FOXP3 and rheumatoid arthritis: The expression of Helios [58.52 (50.70–63.42) % vs. 76.18 (72.28–80.39) %; p < 0.001] on CD4+CD25−Foxp3+ T cells was significantly lower than that on CD4+CD25+Foxp3+ Treg cells in the RA group.