The NCTC 2544 IL-18 assay for the in vitro identification of contact allergens.

Assessment of allergenic potency of low-molecular-weight compounds is generally performed using animal models, such as the murine Local Lymph Node Assay (LLNA) and the Guinea Pig Maximization Test (GMT). Progress in understanding the mechanism of skin sensitization, including effects on the production of cytokines by different cell types within the skin, provides the opportunity to develop in vitro tests as an alternative to in vivo sensitization testing. This unit will describe a method for differentiating contact allergens from low-molecular-weight respiratory allergens and irritants, based on the selective induction of intracellular interleukin 18 (IL-18) in the human keratinocyte cell line NCTC 2544. Similar results could also be obtained using primary human keratinocytes or other human keratinocyte cell lines, e.g., HaCaT, HPKII, etc. IL-18 was chosen because this cytokine has been demonstrated to favor Th-1-type immune responses by enhancing the secretion of pro-inflammatory mediators such as TNF-α, IL-8, and IFN-γ, and to play a key proximal role in the induction of allergic contact dermatitis.