Immunopathogenesis of multiple sclerosis

Abstract

Multiple sclerosis (MS) is a suspected autoimmune disease in which myelin-specific CD4+ and CD8+ T cells enter the central nervous system (CNS) and initiate an inflammatory response directed against myelin and other components of the CNS. Acute MS exacerbations are believed be the result of active inflammation, and progression of disability is generally believed to reflect accumulation of damage to the CNS, particularly axonal damage. Over the last several years, the pathophysiology of MS is being appreciated to be much more complex, and it appears that the development of the MS plaque involves a large number of cell populations, including CD8+ T lymphocytes, B cells, and Th17 cells (a population of helper T cells that secrete the inflammatory cytokine IL-17). The axonal transection and degeneration that is thought to represent the basis for progressive MS is now recognized to begin early in the disease process and to continue in the progressive forms of the disease. Molecules important for limiting aberrant neural connections in the CNS have been identified, which suppress axonal sprouting and regeneration of transected axons within the CNS. Pathways have also been identified that prevent remyelination of the MS lesion by oligodendrocyte precursors. Novel neuroimaging methodologies and potential biomarkers are being developed to monitor various aspects of the disease process in MS. As we identify the pathways responsible for the clinical phenomena of MS, we will be able to develop new therapeutic strategies for this disabling illness of young adults.

Keywords: Magnetic resonance imaging; multiple sclerosis; pathogenesis; review.

Figure 1

Th17 cells are present in the CNS and expand in the presence of IL-23. Resident CNS microglial cells have the capacity to produce IL-23, IL-6, and TGF-β, which could contribute to the differentiation and expansion of this unique Th17 cell population observed in the CNS. Silencing T-bet with siRNA inhibits IL-23R expression and subsequent expansion of Th17 cells.[24]