The median proportion of Treg cells (in CD4+ cells) in PB and SF of RA patients was 6.38% [interquartile range (IQR) 4.43–7.75%] and 7.71% (IQR 4.84–11.68%), respectively, and the median in PB of HC was 4.66% (IQR 2.91–5.90%). This evidence concerns the gene CD4 and rheumatoid arthritis.