The role of regulatory T cells in multiple sclerosis

The dysregulation of inflammatory responses and of immune self-tolerance is considered to be a key element in the autoreactive immune response in multiple sclerosis (MS). Regulatory T (T(REG)) cells have emerged as crucial players in the pathogenetic scenario of CNS autoimmune inflammation. Targeted deletion of T(REG) cells causes spontaneous autoimmune disease in mice, whereas augmentation of T(REG)-cell function can prevent the development of or alleviate variants of experimental autoimmune encephalomyelitis, the animal model of MS. Recent findings indicate that MS itself is also accompanied by dysfunction or impaired maturation of T(REG) cells. The development and function of T(REG) cells is closely linked to dendritic cells (DCs), which have a central role in the activation and reactivation of encephalitogenic cells in the CNS. DCs and T(REG) cells have an intimate bidirectional relationship, and, in combination with other factors and cell types, certain types of DCs are capable of inducing T(REG) cells. Consequently, T(REG) cells and DCs have been recognized as potential therapeutic targets in MS. This Review compiles the current knowledge on the role and function of various subsets of T(REG) cells in MS and experimental autoimmune encephalomyelitis. We also highlight the role of tolerogenic DCs and their bidirectional interaction with T(REG) cells during CNS autoimmunity.