Cells were incubated with or without one of the following linear synthetic 15mer TAHR peptides (Supplementary Fig. 1b): 65-79*LE, a TAHR (residues 65-79 of the DRβ chain) encoded by the SLE-risk allele DRB1*03:01; 65-79*SE, a TAHR encoded by a RA-risk allele DRB1*04:01; or 65-79*PE, a TAHR epitope containing a 70-DERAA-74 motif which is shared by alleles (e.g. DRB1*04:02, DRB1*13:01 & DRB1*13:02), known to associate with autoimmune disease protection17–19. Here, HLA-DRB1 is linked to rheumatoid arthritis.