Update on inflammation, neurodegeneration, and immunoregulation in multiple sclerosis: Therapeutic implications

Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system of uncertain etiology. There is consensus that a dysregulated immune system plays a critical role in the pathogenesis of MS; therefore, we aim to summarize current hypotheses concerning the complex cellular and molecular interactions involved in the immunopathology of MS. Although CD4⁺ T lymphocytes have long been implicated in the immunopathology of MS, the role of other T-cell subtypes has been recognized. CD4⁺ and CD8⁺ cells have been isolated from different locations within MS lesions and γ/δ T cells have been isolated from early MS lesions. The prevalent dogma has been that CD4 ⁺ T_H1 cells release cytokines and mediators of inflammation that may cause tissue damage, although CD4⁺ T _H2 cells may be involved in modulation of these effects. Recent evidence, however, suggests that additional T-cell subsets play a prominent role in MS immunopathology: T_H17 cells, CD8⁺ effector T cells, and CD4⁺ CD25⁺ regulatory T cells. In addition, laboratory and clinical data are accumulating on the prominent role of B lymphocytes and antigen-presenting cells in MS pathogenesis. On the basis of these observations, new therapeutic approaches for MS will need to focus on resetting multiple components of the immune system.