Regulatory T cells in autoimmune disease.

In recent years, the understanding of regulatory T cell (T cell) biology has expanded considerably. Key observations have challenged the traditional definition of T cells and have provided insight into the underlying mechanisms responsible for the development of autoimmune diseases, with new therapeutic strategies that improve disease outcome. This Review summarizes the newer concepts of T cell instability, T cell plasticity and tissue-specific T cells, and their relationship to autoimmunity. Those three main concepts have changed the understanding of T cell biology: how they interact with other immune and non-immune cells; their functions in specific tissues; and the implications of this for the pathogenesis of autoimmune diseases.