Midbrain cytotoxic T cells as a distinct neuropathological feature of progressive supranuclear palsy
Blas Couto, Shelley L. Forrest, Conor Fearon, Seojin Lee, Samantha Knott, Jun Li, Susan H. Fox, Maria Carmela Tartaglia, Anthony E. Lang, Gábor G. Kovács
Abstract
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by four-repeat (4R) tau protein deposition. The substantia nigra (SN) and midbrain tegmentum nuclei (MBT) are consistently affected. Lymphocyte infiltrates are scarce in the brains of patients with neurodegenerative diseases, although a few reports have described their presence in the α-synucleinopathy Parkinson's disease (PD). To evaluate the cytotoxic T-cell response, serial sections spanning 120 μm of the SN were immunostained consecutively for phosphorylated tau (p-tau, AT8) or α-synuclein, cytotoxic T-cell marker and microglia marker HLA-DR. Sections were analysed with stereology software in 9 patients with PSP, 10 with PD and 6 healthy controls. We semiquantitatively scored CD8-positive cells in further brain regions. CD8 lymphocyte cell counts and microglial activation in the SN were higher in PSP than PD and controls. Furthermore, T-cell/neuron contact was observed in PSP. In multivariate models, CD8 counts were not predicted by disease duration, younger age at death or the amount of p-tau pathology. The SN and midbrain tegmentum showed more CD8 cells than the cortex. A more prominent nigral cytotoxic T-cell response in PSP than PD supports the suggestion that p-tau neuropathology in PSP might have potential relationships with autoimmune mechanisms.