CD25+but not CD25- regulatory T cells (Tregs) expanded from systemic lupus erythematosus (SLE) patients suppressed T cell proliferation. Standardized aliquots of peripheral blood mononuclear cells (PBMCs) were cultured for six days in the presence of standardized Tregs (a), CD25+ (c, e) or CD25- (d, f) Tregs expanded in vitro from the PBMCs of SLE patients in the presence of transforming growth factor beta (TGFβ) and retinoic acid (RA). (c-d) and (e-f) CD25+ and CD25- Tregs were obtained from a same patient. Representative profiles of the CD8+ PBMC proliferation in the presence of CD25+ Tregs at the indicated dilutions are depicted (b). A varying amount of suppression was mediated by the CD25+ population, while the CD25- population showed either no effect (top) or appeared to promote proliferation (bottom). These data are representative of six patients prepared in three independent experiments.