NCTC 2544 and IL-18 production: a tool for the identification of contact allergens

Progress in understanding the mechanisms of skin sensitization, provides us with the opportunity to develop in vitro tests as an alternative to in vivo sensitization testing. Keratinocytes play a key role in all phases of skin sensitization. We have recently identified interleukin-18 (IL-18) production in keratinocyte as a potentially useful endpoint for determination of contact sensitization potential of low molecular weight chemicals. The aim of the present article is to further exploit the performance of the NCTC 2544 assay. NCTC 2544 is a commercially available skin epithelial-like cell line originating from normal human skin, which posses a good expression of cytochrome P450-dependent enzymatic activities. Cells were exposed to contact allergens (2-bromo-2-bromomethyl glutaronitrile, cinnamaldehyde, citral, diethylmaleate, dinitrochlorobenzene, glyoxal, 2-mercaptobenzothiazole, nickel sulfate, 4-nitrobenzylbromide, oxazolone, penicillin G, resorcinol, tetramethylthiuram disulfide), to pre- pro-haptens (cinnamyl alcohol, eugenol, isoeugenol, p-phenylediamine), to respiratory allergens (ammonium hexachloroplatinate, diphenylmethane diisocyanate, glutaraldehyde, hexamethylenediisocyanate, maleic anhydride, trimellitic anhydride) and to irritants (benzaldehyde, cholorobenzene, diethylphtalate, hydrobenzoic acid, lactic acid, octanoic acid, phenol, salicylic acid, sodium lauryl sulphate, sulfamic acid). Cell associated IL-18 was evaluated 24 later by ELISA. At not-cytotoxic concentrations (cell viability higher of 80%, as assessed by MTT reduction assay), all contact sensitizers, including pre-pro-haptens, induced a dose-related increase in IL-18, whereas both irritants, with the exception of sulfamic acid, and respiratory allergens failed. A total of 33 chemicals were tested, with an overall accuracy of 97%. Overall, results obtained indicated that cell-associated IL-18 might provide an in vitro tool for identification and discrimination of contact vs. respiratory allergens and/or irritants.