Pathological mechanism of secondary-progressive multiples sclerosis and its animal model.

Development of acute experimental autoimmune encephalomyelitis (EAE) depends on Th17 cells expressing the nuclear factor NR4A2, which we have previously reported to be upregulated in peripheral blood T cells from patients of multiple sclerosis (MS). EAE induced in mice lacking NR4A2 in T cells showed a great reduction in Th17-mediated acute symptoms, whereas a late-onset disease independent of NR4A2 was still inducible. We identified cytotoxic T-cell-like CD4+ T cells expressing the T-box transcription factor Eomesodermin (Eomes) as a pathogenic component for the development of the late-onset disease. Furthermore, T cell-specific deletion of the Eomes gene or Eomes-specific RNA interference in vivo remarkably ameliorated the late-onset EAE. Intriguingly, similar Eomes-expressing CD4+ T cells are increased in the peripheral blood and cerebrospinal fluid only from patients with secondary-progressive MS accompanied by neurodegenerative symptoms, but not in relapsing-remitting MS. Mechanistic analysis revealed that granzyme B was secreted by Eomes-expressing CD4+ T cells and the activation of protease-activated receptor-1 by granzyme B is involved in the neuroinflammation observed in the late-onset EAE.