Sun exposure induces rapid immunological changes in skin and peripheral blood in patients with psoriasis

Abstract

Background Ultraviolet (UV) radiation has immunosuppressive effects and heliotherapy is a well-described treatment modality for psoriasis.

Objectives To characterize early sun-induced immunological changes both local and systemic in patients with psoriasis.

Methods Twenty patients with moderate to severe psoriasis were subjected to controlled sun exposure on Gran Canaria, Canary Islands, Spain. Psoriasis Area and Severity Index (PASI) scores were evaluated. Skin biopsies were obtained from lesional and nonlesional skin in 10 patients at baseline and on day 16 and from five additional patients on day 2. Specimens were examined with immunohistochemistry and polymerase chain reaction. Blood samples were obtained from all patients at the same time points and were examined for T-cell subsets and cytokine production.

Results Significant clinical improvement was achieved during the study period. CD4+ and CD8+ T cells in lesional skin were significantly reduced in both the epidermis and dermis. In contrast, dermal FOXP3+ T cells were relatively increased. In the peripheral blood skin homing cutaneous lymphocyte-associated antigen (CLA)+ T cells were significantly decreased after only 1 day in the sun and in vitro stimulated peripheral blood mononuclear cells demonstrated reduced capacity to secrete cytokines after 16 days.

Conclusions Our data show that clinical improvement of psoriasis following sun exposure is preceded by a rapid reduction in local and systemic inflammatory markers, strongly suggesting that immune modulation mediated the observed clinical effect. We cannot completely rule out that other mechanisms, such as stress reduction, may contribute, but it is extensively documented that UV irradiation is a potent inducer of immunosuppression and we therefore conclude that the observed effect was primarily due to sun exposure.