The monolayer formed by the choroid plexus (CP) epithelium is connected by tight junctions and separates periphery and brain. While CP epithelium produces most cerebrospinal fluid (CSF), CP stroma hosts immune cells. In multiple sclerosis (MS) immune cells are increased in CSF implying CP as an entry site for encephalitogenic T cells into the brain. Despite that CSF components (cells and biologically active molecules) interact with the brain and spinal cord, our understanding of the role of CP in homeostasis and in MS is still scarce. In MS, myelin produced by oligodendrocytes is targeted for destruction by the immune system. The major research theme of this project is to study the CP, a forgotten central player in brain homeostasis and in MS. More specifically, we want to elucidate the role of CP in the pathogenesis of MS by investigating the impact of CP on three key events for MS: myelination, demyelination and remyelination. For that, we will apply single-cell genomics techniques on CP cells to elucidate fundamental aspects of these three events.