Ageing promotes non-remitting experimental autoimmune encephalomyelitis with persistent meningeal inflammation and subpial demyelination in A/T SJL/J mice

Abstract Current therapies for multiple sclerosis (MS) reduce the frequency of relapses but fail to prevent transition from relapse-remitting into progressive MS. Subpial demyelination, meningeal inflammation and neurodegeneration are hallmarks of progressive MS, however there is no single animal model that mimics all these features. Adoptive transfer of proteolipid protein (PLP)-primed Th17 cells into young (~12 weeks old) SJL/J recipient mice induces experimental autoimmune encephalomyelitis (EAE) characterized by subpial demyelination associated with meningeal tertiary lymphoid tissues (TLTs), however young mice develop remitting, non-progressive disease. Since age is a risk factor for transitioning to progressive MS, we hypothesized that adoptive transfer of PLP-primed Th17 cells into old (~12 months old) SJL/J recipient mice would promote a progressive phenotype. Indeed, transfer of cells into aged recipient mice resulted in a non-remitting EAE compared to young recipients despite a similar ability to produce T cell derived cytokines in the CNS at peak disease. However, old mice showed persistent meningeal inflammation as evidenced by more B/T cell rich TLTs in the meninges compared to young mice, and developed increased CNS pathology (subpial demyelination, microglia/macrophage activation, glial limitans disruption, axonal injury, loss of synapses), whereas young EAE mice had recovered most of the pathology seen at peak of disease by day 25 post-transfer. In summary, our model provides an opportunity to assess how subpial demyelination associated with meningeal inflammation impacts the transition from relapse-remitting to progressive MS in a single animal model.