CD4 and rheumatoid arthritis: The OX40/OX40L pathway plays a significant role in the pathogenesis of human autoimmune diseases, including multiple sclerosis (MS) [9], systemic lupus erythematosus (SLE) [10], rheumatoid arthritis (RA) [11], and type 1 diabetes [12], and the expression of OX40 on CD4+ T cells correlates with disease severity in patients with SLE [13, 14].