Dendritic cells: biology of the skin.

Allergic contact dermatitis results from a T-cell-mediated, delayed-type hypersensitivity immune response induced by allergens. Skin dendritic cells (DCs) play a central role in the initiation of allergic skin responses. Following encounter with an allergen, DCs become activated and undergo maturation and differentiate into immunostimulatory DCs and are able to present antigens effectively to T cells. The frequency of allergic skin disorders has increased in the past decades. Therefore, the identification of potential sensitizing chemicals is important for skin safety. Traditionally, predictive testing for allergenicity has been conducted in animal models. For regulatory reasons, animal use for sensitization testing of compounds for cosmetic purposes is shortly to be prohibited in Europe. Therefore, new non-animal-based test methods need to be developed. Several DC-based assays have been described to discriminate allergens from irritants. Unfortunately, current in vitro methods are not sufficiently resilient to identify allergens and therefore need refinement. Here, we review the immunobiology of skin DCs (Langerhans' cells and dermal dendritic cells) and their role in allergic and irritant contact dermatitis and then explore the possible use of DC-based models for discriminating between allergens and irritants.