Alzheimer's Amyloid Disrupts Gut Immunity and Drives Brain-Gut Immune Cell Migration

Alzheimer's disease (AD) involves not just brain pathology but systemic disruptions that extend to the gut. The gut-brain axis—bidirectional communication between intestinal microbiota, immune cells, and the CNS—has emerged as a promising target, yet the specific immunological alterations in the gut during AD remain poorly characterized. This study provides one of the most comprehensive characterizations to date of the colonic immune compartment in an amyloid-driven AD model.

The researchers used the well-validated 5XFAD mouse model, which expresses five familial AD mutations and develops amyloid-β (Aβ) plaques by ~2 months and pyramidal neuron loss by 9 months. Focusing on 9-month-old female mice—the sex more severely affected in this model—they performed single-cell RNA sequencing (scRNA-seq) on sorted CD45+ colonic immune cells from 5XFAD and wild-type littermates, producing a map of 3,443 cells across 17 immune clusters. This was complemented by high-dimensional spectral flow cytometry, immunofluorescence, ELISA, and 16S microbiome sequencing.

Across all colonic immune populations, 5XFAD mice showed 561 differentially expressed genes. Upregulated pathways included ribosomal biogenesis, oxidative phosphorylation, reactive oxygen species, and neurodegenerative disease-associated KEGG pathways—indicating metabolic stress and innate immune activation. Downregulated genes included Igha, Ighm, Cd79b, Cd22, and Irf8, pointing to suppressed B cell and antibody activity. Most strikingly, CXCR4-high antibody-secreting cells (ASCs) were markedly reduced in 5XFAD colons. Concurrently, CXCR4+ B lineage cells accumulated in the 5XFAD brain, and IgA+ plasma cells were elevated in the dura mater—the meningeal border accessible to gut-derived immune cells. The AD brain showed significantly elevated CXCL12, the cognate chemokine ligand for CXCR4. This CXCL12-CXCR4 axis was also confirmed in silico using publicly available human AD brain transcriptomic datasets, suggesting translational relevance.

To test whether dietary modulation of the gut could counter these changes, the team administered inulin—a prebiotic fiber shown to support gut health and cognition—to 5XFAD mice. Inulin expanded colonic IgA+ ASCs, rescued circulating regulatory T cell (Treg) levels, reduced gut dysbiosis, improved serum levels of short-chain fatty acids (SCFAs), bile acids, and indole metabolites, and significantly attenuated overall AD-associated frailty scores. Inulin also reduced brain CXCL12 levels and total CD45+ immune cell infiltration into the brain, suggesting that gut-targeted interventions can modulate neuroimmune trafficking.

These findings establish a mechanistic framework in which Aβ-driven AD reprograms the colonic immune environment, particularly depleting gut-retaining CXCR4+ ASCs, while simultaneously upregulating brain CXCL12 to attract these cells to the CNS. The study positions the gut-brain immune axis as both a driver of and potential intervention target in AD pathology.