Local and systemic effects on the epidermal melanocyte population in UV-irradiated mouse skin.

Local and systemic effects of repeated UVB irradiation on the epidermal melanocytes have been studied in the C57Bl mice. A daily dose of 0.1 joule/cm2 for 10 days induced a 4-fold increase in the epidermal melanocyte population of the irradiated right ear. During the first weeks after the irradiation period, there was a gradual increase in the number of melanocytes also in the shielded left ear, up to about 3 times the age control values. Thereafter, the population density slowly decreased in both ears, but it remained well above original values as late as 20 weeks after the irradiation. Thus, a short UVB irradiation period induces a long-lasting increase in the number of epidermal melanocytes in irradiated skin areas, as well as in covered skin regions. It is suggested that the population increase in the shielded ear is initiated by one or more systemic factors originating from the UVB irradiated skin. Such factors may be involved in the regulation of a balanced melanocyte population over the entrie body surface.