Abstract
In this study, the effect of ultraviolet-B (UVB) radiation on antigen-presenting function was studied, to investigate whether antigen-presenting cells (APC) are inhibited by UVB through a common mechanism. Two types of human APC were used: EBV-B cells and monocytes, and these were irradiated in vitro with single low doses of UVB (range 0-200 J/m2). Irradiation of EBV-B cells or monocytes resulted in similar dose-dependent reduction in APC function, when determined by the allogeneic mixed leucocyte reaction (MLR) or Candida albicans- or tetanus toxoid-specific T cell response. Our study shows that the reduced APC function was not likely to be caused by alterations in antigen processing or cytokine production. However, UVB-irradiated APC displayed marked changes in adhesion molecule expression. Irradiated EBV-B cells showed reduced expression of ICAM-1 (30%), LFA-3 (25%) and B7-1 (35%), while expression of HLA-DR, CD19 and LFA-1 was not affected. UVB irradiation of monocytes did result in reduction in the expression of HLA-DR (30%), LFA-3 (40%), ICAM-1 (65%) AND B7-1 and B7-3 (90%), but had no effect on CD14, LFA-1 and ICAM-3 expression. Addition of non-irradiated cells (but not the supernatant of these cells) or CD28 antibodies partly restored T cell activation, indicating that UVB-induced reduction in APC function is at least partly mediated via impairment of co-stimulatory molecule expression.