Age-associated changes in CD4 T-cell functionality have been linked to chronic inflammation and decreased immunity. However, a detailed characterization of CD4 T cell phenotypes that could explain these dysregulated functional properties is lacking. We used single-cell RNA sequencing and multidimensional protein analyses to profile thousands of CD4 T cells obtained from young and old mice. We found that the landscape of CD4 T cell subsets differs markedly between young and old mice, such that three cell subsets—exhausted, cytotoxic, and activated regulatory T cells (aTregs)—appear rarely in young mice but gradually accumulate with age. Most unexpected were the extreme pro- and anti-inflammatory phenotypes of cytotoxic CD4 T cells and aTregs, respectively. These findings provide a comprehensive view of the dynamic reorganization of the CD4 T cell milieu with age and illuminate dominant subsets associated with chronic inflammation and immunity decline, suggesting new therapeutic avenues for age-related diseases.

The choroid plexus (CP) compartment in the ventricles of the brain comprises fenestrated vasculature and, therefore, it is permeable to blood-borne mediators of inflammation. Here, we explored whether T-cell activation in the CP plays a role in regulating central nervous system (CNS) inflammation. We show that CD4 T cells injected into the lateral ventricles adhere to the CP, transmigrate across its epithelium, and undergo antigen-specific activation and proliferation. This process is enhanced following peripheral immune stimulation and significantly impacts the immune signaling induced by the CP. Ex vivo studies demonstrate that T-cell harboring the CP through its apical surface is a chemokine- and adhesion molecule-dependent process. We suggest that, within the CNS, the CP serves an immunological niche, which rapidly responds to peripheral inflammation and, thereby, promotes two-way T-cell trafficking that impact adaptive immunity in the CNS.

Summary Microglia play a key role in innate immunity in Alzheimer disease (AD), but their role as antigen-presenting cells is as yet unclear. Here we found that amyloid β peptide (Aβ)-specific T helper 1 (Aβ-Th1 cells) T cells polarized to secrete interferon-γ and intracerebroventricularly (ICV) injected to the 5XFAD mouse model of AD induced the differentiation of major histocompatibility complex class II (MHCII)+ microglia with distinct morphology and enhanced plaque clearance capacity than MHCII− microglia. Notably, 5XFAD mice lacking MHCII exhibited an enhanced amyloid pathology in the brain along with exacerbated innate inflammation and reduced phagocytic capacity. Using a bone marrow chimera mouse model, we showed that infiltrating macrophages did not differentiate to MHCII+ cells following ICV injection of Aβ-Th1 cells and did not support T cell-mediated amyloid clearance. Overall, we demonstrate that CD4 T cells induce a P2ry12+ MHCII+ subset of microglia, which play a key role in T cell-mediated effector functions that abrogate AD-like pathology.

Highlights d Optogenetic activation of local sympathetic fibers in the colon attenuates colitis d The local sympathetic activation reduces immune cell abundance d Reduction in immune abundance is mediated by a decrease in endothelial MAdCAM-1

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