Research at the Buck Institute for Research on Aging reveals that in a mouse model of Alzheimer’s disease (5XFAD), gut immune cells migrate into the brain, likely driven by chemokine CXCL12 and its receptor CXCR4. This migration corresponds with reduced gut plasma B cells and increased IgA+ B cells accumulation in the brain, implicating gut-derived immune cells in neurodegenerative pathology. Additionally, dietary fiber ameliorated these immune changes and AD-related symptoms, highlighting the critical role of the gut-brain axis and the potential of nutritional interventions in modulating neuroinflammation.