Leucocytes platelets co-aggregates remain elevated in patients with perfusion defects after pulmonary embolism

<b>Background:</b> Up to 50% of patients develop perfusion defects (PD) after pulmonary embolism (PE) but reasons remain misunderstood. Experimental studies suggest that neutrophils and platelets via neutrophil extracellular traps (NETs) could play a central role in initiation and organisation of venous thrombosis. <b>Aims:</b> We aimed to assess if markers of leucocytes and platelets activation are elevated at the acute phase of PE and remain elevated in patients with PD. <b>Methods:</b> Patients with a first episode of PE were prospectively followed. Ventilation/perfusion lung scan was performed after 6 months of anticoagulation. A pulmonary vascular obstruction &gt;10% defined PD.Leucocytes platelets co-aggregates (CD45+CD41+) and platelets progenitors cells (CD133+CD34+CD41+/CD34+)were measured by flow cytometry at diagnosis of PE and at 6 months. The rates were compared to those from healthy volunteers. In an independent cohort, NETs were measured by ELISA on serum obtained 6 months after PE (n=617) and compared to controls without PE (n=411). <b>Results:</b> 39 patients were included, 9 (23%) had PD. Compared with controls, leucocytes platelets co-aggregates were significantly elevated at diagnosis of PE (3.4 10⁶ cells/mL versus 2.2 10⁶ cells/mL; p=0.0003); and remained elevated at 3 and 6 months after diagnosis in patients with PD as compared with those without. Platelets progenitors cells are lower at diagnosis of PE compared to controls (852 cells/ml vs 1167 cells/ml; p=0.04) but didn9t differ according to PD.NETs were not elevated 6 months after PE whatever the presence of PD. <b>Conclusions:</b> Leucocytes platelets co-aggregates are elevated at the time of acute PE and remained elevated in patients with PD.