Background Anti-citrullinated protein antibodies (ACPA) and IgM-Rheumatoid Factor (IgM-RF) are auto-antibodies that can be detected many years before the clinical diagnosis of Rheumatoid Arthritis (RA) . Since ACPA and IgM-RF are known as predictive and prognostic markers of RA, it is conceivable that these antibodies play a pathogenic role in RA. In recent studies we discovered anti-carbamylated protein (anti-CarP) antibodies as a prognostic marker in RA . In addition anti-CarP antibodies are associated with a conversion to RA in patients that suffer from arthralgia .
Objectives In this study we analyzed whether anti-CarP antibodies can also be detected prior to the onset of the symptoms of RA and which auto-antibody appears first over time.
Methods Sera of 79 RA patients prior to the onset of symptoms and 141 age and sex matched controls that were regular blood donors were tested for the presence of anti-carbamylated fetal calf serum (Ca-FCS) antibodies, anti-carbamylated fibrinogen (Ca-Fib) antibodies, anti-cyclic citrullinated peptide 2 (CCP2) antibodies and RF-IgM. A median of 6 (IQR 4-9) sequential pre-RA sera, obtained at 1-2 year intervals was available for analysis.
Results Anti-CarP antibodies were present in 39% of the serum samples that were drawn just prior to the diagnosis of RA of blood donors compared to 4% of the matched control samples. Anti-CarP antibodies were present in both ACPA positive and ACPA negative patients. Of the 79 individuals that developed RA, 42% were positive for anti-CCP2 antibodies and 24% for IgM RF.
Analysis of the longitudinal samples revealed that anti-CarP antibodies could be detected many years before the onset of symptoms (median 8 years). Comparing the first appearance of the three autoantibody families revealed that both ACPA and anti-CarP antibodies appear (similarly) earlier in time as compared to IgM-RF.
Conclusions Next to ACPA and IgM-RF also the newly identified anti-CarP antibodies appear many years before the onset of clinical symptoms of RA.
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Shi J, et al. Autoantibodies recognizing carbamylated proteins are present in sera of patients with rheumatoid arthritis and predict joint damage. Proc.Natl.Acad.Sci.U.S.A 2011; 108:17372-7.
Shi J, et al. Anti Carbamylated Protein Antibodies (anti-CarP) are present in arthralgia patients and predict the development of rheumatoid arthritis. Arthritis Rheum. 2012.
Acknowledgements L.A.T. receives a fellowship from Janssen Biologics BV, (Johnson & Johnson)
Disclosure of Interest None Declared
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