MAIT cell deficiency exacerbates neuroinflammation in P301S human tau transgenic mice

The role of immune cells in neurodegeneration remains incompletely understood. Our recent study revealed the presence of mucosal-associated invariant T (MAIT) cells in the meninges, where they express antioxidant molecules to maintain meningeal barrier integrity. Accumulation of misfolded tau proteins are a hallmark of neurodegenerative diseases. The role of MAIT cells in tau-related neuroinflammation and neurodegeneration, however, remains unclear. Here we report that the meninges of P301 mutant human tau transgenic mice had increased numbers of MAIT cells, which retained their expression of antioxidant molecules. Mr1-/-P301S mice that lacked MAIT cells exhibited increased tau pathology and hippocampus atrophy compared to control Mr1+/+ P301S mice. Adoptive transfer of MAIT cells reduced tau pathology and hippocampus atrophy in Mr1-/- P301S mice. Meningeal barrier integrity was compromised in Mr/-/-P301S mice, but not in control Mr1+/+ P301S mice. A distinctive microglia subset with proinflammatory gene expression profile (M-inflammatory) was enriched in the hippocampus of Mr1-/- P301S mice. The transcriptomes of the remaining microglia in these mice also shifted towards a proinflammatory state, with increased expression of inflammatory cytokines, chemokines, and genes related with ribosome biogenesis and immune responses to toxic substances. The transfer of MAIT cells restored meningeal barrier integrity and suppressed microglial inflammation in the Mr1-/- P301S mice. Together, our data indicate an important role for MAIT cells in regulating tau-pathology-related neuroinflammation and neurodegeneration.