Deng, W., Oldach, J., Armento, A., Ayehunie, S., Kandarova, H., Letasiova, S., Klausner, M., and Hayden, P. MatTek Corporation, Ashland, MA, USA.

Assessment of the allergic potential of chemicals has traditionally been conducted in animal models such as the local lymph node assay (LLNA). However, recent legislation has prohibited the use of animals for conducting such tests on cosmetics or cosmetic ingredients. Thus, animal alternative tests for contact sensitization are urgently needed. Interluekin-18 (IL-18) secretion has recently been identified as a potentially useful endpoint for determination of contact sensitization potential in keratinocyte monolayer cultures (Naik, SM, et al, J. Invest. Dermatol. 113:766–772, 1999; Corsini, E., et al., Toxicology In Vitro 23: 789-796, 2009). The irritation potential of a chemical may also influence the potency of sensitization abilty. Because epidermal irritation and sensitization are often dependent on chemical penetration and metabolism in the skin, 3D organotypic skin models that possess in vivo-like barrier properties and metabolizing capabilities may provide significant benefits over monolayer culture models for determination of contact sensitization potential. The goal of the current work was to evaluate IL-18 as an endpoint for sensitization potential after topical application of chemicals to the EpiDerm in vitro human skin model. Eleven contact sensitizers and 4 non-sensitizer chemicals were tested based on the chemical set specified by Corsini et al, 2009. A protocol was developed using aqueous or ethanol based vehicles for topical application. Preliminary range-finding experiments were conducted to determine chemical toxicity profiles using the MTT viability assay. Additional doses were then chosen for definitive toxicity and IL-18 secretion experiments. EpiDerm tissue viability and IL-18 secretion by ELISA were evaluated 18-24 hours following topical application of test chemicals. Extreme sensitizers elicited robust IL-18 responses.  Strong, moderate and weak sensitizers also elicited measurable IL-18 responses. Using a cut-off of 2-fold increase of IL-18 above vehicle control, 10/11 contact sensitizers were correctly identified by the IL-18 assay (90.9% sensitivity) with no false positive results (100% specificity). However, nickel and cobalt containing contact allergens were not correctly identified by the IL-18 assay. Thus, the EpiDerm IL-18 assay appears to be a promising tool for in vitro determination of contact sensitization potential.  However additional testing with a larger chemical set will be required to fully evaluate the utility of this assay.


Allergenicity, Allergens, Contact sensitization, EPI-200, EpiDerm, Interleukin-18 (IL-18)

Materials Tested

2,4-Dinitrochlorobenzene (DNCB) , 2-Mercaptobenzothiazole (2-MBT) , 4-Nitrobenzylbromide (4-NBB) , Cinnamaldehyde , Cinnamyl Alcohol , Eugenol , Glycerol , Glyoxal , Isoeugenol , Lactic Acid , Phenol , p-Phenylenediamine (ppd) , Resorcinol , Salicylic Acid , Tetramethylthiranium disulfide (TMTD)

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