Abstract Body: Introduction: Stroke is a leading cause of death and disability worldwide, with diabetes being a significant risk factor that exacerbates stroke outcomes. While previous studies have identified various cell populations characteristic of stroke and other neurological diseases through transcriptomic analysis of brain and blood cells, the interaction between leukocytes and brain endothelial cells during stroke remains inadequately understood. This study aimed to investigate these intercellular interactions in the context of diabetes and stroke. Methods: We utilized a permanent ischemic stroke model in leptin receptor-deficient db/db mice (a model for type 2 diabetes) and their non-diabetic counterparts, db/+ mice. Three days post-stroke, brain cells and circulating leukocytes were isolated and subjected to single-cell RNA sequencing (scRNAseq). The CellChat tool was employed to analyze the intercellular communication between these cells. Additionally, in vivo two-photon microscopy was used to observe real-time interactions between leukocytes and brain endothelial cells in cortical veins. Results: scRNAseq analysis revealed that diabetic mice had a higher proportion of myeloid cells in the blood compared to controls. Post-stroke, both diabetic and non-diabetic mice showed an increased presence of microglia and macrophages in the brain. CellChat analysis indicated that both diabetes and stroke significantly elevated the number and strength of cell-cell interactions, with the highest levels observed in the diabetic stroke group. Notably, interactions involving the integrin family and ICAM/VCAM, known for their roles in cell adhesion between blood leukocytes and brain endothelial cells, were particularly prominent in the diabetic mice. In vivo imaging confirmed significant leukocyte accumulation in the cortical veins immediately after stroke in both genotypes, with delayed clearance observed in the diabetic group. Conclusion: The findings suggest that diabetes exacerbates the inflammatory response in stroke by enhancing leukocyte-endothelial interactions, leading to prolonged leukocyte retention in the cerebral vasculature, which likely contributes to increased inflammation and worsened stroke outcomes in diabetic conditions.