Allergies are an integral part of our industrial society to such an extent that the OMS has classed them as the 4th important pathology in terms of morbidity. Further to this they have been in constant progression for the past 20 years, such that they have become a prominent threat to public health. Their impact on both the financial cost and quality of life (medicine; hospitalizations; downtime due to sickness) is undeniable. Contact dermatitis can be defined as an inflammatory process affecting the surface of the skin that is induced by contact with chemical, physical and/or biotic agents in the environment, and which lesions the skin, mucosa and semi-mucosa by means of allergic and irritant pathogenic mechanisms. In this context, scientific knowledge of basic mechanisms of allergic and inflammatory reactions in the case of the environmental or professional exposure to any chemical is of paramount importance given the frequency of use of these products in everyday life. This project aims at understanding how chemical reactivity can alter the cellular microenvironment of the skin imposing key decisions on innate or adaptive immune responses to chemicals leading to allergic inflammatory diseases such as allergic contact dermatitis or to irritant contact dermatitis. We believe that chemical depending on their intrinsic reactivity (lysine binding, cysteine binding, cytotoxic potential, redox potential…) can specifically modify the epithelial cell environment providing information to dendritic cells or the release of products that will govern the type and the potency of skin allergic diseases. Our proposal has the objective to identify these key events of chemical interaction with biological process (binding to protein, research of gene biomarkers including non-coding RNAs such as miRNA) and the integration of these events in in vivo mouse models (Local Lymph Node Assay,LLNA; Mouse Ear Swelling Test MEST) using genetically modified strains. Our main deliverables are: to provide new understanding of the mechanism of skin allergy to chemical that can be extended to other tissue (lung), to identify new biomarkers of CHS using a genomic approach in vitro that will be confirmed in vivo and to use this new biomarkers for developing new tools to be integrated in in vitro assays or decision tree for the replacement of animals in chemical sensitizer testing. For fulfilling the objectives, the project has been divided in 6 tasks: Task 1: Reactivity pattern of chemical sensitizers; Task 2: Nrf2 gene expression and role of oxidative stress in dendritic cells in response to chemical sensitizers; Task 3: In vivo and in vitro biological response of skin to sensitizers and irritants using a genomic approach (gene and miRNA expression); Task 4: Measurement of the in vivo response in LLNA and MEST tests (WT and Nrf2 KO mice); Task 5: In vivo analysis of immune response in WT and Nrf2 KO mice; Task 6: Integration and analysis of results: functional model for the sensitizing response and establishment of in vivo and in vitro correlations. The consortium is composed of 5 partners representing different area of expertise: allergy, immunology, toxicology, genomics and chemistry. This consortium has complementary expertise in models addressing questions in vitro and in vivo. The teams are experienced in treating cells with chemicals and are familiar with route of administration of chemicals in animals, practical problems dealing with exposing animals to chemicals but also animal welfare, husbandry and ethics.