The number of elevated cytokines and chemokines in preclinical seropositive rheumatoid arthritis predicts time to diagnosis in an age-dependent manner

Abstract

Objective: To evaluate levels of biomarkers in preclinical rheumatoid arthritis (RA) and to use elevated biomarkers to develop a model for the prediction of time to future diagnosis of seropositive RA.

Methods: Stored samples obtained from 73 military cases with seropositive RA prior to RA diagnosis and from controls (mean 2.9 samples per case; samples collected a mean of 6.6 years prior to diagnosis) were tested for rheumatoid factor (RF) isotypes, anti-cyclic citrullinated peptide (anti-CCP) antibodies, 14 cytokines and chemokines (by bead-based assay), and C-reactive protein (CRP).

Results: Preclinical positivity for anti-CCP and/or ≥2 RF isotypes was >96% specific for future RA. In preclinical RA, levels of the following were positive in a significantly greater proportion of RA cases versus controls: interleukin-1α (IL-1α), IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, IL-15, fibroblast growth factor 2, flt-3 ligand, tumor necrosis factor α, interferon-γ-inducible 10-kd protein, granulocyte-macrophage colony-stimulating factor, and CRP. Also, increasing numbers of elevated cytokines/chemokines were present in cases nearer to the time of diagnosis. RA patients who were ≥40 years old at diagnosis had a higher proportion of samples positive for cytokines/chemokines 5-10 years prior to diagnosis than did patients who were <40 years old at diagnosis (P < 0.01). In regression modeling using only case samples positive for autoantibodies highly specific for future RA, increasing numbers of cytokines/chemokines were predictive of decreased time to diagnosis, and the predicted time to diagnosis based on cytokines/chemokines was longer in older compared with younger cases.

Conclusion: Levels of autoantibodies, cytokines/chemokines, and CRP are elevated in the preclinical period of RA development. In preclinical autoantibody-positive cases, the number of elevated cytokines/chemokines is predictive of the time of diagnosis of future RA in an age-dependent manner.

Figure 1. Mixed model regression lines of mean cytokine/chemokine counts in sero-positive rheumatoid arthritis (RA) cases (N=73 with 212 pre-diagnosis samples) versus controls over time in the pre-clinical period of RA development

The mean values for cases are represented by the straight dashed line, and controls are the straight solid line. The curved shaded lines represent standard errors of the mean for each regression line. In this mixed model analysis RA cases had significantly elevated cytokine/chemokine counts compared to controls ~7.2 years prior-to-diagnosis of RA.

Figure 2. Estimation of time-to-diagnosis of future rheumatoid arthritis (RA) by age and cytokine/chemokine counts in subjects with autoantibody positivity highly specific for future RA

This figure represents the results from regression modeling of the outcome time-to-diagnosis of future RA, based on predictor variables of age-at-diagnosis (by decade) and cytokine/chemokine count (p-value for model <0.01). Pre-diagnosis RA case samples included to develop this model were those that were positive for the highly RA-specific (>96%) autoantibodies: anti-CCP and/or 2 or more rheumatoid factor isotypes (N=54 cases with 101 pre-RA diagnosis samples). For example, from this model, in a case diagnosed with RA between ages 50-59, a sample with a cytokine/chemokine count of 10 would be ~4 years prior-to-diagnosis, while for the same cytokine/chemokine count, a sample from an individual in the 20-29 age-group would be ~1 year prior-to-diagnosis. Model: Years to Diagnosis = −2.3861 - 1.0122 × (Decade*) + 0.1782 × (Cytokine/Chemokine count) *Decade 20-29 coded as 0, 30-39 coded as 1, etc.