Background/Purpose: Rheumatoid factor (RF) or anti-citrullinated peptide antibody (ACPA) detection have limited clinical utility for the diagnosis of rheumatoid arthritis (RA), as the specificity and sensitivity of RF is low and ACPAs seem restricted to a subgroup of RA patients. Neutrophil extracellular trap (NET) formation, the extracellular extrusion of chromosomal components from the nucleus upon specific stimulation, reported principally as a response to infectious agents, has also been linked to the pathogenesis of autoimmune and inflammatory diseases such as preeclampsia (PE), systemic lupus erythematosus (SLE), and recently RA^1,2. We have previously observed that serum samples from RA patients showed significantly higher cell-free DNA levels than those of healthy controls and that the serum concentration of cell free nucleosomes (cfNucs) is a surrogate marker for NET formation^3,4.

Our aim was to validate cfNuc measurement in the serum for the diagnosis of RA and to assess its potential to differentiate rheumatoid arthritis cases from similar autoimmune inflammatory conditions and healthy controls.

Methods: Serum from healthy controls and groups of patients with RA, SLE, psoriatic arthritis (PsA) and ankylosing spondylitis (AS) were analyzed for cfNuc levels by ELISA. Healthy and disease control groups were compared by one way ANOVA. Receiver operator characteristic (ROC) curves were calculated with the standard errors. The results presented are from an interim analysis of a targeted 120 cases with RA and 30 each with SLE, PsA and AS.

Results: The mean cfNuc level of the healthy control group (n=47) was 0.3244, of the RA patients 1.813 (n=64), of the SLE patients 0.5753 (n=18), of the PsA patients 0.4684 (n=6) and of the patients with AS 0.6328 (n=10).

The difference between healthy controls and RA was significant at P<0.0001, between RA and SLE 0.0011, between RA and PsA 0.0007, and between RA and AS 0.0001.

Significance between RA and all disease controls and between RA and all controls was P<0.0001. The ROC area under the curve (AUC) for RA versus healthy controls was > 97%, the sensitivity and specificity being 87.5% and 91.5%, respectively, at a 0.58 cutoff. The ROC AUC for distinguishing RA from SLE was 88%, from PsA 92%, from AS 86% and disease controls as a group 88% (sensitivity 81.25%, specificity 80-89% at a cutoff of 0.78). For RA versus all controls, the ROC AUC was 93% (sensitivity 81.25%, specificity 93% at a cutoff of 0.78).

Conclusion: The detection of cell free nucleosomes in the serum of patients with autoimmune conditions can be utilized to discriminate between healthy controls and cases with RA with remarkable sensitivity and specificity. Sensitivity and specificity against disease controls, albeit less, were in a similar range. Upon reaching our target case numbers, we intend to analyze whether cfNuc could provide a tool to monitor and/or predict the response of RA patients to treatment with biologics and to optimize the ELISA assay.

References 1. Mantovani, A et al. Nat Rev Immunol. 2011;25;11:519-31; 2. Dwivedi N et al. Arthritis Rheuma. 2012;64:982-92; 3. Sur Chowdhury C et al. Arthr Res Ther 2014;16:R122

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/neutrophil-extracellular-trap-levels-measured-by-cell-free-nucleosome-elisa-in-serum-are-highly-specific-and-sensitive-for-rheumatoid-arthritis/