Constitutive activation of human Treg cells. (A) Expression of ICOS (left) and Ki-67 (right) by the indicated Th and Treg cell subsets. Data are from 5 donors. (B) Flow cytometric analysis of ICOS and Ki-67 expression by the indicated Treg cell subsets. Data are representative of 4 donors. *P < .0.05; **P < .01; ***P < .001 (ANOVA).