Transiently increased insulin-like growth factor. I. Immunoreactivity in UVB-irradiated mouse skin

UVB-irradiation during 3 d for 90, 180, and 180 sec, respectively, at a daily dose of 0.1 and 0.2 joule/cm2, respectively, induced slight inflammatory reactions in the mouse ear. The insulin-like growth factor I (IGF-I) immunoreactivity, normally demonstrable only in scattered basal epidermal cells, rapidly increased in intensity and frequency in the epidermis. After 3 d of UVB irradiation almost all epidermal cells were outlined by IGF-I immunoreactivity in their plasma membrane. The Langerhans cells expressed intense IGF-I immunoreactivity throughout their cytoplasm. The elevated IGF-I immunoreactivity ceased after 5-7 d and was normalized in 3 weeks. The number of Ia positive epithelial Langerhans cells did not seem to be affected by UVB irradiation. It is concluded that the increased IGF-I immunoreactivity is likely to reflect formation of the trophic peptide IGF-I, most evidently by Langerhans cells, in early events of the inflammatory, reactive response of the skin to UVB irradiation.