Mechanisms of Foxp3+ T Regulatory Cell-Mediated Suppression

Foxp3(+) T regulatory (Treg) cells control all aspects of the immune response. Here, I will review the in vitro model systems that have been developed to define the mechanisms used by Treg cells to suppress a large number of distinct target cell types. These mechanisms can be broadly divided into those that target T cells (suppressor cytokines, IL-2 consumption, cytolysis) and those that primarily target antigen-presenting cells (decreased costimulation or decreased antigen presentation). Although multiple mechanisms for Treg cell suppression have been shown in vitro, it is unclear whether the same or different mechanisms are used by Treg cells in vivo. An increase in our understanding of Treg cell suppressor mechanisms will offer an insight into how Treg cell function can be manipulated either positively or negatively in vivo.