The skin injury induced by high energy dose of ultraviolet in hairless descendants of Mexican hairless dogs.

Histopathological changes in the dorsal skin of hairless descendants of Mexican hairless dogs (MHDs) exposed to artificial irradiation with high energy dose (180 kJ/m2) of ultraviolet (UV) rays (UVA + B) were investigated. Macroscopically, erythema and edema were observed in the irradiated skin at 1 day after irradiation (DAI), and blister formation occurred except one dog at 2 DAI. Erythema almost disappeared at 5 DAI, and at 6 DAI, the skin recovered to almost normal state. Light microscopically, sunburn cells were observed at 1 DAI. Then intercellular edema and blister formation in the epidermis and dermal edema were evident at 2 and 3 DAI. At 6 DAI, the skin showed almost normal features except for slight epidermal thickening, but melanin granules, which were distributed in almost the whole length of the epidermis before UV irradiation, were detected only in cells which seemed to be melanocytes except one dog. Dihydroxyphenylalanine (DOPA)-positive melanocytes almost disappeared at 1 and 2 DAI, and at 6 DAI, the number of DOPA-positive melanocytes increased over the level before UV irradiation. The ultrastructural features of melanocytes were characterized by vacuolated cytoplasm, decreased melanosomes, irregular-shaped nuclei and shortened dendrites at 1 DAI, and returned to normal at 6 DAI. These findings of melanocytes reflect the severity of the skin injury and support weak suntan reaction in this case. In conclusion, severe form of UV-induced skin injury seen in humans could be reproduced in hairless descendants of MHDs exposed to high energy dose of artificial UVA + B.