T-cell clones generated from both CD4+CD25+ and CD8+CD25+ human thymocytes were assessed for their ability to suppress the proliferative response to allogeneic stimulation of type 1 T-helper (Th1) or type 2 T-helper (Th2) clones derived from autologous CD4+CD25- thymocytes. Both CD4+ and CD8+ T-regulatory (Treg) cells completely suppressed the proliferation of Th1 clones but exhibited significa...