CD11c+ CD8 T cells cause IFN-γ-dependent autoimmune neuroinflammation that is restrained by PD-1 signaling

In multiple sclerosis (MS) lesions, CD8 T cells outnumber CD4 T cells, suggesting that they contribute to MS pathology. However, little is known on the role of CD8 T cells in MS, partially due to the nearly ubiquitous use of experimental autoimmune encephalomyelitis (EAE) models that are mediated by CD4 T cells, with no CD8 T cell contribution. Importantly, MS and EAE differ in both their distribution of CNS lesions and their symptoms, indicating differences in CNS inflammation. MS lesions are more prevalent in the brain, while EAE lesions are more frequent in the spinal cord. Additionally, neurologic deficits in MS rarely parallel the paralysis typical for CD4 T cell-mediated EAE (CD4-EAE). In contrast, CD8-EAE models suggest that CD8 T cells preferentially cause brain inflammation, but little is known regarding how brain and spinal cord inflammation may differ, and how CD8 T cells may contribute to those differences. We have established an adoptive CD8-EAE mouse model characterized by brain-centered inflammation, severe ataxia, and weight loss. CNS inflammation in the brain and spinal cord differed in immune cell numbers, cellular composition, and inflammatory signatures. CD8-EAE could be suppressed by blocking IFN-γ, and exacerbated by blocking PD-1, with concomitant changes in numbers of CNS-infiltrating monocytes. Most CD8 T cells in the CNS were CD11c ⁺ , suggesting that they are the pathogenic subset. We describe a robust CD8-EAE model, identify differences between brain and spinal cord inflammation, and characterize mechanisms that control CD8 T cell-mediated neuroinflammation, thereby furthering understanding of these cells in EAE/MS.