Immunochemical detection of cyclobutane thymine dimers in epidermal Langerhans cells of ultraviolet B-irradiated hairless mice.

An immunocytochemical method was developed to study in vivo induction and removal of DNA damage in a specific cell population in the epidermis of hairless mice after ultraviolet B (UVB) exposure: the immunocompetent antigen-presenting Langerhans cells. To this aim, Ia+ cells, which are representative for epidermal Langerhans cells, were compared with the bulk of epidermal cells with respect to the nuclear level of cyclobutane thymine dimers. Mouse Langerhans cells were identified with a membrane-located immunoperoxidase stain, whereas DNA and DNA damage were revealed with fluorescent nuclear stains. After a low dose of UVB (approximately 1 minimal erythema dose), dimer levels were determined both in all murine epidermal cells and in Ia+ cells separately. At 24 h after irradiation, dimer removal was still incomplete, with a persistence of approximately 50% of the initially induced dimers in epidermal cells in general, and of approximately 75% in Langerhans cells. Possible applications of the method developed and the results presented here are discussed in relation to the immunosuppressive effect of UV.