Regulation of CD4+CD25+ regulatory T cell activity: it takes (IL-)two to tango.
Although CD4(+)CD25(+) regulatory T cells (Treg) represent a well-characterized population of T cells with in vitro and in vivo suppressive capacity, the basic mechanisms of suppression are still not understood. The constitutive expression of the high-affinity receptor for IL-2 has raised the question about the role of IL-2 in Treg function. Here, we review recent data indicating that IL-2 is not only necessary for the homeostasis of Treg but is also critical for the activation of Treg function. Since Treg do not produce IL-2 by themselves, their capacity to utilize IL-2 secreted by other T cells appears to be an essential component of Treg biology. This indicates that Treg suppressive activity is controlled by interaction with activated target cells via the soluble mediator IL-2. In Treg, IL-2 has been identified as a potent inducer of the immunosuppressive cytokine IL-10, an important mediator of Treg suppression in vivo. The efficient capture of IL-2 by Treg may, under conditions of limited IL-2 supply, cause IL-2 deprivation of responder T cells. This competition can explain some of the currently discussed discrepancies between in vivo and in vitro activity of Treg.
Scheffold
Alexander
A
Deutsches Rheuma-Forschungszentrum Berlin, Berlin, Germany. scheffold@drfz.de
Hühn
Jochen
J
Höfer
Thomas
T
D000818:Animals; D015704:CD4 Antigens / Q000276:immunology*; D002450:Cell Communication / Q000276:immunology; D006801:Humans; D007376:Interleukin-2 / Q000276:immunology*; D008213:Lymphocyte Activation / Q000276:immunology*; D018448:Models, Immunological; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
D015704:CD4 Antigens; D007376:Interleukin-2; D015375:Receptors, Interleukin-2