PDCD1 and rheumatoid arthritis: This gene not only plays an important role in the regulation of the induction and maintenance of T cell tolerance, but also inhibits effector T cell responses and protects tissues from autoimmune-mediated tissue damage.[8,10,11] Therefore, it is considered to be a strong candidate gene responsible for autoimmune diseases, especially for RA.[22] As indicated, PDCD1 gene polymorphisms are associated with autoimmune disorders, such as SLE,[29] T1D,[30] and AS[31] (one of our previous studies).