B cells and their progenitors reside in homeostatic meninges

The central nervous system (CNS) is ensheathed by the meninges and cerebrospinal fluid. Recent findings suggest complex immunological functions of these CNS-associated border tissues. Unlike myeloid lineage cells, lymphocytes in border compartments have been largely disregarded in previous studies. Based on single cell transcriptomics, we here identified a highly location-specific composition and expression profile of tissue-resident leukocytes in every border compartment. Only the dura layer of the meninges contained a large population of B cells under homeostatic conditions in multiple species. Murine dura B cells exhibited slow turnover, long-term tissue residency and matured in experimental neuroinflammation. The dura also contained B lineage progenitors at the pro-B cell stage unexpected outside of bone marrow, without direct influx from the periphery or the skull bone marrow. This identifies the dura as an unexpected site of B cell residence and potentially development in homeostasis and neuroinflammation. Single-cell RNA sequencing of CNS-associated border compartments in rats and mice (naive and EAE)