Characterizing Region-Specific Lymphocyte Migration Within The Post-Stroke Brain

Abstract Background Studies in our lab show that while B cell-depleted mice exhibit motor deficits, impaired neurogenesis, increased anxiety, and spatial memory deficits after stroke, CD8 T cell depletion reduces post-stroke motor deficits. Therefore, we hypothesized that B cells migrate into brain regions outside the infarct to promote post-stroke motor and cognitive recovery, unlike pro-inflammatory CD8 T cells that migrate to the area of injury. Methods Naïve donor B or CD8 T cells were labeled with e450 dye and injected i.v. into recipient mice at 7, 24, 48 and 72h after receiving a 60-minute transient middle cerebral artery occlusion (tMCAo). Peripheral and brain lymphocyte migration was assessed using flow cytometry and serial two-photon tomography (STPT) 96h after tMCAo. Results e450+ lymphocytes were detected in the periphery 96h after stroke. STPT co-registered with the Common Coordinate Framework (Allen Institute) created a 3D brain reconstruction that identified lymphocyte diapedesis. B cells were found bilaterally in areas outside the ischemic penumbra, such as the olfactory areas (p<0.05) and dentate gyrus (p<0.05), whereas CD8 T cells migrated into ipsilesional areas including the somatosensory cortex (p<0.01) and brainstem (p<0.01). Conclusions B cell diapedesis differs distinctly from that of CD8 T cells throughout the ischemic brain. While B cells migrate bilaterally into brain regions mediating cognitive deficits and neurogenesis, CD8 T cells exhibit greater unilateral migration into the injured hemisphere, including motor and sensory-related areas. Future directions will determine if the spatial location of CD8 T cells or B cells mediates post-stroke pathology or supports functional recovery, respectively.