Background/Purpose: A newly discovered anti-carbamylated protein antibody (anti-CarP) is found prior to disease-onset, associates with the conversion towards arthralgia and with a more severe disease course in patients negative for ACPA. We here studied anti-CarP in162 rheumatoid patients who were clinically active and thus under treatment with biological DMARDs, and also in another group of 268 rheumatoid patients whose sera were measured on their first visit to our hospital.

Methods: Anti-CarP-Fetal Calf Serum (aCarPFCS) was measured by using ELISA in sera of 162 Japanese patients with RA who were clinically active (fulfilling either DAS-CRP > 4.0 or DAS-ESR > 4.2 and either CDAI > 22 or SDAI >26) and under treatment with biological DMARDs, and also in 268 patients with RA whose sera were measured for the first time of their visit to the hospital. The change in van der Heijde-modified total Sharp score per year DTSS was assessed using probability plots. Statistical tests were performed using Mann-Whitney U test.

Results: Cumulative probability plot of DTSS for aCarPFCS showed that radiographic progression was less significant in aCarPFCS-positive patients with RA (n=35) as compared with those negative for aCarPFCS (n=127) (Figure). The difference between the groups was p=0.0425 by using Mann-Whitney U test. The cumulative probability plot of DTSS for aCarPFCS in the sera of 268 rheumatoid patients whose sera could be measured on their first visit to the hospital was also similar, where radiographic progression was less significant in aCarPFCS-positive patients with RA (n=80) as compared with those negative for aCarPFCS (n=188). It was noted that radiographic progression seemed particularly less significant in those with relatively larger DTSS, i.e., relatively progressive patients with RA, suggesting that aCarP antibody may be raised in a similar fashion to anti-citrullinated protein antibody (ACPA) possibly cross-reactively but in fact acts rather inhibitory for disease.

Conclusion: Radiographic progression seems to be less significant in anti-carbamylated antibody positive patients with rheumatoid arthritis (RA) especially when they are basically progressive or when they were clinically active and under the treatment with biological DMARDs. The aCarPFCS and aCarPFib are measured by Drs. Verheul MK and Trouw LA, Department of Rheumatology, Leiden University, Netherlands.