NRSA Fellowship for Annabel McAtee: Elucidating the Role of the Dura Mater in the Post- Stroke B Cell Response

After ischemic stroke, B cells play both detrimental and beneficial roles in injury and/or functional recovery depending on responding subset and timing of activation. There is interest in developing novel immune- modulating therapies for stroke patients, but clinical trials have had limited success, partly because key factors that determine which subsets are helpful or harmful remain to be elucidated. Recent discoveries show that the dura mater plays an active role in the immune environment of the brain in health and disease. Further, the dura was recently shown to be a hub of B cell development from immature to mature antibody-secreting populations. However, the roles of dura-localized B cells after stroke are unknown. The overall objective of this proposal is to determine if, after stroke, B cells in the dura form antibody-secreting subsets that travel to the brain and worsen functional recovery. This project will address a key gap in knowledge on the unique properties of immune cells in this novel niche and may allow for the development of therapies that differentially target these cells without affecting other populations. The central hypothesis is that, after stroke, dura-localized B cells mature into plasma cells, travel to the brain, and release CNS antigen-specific antibodies that impede functional recovery. To test this hypothesis, a mouse model of transient middle cerebral artery occlusion (tMCAo) in aged male and female mice (>16 mos., n=12/sex), combined with B cell depletion methods will be used. Aim 1 hypothesis is that dura B cells are exposed to more inflammatory cytokines compared to cervical lymph node B cells, leading to a robust development of B cell activation and maturation that is stronger than lymph node activation. This aim will achieve a full characterization of dura B cells at 3 days, 10 days, and 7 weeks following stroke using 1) flow cytometry, 2) histology, and 3) single cell B cell receptor sequencing. Aim 2 hypothesis is that ischemic stroke induces autoreactivity of dura-localized B cells that contribute to worsened functional outcome. This aim includes a series of selective B cell depletion assays in human (h)CD20- expressing mice with dura versus systemic population depletion via Rituximab for 7 weeks. Motor and cognitive testing (rotarod, Y maze, open field) will be assessed every week and B cell depletion by niche will be confirmed. The expected outcome is an increased understanding of the role of dura-localized B cells in post- stroke recovery, leading to eventual development of effective immunotherapies. The trainee will gain experience with a number of experimental techniques and statistical analyses, and will be well positioned for a career as a neurosurgeon-scientist.