Treg suppress immune responses through molecular pathways that act directly on T cells or indirectly through antigen-presenting cells such as dendritic cells. These molecular mechanisms are described in Table 1. FGL2 binds to FcγRIIB on dendritic cells to inhibit dendritic cell maturation. DC, dendritic cell; IL-2R, IL-2 receptor; Teff, effector T cell; Treg, regulatory T cell.