Many studies that took place after discovery of regulatory T (Treg) cells have widened our, still incomplete, knowledge about that specialized cell population. Treg cells differentiate mainly in the thymus, but this process occurs also in the periphery. They suppress proliferation of other cells (CD4, CD8, B lymphocytes, NK) in direct, cell to cell, interactions in vitro and therefore are main controllers of the proper immune response. Deficiency as well as functional dysregulation of this population may be responsible for development of autoimmune events.

Recent studies have underscored the importance of regulatory T cells (Treg) in the maintenance of immunological self-tolerance and in the prevention of autoimmune diseases. Regulatory T cells is heterogenic subpopulation of T cells, that is able to suppress functions of effector cells during the immune response. Among them are natural (CD4+CD25+) and induced Treg (Tr1, Th3, CD4+CD25-) that gain their unique fenotype during the development in the thymus or in the periphery, respectively.