Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Microbiology and Immunology

Supervisor

Kerfoot, Steve M.

Abstract

B cell depleting therapies have been effective in the treatment of Multiple Sclerosis (MS), yet to date little is known about how B cells promote disease pathogenesis. B cells can be found invading the meninges around the brain and spinal cord in MS, where they cluster in association with T cells. These meningeal B cells clusters are often adjacent to demyelinating lesions suggesting this may be a site where B cells are exerting their pathogenic effects. The purpose of this thesis was to understand the contribution of meningeal B cells to central nervous system (CNS) autoimmunity, by characterizing their phenotype and determining their susceptibility to B cell depletion. Using an animal model of MS, immunofluorescence analysis, flow cytometry, or single-cell sequencing analysis was used to analyze B cells within the inflamed CNS. Interestingly, while anti-myelin T cells were readily identified in the inflamed CNS, anti-myelin B cells were excluded from this site. Non-specific B cells within the CNS were phenotypically unique from naïve B cells, exhibiting a non-classical activation status. Following treatment with anti-CD20, B cells were rapidly depleted in peripheral tissues such as the blood, lymph node and spleen, while depletion in the CNS was delayed. Following treatment there was minimal evidence that anti-CD20 accessed meningeal B cells directly, but rather that depletion was indirect and the result of ongoing turnover of the meningeal population and elimination of the peripheral pool from which it is sustained. Depleting B cells from the CNS resulted in significantly less demyelination and T cell accumulation within meningeal clusters. This suggests that B cells may be required to help with T cell reactivation within the meninges, and that depletion of B cells over time prevents ongoing local pathology. Collectively, this thesis elucidates the phenotype of B cells within the inflamed CNS of anti-myelin autoimmunity, supporting a role for their involvement in disease pathogenesis. By selectively targeting pathogenic populations of B cells this will help minimize the adverse effects that exist with current complete B cell depletion therapies.

Summary for Lay Audience

B cells, an important cell of the immune system, are the targets of some of the most effective therapies currently used to treat multiple sclerosis (MS). Despite the success these therapies have in treating patients with MS, the removal of B cells may have negative effects over time such as a weakened immune response to fighting infections. These therapies confirm that B cells are involved in MS, yet we still do not understand how B cells are driving disease. Interestingly, B cells can be found gathering into large clusters in the meninges, a protective covering of the brain and spinal cord, next to areas where damage has occurred. In this thesis I used animal models of MS to determine how B cells found within the spinal cord contribute to disease, and whether they can be targeted for removal by current B cell targeting therapies. I found that B cells located next to damaged parts of the spinal cord are unable to recognize myelin antigens, the main target in MS. Our findings suggest these B cells are interacting with other immune cells in the damaged spinal cord to further intensify the immune response. Finally, using a mouse version of B cell targeting therapy used in humans, I revealed that B cells in the spinal cord are not being targeted for removal by treatment, since the drug was not capable of crossing into the brain and spinal cord. However, by removing B cells in the periphery, B cells in the spinal cord were able to slowly be reduced as their replacement over time was stopped. This removal of B cells in the spinal cord reduced the damage that occurred over the course of disease. My thesis provides a new understanding of the damaging role of B cells in MS. Future work to characterize these B cells will allow us to identify specific targets for new MS therapies.

Available for download on Saturday, January 01, 2022

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