Effect of UVB on Alloactivating and Antigen Presenting Capacity of Human Epidermal Langerhans Cells

Human epidermal cell suspensions (EC) were obtained by the suction blister technique and enzyme digestion. EC were irradiated in microtitre plates with doses up to 510 mJ/cm 2 (2.6 minimal erythemal dose (MED)) by means of fluorescent light bulbs emitting a 280‐320 nm continuous spectrum with a peak at 310 nm. Purified allogeneic T cells were added to the EC immediately or 24 h after radiation. Irradiated EC were pulsed with purified protein derivative (PPD) for 90 min immediately or 24 h after radiation and then cocultured with purified autologous T cells. PPD‐pulsed EC were also irradiated before being cocultured with autologous T cells. Pretreatment of EC suspensions with anti‐DR antiserum plus complement abolished both the alloactivating and the antigen‐presenting capacity, indicating that the DR‐positive Langerhans cells are mainly responsible for these functions. There were no differences in the number of DR‐positive cells in EC before or immediately after radiation. A statistically significant and UV‐dose‐dependent reduction of the alloactivating ability of EC was found both when allogeneic T cells were added immediately and when they were added 24 h after radiation. Likewise, a significant and dose‐dependent reduction of the PPD‐specific T‐cell response was obtained in cultures when using irradiated EC that were PPD‐pulsed immediately or 24 h after radiation. EC that were first PPD‐pulsed and then irradiated induced a significantly increased T‐cell response after low UV doses (1 or 2 MED), whereas higher doses induced a significant reduction of the T‐cell responses.