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People living with multiple sclerosis (MS) experience episodic central nervous system (CNS) white matter lesions instigated by autoreactive T cells. With age, MS patients show evidence of grey matter demyelination and experience devastating non-remitting symptomology. What drives progression is unclear and has been hampered by the lack of suitable animal models. Here we show that passive experimental autoimmune encephalomyelitis (EAE) induced by an adoptive transfer of young Th17 cells induces a non-remitting clinical phenotype that is associated with persistent leptomeningeal inflammation and cortical pathology in old, but not young SJL/J mice. While the quantity and quality of T cells did not differ in the brains of old vs young EAE mice, an increase in neutrophils and a decrease in B cells was observed in the brains of old mice. Neutrophils were also found in the leptomeninges of a subset of progressive MS patient brains that showed evidence of leptomeningeal inflammation and subpial cortical demyelination. Taken together, our data show that while Th17 cells initiate CNS inflammation, subsequent clinical symptoms and grey matter pathology are dictated by age and associated with other immune cells such as neutrophils.

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.

CpG-DNA or synthetic oligodeoxynucleotides containing CpG motif (CpG-ODNs) strongly activate dendritic cells (DCs) and macrophages to produce proinflammatory cytokines including IL-6, IL-12 and TNF?. It has been suggested that CpG-DNA activates TLR9, which in turn recruits MyD88, IRAK4, IRAK1 and TRAF6, leading to activation of AP-1 and NF-?B, which are critical for immune gene expression. However, whether DNA binding proteins are involved in activation of the CpG-DNA pathway remains elusive. Here we demonstrate that Ku70 is involved in this process. Administration of CpG-ODN into Ku70-deficient mice and in vitro stimulation of bone marrow-derived DCs (BMDCs) as well as bone marrow-derived macrophages (BMDMs) from these mice resulted in defective induction of IL-6 and TNF?. Loss of Ku70 impaired activation of its downstream kinases, the I?B kinase (IKK) and the mitogen-activated protein kinases (MAPKs), by CpG-ODN. Intriguingly, in macrophages ablation of Ku70 largely abrogated IRF1 expression and subsequent IL-12 response to CpG-ODN; in BMDCs Ku70 deficiency only reduced IL-12 response to CpG-ODN at a low dose within early treatments, and had no apparent effects on this response in late treatments. Thus, our results suggest that Ku70 is important for differential regulation of inflammatory cytokine response to CpG-DNA. In addition, we have identified a mechanism for involvement of Ku70 in activation of the CpG-DNA pathway.