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

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Abstract
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/cm2 (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.