Anti-carbamylated protein antibodies in rheumatoid arthritis: their relationship to joint damage and disease activity

Background Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial inflammation, autoantibody production, and cartilage and bone destruction. The cause of RA is still unknown. Identification of disease-related biomarkers would be helpful in diagnosing and classifying RA. The two autoantibody systems most commonly used are rheumatoid factor and anticitrullinated protein antibodies (ACPA). Several RA-associated autoantibody systems have been identified such as anti-carbamylated protein antibodies (anti-CarP Ab), anti-acetylated protein antibodies, and others. Anti-CarP Abs are the second most vigorously researched anti-modified protein antibodies following ACPA. Research on anti-CarP Ab may provide novel insights into the pathology and etiology of RA. Aim To detect the sensitivity and specificity of serum anti-CarP in diagnosis of RA especially in seronegative ACPA. Patients and method This study included 60 patients with RA fulfilling the ACR/EULAR 2010 criteria. A total of 20 apparently healthy participants were taken as controls. Written consents were taken from the patients before enrollment in this study. IRB of Assiut Faculty of Medicine approved the study. IRB local approval number is 17100085. Result There was a statistically significant increase in the level of anti-CarP among patients with RA in comparison with the control group, but there is an insignificant increased level of anti-CarP in the ACPA seropositive group in comparison with the seronegative ACPA group. Conclusion The level of anti-CarP was significantly higher among patients with RA in comparison with the control group. Five (25%) patients from the healthy control group gave anti-CarP-positive result; this can be explained by that anti-CarP Abs may exist in healthy participants many years earlier than the onset of manifestation of RA.