Development of an in vitro photosensitization assay using human monocyte-derived cells

In this study, with the aim of developing a cell-based in vitro photosensitization assay, we examined whether changes of CD86 and CD54 expression on cells of a human monocytic cell line, THP-1, could be used to assess the photosensitizing potential of chemicals. First, we identified suitable conditions of UV-irradiation (irradiation dose; 5.0 J/cm 2, irradiation intensity; 1.7 mW/cm 2) by investigating the effect of UV-irradiation on CD86 and CD54 expression on untreated or 6-methylcoumarin (a representative photoallergen)-treated THP-1 cells (irradiation method). However, acridine, a representative photo-irritant, augmented CD86 and CD54 expression on THP-1 cells, apparently via induction of reactive oxygen species (ROS). In order to abolish the effect of ROS, we examined CD86 and CD54 expression on THP-1 cells treated with pre-irradiated chemicals (pre-irradiation method). We found that UV-irradiated photoallergens, but not photo-irritants, enhanced CD86 and/or CD54 expression on the THP-1 cells. Finally, based on the results of irradiation, non-irradiation, and pre-irradiation with 18 test chemicals, we built a decision tree, which allows us to distinguish between photoallergens and photo-irritants. We suggest that this system may be useful for in vitro evaluation of the photoallergic potential of chemicals.