CTLA4 and rheumatoid arthritis: Genes involved in regulating peripheral tolerance were found have effects on the development of RA, such as PTPN22 C1858T (rs2476601) [14], CTLA-4 A49G [15], and PDCD-1 (rs36084323) [16], and PD-L1 6777G was associated with the prevalence of rheumatoid nodules [17].