Kinetics of UV light-induced cyclobutane pyrimidine dimers in human skin in vivo: An immunohistochemical analysis of both epidermis and dermis

It is web known that UV exposure of human skin induces DNA damage, and the cumulative effect of such repeated damage is an important contributor to th e development of skin cancer. Here, we demonstrate UV dose- and time-depend ent induction of DNA damage in the form of cyclobutane pyrimidine dimers (C PD) in skin cells following a single exposure of human skin to UV radiation . CPD+ cells were identified by an immunohistochemical technique using mono clonal antibodies to thymine dimers, The percentage of CPD+ cells was UV do se-dependent, even a suberythemal (0.5 minimal erythemal dose [MED]) dose r esulted in detectable level of cells that contained pyrimidine dimers. Fort y-eight hours after irradiation the percent of total epidermal cells positi ve for CPD ranged from 19 +/- 8, 36 +/- 10, 57 +/- 12 and 80 +/- 10, and to tal percent dermal cells positive for (SPD ranged from 1 +/- 1, 7 +/- 3, 16 +/- 3 and 20 +/- 5, respectively, following 0.5, 1.0, 2.0 and 4.0 MED, CPD were also observed in deeper reticular dermis, which suggest the penetrati ng ability of UV radiation into the skin, The change in CPD+ cells from 0.5 to 240 h post-UV exposure in both epidermal and dermal compartments of the skin was also quantitated, CPD+ cells were observed in skin biopsies at ea rly time points after UV exposure which remained elevated for 48 h, then de clined significantly by 3 days post-UV. A close examination of the skin at and after 3 days following UV exposure indicates the significant removal of DNA damaged cells from the epidermis. Ten days after UV exposure the level s of CPD+ cells in both epidermis and dermis were not significantly differe nt from that in unirradiated skin.