Selective induction of interleukin-12 in reconstructed human epidermis by chemical allergens

Keratinocytes play an important role in skin inflammatory and immunological reactions through the release of cytokines and response to them. These cells have been shown to direct T-cell priming by producing cytokines such as interleukin (IL)-10 and IL-12. The purpose of this work was to explore the potential use of IL-12 production to discriminate between skin irritants and contact allergens in vitro. Initially, a reconstituted human epidermis was treated with a known human skin irritant, sodium lauryl sulphate (SLS), and a known human contact allergen, 1-chloro-2,4-dinitrobenzene (DNCB). The expression of IL-12p40 was assessed at specific time intervals by the semi-quantitative reverse transcriptase-polymerase chain reaction (rt-PCR). The data obtained indicated that only DNCB induced an up-regulation of IL-12p40. This up-regulation occurred after exposure to DNCB for 3 hours. Importantly, the application of SLS or vehicles did not induce IL-12 mRNA up-regulation. An increase in total IL-12 protein content was detected in supernatants of allergen-stimulated, but not vehicle-stimulated, reconstituted epidermis. To confirm these results, the effects of benzalkonium chloride, oxazolone and eugenol were assessed. At concentrations that resulted in equivalent IL-1 alpha release, only contact allergens increased IL-12 expression, which confirmed the previous results. These data suggest that IL-12, which is crucial for T-helper type 1 cell responses, could be a useful marker for discriminating between contact allergens and irritants.