Novel pathogenic B cell subsets driving tissue damage in Multiple Sclerosis. – PBS-MS

Wider research context / theoretical framework
B cells are critical to the pathophysiology of autoimmune diseases. Their depletion in the chronic autoimmune disease multiple sclerosis (MS) provides clinical benefit both at the relapsing and progressive stages. In the brain of MS patients, B cells are present in perivascular cuffs and ectopic lymphoid follicles (ELF) and are believed to contribute, at the progressive stage, to cortical grey matter demyelination and the hypoxia driven demise of neurons. The pathophysiology of MS goes beyond autoimmunity, integrating immune dysregulation, progressive immune-senescence and aging. This interdisciplinary proposal addresses these issues from a B cell centric view. We have identified a novel inflammatory B cell subset, that is enriched in the cerebrospinal fluid (CSF) of MS patients. They are susceptible to inflammaging as these B cells expand in the elderly (>65) and contribute to CD8 immune senescence. However, the nature of these B cell subsets, their cellular cross-talk, the mechanisms leading to their mobilisation and the influence of environmental factors or inflammaging on these MS B cells remains largely unknown.
Hypotheses / research questions / objectives
Our preliminary data raise 4-1BBL expressing T-bet+ B cells (4BL cells) as important mediators of inflammation in MS. To address their implication, we will 1) Define the frequency, phenotype and localization of inflammatory T-bet+ B cells and 4BL cells in MS and other inflammatory neurological diseases. 2) Establish their pathogenicity in experimental models of autoimmune demyelination. And 3) Delineate the immune mechanisms of T-bet+ B cells and 4BL cells in MS and its experimental models.
Approach / Methods
We recruit untreated patients at onset of MS, patients with other inflammatory neurological disease and non-inflammatory neurological diseases to assess the frequency and phenotype of 4BL and T-bet+ B cells in peripheral blood and CSF in association with disease activity. Secondly, using the MS brain bank in Vienna, we will study the localization, phenotype and predominance of inflammatory B cells in various brain compartments implicated in relapsing and progressive MS (meninges, perivascular cuffs, parenchyma) and establish their interaction with T cell subsets and microglia activation. Thirdly, adoptive transfer experiments in mouse models demonstrated that T-bet+ B cells expressing 4-1BBL are encephalitogenic whereas other T-bet+ B cells were not. We will use this transfer model to address the molecular and cellular mechanism driving 4BL pathogenicity relative to non-pathogenic T-Bet+ B cells. Their mechanism of action will focus on T cell and microglia interactions. These studies will be performed by using flow cytometry, spatial transcriptomics, scFFPE-RNAseq, spectrometry and spectral fluorescence imaging.
Level of originality / innovation
This project will provide the first description of 4BL and T-bet+ Bcells as mediators of inflammation in MS. The combination of analysis of blood cells, analysis of these cells in the CSF and brain compartments of MS patients and experimental evaluation of the pathogenicity of these cells in the EAE models in association with front edge technology has a high level of originality and is likely to inform novel therapeutic opportunities. Identifying 4BL+ and T-bet+ B cells as inflammatory mediators would represent a meaningful innovation for MS.
Primary researchers involved
This transdisciplinary study is lead by two researchers with a complementary arsenal of techniques and methods. Lennart MARS is trained as an immunologist with a specific interest in the pathophysiology of organ specific autoimmune diseases and has broad experience in using immunological techniques and performing animal models for MS. Jan Bauer has more than 30 years of expertise in neuropathological evaluation of MS and other human inflammatory diseases as well as animal models of MS.