Treg cell subsets are functionally suppressive. (A) Expression of FOXP3 by the indicated Th and Treg cell subsets. Each symbol represents 1 donor; horizontal bars indicate the mean. Data are from 9 donors. (B) Expression of Helios (left) and CTLA-4 (right) by the indicated Th and Treg cell subsets. Data are from 3 or 5 donors. (C) CFSE-labeled CD4⁺CD25⁻ responder T cells were cultured with autologous monocytes plus anti-CD3 (OKT3) in the presence or absence of the indicated sorted Treg cell subset at a 1:1 suppressor/responder ratio. Numbers indicate the frequency of proliferating CFSE^lo T cells after 5 days of culture. Data are representative of 3 independent experiments.