PRTN3 and rheumatoid arthritis: To investigate presence of CPP3+ B cells in the circulation and joints of RA patients, we next analyzed in-house generated mAbs derived from single peripheral blood (PB) (n=36) and synovial fluid (n=139) plasma and memory B cells of 11 ACPA+ RA patients, including 13 CCP2+ clones (30, 31, 33), (Supplementary Table 7).