Cytokines and T cells in atopic dermatitis

Atopic dermatitis (AD) is an inflammatory disorder of the skin characterized by an impaired immune response. Several effector T cell subsets, such as pro-inflammatory cells like Th9, Th17 and Th22 cells, expressing high levels of IL-9, IL-17 and IL-22, together with the anti-inflammatory, immuno-modulating Treg cells constitutively producing IL-10, seem to play a role in this condition. IL-9 and IL-9 receptors are significantly increased in lesional AD skin compared to normal control skin. In addition, some polymorphisms in IL-9 and IL-9r genes have been associated with AD. The role of IL-17 and IL-17-producing T cells remains under debate and conflicting data are available. IL-22-producing T-cells seem to correlate with the severity of the AD. The number and function of Treg cells, producing IL-10, have been widely investigated in AD with conflicting results. Other studies suggest that high levels of IL-31 or low levels of IL-21 might be involved in the pathogenesis of AD. This review was undertaken in order to provide a better understanding of the relevance of certain cytokines in AD. We have analysed the new insight into the pathogenesis of AD, with special attention to those cytokines produced by the different T cell subpopulations.