Regulatory T cells represent unique CD4+CD25+ population of T lymphocytes, which are involved in many immunological events. These cells have very important role in maintaining peripheral tolerance, prevention of autoimmune diseases, in immunological respond to infection, particularly by intracellular microorganisms as well as in a process of tumorogenesiz. There are two populations of regulatory T cells: natural regulatory T cells - nTregs and adaptive, inducible regulatory - iTregs. They differ between each other in accordance to the place of creation, in accordance to the specificity of the T cell receptor, as well as the action mechanism. nTregs and the other T cells arise in thymus, which provides specific inductive environment for maturation and immunological education of progenitor cells to imunocompetent T cells. iTregs arise on periphery from the conventional CD4+ T cells after stimulation by antigen under the different conditions. There is number of subpopulations of iTregs and the most important are Tr1 and Th3 cells. Tr1 cells produce big amounts of interleukin 10 (IL-10), and they are called IL-10-secretory regulatory cells, whereas Th3 cells are necessary for maintenance of peripheral tolerance to mucous surfaces, through their dominant cytokine TGF-â (transforming growth factor-â) and they are most widely spread in the mucosa of the digestive tract. Previous researches have shown that regulatory T cells achieve their suppressor activity via inhibitory cytokines, cytolysis, and induction of metabolic disorders and modulation of maturation or function of dendritic cells.