CD28 and rheumatoid arthritis: For example, AFF3, CCR6, CCL21, IL2RA, and CD28 are associated with ACPA+ RA susceptibility but not with ACPA− RA, whilst markers at TNFAIP3, C5orf30, STAT4, ANKRD55, BLK, and PTPN22 are associated with both serotypes [62].