PRTN3 and rheumatoid arthritis: To comprehensively characterize IgG Fc characteristics of RA patients, we expanded on a recently developed workflow to purify and analyze intact Fc subunits of ACPA and total IgG fractions from paired plasma and SF samples.[38] In brief, ACPA and total IgG were purified by antigen‐ or Fc‐specific affinity beads, respectively followed by the release of intact single‐chain Fc subunits (Fc/2) by proteolysis with the protease IdeS (Figure1a).