Abstract DP166: Prior Cerebral Ischemia Modifies The Peripheral Immune Response To Acute Ischemic Stroke

Introduction: Tissue damage after ischemic stroke triggers a local and systemic inflammatory cascade that contributes significantly to morbidity and mortality after stroke. The contribution of adaptive immunity to the early sequela of ischemic stroke is poorly understood. Prior cerebral ischemia and blood brain barrier breakdown can sensitize the peripheral immune system to CNS antigens. This can result in a more robust immune response to a subsequent stroke, potentially leading to higher morbidity. Methods: We used frozen PBMC samples from male and female patients with acute ischemic stroke (collected 72 hrs from ictus) stored in our biobank. Patient MRIs were reviewed to verify the presence of an acute infarct and prior cerebral ischemia. Samples were grouped by the presence (double stroke, DS) or absence (single stroke, SS) of a prior stroke. Cells were washed, Fc blocked, barcoded and stained with metal conjugated antibodies for mass cytometry (CyTOF). Data was acquired on a Helios mass cytometer and gated to identify cell populations. Differences in the immunological profile between groups was analyzed using Wilcoxon tests. Results: We analyzed the peripheral immune response to acute ischemic stroke in 26 DS patients (13 M, 13 F), and 23 SS patients (12 M, 11 F) using mass cytometry. Staining for 42 cellular markers yielded 8 immune cell types and 30 subpopulations. Male DS patients had a lower percentage of regulatory T cells compared to male SS patients (p<0.05). Compared to female SS patients, female DS patients had more profound differences in the immune response to a second stroke, with higher monocytes, NK cells and CD4 effector memory T cells (p<0.05). Between sexes, male DS patients had a higher percentage of granulocytes, particularly neutrophils, while female DS patients had a higher proportion of CD4 effector memory and regulatory T cells. Females with DS also had worse outcomes at discharge compared to DS males with a higher proportion discharged with an mRS of 4-6 (75% vs 50%). Conclusions: The presence of prior cerebral ischemia modifies the immune response to acute ischemic stroke, which differs between sexes. The immune response to double stroke in females suggests a heightened peripheral inflammatory state with higher innate and adaptive effector immune cells, also reflected in worse discharge outcomes. Sex and prior stroke must be carefully considered in future investigations of biomarkers and therapeutics centered on the immune response to stroke.