SLC22A4 and rheumatoid arthritis: There are 19 RA-associated proteins mapped in the PPI network (HLA-DRB1, STAT4, FCRL3, TRAF1, CCL21, CD40, CDK6, PTPN22, SLC22A4, IRF5, CTLA4, TNFAIP3, CCR6, REL, SPRED2, BLK, FAM107A, and IL2RA).