Aduhelm is a new treatment for Alzheimer’s disease that has been approved in the United States. This treatment involves immunotherapy against a protein that accumulates in the brain. However, it has a side effect called ARIA,  which means that enthusiasm is not high for this novel treatment. Aβ is a peptide found in the brain and evidence suggests that this causes dementia. One idea to explain ARIA is that Aβ removal from the brain by the treatment leads to its accumulation in blood vessel walls associated with inflammation. Human brain tissue from patients with ARIA due to immunotherapy is not available for study. However, there is a very similar natural disease known as cerebral amyloid angiopathy-related inflammation (CAA-ri) which seems to be due to patients spontaneously producing their own antibodies to Aβ, effectively immunising themselves. We want to investigate the inflammatory response underlying ARIA using biopsies from patients who suffer from CAA-ri. This will allow us to understand the side effects occurring with new treatments for Alzheimer’s disease.