Suppression of the elicitation of the immune response to alloantigen by ultraviolet radiation

Low energy X-ray (grenz ray) treatment of purified islets prior to allotransplant markedly decreases passenger leukocyte populations

Grenz rays, or minimally penetrating X-rays, are known to be an effective treatment of certain recalcitrant immune-mediated skin diseases, but their use in modulating allograft rejection has not been tested. We examined the capacity of grenz ray treatment to minimize islet immunogenicity and extend allograft survival in a mouse model. In a preliminary experiment, 1 of 3 immunologically intact animals demonstrated long-term acceptance of their grenz ray treated islet allograft. Further experiments revealed that 28.6% (2 of 7) grenz ray treated islet allografts survived >60 d. A low dose of 20Gy, was important; a 4-fold increase in radiation resulted in rapid graft failure, and transplanting a higher islet mass did not alter this outcome. To determine whether increased islet allograft survival after grenz treatment would be masked by immunosuppression, we treated the recipients with CTLA-4 Ig, and found an additive effect, whereby 17.5% more animals accepted the graft long-term versus those with CTLA-4 Ig alone. Cell viability assays verified that islet integrity was maintained after treatment with 20Gy. As well, through splenocyte infiltration analysis, donor CD4+ T cell populations 24-hours after transplant were decreased by more than16-fold in recipients receiving irradiated islets compared with control. Donor CD8+ T cell populations, although less prevalent, decreased in all treatment groups compared with control. Our results suggest that brief treatment of isolated islets with low energy grenz rays before allotransplantation can significantly reduce passenger leukocytes and promote graft survival, possibly by inducing donor dendritic cells to differentiate toward a tolerogenic phenotype.

Alloantigen-specific CD4(+) regulatory T cells induced in vivo by ultraviolet irradiation after alloantigen immunization require interleukin-10 for their induction and activation, and flexibly mediate bystander immunosuppression of allograft rejection

Ultraviolet (UV) irradiation prior to antigen immunization is employed to induce antigen-specific regulatory T cells (Tregs). UV-induced Tregs demonstrate unique bystander suppression, although antigen-specific activation is required initially. We previously reported the phenotype of alloantigen-specific transferable Tregs induced by UV-B irradiation after immunization was the same as T regulatory type 1-like CD4(+) T cells, with antigen-specific interleukin (IL)-10 production. Here, by using semi-allogeneic transplantation models in vivo, we investigated the role of IL-10 in the induction and activation of these Tregs, and the possibility of bystander suppression of third-party allograft rejection. Naïve mice (H-2(b)) were immunized with alloantigen (H-2(b/d)), and received UV-B irradiation (40 kJ/m(2)) 1 week later. Four weeks afterwards, splenic CD4(+) T cells were purified from the UV-irradiated immunized mice, and were transferred into naïve mice (H-2(b)). Allografts expressing the same alloantigen as T-cell donors were immunized against (H-2(b/d)) or an irrelevant alloantigen (H-2(b/k)) were transplanted to CD4(+) T-cell-transferred mice, and an alloantigen-specific prolongation of allograft survival observed. Experiments where IL-10 was neutralized by monoclonal antibody in the induction or effector phase revealed that IL-10 is critical, not only for induction but also for immunosuppressive function of CD4(+) Tregs induced by UV irradiation after alloantigen immunization. Third-party allografts (H-2(d/k)) were transplanted to CD4(+) T-cell-transferred mice, and graft survival was also prolonged. Even a graft only partially compatible with immunized alloantigen worked well in vivo to activate CD4(+) Tregs induced by UV irradiation after alloantigen immunization, which resulted in the bystander suppression of third-party allograft rejection.

Ultraviolet-induced alloantigen-specific immunosuppression in transplant immunity

After the first observation of the immunosuppressive effects of ultraviolet (UV) irradiation was reported in 1974, therapeutic modification of immune responses by UV irradiation began to be investigated in the context immunization. UV-induced immunosuppression is via the action of regulatory T cells (Tregs). Antigen-specific Tregs were induced by high-dose UV-B irradiation before antigen immunization in many studies, as it was considered that functional alteration and/or modulation of antigen-presenting cells by UV irradiation was required for the induction of antigen-specific immunosuppression. However, it is also reported that UV irradiation after immunization induces antigen-specific Tregs. UV-induced Tregs are also dominantly transferable, with interleukin-10 being important for UV-induced immunosuppression. Currently, various possible mechanisms involving Treg phenotype and cytokine profile have been suggested. UV irradiation accompanied by alloantigen immunization induces alloantigen-specific transferable Tregs, which have potential therapeutic applications in the transplantation field. Here we review the current status of UV-induced antigen-specific immunosuppression on the 40^th anniversary of its discovery.

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.

Mechanisms underlying UV-induced immune suppression: implications for sunscreen design

The ultraviolet (UV) radiation present in sunlight is immune-suppressive. Recently we showed that solar-simulated UV radiation (UVA + UVB; 295-400 nm), applied after immunization, suppressed immunological memory and the elicitation of delayed-type hypersensitivity to the common opportunistic pathogen, Candida albicans. Further, we found that wavelengths in the UVA region of the solar spectrum (320-400 nm), devoid of UVB, were equally effective in activating immune suppression as UVA + UVB radiation. Here we report on the mechanisms involved. No immune suppression was found in UV-irradiated mice injected with monoclonal anti-interleukin (IL)-10 antibody, or mice exposed to solar-simulated UV radiation and injected with recombinant IL-12. Antigen-specific suppressor T cells were found in the spleens of mice exposed to UVA + UVB radiation. Applying liposomes containing bacteriophage T4N5 to the skin of mice exposed to solar-simulated UVA + UVB radiation or mice exposed to UVA radiation blocked immune suppression, demonstrating an essential role for UV-induced DNA damage in the suppression of established immune reactions. These findings indicate that UV radiation activates similar immunological pathways to suppress the induction, or the elicitation, of the immune response.

Ultraviolet radiation-induced immunosuppression of delayed-type hypersensitivity in mice

Ultraviolet (UV) radiation present in sunlight plays a critical role in the initiation and promotion of nonmelanoma skin carcinogenesis and immune suppression. The immune suppressive effects of UV have been identified as a risk factor for skin cancer induction. For these reasons, scientists have focused on elucidating the mechanisms of UV-induced immune suppression to better understand the pathogenesis of skin cancer induction. A hallmark of UV-induced immune suppression is the generation of antigen-specific suppressor T cells. These suppressor cells have been shown to suppress antitumor immunity as well as other cell-mediated responses such as delayed-type hypersensitivity (DTH) reactions. Due to the excessive cost and time involved in traditional UV carcinogenic experiments, scientists have opted to use UV-induced suppression of DTH reactions as a surrogate model. DTH has been, and continues to be, a widely used assay system to measure in vivo immune function. Although somewhat unsophisticated by today's standards, this assay has great advantages because it presents a fast, inexpensive, and reliable model system to help dissect the mechanisms involved in UV-induced immune suppression. Furthermore, the murine model of DTH enables scientists to perform additional procedures, such as adoptive transfer studies with suppressor T cells, which are currently unavailable with human subjects.

Mechanisms underlying the suppression of established immune responses by ultraviolet radiation

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

Ultraviolet radiation and the contact hypersensitivity reaction in mice

The article reviews the application of the contact hypersensitivity assay in mice to the science of photoimmunology. The contact hypersensitivity (CHS) reaction, which is suppressed by UV irradiation in mice similarly to their ability to respond immunologically to skin tumors, has been used very profitably to reveal many of the regulating factors that control photoimmunosuppression, such as the identity of the photoreceptors that initiate immunosuppression, the defects induced in the cutaneous antigen presenting pathway, the local cytokine imbalance, and the protective intervention by various molecules, drugs, or interacting UV wavebands. Technical hints to optimize the measurement of the CHS response are suggested, including information on UV radiation wavebands and dosages and sensitivities of different mouse strains.

Dermal application of jet fuel suppresses secondary immune reactions

Applying military jet fuel (JP-8) to the skin of mice activates systemic immune suppression. In all of our previous experiments, JP-8 was applied to immunologically naïve mice. The effect of jet fuels on established immune reactions, such as immunological memory, is unknown. The focus of the experiments presented here was to test the hypothesis that jet fuel exposure [both JP-8 and commercial jet fuel (Jet-A)] suppresses established immune reactions. Mice were immunized with the opportunistic fungal pathogen Candida albicans and, at different times after immunization (10 to 30 days), various doses of undiluted JP-8 or Jet-A were applied to their skin. Both the elicitation of delayed-type hypersensitivity (DTH) (mice challenged 10 days after immunization) and immunological memory (mice challenged 30 days after immunization) were significantly suppressed in a dose-dependent manner. Dermal exposure to either multiple small doses (50 microl over 4 days) or a single large dose (approximately 200-300 microl) of JP-8 and/or Jet-A suppressed DTH to C. albicans. The mechanism by which dermal application of JP-8 and Jet-A suppresses immunological memory involves the release of immune biologic response modifiers. Blocking the production of prostaglandin E(2) by a selective cyclooxygenase-2 inhibitor (SC 236) significantly reversed jet fuel-induced suppression of immunologic memory. These findings indicate, for the first time, that dermal exposure to commercial jet fuel (Jet-A) suppresses the immune response. In addition, the data reported here expand on previous findings by suggesting that jet fuel exposure may depress the protective effect of prior vaccination.

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

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

Ultraviolet radiation decreases the granulomatous response to lepromin in humans

Ultraviolet radiation (UVR) modulates cellular immunity in humans and experimental animals and can interfere with immune responses against infectious agents in animal models. We used the lepromin reaction, a cell-mediated immune response to antigens of Mycobacterium leprae, to determine whether UVR affects the cellular immune response to an infectious agent in humans. We selected 29 healthy, lepromin-positive contacts of leprosy patients and determined their minimal erythema dose (MED) of UVR. Immediately afterward, each subject was injected with 0.1 ml of lepromin in two areas of the buttocks: one at the site that had received twice the MED of UVR and the other on the contralateral, unirradiated site. The irradiated site was given twice the MED every 4 d for a total of five treatments. One week after the last irradiation, both lepromin reactions were measured and biopsied. The size of the lepromin-induced granulomas was significantly reduced in the irradiated site, as was the number of lymphocytes. Immunohistochemical analysis showed a depletion in the number of infiltrating cells and a lower percentage of T cells, particularly the CD4+ subpopulation, in granulomas formed in UV-irradiated skin. This study demonstrates that local UV irradiation reduces the granulomatous reaction to lepromin in sensitized individuals. These findings are of clinical relevance because of the fundamental role played by the delayed-type hypersensitivity response in defense against intracellular pathogens and because of potential increases in the amount of UVR in sunlight reaching the earth's surface.

Photoimmunology of experimental melanoma

Increases in the incidence of cutaneous melanoma during the past few decades has drawn attention to the possible causes of this cancer. Although sunlight exposure has long been suspected of being a contributing factor, direct evidence of its participation has been difficult to obtain using epidemiological approaches. We have used murine models to investigate the possible contributions of UV radiation to the induction and pathogenesis of melanoma. Our studies demonstrate that UV radiation contributes to the induction of melanoma in a variety of ways, including an indirect, local effect on the skin. Recent evidence suggests that this indirect effect is immunologically mediated.

Alteration of the immune response to Mycobacterium bovis BCG in mice exposed chronically to low doses of UV radiation

BALB/c mice were exposed on shaved dorsal skin to 1 minimal erythemal dose (MED) of UVB radiation (2.25 kJ/m2) from a bank of six FS-40 sunlamps three times per week. The total number of irradiations ranged from 1 to 27. At regular intervals, groups of mice were injected in the left hind foot pad with 1 x 10(6) live mycobacteria (Mycobacterium bovis BCG) 3 days after the last UVB exposure. The mice were tested 21 and 42 days after infection for a delayed type hypersensitivity (DTH) response to the purified protein derivative (PPD) of tubercle bacilli by injecting PPD into the right hind foot pad and measuring the foot pad swelling 24 hr later. The course of infection was followed by assessing the number of bacterial colony forming units in the lymph node draining the site of BCG infection and the spleen. Mice exposed from 1 to 15 times to 1 MED of UV radiation showed a significant suppression in their DTH response to PPD compared with the unirradiated mice. At the same time, the number of bacterial colony-forming units in the lymph node and spleen of the UV-irradiated mice was greater than in control mice. With continued exposure to UVB, however, the DTH response recovered to a normal level, and there was no longer an increase in the number of viable bacteria in the lymphoid organs. These results indicate that early in the course of chronic UV irradiation, mice were impaired in their ability to mount a DTH response to BCG and to clear these bacteria from their lymphoid organs; later the mice recovered from these effects of UV, with continued treatment. A dose-response study using single doses of UV radiation indicated that a dose of 2.7 kJ/m2 suppressed the DTH response by 50%. Thus, exposure of mice to a single or multiple low doses of UV radiation prior to infection can interfere with systemic immunity to mycobacteria.