Photoimmunology

Toll-like receptors: role in dermatological disease

Toll-like receptors (TLRs) are a class of conserved receptors that recognize pathogen-associated molecular patterns (PAMPs) present in microbes. In humans, at least ten TLRs have been identified, and their recognition targets range from bacterial endotoxins to lipopeptides, DNA, dsRNA, ssRNA, fungal products, and several host factors. Of dermatological interest, these receptors are expressed on several skin cells including keratinocytes, melanocytes, and Langerhans cells. TLRs are essential in identifying microbial products and are known to link the innate and adaptive immune systems. Over the years, there have been significant advances in our understanding of TLRs in skin inflammation, cutaneous malignancies, and defence mechanisms. In this paper, we will describe the association between TLRs and various skin pathologies and discuss proposed TLR therapeutics.

PUVA treatment of the nasal cavity improves the clinical symptoms of allergic rhinitis and inhibits the immediate-type hypersensitivity reaction in the skin

We earlier reported that intranasal irradiation with the 308 nm xenon chloride (XeCl) ultraviolet-B laser and irradiation with a combination of ultraviolet-B (UVB), ultraviolet-A (UVA) and visible light (VIS) is highly effective in the treatment of allergic rhinitis and inhibit the immediate-type hypersensitivity reaction in the skin. Since photochemotherapy with 8-methoxypsoralen (8-MOP) plus UVA light (PUVA) is widely used in the treatment of different inflammatory skin disorders due to its immunosuppressive effect, in the present study we investigated the efficacy of intranasal PUVA treatment in allergic rhinitis and the effect of PUVA treatment on the skin prick test (SPT) reaction. An open study was performed in 17 patients with hay fever. Intranasal PUVA therapy was given four times weekly for 3 weeks. The treatment was started with a fluence of 0.5x of the individual minimal phototoxic dose (MPD) and the dosages were gradually increased. Evaluation was based on the symptom scores. The effect of PUVA treatment on the allergen-induced wheal formation was also studied in the SPT. PUVA treatment of the nasal cavity significantly decreased the nasal symptoms of the patients with allergic rhinitis. Treatment of the skin with PUVA also significantly suppressed the allergen-induced wheal formation in the SPT reaction. These data suggest that intranasal PUVA phototherapy is also an effective modality in the treatment of allergic rhinitis.

Ultraviolet radiation properties as applied to photoclimatherapy at the Dead Sea

BACKGROUND

The Dead Sea basin, the lowest terrestrial point on earth, is recognized as a natural treatment center for patients with various cutaneous and rheumatic diseases. Psoriasis is the major skin disease treated at the Dead Sea with excellent improvement to complete clearance exceeding 85% after 4 weeks of treatment. These results were postulated to be associated with a unique spectrum of ultraviolet radiation present in the Dead Sea area.

METHODS

The UVB and UVA radiation at two sites is measured continuously by identical sets of broad-band Solar Light Co. Inc. meters (Philadelphia, PA). The spectral selectivity within the UVB and UVA spectrum was determined using a narrow-band spectroradiometer, UV-Optronics 742 (Orlando, FL). The optimum exposure time intervals for photoclimatherapy, defined as the minimum ratio of erythema to therapeutic radiation intensities, were also determined using a Solar Light Co. Inc. Microtops II, Ozone Monitor-Sunphotometer.

RESULTS

The ultraviolet radiation at the Dead Sea is attenuated relative to Beer Sheva as a result of the increased optical path length and consequent enhanced scattering. The UVB radiation is attenuated to a greater extent than UVA and the shorter erythema UVB spectral range decreased significantly compared with the longer therapeutic UVB wavelengths.

CONCLUSIONS

It was demonstrated that the relative attenuation within the UVB spectral range is greatest for the shorter erythema rays and less for the longer therapeutic UVB wavelengths, thus producing a greater proportion of the longer therapeutic UVB wavelengths in the ultraviolet spectrum. These measurements can be utilized to minimize the exposure to solar radiation by correlating the cumulative UVB radiation dose to treatment efficacy and by formulating a patient sun exposure treatment protocol for Dead Sea photoclimatherapy.

Antibody-targeted polymer-bound drugs

Drug targeting is an attractive new approach to killing cancer cells while leaving normal tissue unharmed. Recently we have developed a new generation of antibody-targeted immunosuppressive (cyclosporin A) and cytostatic (daunomycin, doxorubicin) drugs and photosensitizers (chlorin e6) effective in vitro and in vivo. The drugs and the targeting antibody (polyclonal and monoclonal) are conjugated to the oligopeptidic side chains of a water-soluble synthetic carrier, copolymer of N-(2-hydroxypropyl)methacrylamide. The composition of the side chains ensures the stability of the linkage between the drug and the polymeric carrier in the bloodstream and its intralysosomal degradability which is a prerequisite for the pharmacological activity of the preparation. Antibody-targeted polymer bound drugs show considerably decreased hepatotoxicity, cardiotoxicity, myelotoxicity and nephrotoxicity. Two adriamycin-HPMA copolymers are in Phase I/II clinical trials in United Kingdom.

Basal cell carcinoma of the eyelid and periocular skin

Basal cell carcinoma is the most common human malignancy. This locally invasive tumor rarely metastasizes, but can cause considerable morbidity when on the eyelids and periocular skin. The successful management of BCC requires an awareness of its broad clinical spectrum and knowledge of the risk factors associated with therapeutic failure. The optimal therapy for basal cell carcinoma is controversial. Treatment strategy is formulated on an individual basis, taking into account tumor size, anatomic location, and growth pattern. The immune status and life expectancy of the patient also must be considered. While complete eradication of the tumor is desirable, this can be challenging since basal cell carcinomas often extend beyond their apparent clinical margins. Since prevention is preferable to treatment, the public needs to be informed that the incidence of periocular skin cancers can be reduced with the longterm use of sunscreens, sunglasses, and hats with brims.

UV exposure reduces immunization rates and promotes tolerance to epicutaneous antigens in humans: relationship to dose, CD1a-DR+ epidermal macrophage induction, and Langerhans cell depletion

Increasing UVB radiation at the earth's surface might have adverse effects on in vivo immunologic responses in humans. We prospectively randomized subjects to test whether epicutaneous immunization is altered by prior administration of biologically equalized doses of UV radiation. Multiple doses of antigens on upper inner arm skin (UV protected) were used to elicit contact sensitivity responses, which were quantitated by measuring increases in skin thickness. If a dose of UVB sufficient to induce redness (erythemagenic) was administered to the immunization site prior to sensitization with dinitrochlorobenzene (DNCB), we noted a marked reduction in the degree of sensitization (P less than 0.0006) that was highly dose responsive (r = 0.98). Even suberythemagenic UV (less than a visible sunburn) resulted in a decreased frequency of strongly positive responses (32%) as compared to controls (73%) (P = 0.019). The rate of immunologic tolerance to DNCB (active suppression of a subsequent repeat immunization) in the groups that were initially sensitized on skin receiving erythemagenic doses of UV was 31% (P = 0.0003). In addition, a localized moderate sunburn appeared to modulate immunization with diphenylcyclopropenone through a distant, unirradiated site (41% weak responses) as compared to the control group (9%) (P = 0.05). Monitoring antigen presenting cell content in the epidermis revealed that erythemagenic regimens induced CD1a-DR+ macrophages and depleted Langerhans cells. In conclusion, relevant and even subclinical levels of UV exposure have significant down modulatory effects on the ability of humans to generate a T-cell-mediated response to antigens introduced through irradiated skin.

Side-effects of psoralen photochemotherapy (PUVA)

Although psoralen photochemotherapy (PUVA) is one of the most effective forms of therapy for psoriasis, the risk of potential long-term side-effects is, as yet, not clearly determined. Chronic degenerative and pigmentary skin changes similar to those of chronic solar exposure occur after long-term PUVA treatment; PUVA also causes non-melanoma skin cancers in man, although there is, as yet, no consensus as to what cumulative phototoxic PUVA dose is carcinogenic. Long-term multicentre studies from the U.S.A. indicate a definite risk of squamous cell carcinoma for long-term PUVA-treated patients, whereas European studies reveal no overall increase in skin cancers in similar patients except for those exposed to other carcinogens. Assignment to PUVA should be based on the risk:benefit ratio for the individual patient. Careful patient selection is therefore mandatory and should be limited to those who can be monitored and controlled by informed, competent and conscientious physicians.

The prodrome of bullous pemphigoid

Bullous pemphigoid is an autoimmune bullous dermatosis that can be preceded by a prodromal phase, usually lasting weeks to months, during which the cutaneous changes are dermatitic rather than bullous. Two cases of unusually long prodromal periods, 18 months and 6 years, are reported.

PUVA and UVB inhibit the intra-epidermal accumulation of polymorphonuclear leukocytes

Healthy volunteers were treated on test areas with UVB irradiation or topical PUVA therapy. The trauma-induced and leukotriene B4 (LTB4)-induced intra-epidermal accumulation of polymorphonuclear leukocytes (PMN) was quantified after these treatments, using elastase as a marker enzyme. Both UVB and PUVA treatment caused a profound inhibition of trauma- and LTB4-induced PMN accumulation. This observation indicates that reduction of the transepidermal migration of PMN might be part of the mechanism of action of UV therapies in psoriasis. Several possibilities are discussed to explain this hypothesis.

[Problems posed by the therapeutic use of photosensitizers in dermatology]

Three phototherapeutic regimens with photosensitization are now used in dermatology: PUVA (psoralen + UVA), TUV (crude coaltar + UV), PRT (phototherapy with hematoporphyrin derivative). The efficiency of PUVA and TUV is well known in several dermatoses. PRT is now being tested experimentally. For TUV, the lack of a standardized regimen does not allow a clear-cut evaluation of the therapy. For PUVA, late side-effects, particularly carcinogenicity have to be considered. To improve efficiency and minimize the side-effects of PUVA some procedures, such as association with retinoïds, pharmaco-kinetic studies for individual adaptation of the therapeutic regimen and the use of new less mutagenic psoralens are helpful. The persistent phototoxicity following treatments with hematoporphyrin derivative constitutes the major side-effect observed, for this phototherapy.

Psoriasis treatment at the Dead Sea: a natural selective ultraviolet phototherapy

A naturally filtered ultraviolet spectrum of sunlight along with other natural factors are utilized in the management of psoriasis at the Dead Sea area in Israel. In 110 patients with psoriasis, 85.5% achieved complete clearing or excellent improvement. These results compare favorably with other therapeutic regimens used today in the treatment of psoriasis. Since systemic medications are avoided, the potential risks may be considerably lessened. Therefore, this therapeutic modality may be considered in the management spectrum of psoriasis.

Methoxsalen and ultraviolet A radiation in treatment of chronic cutaneous graft-versus-host reaction

Chronic cutaneous graft-versus-host reaction following bone marrow transplantation has been difficult to manage in some patients because of poor response to immunosuppressive agents or because of toxicity to these drugs. We recently used methoxsalen and ultraviolet A therapy and found it to be successful in controlling chronic cutaneous lichenoid graft-versus-host reaction in a bone marrow transplant patient. Although there was an initial flare of an eruption resembling acute cutaneous graft-versus-host reaction, both this acute eruption and the lichenoid lesions subsided and cleared with continued treatment. The skin lesions recurred when treatment was discontinued but responded promptly when it was initiated for the second time. Other than mild phototoxicity, there were no other significant side effects.

Prolongation of the survival of skin grafts in mice by PUVA treatment

The combined application of psoralen and UVA radiation to skin grafts induced a prolongation of the survival time of the grafts in mice. This was observed using the H-Y barrier, an allogeneic barrier without H-2 disparities, and a strong H-2 incompatible barrier. The effect is probably due to a reduction of antigen-presenting cells, or to other, unknown mechanisms.

Detection of interferon in the sera of patients with psoriasis, and its enhancement by PUVA treatment

Interferon-like activity could be detected in the sera of nineteen psoriatic patients (interferon titres between 8 and 64 i.u./ml), whereas healthy controls were negative. Following PUVA treatment the interferon levels increased significantly (interferon titres between 32 and 128 i.u./ml). An enhanced interferon production could explain some of the immunological phenomena connected with PUVA treatment.

The occurrence of vitiligo after psoralens and ultraviolet a therapy

The ability of photochemotherapy with 8-methoxypsoralen in conjunction with high-intensity long-wave ultraviolet light (PUVA) to stimulate melanogenesis is well known. This effect on the pigmentary system is evidenced by the diffuse tanning of clinically normal skin in PUVA-treated patients with psoriasis and other disorders, as well as by the repigmentation of lesions in vitiligo. It is now recognized that there may be additional pigmentary effects, resulting in clinical lesions such as PUVA mottling, PUVA lentigines, and localized hypopigmentation. We have documented the occurrence of yet another association with PUVA therapy--the paradoxical appearance of widespread hypopigmentation consistent with vitiligo in three PUVA-treated patients, one with psoriasis and two with mycosis fungoides. Histologic and ultrastructural findings are presented.

Abnormal lymphocyte function following long-term PUVA therapy for psoriasis

The surface markers and function of peripheral blood lymphocytes were examined in patients on long-term therapy with methoxsalen and UV-A radiation (PUVA). Ten patients with psoriasis were selected because they had received a high exposure to PUVA therapy, i.e., more than 200 treatments over 2-6 years with cumulative exposure doses of 1700-6000 J/cm2 UV-A radiation. Results were compared to those obtained with lymphocytes from untreated patients and UV-B treated patients with psoriasis. The PUVA-treated patients had low levels of E rosette-forming cells in the peripheral blood and markedly impaired lymphocyte responses following stimulation with optimal and suboptimal doses of mitogens. The sensitivity of lymphocytes to in vitro treatment with PUVA was similar in the three groups of patients. The results of this study indicate that long-term PUVA therapy alters the function and cell-surface markers or distribution of lymphocytes.

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

Pretreatment by topical application of 8-methoxypsoralen and subsequent exposure to long-wave ultraviolet light (PUVA) on the induction site of contact sensitization to dinitrochlorobenzene (DNCB) significantly diminished the challenge reactions in guinea pigs. A single treatment with PUVA in a small area was enough to exhibit such an effect. Furthermore, the animals that had been first exposed to DNCB through PUVA-treated skin failed to become sensitized to the subsequent sensitization regimen of the same hapten even through previously untreated skin. The unresponsiveness in these animals was hapten-specific, since their capacity to become sensitized to an unrelated hapten, oxasolon, was not impaired. The intraperitoneal administration of cyclophosphamide at a dose of 200 mg/kg shortly before contact sensitization reversed the unresponsiveness in tolerant animals. These findings suggest that tolerance in these animals is a specific immunologic unresponsiveness mediated by suppressor cells.

Position paper--PUVA therapy. American Academy of Dermatology

PUVA, the combination of psoralen (P) and long-wave ultraviolet radiation (UVA), is being used increasingly in the management of psoriasis and several other dermatologic disorders. While the acute toxicity of this modality, which includes erythema and blistering of the skin, can be avoided with careful monitoring of the dosimetry of the administered radiation, the potential chronic toxicity remains a source of concern. Since psoralens and UVA are clearly mutagenic, carcinogenic, cataractogenic, and may have as yet poorly understood effects on the immune system, it is imperative that all patients treated with this modality be carefully monitored for the development of neoplasia and cataracts. PUVA therapy should only be administered using specialized equipment that can be accurately monitored for its spectral irradiance by physicians thoroughly familiar with the risks and benefits of the modality.

Significant progress in dermatologic research since 1977

Some active fields of experiment dermatology have been selected to demonstrate the interaction between basic research and clinical dermatology. The identification of the Langerhans cell, the typing of mononuclear cells, and the identification of T cell growth factors have significant implication in contact dermatitis, lymphomas, etc. The group of papovaviruses is better defined in relationship to the type of disease that they produce and its oncogenic potential. Various types of vasculitis are better understood, thanks to research in humoral immunity and complement activation. Melanogenesis and its control by peptides is progressing. New specific proteins have been identified in the connective tissues, and their role has been clarified. Identification of specific proteins of keratinocytes and study of differentiation of these cells have provided useful information and some skin disorders. The control of epidermal cell proliferation and differentiation, through membrane receptors, growth factors, and intracellular enzymes, is progressively giving clues to the understanding of genetic disorders, cancers, the effect of retinoids and phototherapy.