Mechanisms of Multiple Sclerosis Tissue Pathology

Multiple sclerosis (MS) research has largely focused on white matter (WM) pathology, however recent studies on MS tissue from late stage disease suggest cortical damage is an important correlate of disability; is driven by organized late meningeal inflammation; and cortical demyelinated (CDM) lesions lack macrophage and lymphocytic infiltrates. Since actively demyelinating cortical lesions are sparse at this late stage, it is difficult to characterize the mechanisms behind the cortical damage. Our prior funded research focused on early biopsy and autopsy MS cases and revealed CDM occurs early; can be inflammatory; and meningeal inflammation is prominent. These findings correlate well with recent MRI reports demonstrating cortical damage in early MS. In concert with recent experimental reports, we propose novel hypotheses about the role(s) of meningeal inflammation and cortical pathology in promoting the MS disease process. We hypothesize cortical pathology can be an early event in MS, and is related to early meningeal inflammation. We will define the frequency and extent of CDM in an early MS cohort and determine its relationship to meningeal aggregates in early and late disease. We propose contact between myelin-specific T cells from the periphery and meningeal antigen presenting cells (APCs) occurs early in the subarachnoid space (SAS); expands myelin-specific T cells; and generates new memory cells which traffic to cervical lymph nodes (LN) via CSF, promoting subpial DM. We will characterize T cells and APCs in the SAS and define the nature of T cell-APC contacts. Our preliminary data demonstrates myelin laden macrophages in both SAS and CDM lesions. We hypothesize CDM generates macrophage/dendritic cells laden with myelin antigen and bearing trafficking determinants indicative of capability to access lymph nodes via CSF and perpetuate (auto)immunity. We aim to characterize if these cells have a mature dendritic phenotype. We have identified meningeal inflammation during early MS. We propose these early meningeal aggregates set the stage for long-lasting lymphoid aggregates in the SAS which drive ongoing cortical damage in progressive MS. We will characterize these infiltrates for indications of early lymphoid aggregate character. We find T-cell inflammation may be prominent in early CDM, but more transient than WM lesions. We propose this transient inflammation relates to expression of LN trafficking chemokines on cortical T cells which facilitate their rapid exit. We will examine T cells in CDM and WM lesions for these trafficking determinants. We propose CDM and inflammation mediate cortical injury, and that subpial DM will proceed by mechanisms distinct from those observed in WM based lesions. We will characterize and define relationships between inflammatory and neurodegenerative pathology in cortical lesions, and compare CDM and WM lesions with respect to targets and mechanisms of DM. These experiments addressing novel hypotheses; provide a rare opportunity to assess pathogenic relevance of animal data to MS pathology; build upon our unique well phenotyped tissue resources; and carry the potential to discern new therapeutic targets.