PRTN3 and rheumatoid arthritis: Taking 0.05 as a cut-off for background reactivity (dotted blue line in Fig. 6E), RA patient ACPA reacted best with citrullinated MYH9-R867 and MYL6-R94 peptides, while only a few patients reacted with citrullinated MYH9-R1888, MYH9-R1912, or MYL12A-R132 (Fig. 6E).