Allergic contact dermatitis (ACD) is a delayed hypersensitivity response that is one of the most prevalent types of hypersensitivity reactions experienced by humans, especially in terms of allergy to metals. Key to the underlying biology responsible for this adverse skin reaction is the activation of allergen-specific T-lymphocytes. Metals and other chemicals can stimulate T-cells directly via drug specific receptors or, most generally, by a mechanism that is dependent upon antigen presenting dentritic cells. Allergen specific, reactive T-cells clones expand by proliferating and produce pro-inflammatory cytokines. The relative degree of immune reactivity, or activation, can be measured experimentally ex vivo by use of the lymphocyte transformation test (LTT).
Nyfeler and Pichler (1997) and Popple and coworkers (2016) defined the LTT as an experimental recall assay in which allergen-reactive memory T-lymphocytes obtained from the peripheral blood of sensitized (allergic) individuals are re-stimulated in vitro with relevant allergen to provoke a specific response. The basic assay design is outlined below:
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