CD33 is a genetic risk factor for late-onset Alzheimer's disease. Research found that CD33 inhibits the uptake of amyloid beta by microglia in the brain. Studies in mice and human brain tissue showed that deleting or inhibiting CD33 promotes the clearance of amyloid beta by microglia. This identifies a novel pathway by which the CD33 gene impacts amyloid accumulation in the aging brain and suggests targeting CD33 activity may help slow cognitive decline in Alzheimer's disease.