Abstract TP107: B cells Migrate to Remote Areas Supporting Functional Recovery After Stroke

Abstract

Background: Neuronal networks in the post-stroke CNS undergo significant reorganization and plasticity to compensate for loss of function in stroke-injured tissue. Studies in our lab show that B cell-depleted mice exhibit impaired neurogenesis, increased anxiety, and spatial memory deficits after stroke. These post-stroke deficits generally occur in areas outside of the ischemic infarct. Therefore, we hypothesized that B cells migrate into CNS regions outside the ischemic penumbra to promote post-stroke neuroplasticity and functional recovery. Methods: Donor B cells were isolated from spleens of adult 6-8 week old male C57Bl/6J (B6; Jackson Labs) mice 10 days after receiving a 60-minute transient middle cerebral artery occlusion (tMCAo). B cells were labeled with a fluorescent proliferation dye (e450; eBioscience). Recipient mice expressing YFP in cortical neurons (B6 background; Jackson labs) received B cells (0.2-5X10 6 B cells) in the contralesional ventricle 2 days post-tMCAo. B cell migration was assessed 4 days after intraventricular injection using 3D serial two-photon microscopy (TissueCyte 1000 microscope, TissueVision, Cambridge, MA). Peripheral migration of B cells into spleen and cervical lymph nodes was assessed using flow cytometry. Results: 3D brain reconstruction showed infarcted regions characterized by a loss of neuronal YFP and diffuse blue fluorescence. B cells, identified with punctate blue labeling, exhibited CNS regional-specific migration after stroke. This included B cell populations in bilateral hippocampus, amygdala, and brain stem nuclei; all areas outside the identified infarct region. Furthermore, migration of B cells into peripheral organs was also detected 4 days post stroke following intraventricular injection. Conclusions: Our in vivo migration studies highlight the migration of B cells to regions outside the ischemic penumbra, coinciding with our preliminary behavioral studies in B cell-depleted mice. We also observed an outward migration of B cells from the CNS to the periphery, which may have local implications that need to be further investigated. These results are the first to indicate the potential for neurotrophic B cell support in remote cortical regions following ischemia.