THE EFFECT OF UV THERAPY ON IMMUNE FUNCTION IN PATIENTS WITH PSORIASIS

Ultraviolet radiation (UVR) is known to suppress some cell-mediated im mune responses to antigens encountered during or soon after exposure. Phototherapy is widely used in psoriasis, and this study was undertake n to monitor changes in a range of immunological parameters during sta ndard courses of treatment, with the aim of ascertaining whether such modulations contribute to the effectiveness of therapy. The responses of 17 patients with psoriasis undergoing UVB therapy, and four receivi ng PUVA therapy, were compared with 15 patients receiving coal tar tre atment and four normal subjects undergoing UVB irradiation. In each ca se, samples were taken before starting therapy, after 4 weeks of thera py, and 4 weeks after completion of treatment. Serum immunoglobulin is otypes and complement components were within normal ranges in most of the psoriasis patients, and remained unchanged throughout therapy. Sim ilarly, percentages of subsets of peripheral blood mononuclear cells ( PBMC) were normal, and were unaltered by treatment. Patients who were already infected with herpes simplex virus (HSV), as demonstrated by a positive lymphoproliferation test in vitro, were monitored for asympt omatic HSV shedding and HSV recrudescences during therapy. There was l ittle evidence that phototherapy caused reactivation of the virus. No significant alteration in lymphoproliferative response to HSV and to t he mitogen concanavalin A was observed during therapy. Epidermal cells and blood adherent cells were used to present HSV to PBMC, depleted o f adherent cells and enriched for T cells, in a lymphoproliferative as say. The functional antigen-presenting ability of adherent cells remai ned unchanged throughout therapy, whereas that of epidermal cells was suppressed during UVB irradiation and recovered, in most instances, af ter UVB therapy had been completed. The epidermis of patients with pso riasis contained about three times the quantity of urocanic acid (UCA) of normal subjects, whereas the UCA concentration in suction blister fluid did not differ between the two groups. During UVB irradiation, t he percentage of cis-UCA rose in both the epidermis and suction bliste r fluid of all subjects, and it remained elevated in the blister fluid after therapy had finished. Tumour necrosis factor-alpha was measured in suction blister fluid, and its concentration did not alter consist ently as a result of therapy. Whether any of the immunological paramet ers measured, and the changes noted, contribute to the effectiveness o f phototherapy in the treatment of psoriasis remains uncertain.