Autoantibodies to Disease‐Related Proteins in Joints as Novel Biomarkers for the Diagnosis of Rheumatoid Arthritis

Abstract

Objective. This study was undertaken to develop and characterize a multiplex immunoassay for detection of autoantibodies against peptides derived from proteins known to play a role in development of arthritis and that are also expressed in joints.Methods. We selected peptides from the human counterpart of proteins expressed in the joints, based on mouse models that showed these to be targeted by pathogenic or regulatory antibodies in vivo. Using bead-based flow immunoassays measuring IgG antibodies, we selected triple helical or cyclic peptides, containing the epitopes, to avoid collinear reactivity. We characterized the analytical performance of the immunoassay and then validated it in 3 independent rheumatoid arthritis (RA) cohorts (n = 2,110), Swedish age-and sex-matched healthy controls, and patients with osteoarthritis (OA), patients with psoriatic arthritis (PsA), and patients with systemic lupus erythematosus (SLE).Results. Screening assays showed 5 peptide antigens that discriminated RA patients from healthy controls with 99% specificity (95% confidence interval [CI] 98-100%). In our validation studies, we reproduced the discriminatory capacity of the autoantibodies in 2 other RA cohorts, showing that the autoantibodies had high discriminatory capacity for RA versus OA, PsA, and SLE. The novel biomarkers identified 22.5% (95% CI 19-26%) of early RA patients seronegative for anti-cyclic citrullinated peptide and rheumatoid factor. The usefulness of the biomarkers in identifying seronegative RA patients was confirmed in validation studies using 2 independent cohorts of RA patients and cohorts of patients with OA, PsA, and SLE.Conclusion. A multiplex immunoassay with peptides from disease-related proteins in joints was found to be useful for detection of specific autoantibodies in RA serum. Of note, this immunoassay had high discriminatory capacity for early seronegative RA.

Development and assessment of a predictive model for early diagnosis of rheumatoid arthritis in southwest China: A new nomogram

“…The above results indicated that the detection subtype of RF was an important supplementary test for seronegative RA. [ 15 ] In this study, results indicated that although RF, ESR, CCP, RF-IgA, RF-IgM, RA33, and C3 were significantly higher in ERA patients, only RF and ESR had significant differences in the independent prediction of ERA. However, this nomogram model suggested that RA33 had certain value for the combined diagnosis of ERA in addition to RF and ESR.…”

Shift in perspective: autoimmunity protecting against rheumatoid arthritis

“…Thus, the aetiological triggering is likely an event predating the induction of RF and ACPA. Furthermore, based on the binding pattern by E4 on large peptide libraries tested in cohorts of early and established RA, we assume that a substantial fraction of circulating ACPA will be protective 21 47 48. However, a peptide library in vitro only poorly reflects the specificity of the antibodies in vivo, which is remarkably more restrictive.…”

“…In fact, it has been reported that the standard CCP2 assay does not detect up to 20% of seronegative patients with antibodies binding to other citrullinated antigens,49 and the fact that most ACPA-positive individuals without RA never developed RA further indicates that CCP2 might not reflect the ideal in vivo target. Thus, although the CCP2 test has been a useful diagnostic tool for clinical RA, a new approach using various RA-related citrullinated proteins/peptides defined in vivo may be helpful to capture more seronegative RA,48 identify more subgroups with RA, contribute to preclinical RA diagnosis or perhaps distinguish antibody responses (ie, protective vs non-protective). In addition, the antibody response is polyclonal, and antibodies with different specificities carrying different functions are mixed.…”

Seronegative rheumatoid arthritis: one year in review 2023

“…Furthermore, antibodies to an outer mitochondrial membrane protein, MFN1, predicted the development of erosive disease in seronegative RA. A multiplex immunoassay with peptides from disease-related proteins in joints of RA patients detected a set of five peptides composed principally by new ACPA (cross)reactivities but also included a peptide without citrulline, that identified 22.5% (n=125) of seronegative patients (n=556) with 99% specificity (39).…”