PRTN3 and rheumatoid arthritis: The analysis of anti FN-Cit1035,1036 reactivity in 131 anti-CCP2-positive and 28 anti-CCP2-negative RA sera (Figure 4) showed that the anti-citrullinated fibronectin antibodies were hardly present in anti-CCP2-negative RA sera, corroborating the idea that these antibodies are part of the ACPA response in anti-CCP2-positive RA patients.