AB0131 Rheumatoid factor is detected on circulating extracellular vesicles in a subpopulation of rheumatoid arthritispatients with a more severe disease phenotype

Abstract

BackgroundExtracellular vesicles (EVs) play a role in cell-cell communication and contain numerous signalling molecules inside and on their cell membrane. Although their function remains to be elucidated, evidence accumulates that EVs play a regulatory role in immunity during health and disease. They contain numerous proteins, lipids, RNA, DNA and sometimes cell organelles such as mitochondria. In a recent study was shown that Immunoglobuline M-Rheumatoid factor (IgM-RF) is present on milk derived exosomes.1 High IgM-RF levels in Rheumatoid Arthritis (RA) predict a more severe disease and comorbidities, probably due to their involvement in immune complex formation and activation of complement (crucial mediators of the effector phase of inflammation in the pathogenesis of RA).ObjectivesIn this study we investigate whether RF +EVs are detectable in the circulation of RA patients and if this relates to parameters of disease activity.MethodsEVs were isolated from platelet-free plasma of 38 RA patients and from age and sex-matched 24 healthy controls (HC) by size exclusion chromatography. EV markers (tetraspanins) were detected by Western blot and miRNA content by RT-qPCR. Particle size and concentration were measured by electron microscopy and nanosight tracking analysis. Protein concentration was determined by micro-BCA. RF levels were measured using a commercial ELISA. The percentage of RF +EVs was determined by measuring bound and unbound PHK labelled EVs to Protein L magnetic beads in a fluorometer.ResultsMean EV particle size, concentration and protein content were not different between RA patients and HC. 27 of the 38 RA patients were classified as RF+ (>10 IU/ml) and of the clinical parameters studied only their erythrocyte sedimentation rate (ESR) was higher (31 vs 14 mm/hr). In 14 RF +patients, RF was detectable on a small portion of EVs not exceeding 4% of the total number of circulating EVs. Interestingly, RA patients with RF +EVs showed higher disease activity as assessed by patient global health assessment using a visual analogue scale (63 vs 31), blood C-reactive protein (22 vs 9 mg/L) and ESR (43 vs 19 mm/hr) levels, than RA patients with undetectable RF +EVs.ConclusionsThis study shows for the first time that in a subpopulation of RA patients RF is present on EVs, which might originate from their B-cells. The higher disease activity in RA patients expressing RF on their EVs suggests that RF +EVs are involved in RA pathogenesis.Reference[1] Yang M, et al. Comparative proteomic analysis ofmilk-derived exosomes in human and bovine colostrumandmature milk samples by iTRAQ-coupled LC-MS/MS. Food Research International2017;92(2017):17–25.Disclosure of InterestNone declared