However, no significant differences in the expression levels of CTLA4 [36.36 (28.29–42.95) % vs. 40.40 (27.40–54.00) %; p > 0.05], GITR [51.52 (32.35–61.85) % vs. 35.92 (27.18–61.66) %; p > 0.05] or ICOS [40.74 (26.86–47.78) % vs. 44.96 (35.15–51.90) %; p > 0.05] were identified between CD4+CD25−Foxp3+ T cells and CD4+CD25+Foxp3+ Treg cells in RA patients. Here, ICOS is linked to rheumatoid arthritis.