Abstract Body: Introduction: The cross-talk between the brain and peripheral immune organs plays a crucial role in the response to stroke injury. Spleen responses are implicated in stroke pathology and inflammatory responses. Hyperglycemia is known to worsen stroke outcomes, with increased immune cell infiltration into the brain. However, it remains unclear whether hyperglycemia exacerbates spleen immune cell responses and whether this contributes to the heightened immune response in hyperglycemic stroke.
Method: Male C57/BL6 mice (10-12 weeks) were subjected to transient middle cerebral artery occlusion (MCAO) for 30 minutes, followed by reperfusion to mimic ischemic stroke. Acute hyperglycemia was induced by glucose injection 10 minutes before MCAO. The study included three groups: sham, MCAO only, and MCAO with hyperglycemia (n=6-7 per group). At 24 hours post-stroke, spleen and brain immune cell populations were analyzed using our established 12-color flow cytometry technique, which simultaneously analyzes myeloid and lymphoid subpopulations.
Results: Compared with sham controls, stroke significantly decreased the numbers of dendritic cells (2.33 ± 0.48 vs. 1.50 ± 0.42 million; p<0.05), NK cells (2.30 ± 0.37 vs. 1.21 ± 0.37 million; p<0.01), Ly6C+ macrophages (0.29 ± 0.12 vs. 0.11 ± 0.06 million; p<0.01), and total lymphocytes (56.9 ± 16.6 vs. 37.0 ± 5.1 million; p<0.05) at 24 hours post-stroke in the spleen, whereas there were no significant changes in neutrophils and Ly6C+ monocytes cell counts. Hyperglycemia during stroke did not alter spleen immune cell numbers compared to stroke alone. However, hyperglycemia significantly increased brain-infiltrating immune cells at 24 hours after stroke, including neutrophils, B cells, and CD8+ T cells compared to normoglycemic mice.
Conclusion: This study provides insights into spleen immune cell responses to acute ischemic stroke and hyperglycemia. Significant changes in spleen immune cell populations after stroke confirm their potential roles in stroke pathology and recovery, warranting further investigation. Acute hyperglycemia, however, does not significantly affect spleen immune cell numbers after stroke, implying that the spleen is not the primary target of hyperglycemia-exacerbated immune cell infiltration into ischemic stroke brains. These results pave the way for exploring other mechanisms driving immune cell infiltration under hyperglycemic conditions.