The proportion of memory Treg (mTreg) cells (in CD4+ cells) in RA PB, RA SF, and HC PB was 4.96 (IQR 3.72–6.48)%, 5.51 (IQR 4.05–8.84)%, and 3.36 (IQR 2.04–4.79)%, respectively. Here, CD4 is linked to rheumatoid arthritis.