NCTC 2544 and IL-18 Production: A Tool for the Identification of Contact Allergens

Abstract

This chapter describes the NCTC 2544 assay and its performance in the in vitro evaluation of low molecular weight contact allergens. The NCTC 2544 assay is based on the selective induction of intracellular interleukin-18 (IL-18) by contact allergens in the human keratinocyte cell line NCTC 2544. The assay proved to be useful in the identification and discrimination of contact allergens from respiratory sensitizers and irritants. NCTC 2544 is a commercially available skin epithelial-like cell line originating from normal human skin. Due to their anatomical location, keratinocytes can sense haptens and in turn initiate a program of enhances or de novo expression of inflammatory molecules representing the starting point of primary inflammation. IL-18 has been shown to play a key proximal role in the induction of allergic contact sensitization and to favor Th-1 type immune response. Human keratinocytes constitutively express IL-18 mRNA and protein, and works published showed the induction of IL-18 following exposure to contact sensitizers. The majority of sensitizers so far tested, including pre- and pro-haptens, induced a dose-related increase in IL-18, whereas the majority of irritants and respiratory allergens failed. A total of 47 chemicals were tested with an overall accuracy of 84.4%. The NCTC 2544 assay holds promise. A 96-well format assay was also developed, and the method was also adapted for the assessment of photoallergens. We believe, however, that the release of IL-18 in reconstituted epidermis represents the future of the assay.