P079 Is IgM rheumatoid factor present on circulating extracellular vesicles of rheumatoid arthritis patients a potential biomarker for disease severity?
Authors: O Arntz, B Pieters, R Thurlings, PVD Kraan, FVD Loo
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Career situation of first and presenting author</h3> Student for a master or a PhD. <h3>Introduction</h3> Rheumatoid factor (RF) are autoantibodies and measured in serum of rheumatoid arthritis patients (RA) to diagnose the disease. High serum RF levels are also predictors of more severe disease forms although the functional role of RF is still unclear.<sup>1</sup> Most research on RA has been focused on cytokines as main effectors in the disease process but cell-cell communication involves a much broader scope of responses such as via the release of extracellular vesicles (EVs).<sup>2</sup> EVs are small particles of around 100 nm and released by cells. They mediate intercellular communication by exchange their content (RNA, miRNA and proteins). <h3>Objectives</h3> As EVs are communicators that carry a multitude of signals and can be derived from all cells including B-cells we set out to determine whether RF is detectable on circulating EVs in RA patients and if this relates to parameters of disease activity. <h3>Methods</h3> EVs were isolated from platelet-free plasma of 41 RA patients by size exclusion chromatography. We quantified the particle and protein concentration, using NanoSight particle tracking analysis and micro-BCA. Tender (TJC) and swollen joints (SJC) were assessed by physicians and the global patient visual analogue score (VAS) was determined by the patient. IgM-RF, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were determined by standard laboratory blood tests in our hospital. Disease activity score (DAS28) was calculated. <h3>Results</h3> In plasma of 28 out of 41 RA patients RF was detectable, and in 13 out of these 28 RA +RF was also detected on their isolated pEVs (RF<sup>+</sup>pEVs). No statistical differences were found on particle size, protein content per particle and amount of particles of pEVs between seronegative (RA-) and seropositive (RA+) patients (116 nm, 39fg, 5.4 × 10<sup>10</sup> and 114 nm, 58fg, 1.8 × 10<sup>10</sup>, respectively). Comparing disease parameters no differences were found between RA+ and RA- patients, except for increased ESR levels in RA+ patients. However, RA+ patients having circulating RF<sup>+</sup>pEVs showed significant higher CRP and ESR levels and VAS and DAS28 scores as compared to RA+ patients without circulating RF<sup>+</sup>pEVs while no differences were found on TJC and SJC. <h3>Conclusions</h3> This study shows for the first time the presence of RF on pEVs in a subset of RA+ patients and this could be a plasma marker to distinguish RA patients with a more severe disease. We found that RF+ EVs is not a reflection of the number of affected joints but might be more indicative for the underlying pathophysiology of RA. <h3>References</h3> Gonzalez, A. <i>The Journal of Rheumatology</i> 2008. György, B. <i>Cellular and Molecular Life Sciences</i>2011. <h3>Disclosure of Interest</h3> None declared.