The same epitope is recognized by citGRP78 antibodies in RA as peptide P23 [41], confirming that the N-terminal region of GRP78 is a target of PAD enzymes, leading to citrullination and autoantigenicity of the same epitopes both in RA [44] and T1D [74], resulting from dysfunctions of the ER common to both autoimmune diseases. Here, PADI4 is linked to rheumatoid arthritis.