Objective
Autoantibodies have been demonstrated in single serum samples from healthy subjects up to 10 years before they developed rheumatoid arthritis (RA). However, the time course for the development of antibodies before onset of clinical RA is unknown, nor is it known which antibody, or combinations of antibodies, might be most sensitive or specific for predicting future development of the disease. The present study was undertaken to investigate this.

Methods
Patients with RA who had been blood donors before the onset of disease symptoms were enrolled. Frozen serum samples from each donor were retrieved, together with 2 serum samples from controls matched for age, sex, and date of donation. All samples were tested for IgM rheumatoid factor (IgM-RF) and anti–cyclic citrullinated peptide (anti-CCP) antibodies.

Results
Seventy-nine patients with RA (62% female; mean age at onset of symptoms 51 years) were included. A median of 13 samples (range 1–51) per patient were available; the earliest samples had been collected a median of 7.5 years (range 0.1–14.5) before the onset of symptoms. Thirty-nine patients (49%) were positive for IgM-RF and/or anti-CCP on at least one occasion before the development of RA symptoms, a median of 4.5 years (range 0.1–13.8) before symptom onset. Of the 2,138 control samples, 1.1% were positive for IgM-RF, and 0.6% were positive for anti-CCP.

Conclusion
Approximately half of patients with RA have specific serologic abnormalities several years before the onset of symptoms. A finding of an elevated serum level of IgM-RF or anti-CCP in a healthy individual implies a high risk for the development of RA. We conclude that IgM-RF and anti-CCP testing with appropriately high specificity may assist in the early detection of RA in high-risk populations.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/art.20018

Specific autoantibodies precede the symptoms of rheumatoid arthritis: A study of serial measurements in blood donors

Objective
Since modern treatment of rheumatoid arthritis (RA) is shifting toward aggressive antirheumatic therapy in an early phase of the disease, diagnostic tests with high specificity are desirable. A new serologic test (anti–cyclic citrullinated peptide [anti-CCP] enzyme-linked immunosorbent assay [ELISA]) was developed to determine the presence of antibodies directed toward citrullinated peptides, using a synthetic peptide designed for this purpose.

Methods
A cyclic peptide variant that contains deiminated arginine (citrulline) was designed and used as antigenic substrate in ELISA. Test parameters and diagnostic characteristics of the test were studied in patients with and without RA, in patients with various infectious diseases, and in a group of patients from an early arthritis clinic (EAC).

Results
Using prevalent RA and non-RA sera, the anti-CCP ELISA proved to be extremely specific (98%), with a reasonable sensitivity (68%). Also, in the EAC study group, the anti-CCP ELISA appeared to be highly specific for RA (96%). In comparison with the IgM rheumatoid factor (IgM-RF) ELISA, the anti-CCP ELISA had a significantly higher specificity (96% for CCP versus 91% for IgM-RF; P = 0.016) at optimal cut-off values. The sensitivity of both tests for RA was moderate: 48% and 54% for the anti-CCP ELISA and the IgM-RF ELISA, respectively (P = 0.36). Combination of the anti-CCP and the IgM-RF ELISAs resulted in a significantly higher positive predictive value of 91% (P = 0.013) and a slightly lower negative predictive value of 78% (P = 0.35) as compared with the use of the IgM-RF ELISA alone. The ability of the 2 tests performed at the first visit to predict erosive disease at 2 years of followup in RA patients was comparable (positive predictive value 91%).

Conclusion
The anti-CCP ELISA might be very useful for diagnostic and therapeutic strategies in RA of recent onset.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1529-0131%28200001%2943%3A1%3C155%3A%3AAID-ANR20%3E3.0.CO%3B2-3

The diagnostic properties of rheumatoid arthritis antibodies recognizing a cyclic citrullinated peptide.

A new model for an etiology of rheumatoid arthritis : smoking may trigger HLA-DR (shared epitope)-restricted immune reactions to autoantigens modified by citrullination.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/art.21575

A new model for an etiology of rheumatoid arthritis: smoking may trigger HLA-DR (shared epitope)-restricted immune reactions to autoantigens modified by citrullination.

Individuals with rheumatoid arthritis frequently have autoantibodies to citrullinated peptides, suggesting the involvement of the peptidylarginine deiminases citrullinating enzymes (encoded by PADI genes) in rheumatoid arthritis. Previous linkage studies have shown that a susceptibility locus for rheumatoid arthritis includes four PADI genes but did not establish which PADI gene confers susceptibility to rheumatoid arthritis. We used a case-control linkage disequilibrium study to show that PADI type 4 is a susceptibility locus for rheumatoid arthritis (P = 0.000008). PADI4 was expressed in hematological and rheumatoid arthritis synovial tissues. We also identified a haplotype of PADI4 associated with susceptibility to rheumatoid arthritis that affected stability of transcripts and was associated with levels of antibody to citrullinated peptide in sera from individuals with rheumatoid arthritis. Our results imply that the PADI4 haplotype associated with susceptibility to rheumatoid arthritis increases production of citrullinated peptides acting as autoantigens, resulting in heightened risk of developing the disease.

Functional haplotypes of PADI4, encoding citrullinating enzyme peptidylarginine deiminase 4, are associated with rheumatoid arthritis.

The disease mechanisms of complex inflammatory disorders are difficult to define because of extensive interactions between genetic and environmental factors. Coeliac disease is a typical complex inflammatory disorder, but this disease is unusual in that crucial genetic and environmental factors have been identified. This knowledge has allowed functional studies of the predisposing HLA molecules, the identification of antigenic epitopes and detailed studies of disease-relevant T cells in coeliac disease. This dissection of the pathogenic mechanisms of coeliac disease has uncovered principles that are relevant to other chronic inflammatory diseases.

Coeliac disease: dissecting a complex inflammatory disorder

Only a few autoantibodies that are more or less specific for RA have been described so far. The rheumatoid factor most often tested for is not very specific for RA, while the more specific antiperinuclear factor for several reasons is not routinely used as a serological parameter. Here we show that autoantibodies reactive with synthetic peptides containing the unusual amino acid citrulline, a posttranslationally modified arginine residue, are specifically present in the sera of RA patients. Using several citrulline-containing peptide variants in ELISA, antibodies could be detected in 76% of RA sera with a specificity of 96%. Sera showed a remarkable variety in the reactivity pattern towards different citrulline-containing peptides. Affinity-purified antibodies were shown to be positive in the immunofluorescence-based antiperinuclear factor test, and in the so-called antikeratin antibody test, and were reactive towards filaggrin extracted from human epidermis. The specific nature of these antibodies and the presence of these antibodies early in disease, even before other disease manifestations occur, are indicative for a possible role of citrulline-containing epitopes in the pathogenesis of RA.

/pdf/citrulline-is-an-essential-constituent-of-antigenic-1e2gbhji0x.pdf

Citrulline is an essential constituent of antigenic determinants recognized by rheumatoid arthritis-specific autoantibodies.

Objective

Rheumatoid arthritis (RA) is a common, severe, chronic inflammatory joint disease. Since the disease may initially be indistinguishable from other forms of arthritis, early diagnosis can be difficult. Autoantibodies seen in RA can be detected years before clinical symptoms develop. In an inception cohort of patients with recent-onset arthritis, we undertook this study to assess the predictive value of RA-specific autoantibodies to cyclic citrullinated peptides (CCPs) in patients with undifferentiated arthritis (UA).



Methods

Anti-CCP2 antibody tests were performed at baseline in 936 consecutive, newly referred patients with recent-onset arthritis. Patients who could not be properly classified 2 weeks after inclusion were categorized as having UA. Patients with UA were followed up for 3 years and evaluated for progression of their disease to RA as defined by the American College of Rheumatology (ACR) 1987 revised criteria.



Results

Three hundred eighteen of 936 patients with recent-onset arthritis were classified as having UA and were available for analysis. After 3 years of followup, 127 of 318 UA patients (40%) had been classified as having RA. RA had developed in 63 of 249 patients (25%) with a negative anti-CCP test and in 64 of 69 patients (93%) with a positive anti-CCP test (odds ratio 37.8 [95% confidence interval 13.8–111.9]). Multivariate analysis of the presence of anti-CCP antibodies and parameters from the ACR criteria identified polyarthritis, symmetric arthritis, erosions on radiographs, and anti-CCP antibodies as significant predictors of RA.



Conclusion

Testing for anti-CCP antibodies in UA allows accurate prediction of a substantial number of patients who will fulfill the ACR criteria for RA.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/art.20044

Autoantibodies to cyclic citrullinated peptides predict progression to rheumatoid arthritis in patients with undifferentiated arthritis: a prospective cohort study.

Small nuclear ribonucleoprotein (snRNP) particles are a class of RNA-containing particles in the nucleus of eukaryotic cells. They consist of uridylate-rich small nuclear RNA complexed with several proteins. snRNP particles U1, U2, U4/U6, and U5 all contain a common protein core consisting of proteins B'/B, D, D', E, F, and G. In addition to this core, U1 snRNP particles contain proteins 70K, A, and C, whereas U2 snRNP particles contain proteins A' and B". Almost any of the small nuclear RNA-associated polypeptides is targeted by autoantibodies in the sera from patients with SLE or related connective tissue diseases. We immunized a genetically non-autoimmune mouse with recombinant human B" protein and obtained three mAb reactive with native U2 snRNP particles. Two of these mAb particles cross-reacted with U1 snRNP, 9A9 and 11A1, via epitopes present on the U2 snRNP B" protein as well as on the U1 snRNP-specific A protein. A third mAb 4g3, reacted exclusively with U2 snRNP via a unique epitope on protein B". Two epitopes mapped at the carboxy-terminal region of the B" protein, whereas binding of the third mAb involved both amino- and carboxy-terminal amino acids of the B" protein. Epitope mapping, employing a DNAse I fragment library of the B" cDNA, revealed that the three mAb-reactive sites were discontinuous. Autoantibodies in sera from patients with SLE and other connective tissue diseases competed for binding with the mAb, implying that the mAb define a major autoantibody-reactive region on protein B".

Mapping of B cell epitopes on small nuclear ribonucleoproteins that react with human autoantibodies as well as with experimentally-induced mouse monoclonal antibodies.

B.A. de Jong

Papers

Citrulline is an essential constituent of antigenic determinants recognized by rheumatoid arthritis-specific autoantibodies.

Autoantibodies to cyclic citrullinated peptides predict progression to rheumatoid arthritis in patients with undifferentiated arthritis: a prospective cohort study.

Mapping of B cell epitopes on small nuclear ribonucleoproteins that react with human autoantibodies as well as with experimentally-induced mouse monoclonal antibodies.