Acute effects of UVB radiation on the proliferation and differentiation of keratinocytes

Purpose: The effects of UVB radiation on the proliferation and differentiation of epidermal keratinocytes were investigated with respect to timing, dosage, and repeated exposures. Methods: Nine healthy volunteers were placed into three subgroups and exposed to UVB radiation on buttock skin using a Waldmann UV 800 unit fitted with Philips TL‐20W/12 fluorescent lamps. Three volunteers were given 2 MED of UVB and biopsied at: pre‐exposure, 24, 48 and 72 h after UVB exposure. For three volunteers, 1 MED, 2 MED, 3 MED of UVB were applied. After 48 h, biopsies were taken from non‐irradiated and irradiated sites. Finally, three volunteers received 1 MED of UVB daily for 5 days, and the non‐irradiated and irradiated sites were biopsied 48 h after the final exposure. The expression of proliferation and differentiation markers by keratinocytes were detected by immunohistochemical staining, and the results were analysed quantitatively by image analysis. Results: The expression of proliferation and differentiation markers was observed prominently 48 h after irradiation. Higher doses of UVB caused an increase in proliferation and differentiation marker expression. Repeated exposures potentiated the effect of UVB radiation. Conclusion: UVB irradiation concomitantly promotes epidermal proliferation and differentiation. Responses were maximal 48 h after irradiation. This effect of UVB increases linearly according to dose and repetition.