The objective of this study was to determine if HLA alleles associate with ACPA reactivity patterns.<h4>Methods</h4>For 100 ACPA+RF+ participants with RA, serum IgG binding was quantified by enzyme-linked immunosorbent assay to 10 citrulline-containing peptides derived from Type II collagen and IgG1 (nine with motifs), and HLA loci were genotyped. Here, PRTN3 is linked to rheumatoid arthritis.