Effect of ultraviolet irradiation on mast cell-deficient W/Wv mice

The effect of UV irradiation on the skin was investigated in (WB-W/+) X (C57BL/6J-Wv/+)F1-W/Wv mice, which are genetically deficient in tissue mast cells. Their congenic littermates (+/+) and normal albino mice (ICR or BALB/c) were used as controls. Mice were irradiated with 500 mJ/cm2 of UVB and the increment of ear thickness was measured before and 6, 12, and 24 h after irradiation. Ear swelling in W/Wv mice at 12 and 24 h after irradiation was significantly smaller than that in +/+ and ICR mice. In contrast, the number of sunburn cells formed 24 h after UVB irradiation (200 or 500 mJ/cm2) was similar in W/Wv, +/+ and ICR mice. On the other hand, when mice were treated with 8-methoxy-psoralen (0.5%) plus UVA irradiation (4 J/cm2) (topical PUVA), ears of W/Wv and BALB/c mice, which were both white in color, were thickened similarly 72 h after treatment, but less swelling was observed in +/+ mice, which were black in skin color. The amount of prostaglandin D2 (PGD2) in ears, determined by radioimmunoassay specific for PGD2, was elevated 3-fold in +/+ and ICR mice at 3 h after irradiation with 500 mJ/cm2 of UVB in comparison with basal level without irradiation. However, such elevation was not observed in W/Wv mice. These results suggest that mast cells play an important role in UVB-induced inflammation, and PGs from mast cells are responsible at least in part for the development of this reaction. However, neither mast cells nor PGs contribute to the sunburn cell formation and ear swelling response by PUVA treatment.