Detection of active UV-photoproduct repair in monkey skin in vivo by quantitative immunohistochemistry

Abstract Ultraviolet-induced cyclobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4)photoproducts in DNA were quantitatively measured in monkey skin using an immunohistochemical method with two specific monoclonal antibodies. The skins of Cynomolgus monkeys ( Macaca fascicularis ) were irradiated with UV light and processed for preparation of conventional formalin-fixed, paraffin-embedded histological sections. Both of the photoproducts were detectable in the nuclei of epidermal cells at doses of 500 J/m 2 for UVB and 50 J/m 2 for UVC, respectively, nuclear staining being clearly dose-dependent. Time course studies also showed a statistically significant decrease in nuclear staining with time after exposure to either UVB or UVC irradiation. Although only 30% of CPDs were removed from DNA in the first 24 h, about half of the (6-4) photoproducts were repaired within 3 h post-UV irradiation. Staining completely disappeared by 48 h in the (6-4) photoproduct case and by 72 h in the case of CPDs. The results suggest that epidermal cells of monkey skin can efficiently repair UV-photoproducts in DNA, but that the capacity is slightly less than in man.