Peripheral Immune Memory at the Neuroimmune Interface

Resolve which peripheral memory compartments actually seed or amplify CNS inflammation during aging and neurodegeneration. Boundary domains: neuroinflammation, neurodegeneration. Representative papers: Traumatic Brain Injury and Risk of Neurodegenerative Disorder.; Role of gut-brain axis, gut microbial composition, and probiotic intervention in Alzheimer’s disease.; The path to next-generation disease-modifying immunomodulatory combination therapies in Alzheimer’s disease.

Resolution requires: (1) Identification of >=2 peripheral immune memory compartments linked to CNS inflammation via Mendelian randomization; (2) Fluid biomarker distinguishing memory vs. naive immune cells (AUC >= 0.80); (3) Functional validation depleting identified compartment reduces CNS inflammation (>=30% reduction); (4) KG edges linking peripheral immune to neurodegeneration. Deliverable: mechanistic validation + biomarker panel.

Peripheral immune memory cells—particularly tissue-resident memory T cells (TRM) and long-lived plasma cells—are increasingly recognized as active participants in CNS immunosurveillance and neuroinflammation. Studies in aging and neurodegeneration models demonstrate that systemic inflammatory states driven by dysregulated peripheral memory compartments can trigger microglial priming, accelerating neuroinflammatory phenotypes. A study of systemic inflammation causing microglial dysfunction with a vascular AD phenotype (Brain, Behavior and Immunity 2023) showed that peripheral inflammatory priming directly translates to CNS microglial state transitions. The gut-brain axis further connects peripheral immune memory shaped by microbiome composition to CNS inflammatory status, with microbial metabolites and microbiome-primed immune cells trafficking signals to the brain via vagal afferents, enteric nervous system, and systemic circulation (Gut-brain axis, gut microbial composition, and probiotic intervention, Life Sciences 2021).

The gap is resolving which peripheral memory compartments actually seed or amplify CNS inflammation during aging and neurodegeneration. The meningeal lymphatic system and choroid plexus serve as critical interfaces, but the trafficking routes of specific memory subsets—effector-memory vs. central-memory T cells; IgG vs. IgA plasma cells—into the CNS parenchyma during aging are poorly mapped. Whether peripheral TRM cells at barrier sites (gut, lung) exert remote effects on microglia through soluble mediators or require physical CNS entry is contested. The role of the hippocampus as an immunologically sensitive structure has been highlighted in studies linking peripheral immune dysregulation to impaired adult neurogenesis, suggesting a direct neurogenic consequence of peripheral immune memory dysregulation (Hippocampal adult neurogenesis and the immune system, Journal of Neurological Sciences 2017).

Recent work has revealed that meningeal B cells producing antibodies against self-antigens are elevated in aged mice and may seed neuroinflammatory cascades. Single-cell atlases of the aging CNS immune compartment are capturing peripheral-derived infiltrates with increasing resolution. Tools combining parabiosis, fate-mapping, and spatial transcriptomics are beginning to dissect the peripheral-CNS immune interface, but causality between peripheral memory dynamics and neurodegeneration onset—versus correlation driven by shared inflammatory environments—remains to be established definitively in human cohorts.