Role of Ros and HMGB1 In Contact Allergen-Induced IL-18 Production in Human Keratinocytes

Keratinocytes play a key role in all phases of allergic contact dermatitis. We have recently identified the possibility to use IL-18 production for the in vitro identification of contact allergens. The purpose of this study was to characterize the molecular mechanisms underlying allergen-induced IL-18 production, in order to identify the cellular source of ROS and the danger signals involved. The NCTC2544 was exposed to three contact allergens, namely PPD, 2,4-dinitrochlorobenzene and citral in the presence or absence of diphenylene iodonium (DPI), allopurinol and rotenone to identify the source of ROS, and to anti-TLR4 antibody and glycirrizic acid to characterize the DAMPs. In the case of PPD, the induction of IL-18 can be modulated by rotenone, allopurinol and DPI. In the case of DNCB, rotenone completely prevents the induction of IL-18 while for citral DPI completely prevents the induction of IL-18. We demonstrated the ability of all allergens tested to induce the release of HMGB1 (high-mobility group protein B1). Its sequester by glycirrizic acid significantly modulate PPD-induced IL-18 production and completely prevents DNCB and citral-induced IL-18. We found that different intracellular source of ROS are triggered by contact allergens and an important role for HMGB1 in chemical allergen-induced IL-18 production was demonstrated.