NCTC 2544 and IL-18 production: a tool for the in vitro identification of photoallergens

Differentiation between photoallergenic and phototoxic reactions induced by low molecular weight compounds represents a current problem. The use of keratinocytes as a potential tool for the detection of photoallergens as opposed to photoirritants is considered an interesting strategy for developing in vitro methods. We have previously shown that IL-18 production in the human keratinocyte cell line NCTC 2455 is a good model for the in vitro identification of contact sensitizers. The purpose of this manuscript is to summarize data obtained in the NCTC 2544 assay as an in vitro model to identify photoallergens and discriminate them from phototoxic chemicals. METHODS: The effect of UVA radiation (3.5J/cm(2)) over NCTC 2544 cells irradiated and non irradiated, and treated with increasing concentrations of various compounds including negative compounds (irritants and allergens), ibuprofen and acridine (photoirritants); ketoprofen, promethazine and chlorpromazine (photoirritants/photoallergens); benzophenone, 4-tert-butyl-4-methoxy-dibenzoylmethane, 2-ethylexyl-p-methoxycinnamate and 6-methylcumarin (photoallergens) was investigated. Twenty-four hours after exposure, cytotoxicity was evaluated by the MTT assay, while a commercially available ELISA kit was used to assess the intracellular content of IL-18. RESULT: At no cytotoxic concentrations, allergens and photoallergens induce a dose-related increase in the production of IL-18, whereas irritants and photoirritants failed, indicating the possibility to use the NCTC 2544 assay to identify in vitro photoallergens.