic cells/macrophages to secrete immune-suppressive IL-12p40 homodimers

UV-induced immune suppression is a risk factor for sunlight-induced skin cancer. Exposure to UV radiation has been shown to suppress the rejection of highly antigenic UV-induced skin cancers, suppresses delayed and contact hypersensitivity, and depress the ability of dendritic cells to present Ag to T cells. One consequence of UV exposure is altered activation of T cell subsets. APCs from UV-irradiated mice fail to present Ag to Th1 T cells; however, Ag presentation to Th2 T cells is normal. While this has been known for some time, the mechanism behind the preferential suppression of Th1 cell activation has yet to be explained. We tested the hypothesis that this selective impairment of APC function results from altered cytokine production. We found that dendritic cells/macrophages (DC/Mphi) from UV-irradiated mice failed to secrete biologically active IL-12 following in vitro stimulation with LPS. Instead, DC/Mphi isolated from the lymphoid organs of UV-irradiated mice secreted IL-12p40 homodimer, a natural antagonist of biologically active IL-12. Furthermore, when culture supernatants from UV-derived DC/Mphi were added to IL-12-activated T cells, IFN-gamma secretion was totally suppressed, indicating that the IL-12p40 homodimer found in the supernatant fluid was biologically active. We suggest that by suppressing DC/Mphi IL-12p70 secretion while promoting IL-12p40 homodimer secretion, UV exposure preferentially suppress the activation of Th1 cells, thereby suppressing Th-1 cell-driven inflammatory immune reactions.

Reversal of ultraviolet radiation-induced immune suppression by recombinant interleukin-12: suppression of cytokine production

Exposure to ultraviolet (UV) radiation, a complete carcinogen, suppresses the immune response. Data from a number of laboratories have indicated that one consequence of UV exposure is suppressed T helper type 1 (Th1) cell function with normal Th2 cell activation, resulting in a shift to a Th2-like phenotype. The reversal of UV-induced immune suppression and tolerance induction by recombinant interleukin-12 (rIL-12) supports this observation. The focus of this study was to determine the mechanism(s) by which rIL-12 reverses UV-induced immune suppression. Two possibilities were considered: up-regulation of interferon-gamma (IFN-gamma) secretion by rIL-12 and suppression of UV-induced cytokine secretion by rIL-12. To our surprise we found that the ability of rIL-12 to overcome UV-induced immune suppression was independent of its ability to up-regulate IFN-gamma secretion. Rather, rIL-12 suppressed the production of cytokines that are known to be important in UV-induced immune suppression. Injecting UV-irradiated mice with rIL-12, or adding rIL-12 to UV-irradiated keratinocyte cultures suppressed IL-10 secretion, in part by affecting the transcription of the IL-10 gene. Furthermore, we found that rIL-12 suppressed UV-induced tumour necrosis factor-alpha (TNF-alpha) production. Because IL-10 is involved in the UV-induced suppression of delayed-type hypersensitivity and TNF-alpha in the UV-induced suppression of contact allergy, these findings provide a mechanism to explain how rIL-12 overcomes UV-induced immune suppression in these related but different immune reactions. In addition, they suggest a novel mechanism by which rIL-12 alters immune reactivity, direct suppression of cytokine secretion induced by UV radiation.

Contact Hypersensitivity Responses Following Ribavirin Treatment In Vivo Are Influenced by Type 1 Cytokine Polarization, Regulation of IL-10 Expression, and Costimulatory Signaling

We previously described the promotion of type 1 cytokine responses by the nucleoside analogue, ribavirin, in human T cells in vitro. In this study, we examined whether type 1 cytokine polarization by ribavirin in vivo could promote contact hypersensitivity (CHS) responses to dinitrofluorobenzene, a type 1 cytokine-mediated immune response. Unexpectedly, although type 1 cytokine responses were enhanced following ribavirin treatment in vitro and in vivo, the magnitude of CHS responses in BALB/c and C57BL/6 mice was influenced more by a second ribavirin-regulated pathway. The key regulatory molecule in this pathway was IL-10. Ribavirin-mediated suppression of IL-10 in BALB/c mice was associated with increased B7-2 expression and enhanced CHS responses, whereas enhanced IL-10 levels, following ribavirin administration, led to increased B7-1 expression and impaired CHS responses in C57BL/6 mice. The effect of ribavirin on the expression of B7 molecules and on CHS responses was neutralized by IL-10 administration in BALB/c and by anti-IL-10 Ab in C57BL/6. Thus, ribavirin controlled CHS responses directly through the modulation of IL-10 expression, and in vivo outcome was dictated by the preferential expression of either B7-1, an inappropriate costimulatory molecule in CHS, or B7-2, the predominant costimulatory molecule in CHS. Replacing dinitrofluorobenzene priming with IFN-α stimulation, we showed that the ribavirin-regulated pathway could function independent of Ag priming. Altogether, these data showed that, although ribavirin treatment induced a type 1 cytokine bias in contact allergen-primed BALB/c and C57BL/6 mice, in vivo CHS responses were dependent on ribavirin-mediated regulation of both IL-10 and preferential costimulatory signaling.

Urocanic Acid Enhances IL-10 Production in Activated CD4+ T Cells

The immunosuppressive effects of UV radiation have been well documented. This suppression has been attributed to the action of the cis form of urocanic acid (UCA), a photoproduct of trans-UCA, a natural constituent of the skin. Here, we show that mouse spleen cells preincubated with cis-UCA have a diminished proliferative response to allogeneic cells in MLC and to stimulation with anti-CD3 mAb. Cells preincubated with cis-UCA also had a decreased ability to serve as APC and to stimulate the proliferation of allogeneic lymphocytes in MLC. Simultaneously, the production of IL-2 and IFN-γ by cells preincubated with cis-UCA was decreased. However, IL-10 gene expression and IL-10 protein secretion by spleen cells stimulated in the presence of cis-UCA were significantly enhanced. The principal cell population displaying the cis-UCA-induced elevated production of IL-10 was CD4+ T cells, which were shown to be a direct target of cis-UCA action. This was also supported by the observation that production of IL-10 by stimulated splenic non-T cells or by macrophages was not altered by cis-UCA. The enhanced production of IL-10 by activated CD4+ T cells may represent a novel pathway of UVB radiation-induced, cis-UCA-mediated immunosuppression. We suggest that the elevated production of IL-10 by activated CD4+ T cells may account for the suppressor T cell phenomena described in UV-irradiated recipients.

Antibodies to the costimulatory molecule CD86 interfere with ultraviolet radiation-induced immune suppression

Although almost all of the energy contained within the ultraviolet (UV) wavelengths of solar radiation is absorbed within the epidermis and upper layers of the dermis, UV irradiation can suppress the immune response to antigens introduced at distant, non-irradiated body sites. The production of immune modulatory cytokines, such as interleukin-10 (IL-10), by UV-irradiated keratinocytes and its effect on T helper type 1 (Th1)/Th2-cell balance are thought to play a major role in the induction of systemic immune suppression. Because it is suggested that costimulatory molecules, such as CD80 and CD86, differentially stimulate Th1 and Th2 cells we wished to investigate the role of these costimulatory molecules in the activation of immune suppression. We injected UV-irradiated mice with monoclonal antibodies to CD80 and CD86 and asked what effect, if any, this would have on UV-induced immune suppression. Anti-CD86, but not anti-CD80 or control rat IgG, blocked UV-induced immune suppression. Moreover, monoclonal anti-CD86 blocked the induction of suppressor T cells normally found in the spleens of the UV-irradiated mice. Monoclonal anti-CD86 also reversed the UV-induced impairment of systemic antigen-presenting cell function. IL-10 was detectable in the serum of UV-irradiated mice as compared with normal controls, and injecting UV-irradiated mice with anti-CD86, but not anti-CD80 or control rat IgG, blocked the secretion of IL-10 into the serum. We propose that UV exposure favours costimulation by CD86, which enhances the production of serum IL-10, thus suppressing Th1-cell-mediated immune reactions.

A Cytokine Cascade Including Prostaglandin E2, IL-4, and IL-10 Is Responsible for UV-Induced Systemic Immune Suppression

Even though all of the energy contained with the UV wavelengths of solar radiation is absorbed within the epidermis and upper layers of the dermis, UV irradiation can suppress immune responses to Ag introduced at distant nonirradiated sites. In addition, data from a number of laboratories have suggested that one consequence of UV exposure is suppressed Th1 cell activation with normal or enhanced Th2 cell activation, resulting in a shift to a Th2-like phenotype. Cytokines secreted by UV-irradiated keratinoctyes, particularly IL-10, have been shown to play a major role in the induction of systemic immune suppression and differential activation of T helper cell subsets. Although IL-10 can influence Th1 cell activation by altering Ag presentation and suppressing IFN-γ secretion, the major signal for the development of a Th2 response is IL-4. Here we tested the hypothesis that UV irradiation induces IL-4 secretion. UV irradiation induced serum IL-4 in a dose-dependent fashion. Injecting UV-irradiated mice with anti-IL-4 blocked immune suppression. We could find no evidence, however, supporting secretion of IL-4 by UV-irradiated keratinocytes. Rather, we suggest that prostaglandins released by irradiated keratinocytes induce serum IL-4 since treating UV-irradiated mice with a cyclooxygenase-2 inhibitor blocked its production. Moreover, we found that treating UV-irradiated mice with anti-IL-4 suppressed serum IL-10 levels. In addition, injecting normal mice with PGE2 induced serum IL-4 and IL-10. We suggest that UV exposure activates a cytokine cascade (PGE2 → IL-4 → IL-10) that ultimately results in systemic immune suppression.

The effect of UVB irradiation on antibody responses during herpes simplex virus type 1 (HSV-1) infections of mice

Ultraviolet B (UVB) exposure suppresses cell-mediated immunity and may alter the cytokine profile, reducing T helper 1 (Th1) cytokines and promoting Th2 cytokines. Th1 cytokines enhance the production of immunoglobulin (Ig) G2a, IgG2b and IgG3 antibodies, while Th2 cytokines enhance the production of IgG1 and IgE antibodies. The effect of suberythemal UVB irradiation on antibody isotypes following infection of C3H/HeN mice with herpes simplex virus (HSV) was investigated using two protocols. First, mice were irradiated prior to two subcutaneous infections with HSV. Second, mice were immunised with inactivated HSV before being irradiated and challenged epidermally with HSV, which led to an increase in the size of the clinical lesions compared with unirradiated animals. In both models, the HSV-specific IgG titre was not affected by the UVB exposure but, generally, the irradiated animals showed a small reduction in both Th1- and Th2-associated HSV antibody isotypes. IL-4 knockout (IL-4-/-) mice were used to investigate the role of IL-4 in UVB-induced isotype switching. Here IL-4-/- and IL-4+/+ strains were irradiated prior to primary and secondary epidermal infections with HSV, followed by measurement of antibody titres and lesion size. In both the mutant and parent mice, UV irradiation led to an increase in lesion severity. In IL-4+/+ mice, UV exposure did not affect the HSV titre of any of the individual isotypes tested but did suppress the total IgG to HSV This suppression may be due to UV-induced IL-4 release because, in the IL-4-/- mice, HSV IgG was elevated by the UVB irradiation. If UV modulates the immune response solely via the action of cytokines, then the downregulation of Th1 cytokines and upregulation of Th2 cytokines should be accompanied by antibody isotype switching from IgG2a and IgG3 towards IgG1 and IgE. This result was not obtained in the models tested, perhaps because HSV infection promotes such a complex array of innate and acquired immune responses that a clear effect on virus-specific isotype production may not be apparent.

Photocarcinogenesis: an overview

Photocarcinogenesis represents the sum of a complex of simultaneous and sequential biochemical events that ultimately lead to the occurrence of skin cancer. These events, initiated by UV radiation of appropriate wavelength, include the formation of DNA photoproducts: DNA repair; mutation of proto-oncogenes and tumor suppressor genes; UV-production of radical species with subsequent effects on mutation and extra-nuclear function; and other epigenetic events that influence the course of carcinogenesis. The epigenetic influences may include immunological responses, antioxidant defenses, and dietary factors. This review represents an effort to provide current research results in the aforementioned areas and an attempt to meld these events into a comprehensive overview of photocarcinogenesis. If effective prevention and intervention strategies for skin cancer are to developed, a more thorough understanding of the disease process is imperative.

Modulation of T-helper cell populations: potential mechanisms of respiratory hypersensitivity and immune suppression

Information presented at this symposium indicates that modulation of Th cell responses is one means by which xenobiotics may cause immunotoxicity. A shift from Th1 to Th2 responses can enhance both infectious and allergic disease. Hence, in some cases, a common mechanism may be responsible for effects that are generally considered to be very different. Because cytokines produced in the inflammatory process play a role in modulation of Th cell responses, there is a mechanism by which agents that appear to have only local effects at the portal of entry may, in fact, affect immune responses systemically. An understanding of conditions which trigger certain cytokine responses may be useful not only in understanding inflammation but also in predicting certain kinds of immunosuppressive and allergic responses. Future studies in this area are likely to provide insights into many areas of immunotoxicology.

The inhibition of antigen-presenting activity of dendritic cells resulting from UV irradiation of murine skin is restored by in vitro photorepair of cyclobutane pyrimidine dimers

Exposing skin to UVB (280-320 nm) radiation suppresses contact hypersensitivity by a mechanism that involves an alteration in the activity of cutaneous antigen-presenting cells (APC). UV-induced DNA damage appears to be an important molecular trigger for this effect. The specific target cells in the skin that sustain DNA damage relevant to the immunosuppressive effect have yet to be identified. We tested the hypothesis that UV-induced DNA damage in the cutaneous APC was responsible for their impaired ability to present antigen after in vivo UV irradiation. Cutaneous APC were collected from the draining lymph nodes of UVB-irradiated, hapten-sensitized mice and incubated in vitro with liposomes containing a photolyase (Photosomes; Applied Genetics, Freeport, NY), which, upon absorption of photoreactivating light, splits UV-induced cyclobutane pyrimidine dimers. Photosome treatment followed by photoreactivating light reduced the number of dimer-containing APC, restored the in vivo antigen-presenting activity of the draining lymph node cells, and blocked the induction of suppressor T cells. Neither Photosomes nor photoreactivating light alone, nor photoreactivating light given before Photosomes, restored APC activity, and Photosome treatment did not reverse the impairment of APC function when isopsoralen plus UVA (320-400 nm) radiation was used instead of UVB. These controls indicate that the restoration of APC function matched the requirements of Photosome-mediated DNA repair for dimers and post-treatment photoreactivating light. These results provide compelling evidence that it is UV-induced DNA damage in cutaneous APC that leads to reduced immune function.

Effects of phototherapy on the production of cytokines by peripheral blood mononuclear cells and on systemic antibody responses in patients with psoriasis

Exposure to ultraviolet B (UVB) radiation results in the suppression of many cell-mediated immune responses, and recent studies mice and murine cells in vitro suggest a shift from a T-helper 1 (Th1) to a Th2 type of response on irradiation. Active psoriasis is considered to be a Th1-type disorder, chiefly on the basis of the cytokines produced by inflammatory cells in psoriatic lesions. We investigated the effect of phototherapy in patients with psoriasis on the cytokine profile of mitogen-stimulated mononuclear cells from peripheral blood and the concentration of IgG subclasses and IgE in the plasma. Eight patients were irradiated with a broad-band UV source (Sylvania UV6; 280-400 nm) three times a week and another eight with a narrow-band UVB source (Philips TL-01; 311-313 nm). Peripheral blood was collected before therapy started and after 1-4 weeks of therapy. Peripheral blood mononuclear cells were stimulated in vitro with phytohemagglutinin; proliferation was measured by incorporation of tritiated thymidine and culture supernatants assayed for interleukin (IL)-2, -4 and -10 and gamma-interferon (IFN) by enzyme-linked immunosorbent assays. Lymphoproliferation was not consistently affected by 4 weeks of UV6 therapy, and there was also no consistent change in the production of IL-2, IL-10 or gamma-IFN. In contrast, 4 weeks of TL-01 therapy significantly suppressed lymphoproliferative responses. In addition the production of IL-2, IL-10 and gamma-IFN was lowered after 1 week of TL-01 therapy, and this was even more apparent after the treatment had been extended to 4 weeks. IL-4 concentrations were below detectable levels in all the samples throughout the study. The amounts of IgG1, -2, -3 and -4 and IgE in the plasma of the patients did not vary with either of the two phototherapies. Thus, although no evidence was obtained to indicate that UV6 exposures affected T-helper subsets in psoriasis, TL-01 inhibited the activity of both Th1 and Th2 subsets while not altering plasma antibody concentrations.

Does exposure to UV radiation induce a shift to a Th-2-like immune reaction?

In addition to being the primary cause of skin cancer, UV radiation is immune suppressive and there appears to be a link between the ability of UV to suppress the immune response and induce skin cancer. Cytokines made by UV-irradiated keratinocytes play an essential role in activating immune suppression. In particular, we have found that keratinocyte-derived interleukin (IL)-10 is responsible for the systemic impairment of antigen-presenting cell function and the UV-induced suppression of delayed-type hypersensitivity (DTH). Antigen presentation by splenic adherent cells isolated from UV-irradiated mice to T helper-1 type T (Th1) cells is suppressed, whereas antigen presentation to T helper-2 type T (Th2) cells is enhanced. The enhanced antigen presentation to Th2 cells and the impaired presentation to Th1 cells can be reversed in vivo by injecting the UV-irradiated mice with monoclonal anti-IL-10 antibody. Furthermore, immune suppression can be transferred from UV-irradiated mice to normal recipients by adoptive transfer of T cells. Injecting the recipient mice with anti-IL-4 or anti-IL-10 prevents the transfer of immune suppression, suggesting the suppressor cells are Th2 cells. In addition, injecting UV-irradiated mice with IL-12, a cytokine that has been shown to be the primary inducer of Th1 cells, and one that prevents the differentiation of Th2 cells in vivo, reverses UV-induced immune suppression. These findings support the hypothesis that UV exposure activates IL-10 secretion, which depresses the function of Th1 cells, while enhancing the activity of Th2 cells.