PRTN3 and rheumatoid arthritis: Also, when analysing the relationship of HLA-SE and the most frequent ACPA reactivities, an additive interaction for development of RA between HLA-SE and some of the ACPA was significant, namely for CEP-1/Eno5-21 (AP = 0.67, 95% CI: 0.57 to 0.73) and Fibß36-52 (AP = 0.60, 95% CI: 0.49 to 0.67), as was being positive for any of the ACPA (AP = 0.61, 95% CI: 0.58 to 0.65).