Normally, there are no T cells in the brain. However, in Alzheimer’s disease, we find T cells in the brain. (Pause: the fact that there are T cells in the Alzheimer’s brain is a relatively new discovery to the Alzheimer’s field, and is quite surprising because for many years neuroscientists believed that the healthy brain did not harbor T cells due to the blood-brain barrier.) Here, in pink, you can see a T cell. The big blue/green cells are neurons. The pink T cell extends microvilli (small little protrusions) that are actually contacting the blue neuron. This is a killer T cell, and we think that this pink T cell might actually be killing this blue neuron. The close contact between the pink killer T cell and the white neuron might therefore represent…the kiss of death.