Abstract:

Objective To study the influence of sunscreens with different efficacy on delayed type hypersensitivity （DTH） and their immunoprotective effect in mice. Methods A cohort of mice were randomly divided into 5 groups with 10 mice in each group: group 1 as the positive control without irradiation, group 2 receiving solar-simulated radiation （SSR） only, group 3 receiving SSR and protected by sunscreen 1 with sun protection factor 15 （SPF15） and persistent pigment darkening （PPD） 12, group 4 receiving SSR and protected by sunscreen 2 with SPF 50 and PPD 28, and group 5 as the negative control receiving SSR only. SSR was carried out on the back of mice with the UVA dose being 1.4 J/cm2 and UVB dose being 100 mJ/cm2 for 10 days. After a 5-day irradiation, the groups 1 to 4 were immunized by intraperitoneal injection with 100 μl （107 cells/ml） of Candida albicans suspension. On the 10th day both sides of the posterior foot pad were measured; then the foot pads were injected with additional 50 μl of the Candida albicans suspension. Twenty-four hours after the injection, the thickness of each foot pad was measured, and immunosuppression rate was calculated. Finally, the mice were sacrificed and skin samples were obtained from the back of these mice followed by the examination of CD1a, CD80 and CD86 expression by Western blot. Results The thickness of edema in foot pads was 0.41 ± 0.38 mm, 0.21 ± 0.23 mm and 0.30 ± 0.25 mm in group 1, 3 and 4, respectively, significantly higher than in group 5 and 2（0.04 ± 0.03 mm, 0.14 ± 0.12 mm, respectively, all P < 0.05）, while no significant difference was observed between the group 3 and 4 （P > 0.05）. Significant differences were observed in the immunosuppression rate between group 2, 3 and 4 （73.0% ± 11.3%, 54.1% ± 6.4%, 29.7% ± 7.5%, respectively, all P < 0.01）. Western blot revealed a significant increment in the expression of CD1a protein in group 1 compared with group 2 as well as in the expression of CD86 protein in group 1 and group 3 compared with group 2 and group 5 （all P < 0.05）, but no statistical difference was observed between the other groups in the expression level of CD1a, CD80 or CD86 （P > 0.05）. Conclusions The exposure to sub-erythema dose of UV can induce DTH, and sunscreens have an immunoprotective effect in this process. Epidermal Langerhans cells are not essential for UV-induced immunosuppression.

Key words: Langerhans cells