Aging impairs regulatory T cell (Treg) cells to affect late-onset (aged) multiple sclerosis (MS) – with the model of experimental autoimmune encephalomyelitis (EAE)

Abstract

Abstract A master immunoregulator FoxP3-expressing CD4+ Treg cellsplay an ameliorative role in the severity of MS/EAE disease. However, it is contradictory that the aged T cell immune system possesses relatively enhanced thymic CD4+ Treg generation and accumulated peripheral CD4+ Treg cells, but coupled with severe MS/EAE symptoms and pathology. Using single-cell (sc)-RNA-Seq assay, we found that CNS-infiltrating CD4+ Treg cells in aged EAE mouse model had increased pathogenic properties, showing co-expression of infg and il17a with foxp3, and reduced suppressive effect, exhibiting increased clonal expansion of pathogenic CD4+ T cells. These indicate changed Treg quality in aged EAE mice. Transient inhibition of aged peripheral FoxP3+ Treg cells mitigated the disease severity in the aged mice. The ameliorative effect was more significant when partially inhibiting FoxP3+ Treg cells with a drug P300i than completely depleting FoxP3+ Treg cells in FoxP3DTR transgenic mice. The mitigation is probably attributed to the correction of Treg cell distribution outside and inside the CNS. By inhibiting accumulated FoxP3+ Treg cells adhering to the brain’s choroid plexus (outside the CNS), the IFN-g-producing cells can be restored, thereby, the impediment of immune cell trafficking into the inflamed CNS is released in aged EAE mice. As a result, the proportion of myelin-specific CD4+ Treg cells inside the CNS was increased for repairing neuroinflammatory damage. Together, the underlying mechanism of severe MS symptoms in elderly patients is associated with the accumulation of Treg cells outside the CNS, which prevents the reparative antigen-specific Treg cells from entering the CNS during the disease. Supported by NIH/NIAID R01AI121147