Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation. The presence of autoantibodies in the sera of RA patients has provided many clues to the underlying disease pathophysiology. Based on the presence of several autoantibodies like rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), anti-carbamylated protein antibodies (anti-CarP), and more recently anti-acetylated protein antibodies RA can be subdivided into seropositive and seronegative disease. The formation of these autoantibodies is associated with both genetic and environmental risk factors for RA, like specific human leukocyte antigen (HLA) alleles and smoking. Autoantibodies can be detected many years before disease onset in a subset of patients, suggesting a sequence of events in which the first autoantibodies develop in predisposed hosts, before an inflammatory response ensues leading to clinically apparent arthritis. Research on the characteristics and effector functions of these autoantibodies might provide more insight in pathophysiological processes underlying arthritis in RA. Recent data suggests that ACPA might play a role in perpetuating inflammation once it has developed. Furthermore, pathophysiological mechanisms have been discovered supporting a direct link between the presence of ACPA and both bone erosions and pain in RA patients. In conclusion, investigating the possible pathogenic potential of autoantibodies might lead to improved understanding of the underlying pathophysiological processes in rheumatoid arthritis.
BackgroundRheumatoid arthritis (RA) is characterized by the presence of autoantibodies like rheumatoid factor (RF), anti-cyclic citrullinated peptide-2 (anti-CCP2), and anti-carbamylated protein (anti-CarP) antibodies. It is currently unclear whether changes in autoantibody levels are associated with disease activity/treatment outcomes and whether they are modified by treatment intensity. Therefore, we determined longitudinal changes in RA-autoantibody levels, the association between these changes and activity score (DAS) and treatment outcomes, and the effect of intensity of immunosuppressive treatment on levels.MethodsIn 381 seropositive RA patients from the IMPROVED study, we measured IgG, IgM, and IgA of anti-CCP2 and anti-CarP; IgM and IgA of RF; and IgG against four citrullinated and two acetylated peptides at 4-month intervals over the first year of treatment. Following initial prednisone and methotrexate (MTX), treatment was changed every 4 months aiming for DAS < 1.6. We investigated changes in autoantibody levels following treatment escalation versus tapering, and the association of levels with DAS over time, EULAR response, and drug-free remission (DFR) ≥ 1 year.ResultsFor all 14 autoantibodies, levels decreased from 0 to 4 months and then rose until 12 months. Following treatment escalation, autoantibody levels dropped markedly, while they rose following tapering: RF IgM levels, a representative autoantibody, dropped 10% after restarting prednisone and rose 15% aU/mL after tapering MTX (p < 0.0001). There was no association between autoantibody levels and DAS over time or EULAR response. Greater relative changes between 0 and 12 months did not predict DFR (0–12-month relative change RF IgM, − 39% for no DFR (n = 126) and − 16% for DFR (n = 18)).ConclusionsChanges in RA-autoantibody levels are not associated with DAS or long-term treatment response, but reflect intensity of immunosuppression. This suggests that autoantibody levels are modifiable by current therapies, but that modifying levels is in itself of limited clinical relevance.Trial registrationISRCTN11916566. Registered on 7 November 2006Electronic supplementary materialThe online version of this article (10.1186/s13075-019-1815-0) contains supplementary material, which is available to authorized users.
BackgroundThe autoantibody profile of seropositive rheumatoid arthritis (RA) is very diverse and consists of various isotypes and antibodies to multiple post-translational modifications. It is yet unknown whether this varying breadth of the autoantibody profile is associated with treatment outcomes. Therefore, we investigated whether the composition of the autoantibody profile in RA, as a marker of the underlying immunopathology, influences initial and long-term treatment outcomes.MethodsIn serum from 399 seropositive patients with RA in the IMPROVED study, drawn at baseline and at the moment of drug tapering, we measured IgG, IgM, and IgA isotypes for anti-cyclic citrullinated peptide-2 and anti‐carbamylated protein antibodies, IgM and IgA rheumatoid factor, and reactivity against four citrullinated and two acetylated peptides (anti-modified protein antibodies (AMPAs)). We investigated the effect of the breadth of the autoantibody profile on (1) change in disease activity score (DAS)44 between 0 and 4 months, (2) initial drug-free remission (DFR, drug-free DAS44 < 1.6) achieved between 1 and 2 years of follow up, and (3) long-term sustained DFR until last follow up.ResultsPatients with a broad autoantibody profile at baseline had a significantly better early treatment response: ΔDAS 0–4 months of 1–2, 3–4, and 5–6 vs 7–8 isotypes, -1.5 (p < 0.001), -1.7 (p = 0.03), and -1.8 (p = 0.04) vs -2.2. Similar results were observed for AMPA number. However, patients with a broad baseline autoantibody profile achieved less initial DFR. For long-term sustained DFR there was no longer an association with the breadth of the autoantibody response. When assessing autoantibodies at the moment of tapering, similar trends were observed.ConclusionsA broad baseline autoantibody profile is associated with a better early treatment response. The breadth of the baseline autoantibody profile, reflecting a break in tolerance against several different autoantigens and extensive isotype switching, may indicate a more active humoral autoimmunity, which could make the underlying disease processes initially more suppressible by medication. The lack of association with long-term sustained DFR suggests that the relevance of the baseline autoantibody profile diminishes over time.Trial registrationISRCTN11916566. Registered on 7 November 2006. EudraCT, 2006- 06186-16. Registered on 16 July 2007.Electronic supplementary materialThe online version of this article (10.1186/s13075-018-1520-4) contains supplementary material, which is available to authorized users.
BackgroundAnti-carbamylated protein (anti-CarP) antibodies have recently been reported to occur in around 45% of rheumatoid arthritis (RA) patients and to have prognostic and diagnostic properties. At present, the breadth and molecular make-up of the anti-CarP antibody response is ill defined. To understand the anti-CarP antibody immune response and potential immune effector mechanisms it can recruit, we determined the anti-CarP antibody isotype and IgG-subclass usage in RA patients.MethodsAnti-CarP antibody IgM, IgA, and IgG or IgG subclasses were detected by enzyme-linked immunosorbent assay (ELISA) in sera from 373 unselected RA patients and 196 healthy controls. An additional 114 anti-citrullinated protein antibody (ACPA) and anti-CarP IgG double-positive patients were selected to study the concomitant presence of both antibody systems.ResultsAnti-CarP IgG was present in around 45% of the patients and comprised all anti-CarP IgG subclasses. The presence of anti-CarP IgG1 particularly associates with radiological damage. Anti-CarP IgM was detected in 16% of RA patients, even in anti-CarP IgG-positive individuals, and is indicative of an actively ongoing immune response. Around 45% of the patients were positive for IgA which included ACPA-positive cases but also 24% of the ACPA-negative cases. In ACPA and anti-CarP double-positive patients, the distribution and number of isotypes and IgG subclasses was similar for both autoantibodies at the group level, but substantial variation was observed within individual patient samples.ConclusionsIn RA, the anti-CarP antibody response uses a broad spectrum of isotypes and seems to be an actively ongoing immune reaction. Furthermore, the anti-CarP and ACPA autoantibody responses seems to be differentially regulated.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-017-1392-z) contains supplementary material, which is available to authorized users.
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