Leading neuroscientists have clarified the role of a controversial immune system protein in Alzheimer’s disease, showing it has opposing effects in early and late stages of the disease. Their discovery unites previous studies that left researchers conflicted and showed the protein both exacerbates and ameliorates disease symptoms. The updated model of disease progression also highlights the need to align certain therapies with disease stages when treating the 1 in 9 Americans over 65 living with Alzheimer’s.