Steen J, et al. - Authors estimated the data to analyze the antigen specificities and mutation patterns of monoclonal antibodies (mAb) derived from rheumatoid arthritis (RA) synovial plasma cells and also to evaluate the antigen cross-reactivity. they identified 4 unrelated anti-citrullinated protein autoantibodies (ACPAs). In turn, the ACPAs identified >3,000 unique peptides altered by either citrullination or carbamylation. They noted that plasma cell-derived mAb targeted discrete amino acid motifs and partially overlapping protein targets. They also carried different effector functions as revealed in an osteoclast activation assay.