PRTN3 and rheumatoid arthritis: In accordance with previous data, we detected a high degree of cross-reactivity between affinity purified ACPA IgGs, with apparent dissociation constants (KD) between 10−6 and 10−8 M. Based on the pattern of cross-reaction, we designed a novel multi-epitope peptide that was specifically recognized by RA sera and was able to deplete specific B cells from in vitro culture.