Regulatory T Cells: Types, Generation and Function

T lymphocytes have been characterized to different subsets such as cytotoxic T، Thelpe 1 (Th1)، Th2، Th3، Th9، Th17، and regulatory T cells. Each of these subsets have specific function which distinct them from other lymphocytes. Regulatory T lymphocytes are effective cells in immune system that play an important role in cancers، autoimmune and infectious diseases. Two main subsets of regulatory T cells (T regs) have been identified: a) naturally occurring T reg cells which are generated during maturation in the thymus and have suppressive activity that is critical for the establishment and maintenance of immune homeostasis in the steady state. b) Induced T reg cells (iT reg) that are produced from naive T cells following self-antigen recognition outside the thymus. The transcription factor Foxp3 has a key role in T reg cell development and function. But the expression of Foxp3 alone is not sufficient for generation and maintenance of T reg cell function and phenotype. T reg cells migrate into both inflammatory sites and draining lymph nodes during an immune response. Multiple mechanisms have been proposed to elucidate how T reg cells suppress effector cells. These mechanisms include the production of inhibitory cytokines (IL-10، TGF-β، and IL-35)، induction of effector cells death by cytokine deprivation (such as IL-2) or cytolysis، local metabolic agitation of target cells، and finally inhibition of dendritic cell functions.