Profiling of IgG antibodies targeting unmodified and corresponding citrullinated autoantigens in a multicenter national cohort of early arthritis in Germany

Abstract

Objective: To assess the diagnostic potential of IgG antibodies to citrullinated and corresponding native autoantigens in early arthritis.

Methods: IgG autoantibodies to 390 distinct unmodified and corresponding in vitro citrullinated recombinant proteins were measured by a multiplex assay in baseline blood samples from a German multicenter national cohort of 411 early arthritis patients (56.5 ± 14.6 years, 62.8% female). The cohort was randomly split into a training cohort (n = 329, 28.6% ACPA positive) and a validation cohort (n = 82, 32.9% ACPA pos.). The diagnostic properties of candidate antibodies to predict a subsequent diagnosis of rheumatoid arthritis (RA) as opposed to a non-RA diagnosis were assessed by receiver operating characteristics analysis and generalized linear modeling (GLM) with Bonferroni correction in comparison to clinically determined IgM rheumatoid factor (RF) and citrullinated peptide antibody (ACPA) status.

Results: Of 411 patients, 309 (75.2%) were classified as RA. Detection rates of antibody responses to citrullinated and uncitrullinated forms of the proteins were weakly correlated (Spearman's r = 0.13 (95% CI 0.029-0.22), p = 0.01). The concentration of 34 autoantibodies (32 to citrullinated and 2 to uncitrullinated antigens) was increased at least 2-fold in RA patients and further assessed. In the training cohort, a significant association of citrullinated "transformer 2 beta homolog" (cTRA2B)-IgG with RA was observed (OR 5.3 × 10³, 95% CI 0.8 × 10³-3.0 × 10⁶, p = 0.047). Sensitivity and specificity of cTRA2B-IgG (51.0%/82.9%) were comparable to RF (30.8%/91.6%) or ACPA (32.1%/94.7%). Similar results were obtained in the validation cohort. The addition of cTRA2B-IgG to ACPA improved the diagnostic performance over ACPA alone (p = 0.026 by likelihood ratio test).

Conclusions: cTRA2B-IgG has the potential to improve RA diagnosis in conjunction with RF and ACPA in early arthritis.

Keywords: Antibody; Autoantigen; Biomarker; Diagnosis; Early arthritis; Rheumatoid arthritis.

Fig. 1

a Detection rates of IgG antibodies to citrullinated and uncitrullinated forms of 390 distinct proteins in patients diagnosed with rheumatoid arthritis (RA patients) (n = 309) out of an early arthritis cohort (n = 411). Each dot represents the percentage of patients with an increased IgG detection towards a distinct citrullinated or uncitrullinated protein. Regression line with 95% confidence interval depicted (Spearman’s r = 0.13, p = 0.01). b Venn diagram representing the number of patients with increased antibody reactivity in rheumatoid arthritis (RA) patients and control patients (non-RA patients) classified as RA by three distinct autoantibodies against citrullinated peptides (ACPA), citrullinated “transformer 2 beta homolog” (cTRA2B), and rheumatoid factor (RF) as well as the respective overlaps. c Proportion of patients who were subsequently diagnosed with RA or not according to a diagnostic score of ≥ 2 (n = 140) or below (n = 271) based on adjusted odds ratios of multivariable generalized linear modeling (ACPA 3 points, RF and cTRA2B 1 point each)