ABSTRACT NUMBER: ESOC2026LB125 INTERLEUKIN-6 RECEPTOR BLOCKADE REDUCES NEUTROPHIL EXTRACELLULAR TRAPS AND PROTECTS THE BLOOD-BRAIN BARRIER IN ISCHEMIC STROKE

Abstract Background and aims Although the Stroke Preclinical Assessment Network (SPAN) reported neutral effects of tocilizumab in rodent stroke models, this does not fully exclude the translational potential of IL-6R inhibition, as tocilizumab is a humanized antibody that does not bind the murine IL-6 receptor. We aim to use a species-matched anti-mouse IL-6R antibody (15A7) to evaluate the efficacy, optimal dose, and underlying mechanisms of IL-6R blockade in ischemic stroke. Methods Transient middle cerebral artery occlusion was induced in mice, followed by intravenous administration of 15A7 (25, 50, or 75 mg/kg) 30 min after ischemia. Infarct volume and neurological deficits were evaluated to determine the lowest effective dose. BBB disruption was assessed by Evans blue extravasation, brain water content, tight-junction protein expression (ZO-1, occludin, claudin-5), and MMP-9 levels. Neutrophil infiltration and NETs formation were examined by immunofluorescence and western blotting. Clinically, serum citH3, MPO-DNA, and occludin were measured using serum samples from 108 stroke patients receiving tocilizumab or placebo. Results 15A7 at 50 and 75 mg/kg comparably reduced infarct volume and improved neurological outcomes; therefore, 50 mg/kg was selected for subsequent experiments. At this dose, 15A7 reduced BBB leakage and cerebral edema, restored tight-junction proteins, decreased MMP-9 expression, and suppressed neutrophil infiltration and NETs formation. Clinically, tocilizumab-treated patients exhibited lower serum citH3, MPO-DNA, and occludin levels. NETs markers correlated with occludin and largely mediated the treatment effect. Conclusions IL-6R blockade could reduce infarct volume and improve neurological function, by preserving BBB integrity and reducing NETs. Conflict of interest