Characterization of Monocyte Subsets in a Prospective Cohort of Patients with Acute Stroke Suspicion: Results of BOOST Study.

Rapidly sorting patients with large vessel occlusion (LVO) ischemic stroke is crucial to ensure efficient transfers to stroke units. Peripheral monocyte subsets (classical Mon1, intermediate Mon2, non-classical Mon3) could be interesting candidate biomarkers in this setting: their profiles in the first hours after stroke symptom onset are unknown.To characterize monocyte subsets in patients admitted to emergency units for acute stroke suspicion.BOOST ("Biomarkers-algOrithm-for-strOke-diagnoSis-and-Treatment-resistance-prediction," NCT04726839) is a prospective multicenter cohort. Adult patients with symptoms suggesting acute stroke within the last 24 hours were included. Blood was collected upon admission before brain imaging. Flow cytometry (FCM) was performed on fresh blood with gating based on CD45/CD14/CD16/CD91 as well as on activation markers (CD62L/CD11b/CD86/HLA-DR/CCR2/ICAM-1/CX3CR1/TF).Of the 298 consecutive patients tested, mean age 64.0 ± 18.7 years, 64 (21.5%) had LVO stroke versus 234 (78.5%) other diagnosis (non-LVO ischemic stroke, cerebral venous thrombosis, intracranial hemorrhage, transient ischemic attack, and stroke mimics). The median time from symptom onset to sampling was 2.3 hours. We found a significantly lower proportion of Mon3 (geometric mean: -47%, p = 0.0093) and a higher proportion of Mon1 (+1.6%, p = 0.0296), suggesting earlier Mon1 mobilization and patrolling Mon3 consumption in LVO patients versus those without. Using linear-mixed-effect model, significant differences in ICAM-1 and HLA-DR expression on monocyte subsets were evidenced between LVO and other patients.This is the first study to evidence monocyte subset differences in LVO versus non-LVO patients at the time of admission, indicating an acute systemic response in LVO. Whether Mon assessment would add value for LVO diagnosis remains to be determined.