REL and rheumatoid arthritis: We also aimed to test whether HLA-DRB1 and other five selected RA susceptibility genes may influence the response to anti-TNF treatment—that is, potential associations between anti-TNF treatment response and risk RA loci related with NF-kB signaling pathway (TRAF1/C5, TNFAIP3, and REL), citrullination (PADI4), and the genetic variants inside the MHC (HLA-DRB1*04 high-resolution (4-digit) genotyping) and outside the MHC (PTPN22 locus) with the strongest association with RA risk.