New insights into T cells and their signature cytokines in atopic dermatitis

An imbalance of the adaptive immune system mediated by various T cells plays a pivotal role in the pathogenesis of atopic dermatitis (AD). Traditionally, sustained exposure of pathogens tailors immune responses and drives the development of specialized T helper (Th) 2-bias cytokine environment. The increasing understanding of T cell biology has refreshed the roles of classical Th2 responses and regulatory T cells in the development of AD. In particular, the identification of novel CD4(+) T cell subsets such as Th9, Th17, and Th22 cells provide further interpretation of immunological mechanisms underlying AD. In this report, we reviewed the functional roles of CD4(+) T cell subsets and their derived signature cytokines in AD. We focused on important discoveries of the contribution of CD4(+) T cell cytokines to immunomodulation in AD, and particularly, highlighted the multiple consequences of immune dysregulation on the barrier defect of the skin. We subsequently discussed the flexibility and plasticity of these T cells in vivo in terms of cytokine production. T cells involved in innate immunity were also mentioned. Taking the pivotal and varied roles of T-cell subpopulations and the functional cytokine milieus into account, T cell targeting therapy may thus open up new opportunities for mechanism-based therapeutic intervention.