Partial Protection Against Epidermal IL-10 Transcription and Langerhans Cell Depletion by Sunscreens after Exposure of Human Skin to UVB

Abstract

Sunscreens capable of inhibiting erythema are assumed to protect against UV-induced carcinogenesis as well. However, the correlation between inflammation and carcinogenesis is uncertain, and the prevention of UV-induced erythema might in fact be biologically irrelevant as an indicator of protection against UV-induced skin cancer. Ultraviolet-B radiation promotes cutaneous immunosuppression by the release of immunoregulatory cytokines and by depletion of Langerhans cells. We investigated the ability of two different sunscreens to inhibit UVB-induced expression of epidermal interleukin (IL)-10 and depletion of Langerhans cells. Chemical and physical sunscreens were applied to the forearms of volunteers 15 min prior to 4 minimal erythemal doses of UVB exposure. Suction blisters were induced 24 h after irradiation, and RNA was extracted from the blister roofs. Reverse transcription polymerase chain reaction was performed using primers for IL-10 and CDla. A chemical sunscreen containing octyl methoxycinnamate (12 sun protection factor [SPF]) and a physical sunscreen containing zinc oxide (16 SPF) were assayed: UVB-induced IL-10 mRNA expression was nearly totally inhibited by both sunscreens (median protection for chemical and physical sunscreens was 95% and 78%, respectively), whereas UVB-induced Langerhans cell depletion was partially prevented (47% and 50% for chemical and physical sunscreens, respectively). Langerhans cell protection by sunscreens was confirmed by estimation of cell density after ATPase staining. In contrast, both sunscreens effectively prevented the induction of UVB-induced erythema. We believe this to be the first demonstration that sunscreens can prevent the induction of cutaneous mediators of immunosuppression, and that the results indicate that the immunoprotection offered by the sunscreens is significantly lower than their ability to prevent erythema.