CD4 and rheumatoid arthritis: In addition, it was shown that Trx1 expression and secretion is higher in human Tregs compared with other CD4-postive T cells.48 As the RA synovium is enriched with CD4+ CD25+ Tregs,49 a Trx1 secretion by these cells might enhance the survival of autoreactive synovial fluid T cells owing to inhibition of apoptosis by Trx1.