Keratinocytes in atopic dermatitis: inflammatory signals.

Atopic dermatitis (AD) is a chronic inflammatory skin disorder that usually predates the development of allergic airway disease. In most cases, this is thought to be an allergen-driven disease with prominent roles played by antigen presenting cells and effector Th2 cells. But keratinocytes, by virtue of their location, provide an important window to the environment and are also thought to contribute to the development of AD. In this review, we discuss several biologic attributes of keratinocytes that are relevant for AD: 1) intrinsic defects in barrier function, 2) production of inflammatory mediators that promote or maintain allergic inflammation, 3) keratinocyte apoptosis, 4) effects of staphylococcal toxins on keratinocytes, and 5) potential consequences of the expression of cosignaling molecules (eg, B7 family members) and receptors important for innate immune responses (eg, Toll receptors). Clearly, these findings have highlighted a more active role played by the epithelium than was previously recognized.