Contact dermatitis and danger models

Conventional models of the immune response are based on distinguishing self and non‐self. However, the more recently proposed ‘danger’ model may be an illuminating alternative for studying allergic contact dermatitis. In the presence of a ‘danger’ signal, which in some cases of allergic contact dermatitis could be cutaneous ‘irritancy’(ie cytokine release from non‐immune/keratinocyte cells in response to chemical stimulus in a non‐sensitising manner), the immune system would become activated, leading first to the induction of sensitisation and then subsequently to the elicitation of a contact hypersensitivity response. In most cases both the antigenic signal and signal for keratinocyte cytokine release will come from the hapten, although for example in an occupational setting, traumiterative dermatitis would be the source of the “danger” signal. A further prediction of this hypothesis is that reported animal experiments demonstrating low dose tolerance with contact allergens may be explained by the loss of the ‘irritant’ effect at lower dilutions whilst an antigenic stimulus remains present.