Photoactivation and binding of photoactive chemicals to proteins is a known prerequisite for the formation of\r\nimmunogenic photoantigens and the induction of photoallergy. The intensive use of products and the availability of new\r\nchemicals, along with an increasing exposure to sun light contribute to the risk of photosensitizing adverse reactions.\r\nDendritic cells (DC) play a pivotal role in the induction of allergic contact dermatitis. Human peripheral blood monocyte\r\nderived dendritic cells (PBMDC) were thus perceived as an obvious choice for the development of a novel in vitro\r\nphotosensitization assay using the modulation of cell surface protein expression in response to photosensitizing agents. In\r\nthis new protocol, known chemicals with photosensitizing, allergenic or non-allergenic potential were pre-incubated with\r\nPBMDCs prior to UVA irradiation (1 J/cm2). Following a 48 h incubation, the expression of the cell surface molecules CD86,\r\nHLA-DR and CD83 was measured by flow cytometry. All tested photosensitizers induced a significant and dose-dependent\r\nincrease of CD86 expression after irradiation compared to non-irradiated controls. Moreover, the phototoxicity of the\r\nchemicals could also be determined. In contrast, (i) CD86 expression was not affected by the chosen irradiation conditions,\r\n(ii) increased CD86 expression induced by allergens was independent of irradiation and (iii) no PBMDC activation was\r\nobserved with the non-allergenic control. The assay proposed here for the evaluation of the photoallergenic potential of\r\nchemicals includes the assessment of their allergenic, phototoxic and toxic potential in a single and robust test system and\r\nis filling a gap in the in vitro photoallergenicity test battery.
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