CD4 and rheumatoid arthritis: Rheumatoid arthritis (RA) is an autoimmune disease of unknown etiology, and one of the major causes of its development is a decrease in the ability of Treg to block the production of interferon γ (IFN ⁃ γ) and tumor necrosis factor α (TNF ⁃ α) by CD4 + CD25 + T cells (37).