The Shemesh group's study reveals a role for the tau protein in the innate immune response to HSV-1 (Herpes Simplex Virus-1) infection within the brain. We performed Expansion Microscopy, a new method that can image brain samples at a nanometric resolution. Using Expansion Microscopy, the investigators discovered a significant accumulation of HSV-1 proteins in the brains of Alzheimer’s disease patients, providing compelling evidence of a potential link between chronic viral infection and Alzheimer’s disease progression. Tau, a protein long considered to be pathological in Alzheimer's, was shown to interact with components of the immune system, decreasing HSV-1 spread and saving neurons from cell death. This discovery expands our understanding of tau beyond its traditional association with neurodegenerative diseases, suggesting that tau plays a crucial role in neuroimmune defense. These findings offer new perspectives on the role of viral infections in Alzheimer’s and may lead to innovative therapeutic strategies aimed at modulating the immune response.