The pathogenesis of chronic inflammatory diseases is assumed to depend on activated T
cells interacting with resident tissue cells or migratory inflammatory cells. The discovery of
new T-cell subsets such as the IL-17–producing TH17 and T-regulatory cells innovated our
understanding of T-cell biology. Studies on new subsets confirm the important role of T cells
in the instruction of tissue cells and also demonstrate the important role of feedback
regulation for the polarization toward distinct T-cell subsets. The understanding of IL-17 and …