PRTN3 and rheumatoid arthritis: Fc/2 portions obtained from IgG fractions, i.e., total IgG from plasma, total IgG from SF, ACPA IgG from plasma, and ACPA IgG from SF, were characterized by a recently developed nanoscale RP HPLC‐MS approach.[38] Eleven RA patients were investigated, whose characteristics are summarized in Table S1 (Supporting Information).