Structure of Y27 and its effect on CD4+CD25+ regulatory T (Treg) cells. (A) Structure of Y27. (B) Structure of H1521. (C) Y27 concentration-dependent enhancement of the suppressive capacity of CD4+CD25+ Treg cells in C57BL/6 mice in vitro. Suppressive activity of CD4+CD25+ Treg cells was expressed as percent suppression calculated as following: 100 × (cpm (CD4+CD25- Tconv) - cpm (CD4+CD25- Tconv + CD4+CD25+ Treg))/cpm (CD4+CD25- Tconv). Tconv, conventional CD4+CD25- effector T cells.