How many mechanisms do regulatory T cells need?

A plethora of new regulatory T cell (Treg) mechanisms have recently emerged. This raises two important questions. First, how many molecules or mechanisms are required for Treg to work? Second, how should we evaluate the contribution of any given Treg molecule/mechanism and how is this likely to relate (or not) to the phenotype seen in Scurfy/Foxp3-deficient mice? In this discussion piece, I will briefly outline our current understanding of the Treg arsenal and address these important questions.