Figure 1: Mechanism(s) of suppression: illustrates various molecular and cellular mechanisms to explain how Tregs can suppress host immune responses. (a) In contact dependent mechanism the costimulatory molecules, namely, CD80/86, interact with CTLA-4 to trigger immunosuppressive signals on T effector cells leading to subtle effector cell function. (b) In contact dependent mechanism, CD80/86 expressed in APC interact with CTLA-4 leading to consequential signalling and activation of IDO leading to immunosuppressive effects. (c) The crosstalk of TGFß expressed in APC to TGFß II receptor leads to immunosuppressive cytokine-mediated suppressor function.