Pathogenetic mechanisms of atopic dermatitis.

Atopic dermatitis (AD) is a chronic inflammatory disease which results from complex interactions between genetic and environmental mechanisms. An altered lipid composition of the stratum corneum is responsible for the xerotic aspect of the skin and determines a higher permeability to allergens and irritants. Keratinocytes of AD patients exhibit a propensity to an exaggerated production of cytokines and chemokines, a phenomenon that can have a major role in promoting and maintaining inflammation. Specific immune responses against a variety of environmental allergens are also implicated in AD pathogenesis, with a bias towards Th2 immune responses. In particular, dendritic cells expressing membrane IgE receptors play a critical role in the amplification of allergen-specific T cell responses. Cross-linkage of specific IgE receptors on dermal mast cells provokes the release and synthesis of a vast series of mediators. Following their recruitment and activation into the skin, eosinophils are also thought to contribute relevantly to tissue damage. Thus, a complex network of cytokines and chemokines contributes to establishing a local milieu that favors the permanence of inflammation in AD skin.