SOLAR-SIMULATED ULTRAVIOLET-IRRADIATION INDUCES SELECTIVE INFLUX OF CD4(-LYMPHOCYTES IN NORMAL HUMAN SKIN() T)

The proportion and composition of the human cutaneous CD3(+) T lymphoc yte population was determined in situ following a single exposure to p hysiological, erythema-inducing doses of simulated solar radiation, ma inly consisting of UV radiation, Biopsies were taken 1, 2 and 7 days a fter local irradiation of normal volunteers with 1, 2 and 4 MED by a x enon-arc lamp and immunohistochemistry was performed on cryostat secti ons Ultraviolet radiation caused an initial decrease of intraepidermal CD3(+) T-cell numbers or even could lead to T-cell depletion 24 and 4 8 h postirradiation, and this was followed by an infiltration of T cel ls in the epidermis as determined 1 week after UV exposure. The number of dermal CD3(+) T cells was increased 24 h after irradiation, reache d a maximum at 48 h and subsequently declined at day 7, though remaine d significantly higher than the unirradiated control. Double staining demonstrated that the CD3(+) T cells, which immigrated into the (epi)d ermis upon UV exposure, coexpressed CD4 but not CD8. Therefore the CD4 /CD8 ratio in skin was markedly increased during the first week upon U V exposure. Our time course study shows that UV radiation affects the T-cell population within human skin by depleting the majority of epide rmal T cells and initiating a selective influx of CD4(+) T cells.