LAUSR

OBJECTIVES Systemic juvenile idiopathic arthritis (sJIA) is a chronic pediatric inflammatory disease of unknown etiology, characterized by fever, rash, hepatosplenomegaly, serositis and arthritis. We hypothesized that intercellular communication, mediated by extracellular vesicles (EVs), contributes to sJIA pathogenesis and that the number and cellular sources of EVs would differ between inactive and active states of sJIA and healthy controls. METHODS We evaluated plasma from healthy pediatric controls and sJIA patients with active systemic flare or inactive disease. We isolated EVs by size-exclusion chromatography and determined total EV abundance and size distribution using microfluidic resistive pulse sensing. Cell-specific EV subpopulations were measured by nanoscale flow cytometry. Isolated EVs were validated using a variety of ways, including Nanotracking and Cryo-EM. EV protein content was analyzed in pooled samples using mass spectrometry. RESULTS Total EV concentration did not significantly differ between controls and sJIA patients. EVs with diameters <200 nm were the most abundant, including the majority of cell-specific EV subpopulations. sJIA patients had significantly higher levels of EVs from activated platelets, intermediate monocytes, and chronically activated endothelial cells, with the latter significantly more elevated in active sJIA relative to inactive disease and controls. Protein analysis of isolated EVs from active patients showed a pro-inflammatory profile, uniquely expressing heat shock protein 47 (HP47), a stress-inducible protein. CONCLUSION Our findings indicate that multiple cell types contribute to altered EV profiles in sJIA. The EV differences between sJIA disease states and healthy controls implicate EV-mediated cellular crosstalk as a potential driver of sJIA disease activity.