Human melanocytes and keratinocytes exposed to UVB or UVA in vivo show comparable levels of thymine dimers

Epidemiology shows a relationship between solar exposure and all types of s kin cancer. Understanding the mechanisms of skin cancer requires knowledge of the photomolecular events that occur within the relevant epidermal cell types in vivo. Studies to date have focused on UVR-induced DNA lesions in k eratinocytes, the majority epidermal cell population which gives rise to mo st skin cancers, Malignant melanoma, arising from melanocytes (5%-10% of ep idermal cells), accounts for most skin cancer deaths. We report on new tech niques to detect DNA photolesions in human epidermal melanocytes in situ. P reviously nonexposed buttock skin of volunteers of skin types I/II was expo sed to clinically relevant doses of narrow bandwidth UVB (300 nm) and WA (3 20 nm, 340 nm, 360 nm) radiation, Biopsies were taken immediately afterward s and processed for routine histology. Microscope sections were prepared an d double-stained with fluorescent-tagged monoclonal antibodies for thymine dimers and melanocytes. UVR dose-response curves for dimer levels within me lanocyte nuclei were determined by image analysis and compared with dimer l evels in adjacent basal cell keratinocytes, Our data show that WE and UVA r eadily induce thymine dimers in melanocytes at levels that are comparable w ith those found in adjacent keratinocytes. This new technique will enable m elanocyte specific studies, such as DNA repair kinetics, to be done in vivo .