Objective:

To investigate the presence of neutrophil-and platelet-derived extracellular vesicles (EVs) in the plasma and synovial fluid of children with juvenile idiopathic arthritis (JIA) and compare these with healthy controls.

Approach:

• Participants: Seven children with active, untreated JIA and ten healthy controls were included.
• Methods: Citrate plasma and synovial fluid were analyzed for neutrophil-and platelet-derived EVs using flow cytometry. Disease activity was assessed using the Juvenile Arthritis Disease Activity Score (JADAS27) and functional impairment via the Childhood Health Assessm…

Key Findings:

• Neutrophil-and platelet-associated EVs were detectable in plasma and synovial fluid in all children with JIA.
• Plasma levels of CD41+ EVs and MPO+ EVs were significantly higher in the JIA group compared with controls.
• Activated platelet EVs were predominantly detected in plasma and at low levels in synovial fluid.
• MPO+ and H3Cit+ EVs were present in both plasma and synovial fluid, indicating neutrophil activation and NET-related components.
• No correlations between EV levels and clinical or laboratory variables were found.

Interpretation:

This exploratory pilot study is the first to assess platelet-and neutrophil/NET-associated EV phenotypes in both plasma and synovial fluid in children with JIA.

Conclusion:

The results indicate systemic platelet activation and NET-related activity in both circulation and the inflamed joint compartment.