T Helper Cells and Cytokine Networks in the Immunopathogenesis of Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic autoimmune disorder of CNS with demyelination, neurodegeneration and compartmentalized inflammatory disorder. Excessive T-helper cell (CD4+) activation and unregulated cytokine signaling play a key role in its onset and progression. These changes impair communication between peripheral immune cells and CNS resident microglia, astrocytes and oligodendrocytes. This review provides an overview on the contribution of specific subsets of T-helper cells to MS pathology/immunity. Th1 cells release interferon-γ and lymphotoxin, that stimulate activation of myeloid cells/antigen presentation. Activated by IL-23, the Th17 cells produce IL-17A/F that lowers the blood-brain barrier (BBB) integrity, recruit neutrophils and monocytes, and enhance microglial killing. Activation of CD4+ T cells leads to activation of B cells via T follicular helper cells which couple these processes through the production of IL-21 and CXCR5. This leads to the development of tissue-like aggregates and intrathecal antibody production. T-cell plasticity adds to epitope spreading as well as chronic inflammation, IL-22, IL-9, IL-1β, IL-6, and TGF-β (these are additional mediators involved in the regulation of effector phenotypes). In MS, the regulation of dendritic cell co-stimulation and of glial activation often does not work. This is due to the lack of control of dendritic-cells co-stimulation and the lack of regulation of glial activation by regulatory pathways such as FOXP3+ regulatory T cells and Tr1 cells that secrete IL-10 and TGF-Beta. The review also explores the cytokine network biomarkers, CSF and serum signatures and single-cell immune states, as well as existing and new drugs. These include migration blockade, targeting of S1P-receptors, anti-CD20 therapy, targeting of Th17/GM-CSF and JAK-STAT pathways, low-dose IL-2, approaches of targeting antigens and engineered Tregs. Investigating the areas of stage and compartment-specific CD4+ T-cell circuits can help to advance targeted immunomodulation in progressive MS and neuro-repair.