CD4 and rheumatoid arthritis: It has been proposed that the onset and pathogenesis of RA critically depends on the balance between two distinct CD4+ T cell subsets: type 17 helper T (TH17) cells, a pathogenic subset of CD4+ T cells that produces IL-17, and thereby promoting osteoclastogenesis, and Treg cells, crucial for the prevention of autoimmune diseases driven by TH17 cells (34, 44).