Abstract TMP36: Sex Differences in Neutrophil-T Cell Immune Responses and Outcome After Ischemic Stroke in Aged Mice

Abstract

Introduction: Sex differences in ischemic stroke are seen in clinical and experimental studies. Men have a higher risk of stroke throughout most of the life-span. Women have greater stroke mortality than men, however a recent multi-continental meta-analysis showed lower mortality in women when adjusted for age, pre-morbid function, stroke severity and other confounding factors. In experimental models, middle-aged female mice have larger strokes, likely due to the loss of estrogen. Less is known about outcomes in very aged animals. Hypothesis: Inflammatory responses are key determinants of stroke outcome and there are important sex differences in the immune response in aged mice. Methods: Male and female C57BL/6 mice (21-22 months) were subjected to 60 min middle cerebral artery occlusion (n=28-32), or sham surgery (n=16). Neutrophils and T cells were quantified in brain and blood at 24 h and 15 days post-stroke by flow cytometry. Functional outcomes were assessed at day 3, 7 and 14. Results: Male mortality was significantly higher than in females (41% vs 16%, P<0.05). Hemorrhagic transformation was seen in 55% of the males that died (6/11) and in none of the females (0/4). Aged males had greater stroke-induced loss of body temperature, splenic contraction and gut permeability (FITC-dextran assay, n=6-7, P<0.05). Acutely after stroke (24 h), aged males had significantly higher brain infiltration of neutrophils and plasma levels of MCP-1 and G-CSF compared to females. Aged males had elevated levels of CD8 + T cells in the blood compared to females at day 15 (73±5% of CD3 + T cells vs 52±3%, P<0.001). Brain T regulatory cells were increased after stroke in males (P<0.01), but not in females. Open-field test showed decreased center visits after stroke at day 3, however males spent more time immobile (P<0.01), indicating decreased locomotor activity/anxiety. This difference equalized at 7 and 14 days post-stroke. Conclusion: Higher mortality and hemorrhagic transformation rates were seen in aged males compared to females after ischemic stroke. This was associated with higher levels of neutrophils/Tregs in the brain and CD8 + T cells in the blood suggesting a greater stroke-induced immune response in aged males.