Sex-dependent APOE4 Neutrophil-microglia interactions drive cognitive impairment in Alzheimer's Disease

APOE4 is the strongest genetic risk factor for Alzheimer's disease (AD), with increased odds ratios in females. Targeting amyloid plaques shows modest improvement in male non-APOE4 carriers. Leveraging single-cell transcriptomics across APOE variants in both sexes, multiplex flow cytometry, and validation in two independent cohorts of APOE4 female AD patients, we identify a new subset of neutrophils interacting with microglia associated with cognitive impairment. This phenotype is defined by increased IL-17 and IL-1 co-expressed gene modules in blood neutrophils and in microglia of cognitively impaired female APOE e4 carriers, showing increased infiltration to the AD brain. APOE4 female IL-17+ neutrophils upregulated the immunosuppressive cytokines IL-10 and TGFB and immune checkpoints, including LAG-3 and PD-1, associated with accelerated immune aging. Deletion of APOE4 in neutrophils reduced this immunosuppressive phenotype and restored the microglial response to neurodegeneration (MGnD), limiting plaque pathology in AD mice. Mechanistically, IL-17F upregulated in APOE4 neutrophils interacts with microglial IL-17RA to suppress the induction of MGnD phenotype, and blocking this axis supported cognitive improvement in AD mice. These findings provide a translational basis to target IL-17F in APOE e4 female carriers with cognitive impairment. Overall design: Nuclei were isolated from frozen human brain tissue and enriched for microglia and astrocytes using Fluorescence-activated nuclei sorting (FANS) and analysed using snRNAseq. Donors included both males and females from an Alzheimer's diseased (AD) cohort and non-demented control (CTRL) cohort that have the APOE 3/3 or 3/4 genotype