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Bcl6 controls meningeal Th17-B cell interaction in murine neuroinflammation

ABSTRACT: Ectopic lymphoid tissue containing B cells forms in the meninges at late stages of human multiple sclerosis (MS) and when neuroinflammation is induced by interleukin (IL)-17 producing T helper (Th17) cells in rodents. B cell differentiation and the subsequent release of class-switched immunoglobulins have been speculated to occur in the meninges, but the exact cellular composition and underlying mechanisms of meningeal-dominated inflammation remain unknown. Here, we performed in depth characterization of meningeal vs. parenchymal Th17-induced rodent neuroinflammation. The most pronounced cellular and transcriptional differences between these compartments was the localization of B cells exhibiting a follicular phenotype exclusively to the meninges. Correspondingly, meningeal but not parenchymal Th17 cells, acquired a B cell-supporting phenotype and resided in close contact with B cells. This preferential B cell tropism for the meninges and the formation of meningeal ectopic lymphoid tissue was partially dependent on the expression of the transcription factor Bcl6 in Th17 cells, that is required in other T cell lineages to induce isotype class-switching in B cells. A function of Bcl6 in Th17 cells was only detected in vivo and was reflected by the induction of B cell-supporting cytokines, the appearance of follicular B cells in the meninges, and of immunoglobulin class-switching in the CSF. We, thus, identify the induction of a B cell-supporting meningeal microenvironment by Bcl6 in Th17 cells as a novel mechanism controlling compartment-specificity in neuroinflammation.

ORGANISM(S): Mus musculus

PROVIDER: GSE178085 | GEO | 2021/07/30

REPOSITORIES: GEO

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Project description:The meningeal space is an important structure in the brain borders, which provides immunosurveillance for the central nervous system, but the impact of infections on the meningeal immune landscape is far from being fully understood. Trypanosoma brucei, the causative agents of Human African Trypanosomiasis or sleeping sickness, accumulates in the meningeal spaces, inducing severe meningitis and resulting in death if left untreated. Thus, sleeping sickness represents an attractive model to study immunological dynamics in the meninges during infection. Here, combining single cell transcriptomics and mass cytometry by time of flight (CyTOF), coupled with in vivo interventions, we found that chronic T. brucei infection triggers the development of ectopic lymphoid aggregates (ELAs) in the murine meninges during chronic infection. These infection-induced ectopic structures are defined by the presence of ER-TR7+ fibroblastic reticular cells (FRCs) and follicular dendritic cells (FDCs) that initiate a signalling cascade driving local T cell activation towards a T follicular helper (TFH)-like phenotype, as well as B cell class switching. Furthermore, the meningeal-resident plasma cells display activity typically associated with germinal centre reactions and are able to produce antibodies able to recognise mouse brain antigens, which correlates with cortical (and white matter) demyelination. Lastly, we found that systemic lymphotoxin (LT) signalling blockade led to a significant depletion of meningeal FDCs and autoreactive B cells, indicating that LTsignalling is critical to induce and maintain local responses in the meninges. Taken together, we provide evidence that the meningeal immune response results in the acquisition of lymphoid tissue-like properties during chronic T. brucei infection. These findings have broader implications for understanding the mechanisms underlying the formation ELAs during chronic inflammation resulting in autoimmunity, as observed in other demyelinating neurodegenerative disorders such as multiple sclerosis.

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Bcl6 controls meningeal Th17-B cell interaction in murine neuroinflammation

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