Role of Polymorphonuclear Myeloid‐Derived Suppressor Cells and Neutrophils in Ischemic Stroke

BACKGROUND: Immune cells play a vital role in the pathology of ischemic stroke. Neutrophils and polymorphonuclear myeloid‐derived suppressor cells share a similar phenotype and have attracted increasing attention in immune regulation research, yet their dynamics in ischemic stroke remain elusive. METHODS AND RESULTS: Mice were randomly divided into 2 groups and intraperitoneally treated with anti‐Ly6G (lymphocyte antigen 6 complex locus G) monoclonal antibody or saline. Distal middle cerebral artery occlusion and transient middle cerebral artery occlusion were applied to induce experimental stroke, and mice mortality was recorded until 28 days after stroke. Green fluorescent nissl staining was used to measure infarct volume. Cylinder and foot fault tests were used to evaluate neurological deficits. Immunofluorescence staining was conducted to confirm Ly6G neutralization and detect activated neutrophils and CD11b(+)Ly6G(+) cells. Fluorescence‐activated cell sorting was performed to evaluate polymorphonuclear myeloid‐derived suppressor cell accumulation in brains and spleens after stroke. Anti‐Ly6G antibody successfully depleted Ly6G expression in mice cortex but did not alter cortical physiological vasculature. Prophylactic anti‐Ly6G antibody treatment ameliorated ischemic stroke outcomes in the subacute phase. Moreover, using immunofluorescence staining, we found that anti‐Ly6G antibody suppressed activated neutrophil infiltration into parenchyma and decreased neutrophil extracellular trap formation in penumbra after stroke. Additionally, prophylactic anti‐Ly6G antibody treatment reduced polymorphonuclear myeloid‐derived suppressor cell accumulation in the ischemic hemisphere. CONCLUSIONS: Our study suggested a protective effect of prophylactic anti‐Ly6G antibody administration against ischemic stroke by reducing activated neutrophil infiltration and neutrophil extracellular trap formation in parenchyma and suppressing polymorphonuclear myeloid‐derived suppressor cell accumulation in the brain. This study may provide a novel therapeutic approach for ischemic stroke.