Immunologic unresponsiveness induced by topical application of hapten to PUVA-treated skin in guinea pigs

Immunosuppression in phototherapy

The successful use of phototherapy, especially psoralen plus UVA (PUVA) therapy, in the treatment of a variety of skin diseases is well known. Because the pathology of diseases such as vitiligo, alopecia and lichen planus is thought to involve immune mechanisms, the beneficial effect of PUVA may be due to immunosuppression. PUVA treatment can induce suppression in two ways. In the first (local suppression) psoralen is applied topically, the skin is irradiated with UVA and the contact allergen is applied directly to the irradiated skin. The induction of contact hypersensitivity (CHS) is suppressed and suppressor cells are found in the spleens of treated animals. Systemic suppression results from the injection of psoralen followed by exposure to UVA. The contact allergen is then applied at a distant non-irradiated site. CHS is suppressed and antigen-specific suppressor cells are found in the spleens of treated mice. The ability to induce specific immunosuppression may provide novel methods of inhibiting unwanted immune responses. We have demonstrated that graft rejection and the induction of graft-versus-host disease can be suppressed in an antigen-specific manner by UV radiation. Thus phototherapy may provide promising new treatments for suppressing graft rejection and perhaps may be beneficial in the treatment of autoimmune disease and allergic reactions.

Treatment of persistent severe atopic dermatitis in 113 Japanese patients with oral psoralen photo-chemotherapy

Oral administration of psoralen and whole body exposure to UVA (oral PUVA) has been used for the treatment of 113 patients with severe atopic dermatitis (AD). 8-Methoxypsoralen (8-MOP) was given at a dose of 0.5-0.6 mg/kg two hours prior to UVA (3-8 J/cm2) irradiation. Patients were treated three times a week while hospitalized. Other medications which had been given before PUVA therapy were permitted. At four and eight weeks after PUVA therapy, the severity score of AD had decreased by 51% and 80%, and the cumulative doses of UVA were 51.2 J/cm2 and 115.3 J/cm2, respectively. The amounts and strength of topical cortico-steroids were decreased during PUVA therapy. No adverse effects that required discontinuation of the PUVA therapy were observed. After discharge, maintenance therapy with UVB phototherapy and/or conventional treatment of AD kept the patients in remission in the outpatient clinic. The QOL of patients was greatly improved. Photochemotherapy with oral 8-MOP can be indicated in patients with severe, widespread AD, especially if standard therapy fails. This is the first report of oral PUVA therapy in a large series of Japanese patients with AD.

Effects of PUVA therapy on kidney allografts: results of a randomized prospective double-blind study

After successful experimental organ transplant studies on the efficacy of PUVA therapy combining donor pretreatment with the photosensitizer 8-methoxypsoralen (P) and the ex vivo irradiation of organs with long-wave ultraviolet light (UVA) prior to transplantation, we started in 1989 the first randomized, prospective, double-blind study to clarify the efficacy of PUVA therapy in human kidney transplantation. This study included 50 kidney donors, 25 of whom were PUVA-treated. A total of 75 kidneys were transplanted in Berlin, Halle and Rostock. The complete data of these 75 recipients were available for the final evaluation. The PUVA group (n = 36) and the non-PUVA group (n = 39) were not statistically significantly different as to donor and recipient data. Regarding the results, no differences were seen in initial hospitalization time, early graft function, rejection rate, number and time of rejection episodes. After a follow-up of 24 months, both graft survival (PUVA vs. non-PUVA: 75% vs. 71.8%) and patient survival (97.2% vs. 97.4%, respectively) were comparably high. PUVA therapy did not influence the development of vascular rejection. Interestingly, the rate of late graft loss after the 6th posttransplant month was lower, but not statistically significantly so, in the PUVA than in the non-PUVA-group (2 vs. 6 graft losses). Thus, PUVA-pretreated kidneys may be associated with a reduced development of chronic rejection.

Indications and action mechanisms of phototherapy

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

PUVA therapy: current concerns in Japan

Photochemotherapy using methoxsalen in combination with long-wave ultraviolet light (PUVA) is an essential modality in the treatment of various skin diseases. Major therapeutic regimens include oral, topical and water-delivery methods. An adequate regimen should be chosen regarding cases of disease, extent of involvement and the age of patients. In Japan, however, treatment techniques and protocols have not yet been standardized. PUVA therapy may be a first choice in the early stages of mycosis fungoides and a second choice or an adjunctive measure in other diseases, such as psoriasis, vitiligo and atopic dermatitis, which have been disabling or resistant to conventional treatments. Japanese guidelines for PUVA therapy of psoriasis are being prepared to be produced. Risks and benefits must be weighed and the patient orientation is necessary to complete the treatment and also to minimize side-effects. Although possible risks for skin cancers in Japanese patients have been reported to be much lower, a careful monitoring of the patient's skin changes is recommended. While action mechanisms are not completely understood, recent investigations suggest that both antiproliferative and immunomodulatory effects are involved. This review article deals with the recent progress in clinical and basic research on PUVA therapy, focusing on our current concerns.

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

The induction of contact hypersensitivity is suppressed when hapten is applied topically to an area irradiated by ultraviolet B (UVB). There is no standardized procedure to induce this local immunosuppression by UVB. We investigated the effects of the following factors on induction of dinitrofluorobenzene contact hypersensitivity in mice. UVB dose, divided UVB exposure, timing of sensitization after irradiation, hapten concentration, hapten volume (application area), sex, age, and simultaneous sensitization on UV-exposed and nonexposed skin. The suppression was enhanced by increasing the UVB dose. When 100 mJ/cm2 of UVB was irradiated, divided daily exposure (25 mJ x 4 d) was more suppressive than single exposure (100 mJ x 1 d). Sensitization 2 d after irradiation (100 mJ/cm2) induced suppression most effectively. When 25 microliters of dinitrofluorobenzene solution was applied to exposed skin, higher concentrations induced lower suppression. When the total dose of hapten was kept constant (92 micrograms), the application of lower concentrations to large areas (0.25%, 25 microliters) caused stronger suppression than higher concentrations (1%, 6.25 microliters) to small areas. Simultaneous sensitization on UV-exposed and nonexposed skin revealed less suppression than sensitization only on exposed skin. The suppression of contact hypersensitivity was significantly greater in young than in old mice. These results provide details that may be useful in designing studies involving immunosuppression by UVB radiation.

Activation of keratinocytes with psoralen plus UVA radiation induces the release of soluble factors that suppress delayed and contact hypersensitivity

Exposure of mice to psoralen plus ultraviolet A (320-400 nm) radiation or midrange ultraviolet B (280-320 nm) radiation causes a systemic suppression of the immune response. Although the mechanisms involved in the induction of suppression are not entirely clear, recent studies have demonstrated that ultraviolet B--irradiated keratinocytes release soluble factors that depress delayed-type hypersensitivity to alloantigens and activate the suppressor cell pathway. The purpose of this study was to determine whether PUVA-treated keratinocytes could also cause the release of such immunosuppressive factors. Treatment of keratinocytes with psoralen and UVA radiation induced the release of a factor that depressed the delayed-type hypersensitivity reaction to alloantigen. The suppressive factor was released regardless of whether the psoralen formed monofunctional or bifunctional adducts with DNA and regardless of its phototoxicity. In addition, keratinocytes treated with psoralen and lower doses of UVA radiation released a factor that inhibited contact but not delayed-type hypersensitivity, suggesting that more than one immunosuppressive factor is released following treatment of keratinocytes with appropriate doses of psoralen and UVA radiation. Our findings provide evidence that immunosuppressive factors released from keratinocytes may play a role in the induction of systemic immune suppression following PUVA treatment. Moreover, they demonstrate that PUVA treatment, unlike UVB treatment, can cause the release of more than one immunosuppressive factor from keratinocytes.

Local suppression of contact hypersensitivity in mice by a new bifunctional psoralen, 4,4',5'-trimethylazapsoralen, and UVA radiation

Although psoralens plus UVA radiation (320-400 nm) have been widely used for the treatment of dermatologic diseases, the toxic effects of these agents have led investigators to develop new photochemotherapeutic compounds. One such compound is 4,4',5'-trimethylazapsoralen (TMAP), a new bifunctional molecule. The purpose of this study was to examine the immunologic side effects of repeated treatment of C3H mice with TMAP plus UVA radiation. During this treatment, the number of ATPase+, la+, and Thy-1+ dendritic epidermal cells greatly decreased in the treated site, despite the lack of phototoxicity. The reduction in the number of detectable cutaneous immune cells was accompanied by a decrease in the induction of contact hypersensitivity to dinitrofluorobenzene applied to the treated skin, an impairment in the antigen-presenting activity of draining lymph node cells, and the presence of suppressor lymphoid cells in the spleen of unresponsive mice. Treatment with UVA radiation alone also reduced the number of ATPase+, Ia+, and Thy-1+ cells in the skin, but did not cause any detectable alterations in immune function. This implies that morphologic alterations in these cells do not necessarily indicate loss of function. Thus, although TMAP in combination with UVA radiation is not overtly phototoxic, it is highly immunosuppressive in mice.

Topical psoralen photochemotherapy for atopic dermatitis: evaluation of two therapeutic regimens for inpatients and outpatients

Forty-seven adolescent and adult patients suffering from long-standing atopic dermatitis (AD) too severe to respond to conventional therapies were treated with topical psoralen photochemotherapy (PUVA) and relatively low doses of ultraviolet (UV) irradiation. For practicality and convenience, two different therapeutic regimens were implemented; short-term hospitalization with almost daily irradiation (inpatient group, n = 23) and weekly irradiation combined with topical corticosteroids which had failed to manage symptoms before initiating the treatment (outpatient group, n = 25). Excellent therapeutic effects were achieved in 72% of the inpatients after 5-38 (mean 18.2) times of irradiation (mean cumulative dose; 44.7 J/cm2). In addition, 56% of outpatients responded excellently to the treatment after 6-22 (mean 13.0) times (mean cumulative dose; 25.8 J/cm2). In fact, 16 of the inpatients and 10 of the outpatients achieved almost complete remission. The duration of remission in these patients was 1-25 months (mean 6.3 months) in the inpatients and 1-6 months (mean 3.0 months) in the outpatients. Peripheral blood eosinophils significantly decreased after the treatments. A follow-up study showed a delayed decrease in serum IgE levels. In contrast, the specific IgE to house dust antigens and the water holding capacity of stratum corneum did not vary after treatment.

Inhibitory effect of 8-methoxypsoralen plus ultraviolet-A on interleukin-1 production by murine keratinocytes

We report the effects of 8-methoxypsoralen (8-MOP) plus ultraviolet-A (UV-A) irradiation on interleukin-1 (IL-1) production by murine epidermal keratinocytes, correlating its effect on IL-1 with cell viability, DNA synthesis, and 8-MOP-DNA photoadduct formation. Freshly isolated murine keratinocytes were treated with various doses of 8-MOP (5-100 ng/mL; incubation time, 30 min) plus 1 J/cm2 UV-A and cultured for 1-3 days. The IL-1/epidermal cell-derived thymocyte-activating factor (ETAF) activity in both supernatant and cell extract was reduced proportionately with increasing doses of 8-MOP/UV-A. Interleukin-1 inhibitors induced by 8-MOP plus UV-A were not detected in either supernatant or cell extract. A clear reduction of the IL-1 production was induced by the treatment as low as 15 ng/mL 8-MOP plus 1 J/cm2 UV-A, which led to the formation of 0.52 8-MOP photoadducts per million DNa bases and affected neither cell viability nor DNA synthesis of the treated cells. Cells treated with 100 ng/mL 8-MOP and 1 J/cm2 UV-A exhibited 57% suppression of IL-1 production in both 2- and 3-day culture samples. This treatment resulted in the formation of 3.8 photoadducts per million bases as well as significant abrogation of DNA synthesis although cell viability was unchanged. These observations provide some insights into the phototoxicity mechanisms of 8-MOP and the effect of PUVA therapy on the cytokine regulation in keratinocytes.

Photochemotherapy improves chronic cutaneous graft-versus-host disease

We have used oral psoralen photochemotherapy (PUVA) to treat four patients with chronic graft-versus-host disease of the skin, oral mucosa, and liver, who had responded only partially to long-term immunosuppressive therapy (prednisolone, cyclosporine, azathioprine). PUVA therapy was delivered to the entire skin but not to the oral mucosa, and immunosuppressive therapy was continued in all patients. Two patients' skin lesions improved considerably; the oral lesions healed and did not recur in one. Immunosuppressive therapy could be reduced in these two patients. One patient with sicca signs did not improve. One patient had to interrupt PUVA therapy because of side effects attributed to 8-methoxypsoralen (nausea and vomiting). No flare of acute cutaneous graft-versus-host disease was noted during PUVA therapy. Chronic graft-versus-host disease of the liver did not improve in any patient.

Local suppression of contact hypersensitivity in mice by a monofunctional psoralen plus UVA radiation

Monofunctional psoralens, plus UVA radiation are not erythemogenic and are less mutagenic than bifunctional psoralens plus UVA radiation. Thus, they have received considerable attention in recent years as potential therapeutic agents for various skin diseases. The purpose of this study was to examine the immunologic side effects following treatment of mice with a monofunctional psoralen plus UVA radiation. We report that angelicin plus UVA radiation suppressed the induction of contact hypersensitivity to dinitrofluorobenzene. This decreased immune response was associated with the presence of splenic suppressor cells that transferred suppression to normal recipients. Treatment with angelicin and UVA radiation also decreased the number of Thy-1+ and Ia+ dendritic epidermal cells in the treated site. We conclude that although this monofunctional psoralen is not phototoxic, it has immunosuppressive activity in mice.

Alteration of lymphocyte functions by 8-methoxypsoralen and long-wave ultraviolet radiation. II. The effect of in vivo PUVA on IL-2 production

Our previous studies demonstrated that psoralen plus long-wave ultraviolet radiation (PUVA) treatment inhibited certain T-lymphocyte functions, such as locomotive ability. To further analyze the effects of PUVA on T-lymphocyte function, we investigated the ability of mouse spleen cells to produce interleukin 2 (IL-2) after treatment of the mice in vivo with PUVA. Interleukin 2 production was impaired in cells from PUVA-treated mice compared with those from UVA-irradiated, 8-methoxypsoralen-treated, or normal mice. This impairment was not dose dependent, over the dose range of UVA (2-20 J/cm2) examined. Interleukin 2 production was markedly suppressed on day 3 after PUVA and returned to normal by day 7 after the treatment. Topical treatment of the mice with croton oil did not affect IL-2 production of their spleen cells. This result indicates that cutaneous inflammation per se may not be responsible for the suppressive effect of PUVA on IL-2 production. Addition of exogenous IL-1 did not reconstitute the decreased ability of spleen cells to produce IL-2 in vitro, indicating that PUVA affected primarily IL-2 producing cells. These suggest that impaired IL-2 production may account for some of the immune dysfunction observed in PUVA-treated animals.

The inhibitory effect of PUVA on the immunity of experimental dermatophytosis in guinea pigs

The effect of topical PUVA on the disease course and immunity of T. mentagrophytes dermatophytosis was investigated in guinea pigs. Animals which had been inoculated on nontreated skin showed mild erythematous lesions with scaling in a few days and then developed the most intense reaction between days 10 and 14. The lesions resolved completely by the third week. On the other hand, animals which had been inoculated on the PUVA-treated sites showed only mild squamous, erythematous lesions until the fourth postinfective week, when the intense reaction began to appear. Complete regression was observed by the fifth week in these animals. Trichophytin tests performed on the 14th day were positive in the guinea pigs of non-treated group, while negative in the PUVA-treated animals. The latter group revealed a positive reaction on the fifth week. PUVA did not show inhibitory effect on the sensitization by intracutaneous injection of trichophytin antigen. The PUVA treatment depleted the ATPase-positive Langerhans' cells. These results indicate that PUVA treatment suppresses the immunity of dermatophytosis and delays the spontaneous resolution of the lesions, and suggest that the Langerhans' cell is involved in the development of cell-mediated immunity in experimental dermatophytosis.

PUVA therapy prevents sensitization to mechlorethamine in patients with psoriasis

Two groups of 20 patients with psoriasis were treated with mechlorethamine applied topically (group A) or with PUVA combined with mechlorethamine (group B). In group B mechlorethamine was started after six PUVA treatments. Results showed a significant decrease of the incidence of contact dermatitis in group B (30%) compared with group A (75%). Allergic dermatitis, demonstrated by a positive patch test to mechlorethamine with an histology of eczema, was observed in 55% of patients in group A and 20% in group B. The incidence of irritant dermatitis was not significantly different in the two groups. Allergic dermatitis was observed later in group B: after an average of 32.2 applications of mechlorethamine compared with 25 applications in group A. Possible mechanisms responsible for these results are reduction of epidermal Langerhans cells by PUVA therapy and induction of antigen-specific suppressor T cells. Patients living far from a specialized centre might be treated initially with PUVA therapy then with mechlorethamine alone, at home. This schedule may reduce the incidence of contact dermatitis to mechlorethamine.

Systemic suppression of contact hypersensitivity by ultraviolet b radiation or methoxsalen/ultraviolet a radiation in the guinea pig

Treatment of strain 2 guinea pigs with ultraviolet b (uvb) (280-320 nm) radiation or methoxsalen, followed by ultraviolet a (uva) (320-400 nm) radiation, decreased the contact hypersensitivity (CHS) reaction to sensitizing agents applied subsequently to unirradiated sites. The decreased reactivity could be transferred to syngeneic animals and appeared to be caused by antigen-specific suppressor T lymphocytes. Ultraviolet b irradiation of sensitized animals did not affect elicitation of CHS in unirradiated skin.