2.4. UV irradiation
UVB was supplied by an array of five G5T5E Sankyo Denki sunlamps containing ∼30% UVA (Kanagawa, Japan) uv-radiation was applied to the backs of the mice three times a week for 12 weeks. The amount of irradiation was progressively increased from 100 mJ/cm2 per exposure at week 1 (1 minimal erythematous dose = 100 mJ/cm2) to 400 mJ/cm2 at week 7.