Sunscreens protect epidermal Langerhans cells and Thy-1+ cells but not local contact sensitization from the effects of ultraviolet light.

This study compares the ability of two commonly used sunscreens--octyl dimethyl para-aminobenzoate (Padimate O) and 2-ethylhexyl-p-methoxycinnamate (2-EHMC)--to protect Langerhans cells (LC), Thy-1+ dendritic epidermal cells (Thy-1+ dEC), and local contact sensitivity (CS) from the effects of ultraviolet (UV) light. Chronic exposure of mice 5 d per week for 4 weeks with an intermediate dose of solar-simulated sunlight from which any UVC had been filtered reduced the LC and Thy-1+ dEC density of murine epidermis. This irradiation procedure was designed to simulate closely the daily exposure of humans to sunlight. This effect on LC and Thy-1+ dEC occurred in both albino and pigmented mice that develop a tan during the irradiation procedure, indicating that a tan does not protect these cells from the effects of UV light. Sunscreen preparations with Padimate O and 2-EHMC, both of which also contained benzophenone-3, as well as Padimate O or 2-EHMC in organic solvent, inhibited UV light from depleting LC from the epidermis of both mouse strains. Padimate O and 2-EHMC in organic solvent were used to ensure that these were the active ingredients in the sunscreen preparations. In contrast to the effects on LC, Padimate O, but not 2-EHMC, protected Thy-1+ dEC from UV exposure in both mouse strains, but neither protected against the development of local immunosuppression using a contact sensitivity model. Thus, even in a mouse strain that is sensitive to UV-induced immunosuppression, local immunosuppression can occur in the presence of normal densities of LC and Thy-1+ dEC.