AlphaScreen profiling of extracellular vesicle-associated platelet, immune, and vascular markers reveals disease-specific signatures in ME/CFS, fibromyalgia, and long COVID

Introduction: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), fibromyalgia (FM), and long COVID (LC-19) are chronic diseases with overlapping clinical features and poorly understood pathophysiology. Increasing evidence suggests the involvement of immune dysregulation, endothelial dysfunction, and altered vascular physiology. Extracellular vesicles (EVs) are key mediators of intercellular communication and are envisioned as sensors of homeostasis and disease. The aim of this study was to determine whether EV marker profiling could provide a basis for the differential diagnosis of ME/CFS, FM and LC-19 and/or patient stratification. Methods: EV-enriched plasma from ME/CFS, FM, cases co-diagnosed with ME/CFS and FM, LC-19 patients, and matched healthy controls (n = 10 per study group) were analyzed. EV concentration and size distribution were assessed by nanoparticle tracking analysis, followed by targeted profiling of EV-associated surface markers via AlphaScreen, including tetraspanins CD9 and CD63, platelet- (CD41/CD61), myeloid- (CD13), immune- (CD74 and CX3CR1), and renin-angiotensin system- associated ACE1 (also known as CD143), and ACE2 surface markers. Results: The studied disease groups presented distinct EV signatures. LC-19 samples exhibited the most pronounced and coordinated alterations, characterized by increased levels of CD9/CD74, CD9/CX3CR1, and CD9/ACE1-positive EVs, along with reduced overall particle concentrations. Notably, platelet-derived CD9/CD41/CD61-positive EVs were significantly elevated in both LC-19 and ME/CFS, as compared to healthy controls, indicating enhanced platelet activation. Immune-associated markers revealed differential pathway activation in LC-19, with CD74-positive EVs reflecting antigen presentation and inflammatory signaling, and CX3CR1-positive EVs indicating altered leukocyte trafficking and vascular interaction. Increased ACE1-positive EVs in LC-19 further suggested a shift toward pro-inflammatory renin-angiotensin signaling. Conclusion: Collectively, these findings support a disease-specific dysregulation of platelet, immune, and vascular pathways. The integrated EV signatures distinguish LC-19 from the related chronic conditions ME/CFS and FM, highlighting the potential of EV-based profiling for differential diagnosis. Our results provide a systems-level perspective on the differential pathophysiology of these disorders and identify EV-associated markers as candidate biomarkers with clinical value.