In patients with neurological diseases like Alzheimer’s disease and multiple sclerosis, immune cells in the brain known as microglia that normally fulfill beneficial functions become harmful to neurons, leading to cognitive dysfunction and motor impairment. These harmful immune cells may also contribute to age-related cognitive decline in people without dementia. For some time, scientists have been trying to better understand the triggers responsible for turning good microglia bad, and their exact contribution during disease. If the researchers could identify what makes microglia toxic, they could find new ways to treat neurological diseases. Now, researchers at Gladstone Institutes led by Senior Investigator Katerina Akassoglou, PhD, have shown that exposure to blood leaking into the brain turns on harmful genes in microglia, transforming them into toxic cells that can destroy neurons.