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Antibodies to carbamylated ?-enolase epitopes in rheumatoid arthritis also bind citrullinated epitopes and are largely indistinct from anti-citrullinated protein antibodies.

ABSTRACT: In addition to anti-citrullinated protein antibodies (ACPAs), antibodies targeting carbamylated (i.e., homocitrullinated) proteins (anti-CarP antibodies) have been described in rheumatoid arthritis (RA). However, the extent to which anti-CarP antibodies are truly distinct from ACPA remains unclear, and few studies have focused on specific autoantigens. Here, we examine cross-reactivity between ACPA and anti-CarP antibodies, in the context of the candidate autoantigen ?-enolase.Cross-reactivity was examined by immunoblotting of citrullinated and carbamylated proteins using purified ACPA; and by peptide absorption experiments, using the citrullinated ?-enolase peptide CEP-1 and a homocitrulline-containing version (carb-CEP-1) in ELISA. The population-based case-control cohort EIRA (n?=?2836 RA; 373 controls) was screened for reactivity with CEP-1 and carb-CEP-1, using the ISAC multiplex array. Associations between anti-CarP antibodies, smoking and genetic risk factors were analysed using unconditional logistic regression models. Differences in antibody levels were investigated using the Mann-Whitney U test.Affinity-purified ACPA was found to bind carbamylated proteins and homocitrulline-containing peptides, demonstrating definitive cross-reactivity between ACPA and anti-CarP antibodies. Anti-carb-CEP-1 reactivity in EIRA was almost exclusively confined to the CEP-1-positive subset, and this group of RA patients (21 %) displayed a particularly strong ACPA response with marked epitope spreading. The small RA subset (3 %) with homocitrulline reactivity in the absence of citrulline reactivity did not associate with smoking or risk genes, and importantly had significantly lower anti-carb-CEP-1 antibody levels.Our data presented herein cast doubt on the specificity of anti-CarP antibodies in RA, which we posit may be a subset of cross-reactive ACPA.

SUBMITTER: Reed E

PROVIDER: S-EPMC4855497 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Antibodies to carbamylated α-enolase epitopes in rheumatoid arthritis also bind citrullinated epitopes and are largely indistinct from anti-citrullinated protein antibodies.

Reed Evan E Jiang Xia X Kharlamova Nastya N Ytterberg A Jimmy AJ Catrina Anca I AI Israelsson Lena L Mathsson-Alm Linda L Hansson Monika M Alfredsson Lars L Rönnelid Johan J Lundberg Karin K

Arthritis research & therapy 20160504 1

<h4>Background</h4>In addition to anti-citrullinated protein antibodies (ACPAs), antibodies targeting carbamylated (i.e., homocitrullinated) proteins (anti-CarP antibodies) have been described in rheumatoid arthritis (RA). However, the extent to which anti-CarP antibodies are truly distinct from ACPA remains unclear, and few studies have focused on specific autoantigens. Here, we examine cross-reactivity between ACPA and anti-CarP antibodies, in the context of the candidate autoantigen α-enolase ...[more]

PMID: 27145822

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Project description:The presence of anticitrullinated protein antibodies (ACPA) in rheumatoid arthritis (RA) indicates a breach in immune tolerance. Recent studies indicate that this breach extends to homocitrullination of lysines with the formation of anti-carbamylated protein (anti-CarP) antibodies. We analyzed the clinical and serologic relationships of anti-CarP in 2 RA cohorts.Circulating levels of immunoglobulin G anti-CarP antibodies were determined by ELISA in established (Dartmouth-Hitchcock Medical Center) and early (Sherbrooke University Hospital Center) cohorts and evaluated for anticyclic citrullinated peptide antibodies (anti-CCP), specific ACPA, and rheumatoid factor (RF) levels using the Student t test and correlation analysis.We identified elevated anti-CarP antibodies titers in 47.0% of seropositive patients (Dartmouth, n = 164), with relationships to anti-CCP (p < 0.0001) and IgM-RF (p = 0.001). Similarly, 38.2% of seropositive patients from the Sherbrooke cohort (n = 171) had elevated anti-CarP antibodies; titers correlated to anti-CCP (p = 0.01) but not IgM-RF (p = 0.09). A strong correlation with anti-Sa was observed: 47.9% anti-Sa+ patients were anti-CarP antibodies+ versus only 25.4% anti-Sa- in the Sherbrooke cohort (p = 0.0002), and 62.6% anti-Sa+ patients versus 26.9% anti-Sa- were anti-CarP antibodies+ in Dartmouth (p < 0.0001). We found a more variable response for reactivity to citrullinated fibrinogen or to citrullinated peptides from fibrinogen and ? enolase.In 2 North American RA cohorts, we observed a high prevalence of anti-CarP antibody positivity. We also describe a surprising and unexpected association of anti-CarP with anti-Sa antibodies that could not be explained by cross-reactivity. Further, considerable heterogeneity exists between anti-CarP reactivity and other citrullinated peptide reactivity, raising the question of how the pathogenesis of antibody responses for carbamylated proteins and citrullinated proteins may be linked in vivo.

Project description:ObjectiveRheumatoid arthritis (RA) is characterized by the presence of autoantibodies, including seropositivity for rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPAs). In addition, antibodies to carbamylated proteins (anti-CarP) are present in patients with RA and are associated with joint damage. This study was undertaken to assess the presence of anti-CarP antibodies in indigenous North Americans (First Nations [FN] populations) with RA compared to their at-risk first-degree relatives (FDRs) and healthy controls.MethodsAnti-CarP IgG and ACPAs (specifically, anti-cyclic citrullinated peptide [anti-CCP] antibodies) were measured by enzyme-linked immunosorbent assay in the sera of FN patients with RA (n = 95), their unaffected FDRs (n = 109), and healthy FN controls (n = 85). Antibodies to additional citrullinated peptides were measured using a multiplex ACPA array, and the number of peptides recognized was reported as an ACPA score. Groups were compared using the chi-square test and Mann-Whitney U test. Associations between RA and seropositivity for RF, ACPAs, and anti-CarP antibodies were determined by logistic regression.ResultsAnti-CarP antibodies were more frequent in FN patients with RA (44.3%) compared to FDRs (18.3%) and FN controls (4.7%) (both P < 0.0001 versus RA). Moreover, anti-CarP antibodies were more frequent in FDRs than in FN controls (P = 0.008). The ACPA score was higher in anti-CCP-positive FN patients with RA than in anti-CCP-positive FN FDRs (median score 7 [interquartile range (IQR) 7] versus median score 1 [IQR 4]; P = 0.04). The association with RA was strongest when all 3 autoantibodies (RF, anti-CCP, and anti-CarP) were present in the patients' serum (odds ratio 194, 95% confidence interval 23-1,609, P < 0.0001).ConclusionAnti-CarP antibodies are prevalent in FN patients with RA and also more common in their at-risk FDRs compared to healthy controls. The results indicate an association of RF, ACPAs, and anti-CarP with RA that is strongest when all 3 autoantibodies are present. These findings may provide new insights into the evolution of autoimmunity in preclinical RA.

Dataset Information

Antibodies to carbamylated ?-enolase epitopes in rheumatoid arthritis also bind citrullinated epitopes and are largely indistinct from anti-citrullinated protein antibodies.

Publications

Antibodies to carbamylated α-enolase epitopes in rheumatoid arthritis also bind citrullinated epitopes and are largely indistinct from anti-citrullinated protein antibodies.

Similar Datasets

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