Intrathrombus NETosis Defines Prognostically Distinct Phenotypes in Large-Vessel Occlusion Stroke

Background: Immunothrombosis is increasingly recognized in large-vessel-occlusion acute ischemic stroke (LVO-AIS), yet most biomarker studies infer thrombus biology from circulating neutrophil extracellular trap (NET) markers or from pre-defined thrombus subtypes. We prospectively studied 160 patients with anterior-circulation LVO-AIS treated with mechanical thrombectomy to determine whether intrathrombus NETosis markers identify thrombus phenotypes with distinct clinical trajectories, and whether plasma NETosis biomarkers reflect the molecular composition of thrombi. Methods: Thrombi underwent quantitative histopathology and immunohistochemistry for citrullinated histone H3 (CitH3), neutrophil elastase (NE) and CD61. Thrombi were analyzed without prior etiological or histological stratification, and intrathrombus markers were dichotomized at cohort medians (CitH3 6.62%, NE 3.95%, CD61 23.09%) to define internally standardized candidate phenotypes. Associations with thrombus composition, collateral circulation (Tan 2-3), 3-month functional independence (modified Rankin Scale 2 or less) and long-term mortality were assessed by correlation analyses and progressively adjusted multivariable models, with cross-compartment correlations corrected by the Benjamini-Hochberg false discovery rate (FDR). Results: Intrathrombus markers defined prognostically distinct phenotypes: CD61 tracked functional recovery, NE preserved collateral circulation and CitH3 long-term survival, each remaining significant after multivariable adjustment. Circulating NE, myeloperoxidase and leukocyte count instead tracked the macroscopic red-blood-cell-fibrin composition of retrieved thrombi. Cross-compartment concordance was limited: after FDR correction the only significant plasma-thrombus association was an inverse correlation between plasma cell-free DNA and intrathrombus NE, and no intrathrombus marker correlated positively with its circulating counterpart. Conclusions: Local immunothrombotic signatures therefore provide clinically relevant information not captured by plasma markers, and median-defined intrathrombus thresholds represent hypothesis-generating cutoffs for external validation and NET-targeted treatment stratification.