The third key event 3 (KE3) in the skin sensitisation AOP relates to dendritic cell activation and refers to the absolute requirement for a sensitising material to bind to and activate local dendritic cells. This ‘effector’ step then facilitates the activation of allergen-reactive T cells within lymph nodes, leading to T cell proliferation (KE4 of the AOP) and the establishment of a sensitised response.

Using OECD 442E h-CLAT, we are able to quickly assess with chemicals, mixtures or formulations that have the ability to activate dendritic cells, enabling chemical safety assessments to be performed under this AOP.

The OECD 442E h-CLAT assay investigates key event 3 of the skin sensitisation adverse outcome pathway – dendritic cell activation. Utilising the monocytic THP-1 cell line, the ability of a test substance to increase expression of CD54 & CD86 cell surface markers is assessed by flow cytometry. Upregulation of these cell surface markers is associated with dendritic cell activation and leads to the stimulation of an immune response required for sensitisation of the skin to the test substance.

When used in combination with the OECD 442C DPRA and OECD 442D KeratinoSens™ assays, the skin sensitisation AOP can be assessed from molecular initiating (DPRA) to Key stage 3 entirely without the use of animals

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