Test No. 442D: In Vitro Skin Sensitisation

The present Key Event based Test Guideline addresses the human health hazard endpoint skin sensitisation, following exposure to a test chemical. Skin sensitisation refers to an allergic response following skin contact with a tested chemical, as defined by the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS). This Test Guideline is proposed to address a Key Event leading to skin sensitisation, namely keratinocyte activation. This Key Event on the Adverse Outcome Pathway (AOP) leading to skin sensitisation takes place in the keratinocytes and includes inflammatory responses as well as gene expression associated with specific cell signalling pathways such as the antioxidant/electrophile response element (ARE)-dependent pathways. This Test Guideline provides five in vitro test methods addressing the same Key Event on the AOP for skin sensitisation: (i) the ARE-Nrf2 luciferase KeratinoSens™ test method, (ii) the ARE-Nrf2 luciferase LuSens test method, (iii) the two Epidermal Sensitisation Assays – EpiSensA and the Epi2SensA, and (iv) the ARE‑Nrf2 luciferase α‑Sens test method. The KeratinoSens, the Lusens and the α‑Sens are in vitro ARE-Nrf2 luciferase-based test methods, while the EpiSensA and Epi2SensA are based on gene expression quantification using Reverse Transcription- quantitative PCR in reconstructed human epidermis models. The proposed test methods are used for supporting the discrimination between skin sensitisers and non-sensitisers in accordance with the UN GHS. Performance standards have been developed to enable the validation of similar test methods.