[Pathomechanisms of the elicitation phase of allergic contact dermatitis]

Allergic contact dermatitis (ACD) is a T-cell mediated, antigen-specific inflammatory response to repeated epicutaneous exposure to haptens. Two immunologically distinct sequential steps are required to produce the clinical picture of ACD. In the sensitization phase, naïve antigen-specific T cells are primed and differentiate into memory or effector T cells. In the elicitation phase, reapplication of the same hapten leads to local recruitment of hapten-specific T cells which are cytotoxic, release cytokines and recruit other inflammatory cells. These events lead to clinically visible tissue inflammation characterized by edema, erythema, scaling, and blistering. For the clinician, the effector phase is especially important, because sensitization is generally asymptomatic, whereas elicitation produces the clinical picture of ACD. Detailed knowledge about the mechanisms of the elicitation phase of ACD is needed in order to develop novel therapeutic approaches.