PRTN3 and rheumatoid arthritis: ACPAs in RA recognize many citrullinated autoantigens (Table 1) and are associated with HLA-DRB1SE (Snir et al., 2009), and HLA-DRB1SE appears to be a risk factor for ACPA production in RA rather than an independent risk factor for RA development (van der Helm-van Mil et al., 2006).