Regulatory T cells are a heterogeneous subset of CD4+ T cells with suppressive properties that play a central role in maintaining CD4+ and CD8+ effector T cells, natural killer cells, NKT cells, and antigen-presenting cells through multiple mechanisms including the secretion of immunosuppressive cytokines (IL-10, IL-35, and TGF-b) and metabolites (Adenosine), production of cytolytic factors (Granzymes A/B and Perforin), disruption of cell metabolism (i.e. IL-2 deprivation), and suppression of effector functions through direct cell-cell contact.
Several subsets of regulatory T cells exist. These include naturally occurring CD4+CD25+FoxP3+ cells that develop in the thymus, peripherally-derived regulatory T cells that are generated from FoxP3- conventional T cells at sites outside of the thymus, and induced regulatory T cells that are generated in vitro by stimulation of mouse conventional T cells with TGF-b.
Cells in the peripheral group have been further classified as either central regulatory T cells, effector regulatory T cells, or tissue-resident regulatory T cells. Additionally, CD4+FoxP3− type I regulatory T cells (Tr1), CD8+ regulatory T cells, and follicular regulatory T cells (TFR) have been described. Characteristics that distinguish these subsets as well as differences in their development and functional activity are active areas of investigation.
There are several mechanisms by which regulatory T cells control the activity of other immune cells types. These include:
Click on the images below to find out more about other immune cell types.