PDCD1 and rheumatoid arthritis: RA is one of the most common and the typical representative of autoimmune diseases, characterized by synovial tissue inflammation and progressive destruction cartilage, which is one of the strongest predictors of long-term outcome and disability in RA patients.[26,27] Environmental and genetic factors participate in the pathogenesis of RA.[28,29] Recently, studies have focused on the identification of genes that influenced the susceptibility to this disease, among them was PDCD1, which was an important negative regulator of autoimmunity.